man-pages-posix-2017/man1p/pax.1p

'\" et
.TH PAX "1P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.\"
.SH NAME
pax
\(em portable archive interchange
.SH SYNOPSIS
.LP
.nf
pax \fB[\fR-dv\fB] [\fR-c|-n\fB] [\fR-H|-L\fB] [\fR-o \fIoptions\fB] [\fR-f \fIarchive\fB] [\fR-s \fIreplstr\fB]\fR...
    \fB[\fIpattern\fR...\fB]\fR
.P
pax -r\fB[\fR-c|-n\fB] [\fR-dikuv\fB] [\fR-H|-L\fB] [\fR-f \fIarchive\fB] [\fR-o \fIoptions\fB]\fR... \fB[\fR-p \fIstring\fB]\fR...
    \fB[\fR-s \fIreplstr\fB]\fR... \fB[\fIpattern\fR...\fB]\fR
.P
pax -w \fB[\fR-dituvX\fB] [\fR-H|-L\fB] [\fR-b \fIblocksize\fB] [[\fR-a\fB] [\fR-f \fIarchive\fB]] [\fR-o \fIoptions\fB]\fR...
    \fB[\fR-s \fIreplstr\fB]\fR... \fB[\fR-x \fIformat\fB] [\fIfile\fR...\fB]\fR
.P
pax -r -w \fB[\fR-diklntuvX\fB] [\fR-H|-L\fB] [\fR-o \fIoptions\fB]\fR... \fB[\fR-p \fIstring\fB]\fR...
    \fB[\fR-s \fIreplstr\fB]\fR... \fB[\fIfile\fR...\fB] \fIdirectory\fR
.fi
.SH DESCRIPTION
The
.IR pax
utility shall read, write, and write lists of the members of archive
files and copy directory hierarchies. A variety of archive formats
shall be supported; see the
.BR \-x
.IR format
option.
.P
The action to be taken depends on the presence of the
.BR \-r
and
.BR \-w
options. The four combinations of
.BR \-r
and
.BR \-w
are referred to as the four modes of operation:
.BR list ,
.BR read ,
.BR write ,
and
.BR copy
modes, corresponding respectively to the four forms shown in the
SYNOPSIS section.
.IP "\fBlist\fP" 10
In
.BR list
mode (when neither
.BR \-r
nor
.BR \-w
are specified),
.IR pax
shall write the names of the members of the archive file read from the
standard input, with pathnames matching the specified patterns, to
standard output. If a named file is of type directory, the file
hierarchy rooted at that file shall be listed as well.
.IP "\fBread\fP" 10
In
.BR read
mode (when
.BR \-r
is specified, but
.BR \-w
is not),
.IR pax
shall extract the members of the archive file read from the standard
input, with pathnames matching the specified patterns. If an extracted
file is of type directory, the file hierarchy rooted at that file shall
be extracted as well. The extracted files shall be created performing
pathname resolution with the directory in which
.IR pax
was invoked as the current working directory.
.RS 10 
.P
If an attempt is made to extract a directory when the directory
already exists, this shall not be considered an error. If
an attempt is made to extract a FIFO when the FIFO already exists,
this shall not be considered an error.
.P
The ownership, access, and modification times, and file mode of the
restored files are discussed under the
.BR \-p
option.
.RE
.IP "\fBwrite\fP" 10
In
.BR write
mode (when
.BR \-w
is specified, but
.BR \-r
is not),
.IR pax
shall write the contents of the
.IR file
operands to the standard output in an archive format. If no
.IR file
operands are specified, a list of files to copy, one per line, shall be
read from the standard input and each entry in this list shall be
processed as if it had been a
.IR file
operand on the command line. A file of type directory shall include
all of the files in the file hierarchy rooted at the file.
.IP "\fBcopy\fP" 10
In
.BR copy
mode (when both
.BR \-r
and
.BR \-w
are specified),
.IR pax
shall copy the
.IR file
operands to the destination directory.
.RS 10 
.P
If no
.IR file
operands are specified, a list of files to copy, one per line, shall be
read from the standard input. A file of type directory shall include
all of the files in the file hierarchy rooted at the file.
.P
The effect of the
.BR copy
shall be as if the copied files were written to a
.IR pax
format archive file and then subsequently extracted, except that
copying of sockets may be supported even if archiving them in write
mode is not supported, and that there may be hard links between the
original and the copied files. If the destination directory is a
subdirectory of one of the files to be copied, the results
are unspecified. If the destination directory is a file of a
type not defined by the System Interfaces volume of POSIX.1\(hy2017, the results are implementation-defined;
otherwise, it shall be an error for the file named by the
.IR directory
operand not to exist, not be writable by the user, or not be a file of
type directory.
.RE
.P
In
.BR read
or
.BR copy
modes, if intermediate directories are necessary to extract an archive
member,
.IR pax
shall perform actions equivalent to the
\fImkdir\fR()
function defined in the System Interfaces volume of POSIX.1\(hy2017, called with the following arguments:
.IP " *" 4
The intermediate directory used as the
.IR path
argument
.IP " *" 4
The value of the bitwise-inclusive OR of S_IRWXU, S_IRWXG, and S_IRWXO
as the
.IR mode
argument
.P
If any specified
.IR pattern
or
.IR file
operands are not matched by at least one file or archive member,
.IR pax
shall write a diagnostic message to standard error for each one that
did not match and exit with a non-zero exit status.
.P
The archive formats described in the EXTENDED DESCRIPTION section shall
be automatically detected on input. The default output archive format
shall be implementation-defined.
.P
A single archive can span multiple files. The
.IR pax
utility shall determine, in an implementation-defined manner, what
file to read or write as the next file.
.P
If the selected archive format supports the specification of linked files,
it shall be an error if these files cannot be linked when the archive
is extracted. For archive formats that do not store file contents with
each name that causes a hard link, if the file that contains the data
is not extracted during this
.IR pax
session, either the data shall be restored from the original file, or a
diagnostic message shall be displayed with the name of a file that can
be used to extract the data. In traversing directories,
.IR pax
shall detect infinite loops; that is, entering a previously visited
directory that is an ancestor of the last file visited. When it detects
an infinite loop,
.IR pax
shall write a diagnostic message to standard error and shall
terminate.
.SH OPTIONS
The
.IR pax
utility shall conform to the Base Definitions volume of POSIX.1\(hy2017,
.IR "Section 12.2" ", " "Utility Syntax Guidelines",
except that the order of presentation of the
.BR \-o ,
.BR \-p ,
and
.BR \-s
options is significant.
.P
The following options shall be supported:
.IP "\fB\-r\fP" 10
Read an archive file from standard input.
.IP "\fB\-w\fP" 10
Write files to the standard output in the specified archive format.
.IP "\fB\-a\fP" 10
Append files to the end of the archive. It is implementation-defined
which devices on the system support appending. Additional file formats
unspecified by this volume of POSIX.1\(hy2017 may impose restrictions on appending.
.IP "\fB\-b\ \fIblocksize\fR" 10
Block the output at a positive decimal integer number of bytes per
write to the archive file. Devices and archive formats may impose
restrictions on blocking. Blocking shall be automatically determined on
input. Conforming applications shall not specify a
.IR blocksize
value larger than 32\|256. Default blocking when creating archives
depends on the archive format. (See the
.BR \-x
option below.)
.IP "\fB\-c\fP" 10
Match all file or archive members except those specified by the
.IR pattern
or
.IR file
operands.
.IP "\fB\-d\fP" 10
Cause files of type directory being copied or archived or archive
members of type directory being extracted or listed to match only the
file or archive member itself and not the file hierarchy rooted at the
file.
.IP "\fB\-f\ \fIarchive\fR" 10
Specify the pathname of the input or output archive, overriding the
default standard input (in
.BR list
or
.BR read
modes) or standard output (\c
.BR write
mode).
.IP "\fB\-H\fP" 10
If a symbolic link referencing a file of type directory is specified on
the command line,
.IR pax
shall archive the file hierarchy rooted in the file referenced by the
link, using the name of the link as the root of the file hierarchy.
Otherwise, if a symbolic link referencing a file of any other file type
which
.IR pax
can normally archive is specified on the command line, then
.IR pax
shall archive the file referenced by the link, using the name of the
link. The default behavior, when neither
.BR \-H
or
.BR \-L
are specified, shall be to archive the symbolic link itself.
.IP "\fB\-i\fP" 10
Interactively rename files or archive members. For each archive member
matching a
.IR pattern
operand or file matching a
.IR file
operand, a prompt shall be written to the file
.BR /dev/tty .
The prompt shall contain the name of the file or archive member, but
the format is otherwise unspecified. A line shall then be read from
.BR /dev/tty .
If this line is blank, the file or archive member shall be skipped. If
this line consists of a single period, the file or archive member shall
be processed with no modification to its name. Otherwise, its name
shall be replaced with the contents of the line. The
.IR pax
utility shall immediately exit with a non-zero exit status if
end-of-file is encountered when reading a response or if
.BR /dev/tty
cannot be opened for reading and writing.
.RS 10 
.P
The results of extracting a hard link to a file that has been renamed
during extraction are unspecified.
.RE
.IP "\fB\-k\fP" 10
Prevent the overwriting of existing files.
.IP "\fB\-l\fP" 10
(The letter ell.) In
.BR copy
mode, hard links shall be made between the source and destination file
hierarchies whenever possible. If specified in conjunction with
.BR \-H
or
.BR \-L ,
when a symbolic link is encountered, the hard link created in the
destination file hierarchy shall be to the file referenced by the
symbolic link. If specified when neither
.BR \-H
nor
.BR \-L
is specified, when a symbolic link is encountered, the implementation
shall create a hard link to the symbolic link in the source file
hierarchy or copy the symbolic link to the destination.
.IP "\fB\-L\fP" 10
If a symbolic link referencing a file of type directory is specified on
the command line or encountered during the traversal of a file
hierarchy,
.IR pax
shall archive the file hierarchy rooted in the file referenced by the
link, using the name of the link as the root of the file hierarchy.
Otherwise, if a symbolic link referencing a file of any other file type
which
.IR pax
can normally archive is specified on the command line or encountered
during the traversal of a file hierarchy,
.IR pax
shall archive the file referenced by the link, using the name of the
link. The default behavior, when neither
.BR \-H
or
.BR \-L
are specified, shall be to archive the symbolic link itself.
.IP "\fB\-n\fP" 10
Select the first archive member that matches each
.IR pattern
operand. No more than one archive member shall be matched for each
pattern (although members of type directory shall still match the file
hierarchy rooted at that file).
.IP "\fB\-o\ \fIoptions\fR" 10
Provide information to the implementation to modify the algorithm for
extracting or writing files. The value of
.IR options
shall consist of one or more
<comma>-separated
keywords of the form:
.RS 10 
.sp
.RS 4
.nf

\fIkeyword\fB[[\fR:\fB]\fR=\fIvalue\fB][\fR,\fIkeyword\fB[[\fR:\fB]\fR=\fIvalue\fB]\fR, ...\fB]\fR
.fi
.P
.RE
.P
Some keywords apply only to certain file formats, as indicated with
each description. Use of keywords that are inapplicable to the file
format being processed produces undefined results.
.P
Keywords in the
.IR options
argument shall be a string that would be a valid portable filename as
described in the Base Definitions volume of POSIX.1\(hy2017,
.IR "Section 3.282" ", " "Portable Filename Character Set".
.TP 10
.BR Note:
Keywords are not expected to be filenames, merely to follow the same
character composition rules as portable filenames.
.P
.P
Keywords can be preceded with white space. The
.IR value
field shall consist of zero or more characters; within
.IR value ,
the application shall precede any literal
<comma>
with a
<backslash>,
which shall be ignored, but preserves the
<comma>
as part of
.IR value .
A
<comma>
as the final character, or a
<comma>
followed solely by white space as the final characters, in
.IR options
shall be ignored. Multiple
.BR \-o
options can be specified; if keywords given to these multiple
.BR \-o
options conflict, the keywords and values appearing later in command
line sequence shall take precedence and the earlier shall be silently
ignored. The following keyword values of
.IR options
shall be supported for the file formats as indicated:
.IP "\fBdelete\fR=\fIpattern\fR" 6
.br
(Applicable only to the
.BR \-x
.BR pax
format.) When used in
.BR write
or
.BR copy
mode,
.IR pax
shall omit from extended header records that it produces any keywords
matching the string pattern. When used in
.BR read
or
.BR list
mode,
.IR pax
shall ignore any keywords matching the string pattern in the extended
header records. In both cases, matching shall be performed using the
pattern matching notation described in
.IR "Section 2.13.1" ", " "Patterns Matching a Single Character"
and
.IR "Section 2.13.2" ", " "Patterns Matching Multiple Characters".
For example:
.RS 6 
.sp
.RS 4
.nf

-o \fBdelete\fR=\fIsecurity\fR.*
.fi
.P
.RE
.P
would suppress security-related information. See
.IR "pax Extended Header"
for extended header record keyword usage.
.P
When multiple
.BR \-o \c
.BR delete=pattern
options are specified, the patterns shall be additive; all keywords
matching the specified string patterns shall be omitted from extended
header records that
.IR pax
produces.
.RE
.IP "\fBexthdr.name\fR=\fIstring\fR" 6
.br
(Applicable only to the
.BR \-x
.BR pax
format.) This keyword allows user control over the name that is written
into the
.BR ustar
header blocks for the extended header produced under the circumstances
described in
.IR "pax Header Block".
The name shall be the contents of
.IR string ,
after the following character substitutions have been made:
.TS
center box tab(!);
cB | cB
cB | cB
lf5 | lw(3.8i).
\fIstring\fP
Includes:!Replaced by:
_
%d!T{
The directory name of the file, equivalent to the result of the
.IR dirname
utility on the translated pathname.
T}
%f!T{
The filename of the file, equivalent to the result of the
.IR basename
utility on the translated pathname.
T}
%p!T{
The process ID of the
.IR pax
process.
T}
%%!T{
A
.BR '%' 
character.
T}
.TE
.RS 6 
.P
Any other
.BR '%' 
characters in
.IR string
produce undefined results.
.P
If no
.BR \-o
.BR exthdr.name=string
is specified,
.IR pax
shall use the following default value:
.sp
.RS 4
.nf

%d/PaxHeaders.%p/%f
.fi
.P
.RE
.RE
.IP "\fBglobexthdr.name\fR=\fIstring\fR" 6
.br
(Applicable only to the
.BR \-x
.BR pax
format.) When used in
.BR write
or
.BR copy
mode with the appropriate options,
.IR pax
shall create global extended header records with
.BR ustar
header blocks that will be treated as regular files by previous
versions of
.IR pax .
This keyword allows user control over the name that is written into the
.BR ustar
header blocks for global extended header records. The name shall be the
contents of string, after the following character substitutions have
been made:
.TS
center box tab(!);
cB | cB
cB | cB
lf5 | lw(3.8i).
\fIstring\fP
Includes:!Replaced by:
_
%n!T{
An integer that represents the sequence number of the global extended
header record in the archive, starting at 1.
T}
%p!T{
The process ID of the
.IR pax
process.
T}
%%!T{
A
.BR '%' 
character.
T}
.TE
.RS 6 
.P
Any other
.BR '%' 
characters in
.IR string
produce undefined results.
.P
If no
.BR \-o
.BR globexthdr.name=string
is specified,
.IR pax
shall use the following default value:
.sp
.RS 4
.nf

$TMPDIR/GlobalHead.%p.%n
.fi
.P
.RE
.P
where $\c
.IR TMPDIR
represents the value of the
.IR TMPDIR
environment variable. If
.IR TMPDIR
is not set,
.IR pax
shall use
.BR /tmp .
.RE
.IP "\fBinvalid\fR=\fIaction\fR" 6
.br
(Applicable only to the
.BR \-x
.BR pax
format.) This keyword allows user control over the action
.IR pax
takes upon encountering values in an extended header record that, in
.BR read
or
.BR copy
mode, are invalid in the destination hierarchy or, in
.BR list
mode, cannot be written in the codeset and current locale of the
implementation. The following are invalid values that shall be
recognized by
.IR pax :
.RS 6 
.IP -- 4
In
.BR read
or
.BR copy
mode, a filename or link name that contains character encodings
invalid in the destination hierarchy. (For example, the name may
contain embedded NULs.)
.IP -- 4
In
.BR read
or
.BR copy
mode, a filename or link name that is longer than the maximum allowed
in the destination hierarchy (for either a pathname component or the
entire pathname).
.IP -- 4
In
.BR list
mode, any character string value (filename, link name, user name, and
so on) that cannot be written in the codeset and current locale of the
implementation.
.P
The following mutually-exclusive values of the
.IR action
argument are supported:
.IP "\fBbinary\fR" 10
In
.BR write
mode,
.IR pax
shall generate a
.BR hdrcharset = BINARY
extended header record for each file with a filename, link name, group
name, owner name, or any other field in an extended header record that
cannot be translated to the UTF\(hy8 codeset, allowing the archive to
contain the files with unencoded extended header record values. In
.BR read
or
.BR copy
mode,
.IR pax
shall use the values specified in the header without translation,
regardless of whether this may overwrite an existing file with a valid
name. In
.BR list
mode,
.IR pax
shall behave identically to the
.BR bypass
action.
.IP "\fBbypass\fR" 10
In
.BR read
or
.BR copy
mode,
.IR pax
shall bypass the file, causing no change to the destination hierarchy.
In
.BR list
mode,
.IR pax
shall write all requested valid values for the file, but its method for
writing invalid values is unspecified.
.IP "\fBrename\fR" 10
In
.BR read
or
.BR copy
mode,
.IR pax
shall act as if the
.BR \-i
option were in effect for each file with invalid filename or link name
values, allowing the user to provide a replacement name interactively.
In
.BR list
mode,
.IR pax
shall behave identically to the
.BR bypass
action.
.IP "\fBUTF\(hy8\fR" 10
When used in
.BR read ,
.BR copy ,
or
.BR list
mode and a filename, link name, owner name, or any other field in an
extended header record cannot be translated from the
.BR pax
UTF\(hy8 codeset format to the codeset and current locale of the
implementation,
.IR pax
shall use the actual UTF\(hy8 encoding for the name. If a
.BR hdrcharset
extended header record is in effect for this file, the character set
specified by that record shall be used instead of UTF\(hy8. If a
.BR hdrcharset = BINARY
extended header record is in effect for this file, no translation shall
be performed.
.IP "\fBwrite\fR" 10
In
.BR read
or
.BR copy
mode,
.IR pax
shall write the file, translating the name, regardless of whether this
may overwrite an existing file with a valid name. In
.BR list
mode,
.IR pax
shall behave identically to the
.BR bypass
action.
.P
If no
.BR \-o
.BR invalid=option
is specified,
.IR pax
shall act as if
.BR \-o \c
.BR invalid=bypass
were specified. Any overwriting of existing files that may be allowed
by the
.BR \-o \c
.BR invalid=
actions shall be subject to permission (\c
.BR \-p )
and modification time (\c
.BR \-u )
restrictions, and shall be suppressed if the
.BR \-k
option is also specified.
.RE
.IP "\fBlinkdata\fP" 6
.br
(Applicable only to the
.BR \-x
.BR pax
format.) In
.BR write
mode,
.IR pax
shall write the contents of a file to the archive even when that file
is merely a hard link to a file whose contents have already been
written to the archive.
.IP "\fBlistopt\fR=\fIformat\fP" 6
.br
This keyword specifies the output format of the table of contents
produced when the
.BR \-v
option is specified in
.BR list
mode. See
.IR "List Mode Format Specifications".
To avoid ambiguity, the
.BR listopt=format
shall be the only or final
.BR keyword=value
pair in a
.BR \-o
option-argument; all characters in the remainder of the option-argument
shall be considered part of the format string. When multiple
.BR \-o \c
.BR listopt=format
options are specified, the format strings shall be considered a single,
concatenated string, evaluated in command line order.
.IP "\fBtimes\fR" 6
.br
(Applicable only to the
.BR \-x
.IR pax
format.) When used in
.BR write
or
.BR copy
mode,
.IR pax
shall include
.BR atime
and
.BR mtime
extended header records for each file. See
.IR "pax Extended Header File Times".
.P
In addition to these keywords, if the
.BR \-x
.IR pax
format is specified, any of the keywords and values defined in
.IR "pax Extended Header",
including implementation extensions, can be used in
.BR \-o
option-arguments, in either of two modes:
.IP "\fBkeyword\fR=\fIvalue\fR" 6
.br
When used in
.BR write
or
.BR copy
mode, these keyword/value pairs shall be included at the beginning of
the archive as
.BR typeflag
.BR g
global extended header records. When used in
.BR read
or
.BR list
mode, these keyword/value pairs shall act as if they had been at the
beginning of the archive as
.BR typeflag
.BR g
global extended header records.
.IP "\fBkeyword\fR:=\fIvalue\fR" 6
.br
When used in
.BR write
or
.BR copy
mode, these keyword/value pairs shall be included as records at the
beginning of a
.BR typeflag
.BR x
extended header for each file. (This shall be equivalent to the
<equals-sign>
form except that it creates no
.BR typeflag
.BR g
global extended header records.) When used in
.BR read
or
.BR list
mode, these keyword/value pairs shall act as if they were included as
records at the end of each extended header; thus, they shall override
any global or file-specific extended header record keywords of the same
names. For example, in the command:
.RS 6 
.sp
.RS 4
.nf

pax -r -o "
gname:=mygroup,
" <archive
.fi
.P
.RE
.P
the group name will be forced to a new value for all files read from
the archive.
.RE
.P
The precedence of
.BR \-o
keywords over various fields in the archive is described in
.IR "pax Extended Header Keyword Precedence".
If the
.BR \-o
.BR delete =\c
.IR pattern ,
.BR \-o
.BR keyword =\c
.IR value ,
or
.BR \-o
.BR keyword :=\c
.IR value
options are used to override or remove any extended header data needed
to find files in an archive (e.g.,
.BR "-o delete=size"
for a file whose size cannot be represented in a
.BR ustar
header or
.BR "-o size=100"
for a file whose size is not 100 bytes), the behavior is undefined.
.RE
.IP "\fB\-p\ \fIstring\fR" 10
Specify one or more file characteristic options (privileges). The
.IR string
option-argument shall be a string specifying file characteristics to be
retained or discarded on extraction. The string shall consist of the
specification characters
.BR a ,
.BR e ,
.BR m ,
.BR o ,
and
.BR p .
Other implementation-defined characters can be included. Multiple
characteristics can be concatenated within the same string and multiple
.BR \-p
options can be specified. The meaning of the specification characters
are as follows:
.RS 10 
.IP "\fRa\fP" 6
Do not preserve file access times.
.IP "\fRe\fP" 6
Preserve the user ID, group ID, file mode bits (see the Base Definitions volume of POSIX.1\(hy2017,
.IR "Section 3.169" ", " "File Mode Bits"),
access time, modification time, and any other implementation-defined
file characteristics.
.IP "\fRm\fP" 6
Do not preserve file modification times.
.IP "\fRo\fP" 6
Preserve the user ID and group ID.
.IP "\fRp\fP" 6
Preserve the file mode bits. Other implementation-defined file mode
attributes may be preserved.
.P
In the preceding list, ``preserve'' indicates that an attribute stored
in the archive shall be given to the extracted file, subject to the
permissions of the invoking process. The access and modification times
of the file shall be preserved unless otherwise specified with the
.BR \-p
option or not stored in the archive. All attributes that are not
preserved shall be determined as part of the normal file creation
action (see
.IR "Section 1.1.1.4" ", " "File Read" ", " "Write" ", " "and Creation").
.P
If neither the
.BR e
nor the
.BR o
specification character is specified, or the user ID and group ID are
not preserved for any reason,
.IR pax
shall not set the S_ISUID and S_ISGID bits of the file mode.
.P
If the preservation of any of these items fails for any reason,
.IR pax
shall write a diagnostic message to standard error. Failure to preserve
these items shall affect the final exit status, but shall not cause the
extracted file to be deleted.
.P
If file characteristic letters in any of the
.IR string
option-arguments are duplicated or conflict with each other, the ones
given last shall take precedence. For example, if
.BR \-p
.BR eme
is specified, file modification times are preserved.
.RE
.IP "\fB\-s\ \fIreplstr\fR" 10
Modify file or archive member names named by
.IR pattern
or
.IR file
operands according to the substitution expression
.IR replstr ,
using the syntax of the
.IR ed
utility. The concepts of ``address'' and ``line'' are meaningless in
the context of the
.IR pax
utility, and shall not be supplied. The format shall be:
.RS 10 
.sp
.RS 4
.nf

-s /\fIold\fR/\fInew\fR/\fB[\fRgp\fB]\fR
.fi
.P
.RE
.P
where as in
.IR ed ,
.IR old
is a basic regular expression and
.IR new
can contain an
<ampersand>,
.BR '\en' 
(where
.IR n
is a digit) back-references, or subexpression matching. The
.IR old
string shall also be permitted to contain
<newline>
characters.
.P
Any non-null character can be used as a delimiter (\c
.BR '/' 
shown here). Multiple
.BR \-s
expressions can be specified; the expressions shall be applied in the
order specified, terminating with the first successful substitution.
The optional trailing
.BR 'g' 
is as defined in the
.IR ed
utility. The optional trailing
.BR 'p' 
shall cause successful substitutions to be written to standard error.
File or archive member names that substitute to the empty string shall
be ignored when reading and writing archives.
.RE
.IP "\fB\-t\fP" 10
When reading files from the file system, and if the user has the
permissions required by
\fIutime\fR()
to do so, set the access time of each file read to the access time that
it had before being read by
.IR pax .
.IP "\fB\-u\fP" 10
Ignore files that are older (having a less recent file modification
time) than a pre-existing file or archive member with the same name.
In
.BR read
mode, an archive member with the same name as a file in the file system
shall be extracted if the archive member is newer than the file. In
.BR write
mode, an archive file member with the same name as a file in the file
system shall be superseded if the file is newer than the archive
member. If
.BR \-a
is also specified, this is accomplished by appending to the archive;
otherwise, it is unspecified whether this is accomplished by actual
replacement in the archive or by appending to the archive. In
.BR copy
mode, the file in the destination hierarchy shall be replaced by the
file in the source hierarchy or by a link to the file in the source
hierarchy if the file in the source hierarchy is newer.
.IP "\fB\-v\fP" 10
In
.BR list
mode, produce a verbose table of contents (see the STDOUT section).
Otherwise, write archive member pathnames to standard error (see the
STDERR section).
.IP "\fB\-x\ \fIformat\fR" 10
Specify the output archive format. The
.IR pax
utility shall support the following formats:
.RS 10 
.IP "\fBcpio\fR" 10
The
.BR cpio
interchange format; see the EXTENDED DESCRIPTION section. The default
.IR blocksize
for this format for character special archive files shall be 5\|120.
Implementations shall support all
.IR blocksize
values less than or equal to 32\|256 that are multiples of 512.
.IP "\fBpax\fR" 10
The
.BR pax
interchange format; see the EXTENDED DESCRIPTION section. The default
.IR blocksize
for this format for character special archive files shall be 5\|120.
Implementations shall support all
.IR blocksize
values less than or equal to 32\|256 that are multiples of 512.
.IP "\fBustar\fR" 10
The
.BR tar
interchange format; see the EXTENDED DESCRIPTION section. The default
.IR blocksize
for this format for character special archive files shall be 10\|240.
Implementations shall support all
.IR blocksize
values less than or equal to 32\|256 that are multiples of 512.
.P
Implementation-defined formats shall specify a default block size as
well as any other block sizes supported for character special archive
files.
.P
Any attempt to append to an archive file in a format different from the
existing archive format shall cause
.IR pax
to exit immediately with a non-zero exit status.
.RE
.IP "\fB\-X\fP" 10
When traversing the file hierarchy specified by a pathname,
.IR pax
shall not descend into directories that have a different device ID (\c
.IR st_dev ;
see the System Interfaces volume of POSIX.1\(hy2017,
\fIstat\fR()).
.P
Specifying more than one of the mutually-exclusive options
.BR \-H
and
.BR \-L
shall not be considered an error and the last option specified shall
determine the behavior of the utility.
.P
The options that operate on the names of files or archive members (\c
.BR \-c ,
.BR \-i ,
.BR \-n ,
.BR \-s ,
.BR \-u ,
and
.BR \-v )
shall interact as follows. In
.BR read
mode, the archive members shall be selected based on the user-specified
.IR pattern
operands as modified by the
.BR \-c ,
.BR \-n ,
and
.BR \-u
options. Then, any
.BR \-s
and
.BR \-i
options shall modify, in that order, the names of the selected files.
The
.BR \-v
option shall write names resulting from these modifications.
.P
In
.BR write
mode, the files shall be selected based on the user-specified
pathnames as modified by the
.BR \-n
and
.BR \-u
options. Then, any
.BR \-s
and
.BR \-i
options shall modify, in that order, the names of these selected files.
The
.BR \-v
option shall write names resulting from these modifications.
.P
If both the
.BR \-u
and
.BR \-n
options are specified,
.IR pax
shall not consider a file selected unless it is newer than the file to
which it is compared.
.SS "List Mode Format Specifications"
.P
In
.BR list
mode with the
.BR \-o
.BR listopt=format
option, the
.IR format
argument shall be applied for each selected file. The
.IR pax
utility shall append a
<newline>
to the
.BR listopt
output for each selected file. The
.IR format
argument shall be used as the
.IR format
string described in the Base Definitions volume of POSIX.1\(hy2017,
.IR "Chapter 5" ", " "File Format Notation",
with the exceptions 1. through 6. defined in the EXTENDED DESCRIPTION
section of
.IR printf ,
plus the following exceptions:
.IP 7. 6
The sequence (\c
.IR keyword )
can occur before a format conversion specifier. The conversion
argument is defined by the value of
.IR keyword .
The implementation shall support the following keywords:
.RS 6 
.IP -- 4
Any of the Field Name entries in
.IR "Table 4-14, ustar Header Block"
and
.IR "Table 4-16, Octet-Oriented cpio Archive Entry".
The implementation may support the
.IR cpio
keywords without the leading
.BR c_
in addition to the form required by
.IR "Table 4-16, Octet-Oriented cpio Archive Entry".
.IP -- 4
Any keyword defined for the extended header in
.IR "pax Extended Header".
.IP -- 4
Any keyword provided as an implementation-defined extension within
the extended header defined in
.IR "pax Extended Header".
.P
For example, the sequence
.BR \(dq%(charset)s\(dq 
is the string value of the name of the character set in the extended
header.
.P
The result of the keyword conversion argument shall be the value from
the applicable header field or extended header, without any trailing
NULs.
.P
All keyword values used as conversion arguments shall be translated
from the UTF\(hy8 encoding (or alternative encoding specified by any
.BR hdrcharset
extended header record) to the character set appropriate for the local
file system, user database, and so on, as applicable.
.RE
.IP 8. 6
An additional conversion specifier character,
.BR T ,
shall be used to specify time formats. The
.BR T
conversion specifier character can be preceded by the sequence (\c
.IR keyword= \c
.IR subformat ),
where
.IR subformat
is a date format as defined by
.IR date
operands. The default
.IR keyword
shall be
.BR mtime
and the default subformat shall be:
.RS 6 
.sp
.RS 4
.nf

%b %e %H:%M %Y
.fi
.P
.RE
.RE
.IP 9. 6
An additional conversion specifier character,
.BR M ,
shall be used to specify the file mode string as defined in
.IR ls
Standard Output. If (\c
.IR keyword )
is omitted, the
.BR mode
keyword shall be used. For example,
.BR %.1M
writes the single character corresponding to the <\fIentry\ type\fP>
field of the
.IR ls
.BR \-l
command.
.IP 10. 6
An additional conversion specifier character,
.BR D ,
shall be used to specify the device for block or special files, if
applicable, in an implementation-defined format. If not applicable,
and (\c
.IR keyword )
is specified, then this conversion shall be equivalent to
\fR%(\fIkeyword\fR)u\fR. If not applicable, and (\c
.IR keyword )
is omitted, then this conversion shall be equivalent to
<space>.
.IP 11. 6
An additional conversion specifier character,
.BR F ,
shall be used to specify a pathname. The
.BR F
conversion character can be preceded by a sequence of
<comma>-separated
keywords:
.RS 6 
.sp
.RS 4
.nf

(\fIkeyword\fB[\fR,\fIkeyword\fB]\fR ... )
.fi
.P
.RE
.P
The values for all the keywords that are non-null shall be concatenated
together, each separated by a
.BR '/' .
The default shall be (\c
.BR path )
if the keyword
.BR path
is defined; otherwise, the default shall be (\c
.BR prefix ,\c
.BR name ).
.RE
.IP 12. 6
An additional conversion specifier character,
.BR L ,
shall be used to specify a symbolic link expansion. If the current
file is a symbolic link, then
.BR %L
shall expand to:
.RS 6 
.sp
.RS 4
.nf

"%s -> %s", <\fIvalue of keyword\fR>, <\fIcontents of link\fR>
.fi
.P
.RE
.P
Otherwise, the
.BR %L
conversion specification shall be the equivalent of
.BR %F .
.RE
.SH OPERANDS
The following operands shall be supported:
.IP "\fIdirectory\fR" 10
The destination directory pathname for
.BR copy
mode.
.IP "\fIfile\fR" 10
A pathname of a file to be copied or archived.
.IP "\fIpattern\fR" 10
A pattern matching one or more pathnames of archive members. A pattern
must be given in the name-generating notation of the pattern matching
notation in
.IR "Section 2.13" ", " "Pattern Matching Notation",
including the filename expansion rules in
.IR "Section 2.13.3" ", " "Patterns Used for Filename Expansion".
The default, if no
.IR pattern
is specified, is to select all members in the archive.
.SH STDIN
In
.BR write
mode, the standard input shall be used only if no
.IR file
operands are specified. It shall be a file containing a list of
pathnames, each terminated by a
<newline>
character.
.P
In
.BR list
and
.BR read
modes, if
.BR \-f
is not specified, the standard input shall be an archive file.
.P
Otherwise, the standard input shall not be used.
.SH "INPUT FILES"
The input file named by the
.IR archive
option-argument, or standard input when the archive is read from there,
shall be a file formatted according to one of the specifications in the
EXTENDED DESCRIPTION section or some other implementation-defined
format.
.P
The file
.BR /dev/tty
shall be used to write prompts and read responses.
.SH "ENVIRONMENT VARIABLES"
The following environment variables shall affect the execution of
.IR pax :
.IP "\fILANG\fP" 10
Provide a default value for the internationalization variables that are
unset or null. (See the Base Definitions volume of POSIX.1\(hy2017,
.IR "Section 8.2" ", " "Internationalization Variables"
the precedence of internationalization variables used to determine the
values of locale categories.)
.IP "\fILC_ALL\fP" 10
If set to a non-empty string value, override the values of all the
other internationalization variables.
.IP "\fILC_COLLATE\fP" 10
.br
Determine the locale for the behavior of ranges, equivalence classes,
and multi-character collating elements used in the pattern matching
expressions for the
.IR pattern
operand, the basic regular expression for the
.BR \-s
option, and the extended regular expression defined for the
.BR yesexpr
locale keyword in the
.IR LC_MESSAGES
category.
.IP "\fILC_CTYPE\fP" 10
Determine the locale for the interpretation of sequences of bytes of
text data as characters (for example, single-byte as opposed to
multi-byte characters in arguments and input files), the behavior of
character classes used in the extended regular expression defined for
the
.BR yesexpr
locale keyword in the
.IR LC_MESSAGES
category, and pattern matching.
.IP "\fILC_MESSAGES\fP" 10
.br
Determine the locale used to process affirmative responses, and the
locale used to affect the format and contents of diagnostic messages
and prompts written to standard error.
.IP "\fILC_TIME\fP" 10
Determine the format and contents of date and time strings when the
.BR \-v
option is specified.
.IP "\fINLSPATH\fP" 10
Determine the location of message catalogs for the processing of
.IR LC_MESSAGES .
.IP "\fITMPDIR\fP" 10
Determine the pathname that provides part of the default global
extended header record file, as described for the
.BR \-o
.BR globexthdr=
keyword in the OPTIONS section.
.IP "\fITZ\fP" 10
Determine the timezone used to calculate date and time strings when the
.BR \-v
option is specified. If
.IR TZ
is unset or null, an unspecified default timezone shall be used.
.SH "ASYNCHRONOUS EVENTS"
Default.
.SH STDOUT
In
.BR write
mode, if
.BR \-f
is not specified, the standard output shall be the archive formatted
according to one of the specifications in the EXTENDED DESCRIPTION
section, or some other implementation-defined format (see
.BR \-x
.IR format ).
.P
In
.BR list
mode, when the
.BR \-o \c
.BR listopt =\c
.IR format
has been specified, the selected archive members shall be written to
standard output using the format described under
.IR "List Mode Format Specifications".
In
.BR list
mode without the
.BR \-o \c
.BR listopt =\c
.IR format
option, the table of contents of the selected archive members shall
be written to standard output using the following format:
.sp
.RS 4
.nf

"%s\en", <\fIpathname\fR>
.fi
.P
.RE
.P
If the
.BR \-v
option is specified in
.BR list
mode, the table of contents of the selected archive members shall be
written to standard output using the following formats.
.P
For pathnames representing hard links to previous members of the
archive:
.sp
.RS 4
.nf

"%s == %s\en", <\fIls\fR -l \fIlisting\fR>, <\fIlinkname\fR>
.fi
.P
.RE
.P
For all other pathnames:
.sp
.RS 4
.nf

"%s\en", <\fIls\fR -l \fIlisting\fR>
.fi
.P
.RE
.P
where <\fIls\ \fR\-l\ \fIlisting\fR> shall be the format specified by
the
.IR ls
utility with the
.BR \-l
option. When writing pathnames in this format, it is unspecified what
is written for fields for which the underlying archive format does not
have the correct information, although the correct number of
<blank>-separated
fields shall be written.
.P
In
.BR list
mode, standard output shall not be buffered more than a pathname
(plus any associated information and a
<newline>
terminator) at a time.
.SH STDERR
If
.BR \-v
is specified in
.BR read ,
.BR write ,
or
.BR copy
modes,
.IR pax
shall write the pathnames it processes to the standard error output
using the following format:
.sp
.RS 4
.nf

"%s\en", <\fIpathname\fR>
.fi
.P
.RE
.P
These pathnames shall be written as soon as processing is begun on the
file or archive member, and shall be flushed to standard error. The
trailing
<newline>,
which shall not be buffered, is written when the file has been read or
written.
.P
If the
.BR \-s
option is specified, and the replacement string has a trailing
.BR 'p' ,
substitutions shall be written to standard error in the following
format:
.sp
.RS 4
.nf

"%s >> %s\en", <\fIoriginal pathname\fR>, <\fInew pathname\fR>
.fi
.P
.RE
.P
In all operating modes of
.IR pax ,
optional messages of unspecified format concerning the input archive
format and volume number, the number of files, blocks, volumes, and
media parts as well as other diagnostic messages may be written to
standard error.
.P
In all formats, for both standard output and standard error, it is
unspecified how non-printable characters in pathnames or link names
are written.
.P
When using the
.BR \-x \c
.BR pax
archive format, if a filename, link name, group name, owner name, or
any other field in an extended header record cannot be translated
between the codeset in use for that extended header record and the
character set of the current locale,
.IR pax
shall write a diagnostic message to standard error, shall process the
file as described for the
.BR \-o
.BR invalid=
option, and then shall continue processing with the next file.
.SH "OUTPUT FILES"
In
.BR read
mode, the extracted output files shall be of the archived file type.
In
.BR copy
mode, the copied output files shall be the type of the file being
copied. In either mode, existing files in the destination hierarchy
shall be overwritten only when all permission (\c
.BR \-p ),
modification time (\c
.BR \-u ),
and invalid-value (\c
.BR \-o \c
.BR invalid= )
tests allow it.
.P
In
.BR write
mode, the output file named by the
.BR \-f
option-argument shall be a file formatted according to one of the
specifications in the EXTENDED DESCRIPTION section, or some other
implementation-defined format.
.SH "EXTENDED DESCRIPTION"
.SS "pax Interchange Format"
.P
A
.IR pax
archive tape or file produced in the
.BR \-x \c
.BR pax
format shall contain a series of blocks. The physical layout of the
archive shall be identical to the
.BR ustar
format described in
.IR "ustar Interchange Format".
Each file archived shall be represented by the following sequence:
.IP " *" 4
An optional header block with extended header records. This header
block is of the form described in
.IR "pax Header Block",
with a
.IR typeflag
value of
.BR x
or
.BR g .
The extended header records, described in
.IR "pax Extended Header",
shall be included as the data for this header block.
.IP " *" 4
A header block that describes the file. Any fields in the preceding
optional extended header shall override the associated fields in
this header block for this file.
.IP " *" 4
Zero or more blocks that contain the contents of the file.
.P
At the end of the archive file there shall be two 512-byte blocks
filled with binary zeros, interpreted as an end-of-archive indicator.
.P
A schematic of an example archive with global extended header records
and two actual files is shown in
.IR "Figure 4-1, pax Format Archive Example".
In the example, the second file in the archive has no extended header
preceding it, presumably because it has no need for extended
attributes.
.sp
.ce 1
\fBFigure 4-1: pax Format Archive Example\fR
.SS "pax Header Block"
.P
The
.BR pax
header block shall be identical to the
.BR ustar
header block described in
.IR "ustar Interchange Format",
except that two additional
.IR typeflag
values are defined:
.IP "\fRx\fP" 6
Represents extended header records for the following file in the
archive (which shall have its own
.BR ustar
header block). The format of these extended header records shall be as
described in
.IR "pax Extended Header".
.IP "\fRg\fR" 6
Represents global extended header records for the following files in
the archive. The format of these extended header records shall be as
described in
.IR "pax Extended Header".
Each value shall affect all subsequent files that do not override that
value in their own extended header record and until another global
extended header record is reached that provides another value for the
same field. The
.IR typeflag
.BR g
global headers should not be used with interchange media that could
suffer partial data loss in transporting the archive.
.P
For both of these types, the
.IR size
field shall be the size of the extended header records in octets. The
other fields in the header block are not meaningful to this version of
the
.IR pax
utility. However, if this archive is read by a
.IR pax
utility conforming to the ISO\ POSIX\(hy2:\|1993 standard, the header block fields are used to
create a regular file that contains the extended header records as
data. Therefore, header block field values should be selected to
provide reasonable file access to this regular file.
.P
A further difference from the
.BR ustar
header block is that data blocks for files of
.IR typeflag
1 (the digit one) (hard link) may be included, which means that the
size field may be greater than zero. Archives created by
.IR pax
.BR \-o
.BR linkdata
shall include these data blocks with the hard links.
.SS "pax Extended Header"
.P
A
.BR pax
extended header contains values that are inappropriate for the
.BR ustar
header block because of limitations in that format: fields requiring a
character encoding other than that described in the ISO/IEC\ 646:\|1991 standard, fields
representing file attributes not described in the
.BR ustar
header, and fields whose format or length do not fit the requirements
of the
.BR ustar
header. The values in an extended header add attributes to the
following file (or files; see the description of the
.IR typeflag
.BR g
header block) or override values in the following header block(s), as
indicated in the following list of keywords.
.P
An extended header shall consist of one or more records, each
constructed as follows:
.sp
.RS 4
.nf

"%d %s=%s\en", <\fIlength\fR>, <\fIkeyword\fR>, <\fIvalue\fR>
.fi
.P
.RE
.P
The extended header records shall be encoded according to the ISO/IEC\ 10646\(hy1:\|2000 standard
UTF\(hy8 encoding. The <\fIlength\fP> field,
<blank>,
<equals-sign>,
and
<newline>
shown shall be limited to the portable character set, as encoded in
UTF\(hy8. The <\fIkeyword\fP> fields can be any UTF\(hy8 characters.
The <\fIlength\fP> field shall be the decimal length of the extended
header record in octets, including the trailing
<newline>.
If there is a
.BR hdrcharset
extended header in effect for a file, the
.IR value
field for any
.BR gname ,
.BR linkpath ,
.BR path ,
and
.BR uname
extended header records shall be encoded using the character set
specified by the
.BR hdrcharset
extended header record; otherwise, the
.IR value
field shall be encoded using UTF\(hy8. The
.IR value
field for all other keywords specified by POSIX.1\(hy2008 shall be
encoded using UTF\(hy8.
.P
The <\fIkeyword\fP> field shall be one of the entries from the
following list or a keyword provided as an implementation extension.
Keywords consisting entirely of lowercase letters, digits, and periods
are reserved for future standardization. A keyword shall not include an
<equals-sign>.
(In the following list, the notations ``file(s)'' or ``block(s)'' is used
to acknowledge that a keyword affects the following single file after a
.IR typeflag
.BR x
extended header, but possibly multiple files after
.IR typeflag
.BR g .
Any requirements in the list for
.IR pax
to include a record when in
.BR write
or
.BR copy
mode shall apply only when such a record has not already been provided
through the use of the
.BR \-o
option. When used in
.BR copy
mode,
.IR pax
shall behave as if an archive had been created with applicable extended
header records and then extracted.)
.IP "\fBatime\fP" 10
The file access time for the following file(s), equivalent to the value
of the
.IR st_atime
member of the
.BR stat
structure for a file, as described by the
\fIstat\fR()
function. The access time shall be restored if the process has
appropriate privileges required to do so. The format of the
<\fIvalue\fP> shall be as described in
.IR "pax Extended Header File Times".
.IP "\fBcharset\fP" 10
The name of the character set used to encode the data in the following
file(s). The entries in the following table are defined to refer to
known standards; additional names may be agreed on between the
originator and recipient.
.TS
center box tab(!);
cB | cB
lf5 | l.
<value>!Formal Standard
_
ISO-IR 646 1990!ISO/IEC 646:\|1990
ISO-IR 8859 1 1998!ISO/IEC 8859\(hy1:\|1998
ISO-IR 8859 2 1999!ISO/IEC 8859\(hy2:\|1999
ISO-IR 8859 3 1999!ISO/IEC 8859\(hy3:\|1999
ISO-IR 8859 4 1998!ISO/IEC 8859\(hy4:\|1998
ISO-IR 8859 5 1999!ISO/IEC 8859\(hy5:\|1999
ISO-IR 8859 6 1999!ISO/IEC 8859\(hy6:\|1999
ISO-IR 8859 7 1987!ISO/IEC 8859\(hy7:\|1987
ISO-IR 8859 8 1999!ISO/IEC 8859\(hy8:\|1999
ISO-IR 8859 9 1999!ISO/IEC 8859\(hy9:\|1999
ISO-IR 8859 10 1998!ISO/IEC 8859\(hy10:\|1998
ISO-IR 8859 13 1998!ISO/IEC 8859\(hy13:\|1998
ISO-IR 8859 14 1998!ISO/IEC 8859\(hy14:\|1998
ISO-IR 8859 15 1999!ISO/IEC 8859\(hy15:\|1999
ISO-IR 10646 2000!ISO/IEC 10646:\|2000
ISO-IR 10646 2000 UTF-8!ISO/IEC 10646, UTF-8 encoding
BINARY!None.
.TE
.RS 10 
.P
The encoding is included in an extended header for information only;
when
.IR pax
is used as described in POSIX.1\(hy2008, it shall not translate the file data
into any other encoding. The
.BR BINARY
entry indicates unencoded binary data.
.P
When used in
.BR write
or
.BR copy
mode, it is implementation-defined whether
.IR pax
includes a
.BR charset
extended header record for a file.
.RE
.IP "\fBcomment\fP" 10
A series of characters used as a comment. All characters in the
<\fIvalue\fP> field shall be ignored by
.IR pax .
.IP "\fBgid\fP" 10
The group ID of the group that owns the file, expressed as a decimal
number using digits from the ISO/IEC\ 646:\|1991 standard. This record shall override the
.IR gid
field in the following header block(s). When used in
.BR write
or
.BR copy
mode,
.IR pax
shall include a
.IR gid
extended header record for each file whose group ID is greater than
2\|097\|151 (octal 7\|777\|777).
.IP "\fBgname\fP" 10
The group of the file(s), formatted as a group name in the group
database. This record shall override the
.IR gid
and
.IR gname
fields in the following header block(s), and any
.IR gid
extended header record. When used in
.BR read ,
.BR copy ,
or
.BR list
mode,
.IR pax
shall translate the name from the encoding in the header record to
the character set appropriate for the group database on the
receiving system. If any of the characters cannot be
translated, and if neither the
.BR \-o \c
.BR invalid=UTF\(hy8
option nor the
.BR \-o \c
.BR invalid=binary
option is specified, the results are implementation-defined.
When used in
.BR write
or
.BR copy
mode,
.IR pax
shall include a
.BR gname
extended header record for each file whose group name cannot be
represented entirely with the letters and digits of the portable
character set.
.IP "\fBhdrcharset\fR" 10
The name of the character set used to encode the value field of the
.BR gname ,
.BR linkpath ,
.BR path ,
and
.BR uname
.IR pax
extended header records. The entries in the following table are defined
to refer to known standards; additional names may be agreed between the
originator and the recipient.
.br
.TS
center box tab(!);
cB | cB
lf5 | l.
<value>!Formal Standard
_
ISO-IR 10646 2000 UTF-8!ISO/IEC 10646, UTF-8 encoding
BINARY!None.
.TE
.RS 10 
.P
If no
.BR hdrcharset
extended header record is specified, the default character set used to
encode all values in extended header records shall be the ISO/IEC\ 10646\(hy1:\|2000 standard
UTF\(hy8 encoding.
.P
The
.BR BINARY
entry indicates that all values recorded in extended headers for
affected files are unencoded binary data from the underlying system.
.RE
.IP "\fBlinkpath\fP" 10
The pathname of a link being created to another file, of any type,
previously archived. This record shall override the
.IR linkname
field in the following
.BR ustar
header block(s). The following
.BR ustar
header block shall determine the type of link created. If
.IR typeflag
of the following header block is 1, it shall be a hard link. If
.IR typeflag
is 2, it shall be a symbolic link and the
.BR linkpath
value shall be the contents of the symbolic link. The
.IR pax
utility shall translate the name of the link (contents of the symbolic
link) from the encoding in the header to the character set appropriate
for the local file system. When used in
.BR write
or
.BR copy
mode,
.IR pax
shall include a
.BR linkpath
extended header record for each link whose pathname cannot be
represented entirely with the members of the portable character set
other than NUL.
.IP "\fBmtime\fP" 10
The file modification time of the following file(s), equivalent to the
value of the
.IR st_mtime
member of the
.BR stat
structure for a file, as described in the
\fIstat\fR()
function. This record shall override the
.IR mtime
field in the following header block(s). The modification time shall be
restored if the process has appropriate privileges required to do
so. The format of the <\fIvalue\fP> shall be as described in
.IR "pax Extended Header File Times".
.IP "\fBpath\fP" 10
The pathname of the following file(s). This record shall override the
.IR name
and
.IR prefix
fields in the following header block(s). The
.IR pax
utility shall translate the pathname of the file from the encoding in
the header to the character set appropriate for the local file system.
.RS 10 
.P
When used in
.BR write
or
.BR copy
mode,
.IR pax
shall include a
.IR path
extended header record for each file whose pathname cannot be
represented entirely with the members of the portable character set
other than NUL.
.RE
.IP "\fBrealtime.\fIany\fR" 10
The keywords prefixed by ``realtime.'' are reserved for future
standardization.
.IP "\fBsecurity.\fIany\fR" 10
The keywords prefixed by ``security.'' are reserved for future
standardization.
.IP "\fBsize\fP" 10
The size of the file in octets, expressed as a decimal number using
digits from the ISO/IEC\ 646:\|1991 standard. This record shall override the
.IR size
field in the following header block(s). When used in
.BR write
or
.BR copy
mode,
.IR pax
shall include a
.IR size
extended header record for each file with a size value greater than
8\|589\|934\|591 (octal 77\|777\|777\|777).
.IP "\fBuid\fP" 10
The user ID of the file owner, expressed as a decimal number using
digits from the ISO/IEC\ 646:\|1991 standard. This record shall override the
.IR uid
field in the following header block(s). When used in
.BR write
or
.BR copy
mode,
.IR pax
shall include a
.IR uid
extended header record for each file whose owner ID is greater than
2\|097\|151 (octal 7\|777\|777).
.IP "\fBuname\fP" 10
The owner of the following file(s), formatted as a user name in the
user database. This record shall override the
.IR uid
and
.IR uname
fields in the following header block(s), and any
.IR uid
extended header record. When used in
.BR read ,
.BR copy ,
or
.BR list
mode,
.IR pax
shall translate the name from the encoding in the header record to the
character set appropriate for the user database on the receiving
system. If any of the characters cannot be translated, and if neither
the
.BR \-o \c
.BR invalid=UTF\(hy8
option nor the
.BR \-o \c
.BR invalid=binary
option is specified, the results are implementation-defined.
When used in
.BR write
or
.BR copy
mode,
.IR pax
shall include a
.BR uname
extended header record for each file whose user name cannot be
represented entirely with the letters and digits of the portable
character set.
.P
If the <\fIvalue\fP> field is zero length, it shall delete any header
block field, previously entered extended header value, or global
extended header value of the same name.
.P
If a keyword in an extended header record (or in a
.BR \-o
option-argument) overrides or deletes a corresponding field in the
.BR ustar
header block,
.IR pax
shall ignore the contents of that header block field.
.P
Unlike the
.BR ustar
header block fields, NULs shall not delimit <\fIvalue\fP>s; all
characters within the <\fIvalue\fP> field shall be considered data for
the field. None of the length limitations of the
.BR ustar
header block fields in
.IR "Table 4-14, ustar Header Block"
shall apply to the extended header records.
.SS "pax Extended Header Keyword Precedence"
.P
This section describes the precedence in which the various header
records and fields and command line options are selected to apply to a
file in the archive. When
.IR pax
is used in
.BR read
or
.BR list
modes, it shall determine a file attribute in the following sequence:
.IP " 1." 4
If
.BR \-o \c
.BR delete=keyword-prefix
is used, the affected attributes shall be determined from step 7., if
applicable, or ignored otherwise.
.IP " 2." 4
If
.BR \-o \c
.IR keyword :=
is used, the affected attributes shall be ignored.
.IP " 3." 4
If
.BR \-o \c
.BR keyword:=value
is used, the affected attribute shall be assigned the value.
.IP " 4." 4
If there is a
.IR typeflag
.BR x
extended header record, the affected attribute shall be assigned the
<\fIvalue\fP>. When extended header records conflict, the last one
given in the header shall take precedence.
.IP " 5." 4
If
.BR \-o \c
.BR keyword=value
is used, the affected attribute shall be assigned the value.
.IP " 6." 4
If there is a
.IR typeflag
.BR g
global extended header record, the affected attribute shall be assigned
the <\fIvalue\fP>. When global extended header records conflict, the
last one given in the global header shall take precedence.
.IP " 7." 4
Otherwise, the attribute shall be determined from the
.BR ustar
header block.
.SS "pax Extended Header File Times"
.P
The
.IR pax
utility shall write an
.BR mtime
record for each file in
.BR write
or
.BR copy
modes if the file's modification time cannot be represented exactly in
the
.BR ustar
header logical record described in
.IR "ustar Interchange Format".
This can occur if the time is out of
.BR ustar
range, or if the file system of the underlying implementation supports
non-integer time granularities and the time is not an integer. All of
these time records shall be formatted as a decimal representation of
the time in seconds since the Epoch. If a
<period>
(\c
.BR '.' )
decimal point character is present, the digits to the right of the
point shall represent the units of a subsecond timing granularity,
where the first digit is tenths of a second and each subsequent digit
is a tenth of the previous digit. In
.BR read
or
.BR copy
mode, the
.IR pax
utility shall truncate the time of a file to the greatest value that is
not greater than the input header file time. In
.BR write
or
.BR copy
mode, the
.IR pax
utility shall output a time exactly if it can be represented exactly as
a decimal number, and otherwise shall generate only enough digits so
that the same time shall be recovered if the file is extracted on a
system whose underlying implementation supports the same time
granularity.
.SS "ustar Interchange Format"
.P
A
.BR ustar
archive tape or file shall contain a series of logical records. Each
logical record shall be a fixed-size logical record of 512 octets (see
below). Although this format may be thought of as being stored on
9-track industry-standard 12.7 mm (0.5 in) magnetic tape, other types of
transportable media are not excluded. Each file archived shall be
represented by a header logical record that describes the file,
followed by zero or more logical records that give the contents of the
file. At the end of the archive file there shall be two 512-octet
logical records filled with binary zeros, interpreted as an
end-of-archive indicator.
.P
The logical records may be grouped for physical I/O operations, as
described under the
.BR \-b \c
.IR blocksize
and
.BR \-x
.BR ustar
options. Each group of logical records may be written with a single
operation equivalent to the
\fIwrite\fR()
function. On magnetic tape, the result of this write shall be a single
tape physical block. The last physical block shall always be the full
size, so logical records after the two zero logical records may contain
undefined data.
.P
The header logical record shall be structured as shown in the following
table. All lengths and offsets are in decimal.
.br
.sp
.ce 1
\fBTable 4-14: ustar Header Block\fR
.TS
center box tab(@);
cB | cB | cB
lI | n | n.
Field Name@Octet Offset@Length (in Octets)
_
name@0@100
mode@100@8
uid@108@8
gid@116@8
size@124@12
mtime@136@12
chksum@148@8
typeflag@156@1
linkname@157@100
magic@257@6
version@263@2
uname@265@32
gname@297@32
devmajor@329@8
devminor@337@8
prefix@345@155
.TE
.P
All characters in the header logical record shall be represented in the
coded character set of the ISO/IEC\ 646:\|1991 standard. For maximum portability between
implementations, names should be selected from characters represented
by the portable filename character set as octets with the most
significant bit zero. If an implementation supports the use of
characters outside of
<slash>
and the portable filename character set in names for files, users, and
groups, one or more implementation-defined encodings of these characters
shall be provided for interchange purposes.
.P
However, the
.IR pax
utility shall never create filenames on the local system that cannot
be accessed via the procedures described in POSIX.1\(hy2008. If a filename is
found on the medium that would create an invalid filename, it is
implementation-defined whether the data from the file is stored on the
file hierarchy and under what name it is stored. The
.IR pax
utility may choose to ignore these files as long as it produces an
error indicating that the file is being ignored.
.P
Each field within the header logical record is contiguous; that is,
there is no padding used. Each character on the archive medium shall be
stored contiguously.
.P
The fields
.IR magic ,
.IR uname ,
and
.IR gname
are character strings each terminated by a NUL character. The fields
.IR name ,
.IR linkname ,
and
.IR prefix
are NUL-terminated character strings except when all characters in the
array contain non-NUL characters including the last character. The
.IR version
field is two octets containing the characters
.BR \(dq00\(dq 
(zero-zero). The
.IR typeflag
contains a single character. All other fields are leading zero-filled
octal numbers using digits from the ISO/IEC\ 646:\|1991 standard IRV. Each numeric field is
terminated by one or more
<space>
or NUL characters.
.P
The
.IR name
and the
.IR prefix
fields shall produce the pathname of the file. A new pathname shall
be formed, if
.IR prefix
is not an empty string (its first character is not NUL), by
concatenating
.IR prefix
(up to the first NUL character), a
<slash>
character, and
.IR name ;
otherwise,
.IR name
is used alone. In either case,
.IR name
is terminated at the first NUL character. If
.IR prefix
begins with a NUL character, it shall be ignored. In this manner,
pathnames of at most 256 characters can be supported. If a pathname
does not fit in the space provided,
.IR pax
shall notify the user of the error, and shall not store any part of the
file\(emheader or data\(emon the medium.
.P
The
.IR linkname
field, described below, shall not use the
.IR prefix
to produce a pathname. As such, a
.IR linkname
is limited to 100 characters. If the name does not fit in the space
provided,
.IR pax
shall notify the user of the error, and shall not attempt to store the
link on the medium.
.P
The
.IR mode
field provides 12 bits encoded in the ISO/IEC\ 646:\|1991 standard octal digit representation.
The encoded bits shall represent the following values:
.br
.sp
.ce 1
\fBTable: ustar \fImode\fP Field\fR
.TS
tab(!) center box;
cB | cB | cB
n | l | l.
Bit Value!POSIX.1\(hy2008 Bit!Description
_
04\|000!S_ISUID!Set UID on execution.
02\|000!S_ISGID!Set GID on execution.
01\|000!<reserved>!Reserved for future standardization.
00\|400!S_IRUSR!Read permission for file owner class.
00\|200!S_IWUSR!Write permission for file owner class.
00\|100!S_IXUSR!Execute/search permission for file owner class.
00\|040!S_IRGRP!Read permission for file group class.
00\|020!S_IWGRP!Write permission for file group class.
00\|010!S_IXGRP!Execute/search permission for file group class.
00\|004!S_IROTH!Read permission for file other class.
00\|002!S_IWOTH!Write permission for file other class.
00\|001!S_IXOTH!Execute/search permission for file other class.
.TE
.P
When appropriate privileges are required to set one of these mode bits,
and the user restoring the files from the archive does not have
appropriate privileges, the mode bits for which the user does not have
appropriate privileges shall be ignored. Some of the mode bits in the
archive format are not mentioned elsewhere in this volume of POSIX.1\(hy2017. If the
implementation does not support those bits, they may be ignored.
.P
The
.IR uid
and
.IR gid
fields are the user and group ID of the owner and group of the file,
respectively.
.P
The
.IR size
field is the size of the file in octets. If the
.IR typeflag
field is set to specify a file to be of type 1 (a link) or 2 (a
symbolic link), the
.IR size
field shall be specified as zero. If the
.IR typeflag
field is set to specify a file of type 5 (directory), the
.IR size
field shall be interpreted as described under the definition of that
record type. No data logical records are stored for types 1, 2, or 5.
If the
.IR typeflag
field is set to 3 (character special file), 4 (block special file), or
6 (FIFO), the meaning of the
.IR size
field is unspecified by this volume of POSIX.1\(hy2017, and no data logical records shall be
stored on the medium. Additionally, for type 6, the
.IR size
field shall be ignored when reading. If the
.IR typeflag
field is set to any other value, the number of logical records written
following the header shall be (\c
.IR size +511)/512,
ignoring any fraction in the result of the division.
.P
The
.IR mtime
field shall be the modification time of the file at the time it was
archived. It is the ISO/IEC\ 646:\|1991 standard representation of the octal value of the
modification time obtained from the
\fIstat\fR()
function.
.P
The
.IR chksum
field shall be the ISO/IEC\ 646:\|1991 standard IRV representation of the octal value of the
simple sum of all octets in the header logical record. Each octet in
the header shall be treated as an unsigned value. These values shall be
added to an unsigned integer, initialized to zero, the precision of
which is not less than 17 bits. When calculating the checksum, the
.IR chksum
field is treated as if it were all
<space>
characters.
.P
The
.IR typeflag
field specifies the type of file archived. If a particular
implementation does not recognize the type, or the user does not have
appropriate privileges to create that type, the file shall be extracted
as if it were a regular file if the file type is defined to have a
meaning for the
.IR size
field that could cause data logical records to be written on the medium
(see the previous description for
.IR size ).
If conversion to a regular file occurs, the
.IR pax
utility shall produce an error indicating that the conversion took
place. All of the
.IR typeflag
fields shall be coded in the ISO/IEC\ 646:\|1991 standard IRV:
.IP "\fR0\fR" 8
Represents a regular file. For backwards-compatibility, a
.IR typeflag
value of binary zero (\c
.BR '\e0' )
should be recognized as meaning a regular file when extracting files
from the archive. Archives written with this version of the archive
file format create regular files with a
.IR typeflag
value of the ISO/IEC\ 646:\|1991 standard IRV
.BR '0' .
.IP "\fR1\fR" 8
Represents a file linked to another file, of any type, previously
archived. Such files are identified by having the same device
and file serial numbers, and pathnames that refer to different
directory entries. All such files shall be archived as linked files.
The linked-to name is specified in the
.IR linkname
field with a NUL-character terminator if it is less than 100 octets in
length.
.IP "\fR2\fR" 8
Represents a symbolic link. The contents of the symbolic link shall be
stored in the
.IR linkname
field.
.IP "\fR3,4\fR" 8
Represent character special files and block special files respectively.
In this case the
.IR devmajor
and
.IR devminor
fields shall contain information defining the device, the format of
which is unspecified by this volume of POSIX.1\(hy2017. Implementations may map the device
specifications to their own local specification or may ignore the
entry.
.IP "\fR5\fR" 8
Specifies a directory or subdirectory. On systems where disk allocation
is performed on a directory basis, the
.IR size
field shall contain the maximum number of octets (which may be rounded
to the nearest disk block allocation unit) that the directory may hold.
A
.IR size
field of zero indicates no such limiting. Systems that do not support
limiting in this manner should ignore the
.IR size
field.
.IP "\fR6\fR" 8
Specifies a FIFO special file. Note that the archiving of a FIFO file
archives the existence of this file and not its contents.
.IP "\fR7\fR" 8
Reserved to represent a file to which an implementation has associated
some high-performance attribute. Implementations without such
extensions should treat this file as a regular file (type 0).
.IP "\fRA\(hyZ\fR" 8
The letters
.BR 'A' 
to
.BR 'Z' ,
inclusive, are reserved for custom implementations. All other values
are reserved for future versions of this standard.
.P
It is unspecified whether files with pathnames that refer to the same
directory entry are archived as linked files or as separate files. If
they are archived as linked files, this means that attempting to
extract both pathnames from the resulting archive will always cause an
error (unless the
.BR \-u
option is used) because the link cannot be created.
.P
It is unspecified whether files with the same device and file serial
numbers being appended to an archive are treated as linked files to
members that were in the archive before the append.
.P
Attempts to archive a socket shall produce a diagnostic message when
.BR ustar
interchange format is used, but may be allowed when
.BR pax
interchange format is used. Handling of other file types is
implementation-defined.
.P
The
.IR magic
field is the specification that this archive was output in this archive
format. If this field contains
.BR ustar
(the five characters from the ISO/IEC\ 646:\|1991 standard IRV shown followed by NUL), the
.IR uname
and
.IR gname
fields shall contain the ISO/IEC\ 646:\|1991 standard IRV representation of the owner and
group of the file, respectively (truncated to fit, if necessary). When
the file is restored by a privileged, protection-preserving version of
the utility, the user and group databases shall be scanned for these
names. If found, the user and group IDs contained within these files
shall be used rather than the values contained within the
.IR uid
and
.IR gid
fields.
.SS "cpio Interchange Format"
.P
The octet-oriented
.BR cpio
archive format shall be a series of entries, each comprising a header
that describes the file, the name of the file, and then the contents of
the file.
.P
An archive may be recorded as a series of fixed-size blocks of octets.
This blocking shall be used only to make physical I/O more efficient.
The last group of blocks shall always be at the full size.
.P
For the octet-oriented
.BR cpio
archive format, the individual entry information shall be in the order
indicated and described by the following table; see also the
.IR <cpio.h> 
header.
.br
.sp
.ce 1
\fBTable 4-16: Octet-Oriented cpio Archive Entry\fR
.TS
center box tab(!);
cB | cB | cB
lI | n | l.
Header Field Name!Length (in Octets)!Interpreted as
_
c_magic!6!Octal number
c_dev!6!Octal number
c_ino!6!Octal number
c_mode!6!Octal number
c_uid!6!Octal number
c_gid!6!Octal number
c_nlink!6!Octal number
c_rdev!6!Octal number
c_mtime!11!Octal number
c_namesize!6!Octal number
c_filesize!11!Octal number
_
.T&
cB | cB | cB
lI lI l.
Filename Field Name!Length!Interpreted as
_
c_name!c_namesize!Pathname string
_
.T&
cB | cB | cB
lI lI l.
File Data Field Name!Length!Interpreted as
_
c_filedata!c_filesize!Data
.TE
.SS "cpio Header"
.P
For each file in the archive, a header as defined previously shall be
written. The information in the header fields is written as streams of
the ISO/IEC\ 646:\|1991 standard characters interpreted as octal numbers. The octal numbers
shall be extended to the necessary length by appending the ISO/IEC\ 646:\|1991 standard IRV
zeros at the most-significant-digit end of the number; the result is
written to the most-significant digit of the stream of octets first.
The fields shall be interpreted as follows:
.IP "\fIc_magic\fR" 10
Identify the archive as being a transportable archive by containing the
identifying value
.BR \(dq070707\(dq .
.IP "\fIc_dev\fR,\ \fIc_ino\fR" 10
Contains values that uniquely identify the file within the archive
(that is, no files contain the same pair of
.IR c_dev
and
.IR c_ino
values unless they are links to the same file). The values shall be
determined in an unspecified manner.
.IP "\fIc_mode\fR" 10
Contains the file type and access permissions as defined in the
following table.
.br
.sp
.ce 1
\fBTable 4-17: Values for cpio c_mode Field\fR
.TS
center box tab(@);
cB | cB | cB
l | n | l.
File Permissions Name@Value@Indicates
_
C_IRUSR@000\|400@Read by owner
C_IWUSR@000\|200@Write by owner
C_IXUSR@000\|100@Execute by owner
C_IRGRP@000\|040@Read by group
C_IWGRP@000\|020@Write by group
C_IXGRP@000\|010@Execute by group
C_IROTH@000\|004@Read by others
C_IWOTH@000\|002@Write by others
C_IXOTH@000\|001@Execute by others
C_ISUID@004\|000@Set \fIuid\fP
C_ISGID@002\|000@Set \fIgid\fP
C_ISVTX@001\|000@Reserved
_
.T&
cB | cB | cB
l | n | l.
File Type Name@Value@Indicates
_
C_ISDIR@040\|000@Directory
C_ISFIFO@010\|000@FIFO
C_ISREG@0100\|000@Regular file
C_ISLNK@0120\|000@Symbolic link
.RS 10 
.P
C_ISBLK@060\|000@Block special file
C_ISCHR@020\|000@Character special file
C_ISSOCK@0140\|000@Socket
.P
C_ISCTG@0110\|000@Reserved
.TE
.P
Directories, FIFOs, symbolic links, and regular files shall be
supported on a system conforming to this volume of POSIX.1\(hy2017; additional values defined
previously are reserved for compatibility with existing systems.
Additional file types may be supported; however, such files should not
be written to archives intended to be transported to other systems.
.RE
.IP "\fIc_uid\fR" 10
Contains the user ID of the owner.
.IP "\fIc_gid\fR" 10
Contains the group ID of the group.
.IP "\fIc_nlink\fR" 10
Contains a number greater than or equal to the number of links in the
archive referencing the file. If the
.BR \-a
option is used to append to a
.IR cpio
archive, then the
.IR pax
utility need not account for the files in the existing part of the
archive when calculating the
.IR c_nlink
values for the appended part of the archive, and need not alter the
.IR c_nlink
values in the existing part of the archive if additional files with the
same
.IR c_dev
and
.IR c_ino
values are appended to the archive.
.IP "\fIc_rdev\fR" 10
Contains implementation-defined information for character or block
special files.
.IP "\fIc_mtime\fR" 10
Contains the latest time of modification of the file at the time the
archive was created.
.IP "\fIc_namesize\fR" 10
Contains the length of the pathname, including the terminating NUL
character.
.IP "\fIc_filesize\fR" 10
Contains the length in octets of the data section following the
header structure.
.SS "cpio Filename"
.P
The
.IR c_name
field shall contain the pathname of the file. The length of this field
in octets is the value of
.IR c_namesize .
.P
If a filename is found on the medium that would create an invalid
pathname, it is implementation-defined whether the data from the file
is stored on the file hierarchy and under what name it is stored.
.P
All characters shall be represented in the ISO/IEC\ 646:\|1991 standard IRV. For maximum
portability between implementations, names should be selected from
characters represented by the portable filename character set as
octets with the most significant bit zero. If an implementation
supports the use of characters outside the portable filename character
set in names for files, users, and groups, one or more
implementation-defined encodings of these characters shall be provided
for interchange purposes. However, the
.IR pax
utility shall never create filenames on the local system that cannot
be accessed via the procedures described previously in this volume of POSIX.1\(hy2017. If a
filename is found on the medium that would create an invalid filename,
it is implementation-defined whether the data from the file is stored on
the local file system and under what name it is stored. The
.IR pax
utility may choose to ignore these files as long as it produces an
error indicating that the file is being ignored.
.SS "cpio File Data"
.P
Following
.IR c_name ,
there shall be
.IR c_filesize
octets of data. Interpretation of such data occurs in a manner
dependent on the file. For regular files, the data shall consist
of the contents of the file. For symbolic links, the data shall
consist of the contents of the symbolic link. If
.IR c_filesize
is zero, no data shall be contained in
.IR c_filedata .
.P
When restoring from an archive:
.IP " *" 4
If the user does not have appropriate privileges to create a file of
the specified type,
.IR pax
shall ignore the entry and write an error message to standard error.
.IP " *" 4
Only regular files and symbolic links have data to be restored. Presuming
a regular file meets any selection criteria that might be imposed on
the format-reading utility by the user, such data shall be restored.
.IP " *" 4
If a user does not have appropriate privileges to set a particular mode
flag, the flag shall be ignored. Some of the mode flags in the archive
format are not mentioned elsewhere in this volume of POSIX.1\(hy2017. If the implementation does
not support those flags, they may be ignored.
.SS "cpio Special Entries"
.P
FIFO special files, directories, and the trailer shall be recorded with
.IR c_filesize
equal to zero. Symbolic links shall be recorded with
.IR c_filesize
equal to the length of the contents of the symbolic link.
For other special files,
.IR c_filesize
is unspecified by this volume of POSIX.1\(hy2017. The header for the next file entry in the
archive shall be written directly after the last octet of the file
entry preceding it. A header denoting the filename
.BR TRAILER!!!
shall indicate the end of the archive; the contents of octets in the
last block of the archive following such a header are undefined.
.SH "EXIT STATUS"
The following exit values shall be returned:
.IP "\00" 6
All files were processed successfully.
.IP >0 6
An error occurred.
.SH "CONSEQUENCES OF ERRORS"
If
.IR pax
cannot create a file or a link when reading an archive or cannot find a
file when writing an archive, or cannot preserve the user ID, group ID,
or file mode when the
.BR \-p
option is specified, a diagnostic message shall be written to standard
error and a non-zero exit status shall be returned, but processing
shall continue. In the case where
.IR pax
cannot create a link to a file,
.IR pax
shall not, by default, create a second copy of the file.
.P
If the extraction of a file from an archive is prematurely terminated
by a signal or error,
.IR pax
may have only partially extracted the file or (if the
.BR \-n
option was not specified) may have extracted a file of the same name as
that specified by the user, but which is not the file the user wanted.
Additionally, the file modes of extracted directories may have
additional bits from the S_IRWXU mask set as well as incorrect
modification and access times.
.LP
.IR "The following sections are informative."
.SH "APPLICATION USAGE"
Caution is advised when using the
.BR \-a
option to append to a
.IR cpio
format archive. If any of the files being appended happen to be given
the same
.IR c_dev
and
.IR c_ino
values as a file in the existing part of the archive, then they may be
treated as links to that file on extraction. Thus, it is risky to use
.BR \-a
with
.IR cpio
format except when it is done on the same system that the original
archive was created on, and with the same
.IR pax
utility, and in the knowledge that there has been little or no file
system activity since the original archive was created that could lead
to any of the files appended being given the same
.IR c_dev
and
.IR c_ino
values as an unrelated file in the existing part of the archive. Also,
when (intentionally) appending additional links to a file in the
existing part of the archive, the
.IR c_nlink
values in the modified archive can be smaller than the number of links
to the file in the archive, which may mean that the links are not
preserved on extraction.
.P
The
.BR \-p
(privileges) option was invented to reconcile differences between
historical
.IR tar
and
.IR cpio
implementations. In particular, the two utilities use
.BR \-m
in diametrically opposed ways. The
.BR \-p
option also provides a consistent means of extending the ways in which
future file attributes can be addressed, such as for enhanced security
systems or high-performance files. Although it may seem complex, there
are really two modes that are most commonly used:
.IP "\fB\-p\ e\fR" 8
``Preserve everything''. This would be used by the historical
superuser, someone with all appropriate privileges, to preserve all
aspects of the files as they are recorded in the archive. The
.BR e
flag is the sum of
.BR o
and
.BR p ,
and other implementation-defined attributes.
.IP "\fB\-p\ p\fR" 8
``Preserve'' the file mode bits. This would be used by the user with
regular privileges who wished to preserve aspects of the file other
than the ownership. The file times are preserved by default, but two
other flags are offered to disable these and use the time of
extraction.
.P
The one pathname per line format of standard input precludes
pathnames containing
<newline>
characters. Although such pathnames violate the portable filename
guidelines, they may exist and their presence may inhibit usage of
.IR pax
within shell scripts. This problem is inherited from historical archive
programs. The problem can be avoided by listing filename arguments on
the command line instead of on standard input.
.P
It is almost certain that appropriate privileges are required for
.IR pax
to accomplish parts of this volume of POSIX.1\(hy2017. Specifically, creating files of type
block special or character special, restoring file access times unless
the files are owned by the user (the
.BR \-t
option), or preserving file owner, group, and mode (the
.BR \-p
option) all probably require appropriate privileges.
.P
In
.BR read
mode, implementations are permitted to overwrite files when the archive
has multiple members with the same name. This may fail if permissions
on the first version of the file do not permit it to be overwritten.
.P
The
.BR cpio
and
.BR ustar
formats can only support files up to 8\|589\|934\|592 bytes
(8 \(** 2^30) in size.
.P
When archives containing binary header information are listed , the
filenames printed may cause strange behavior on some terminals.
.P
When all of the following are true:
.IP " 1." 4
A file of type directory is being placed into an archive.
.IP " 2." 4
The
.BR ustar
archive format is being used.
.IP " 3." 4
The pathname of the directory is less than or equal to 155 bytes long
(it will fit in the
.IR prefix
field in the
.BR ustar
header block).
.IP " 4." 4
The last component of the pathname of the directory is longer than 100
bytes long (it will not fit in the
.IR name
field in the
.BR ustar
header block).
.P
some implementations of the
.IR pax
utility will place the entire directory pathname in the
.IR prefix
field, set the
.IR name
field to an empty string, and place the directory in the archive.
Other implementations of the
.IR pax
utility will give an error under these conditions because the
.IR name
field is not large enough to hold the last component of the directory name.
This standard allows either behavior. However, when extracting a directory
from a
.BR ustar
format archive, this standard requires that all implementations be able
to extract a directory even if the
.IR name
field contains an empty string as long as the
.IR prefix
field does not also contain an empty string.
.SH EXAMPLES
The following command:
.sp
.RS 4
.nf

pax -w -f /dev/rmt/1m .
.fi
.P
.RE
.P
copies the contents of the current directory to tape drive 1, medium
density (assuming historical System V device naming procedures\(emthe
historical BSD device name would be
.BR /dev/rmt9 ).
.P
The following commands:
.sp
.RS 4
.nf

mkdir \fInewdir\fR
pax -rw \fIolddir newdir\fR
.fi
.P
.RE
.P
copy the
.IR olddir
directory hierarchy to
.IR newdir .
.sp
.RS 4
.nf

pax -r -s \(aq,\(ha//*usr//*,,\(aq -f a.pax
.fi
.P
.RE
.P
reads the archive
.BR a.pax ,
with all files rooted in
.BR /usr
in the archive extracted relative to the current directory.
.P
Using the option:
.sp
.RS 4
.nf

-o listopt="%M %(atime)T %(size)D %(name)s"
.fi
.P
.RE
.P
overrides the default output description in Standard Output and instead
writes:
.sp
.RS 4
.nf

-rw-rw--- Jan 12 15:53 2003 1492 /usr/foo/bar
.fi
.P
.RE
.P
Using the options:
.sp
.RS 4
.nf

-o listopt=\(aq%L\et%(size)D\en%.7\(aq \e
-o listopt=\(aq(name)s\en%(atime)T\en%T\(aq
.fi
.P
.RE
.P
overrides the default output description in Standard Output and instead
writes:
.sp
.RS 4
.nf

/usr/foo/bar -> /tmp   1492
/usr/fo
Jan 12 15:53 1991
Jan 31 15:53 2003
.fi
.P
.RE
.SH RATIONALE
The
.IR pax
utility was new for the ISO\ POSIX\(hy2:\|1993 standard. It represents a peaceful
compromise between advocates of the historical
.IR tar
and
.IR cpio
utilities.
.P
A fundamental difference between
.IR cpio
and
.IR tar
was in the way directories were treated. The
.IR cpio
utility did not treat directories differently from other files, and to
select a directory and its contents required that each file in the
hierarchy be explicitly specified. For
.IR tar ,
a directory matched every file in the file hierarchy it rooted.
.P
The
.IR pax
utility offers both interfaces; by default, directories map into the
file hierarchy they root. The
.BR \-d
option causes
.IR pax
to skip any file not explicitly referenced, as
.IR cpio
historically did. The
.IR tar
.BR \- \c
.IR style
behavior was chosen as the default because it was believed that this
was the more common usage and because
.IR tar
is the more commonly available interface, as it was historically
provided on both System V and BSD implementations.
.P
The data interchange format specification in this volume of POSIX.1\(hy2017 requires that
processes with ``appropriate privileges'' shall always restore the
ownership and permissions of extracted files exactly as archived. If
viewed from the historic equivalence between superuser and
``appropriate privileges'', there are two problems
with this requirement. First, users running as superusers may
unknowingly set dangerous permissions on extracted files. Second, it is
needlessly limiting, in that superusers cannot extract files and own
them as superuser unless the archive was created by the superuser. (It
should be noted that restoration of ownerships and permissions for the
superuser, by default, is historical practice in
.IR cpio ,
but not in
.IR tar .)
In order to avoid these two problems, the
.IR pax
specification has an additional ``privilege'' mechanism, the
.BR \-p
option. Only a
.IR pax
invocation with the privileges needed, and which has the
.BR \-p
option set using the
.BR e
specification character, has appropriate privileges to restore
full ownership and permission information.
.P
Note also that this volume of POSIX.1\(hy2017 requires that the file ownership and access
permissions shall be set, on extraction, in the same fashion as the
\fIcreat\fR()
function when provided with the mode stored in the archive. This means
that the file creation mask of the user is applied to the file
permissions.
.P
Users should note that directories may be created by
.IR pax
while extracting files with permissions that are different from those
that existed at the time the archive was created. When extracting
sensitive information into a directory hierarchy that no longer exists,
users are encouraged to set their file creation mask appropriately to
protect these files during extraction.
.P
The table of contents output is written to standard output to
facilitate pipeline processing.
.P
An early proposal had hard links displaying for all pathnames. This
was removed because it complicates the output of the case where
.BR \-v
is not specified and does not match historical
.IR cpio
usage. The hard-link information is available in the
.BR \-v
display.
.P
The description of the
.BR \-l
option allows implementations to make hard links to symbolic links.
Earlier versions of this standard did not specify any way to create a
hard link to a symbolic link, but many implementations provided this
capability as an extension. If there are hard links to symbolic links
when an archive is created, the implementation is required to archive
the hard link in the archive (unless
.BR \-H
or
.BR \-L
is specified). When in
.BR read
mode and in
.BR copy
mode, implementations supporting hard links to symbolic links should
use them when appropriate.
.P
The archive formats inherited from the POSIX.1\(hy1990 standard have certain restrictions
that have been brought along from historical usage. For example, there
are restrictions on the length of pathnames stored in the archive.
When
.IR pax
is used in
.BR copy (\c
.BR \-rw )
mode (copying directory hierarchies), the ability to use extensions
from the
.BR \-x \c
.BR pax
format overcomes these restrictions.
.P
The default
.IR blocksize
value of 5\|120 bytes for
.IR cpio
was selected because it is one of the standard block-size values for
.IR cpio ,
set when the
.BR \-B
option is specified. (The other default block-size value for
.IR cpio
is 512 bytes, and this was considered to be too small.) The default
block value of 10\|240 bytes for
.IR tar
was selected because that is the standard block-size value for BSD
.IR tar .
The maximum block size of 32\|256 bytes (2**15\-512 bytes)
is the largest multiple of 512 bytes that fits into a signed 16-bit
tape controller transfer register. There are known limitations in some
historical systems that would prevent larger blocks from being
accepted. Historical values were chosen to improve compatibility with
historical scripts using
.IR dd
or similar utilities to manipulate archives. Also, default block sizes
for any file type other than character special file has been deleted
from this volume of POSIX.1\(hy2017 as unimportant and not likely to affect the structure of the
resulting archive.
.P
Implementations are permitted to modify the block-size value based on
the archive format or the device to which the archive is being
written. This is to provide implementations with the opportunity to
take advantage of special types of devices, and it should not be used
without a great deal of consideration as it almost certainly decreases
archive portability.
.P
The intended use of the
.BR \-n
option was to permit extraction of one or more files from the archive
without processing the entire archive. This was viewed by the standard
developers as offering significant performance advantages over
historical implementations. The
.BR \-n
option in early proposals had three effects; the first was to cause
special characters in patterns to not be treated specially. The second
was to cause only the first file that matched a pattern to be
extracted. The third was to cause
.IR pax
to write a diagnostic message to standard error when no file was found
matching a specified pattern. Only the second behavior is retained by
this volume of POSIX.1\(hy2017, for many reasons. First, it is in general not acceptable for a
single option to have multiple effects. Second, the ability to make
pattern matching characters act as normal characters
is useful for parts of
.IR pax
other than file extraction. Third, a finer degree of control over the
special characters is useful because users may wish to normalize only a
single special character in a single filename. Fourth, given a more
general escape mechanism, the previous behavior of the
.BR \-n
option can be easily obtained using the
.BR \-s
option or a
.IR sed
script. Finally, writing a diagnostic message when a pattern specified
by the user is unmatched by any file is useful behavior in all cases.
.P
In this version, the
.BR \-n
was removed from the
.BR copy
mode synopsis of
.IR pax ;
it is inapplicable because there are no pattern operands specified in
this mode.
.P
There is another method than
.IR pax
for copying subtrees in POSIX.1\(hy2008 described as part of the
.IR cp
utility. Both methods are historical practice:
.IR cp
provides a simpler, more intuitive interface, while
.IR pax
offers a finer granularity of control. Each provides additional
functionality to the other; in particular,
.IR pax
maintains the hard-link structure of the hierarchy while
.IR cp
does not. It is the intention of the standard developers that the
results be similar (using appropriate option combinations in both
utilities). The results are not required to be identical; there seemed
insufficient gain to applications to balance the difficulty of
implementations having to guarantee that the results would be exactly
identical.
.P
A single archive may span more than one file. It is suggested that
implementations provide informative messages to the user on standard
error whenever the archive file is changed.
.P
The
.BR \-d
option (do not create intermediate directories not listed in the
archive) found in early proposals was originally provided as a
complement to the historic
.BR \-d
option of
.IR cpio .
It has been deleted.
.P
The
.BR \-s
option in early proposals specified a subset of the substitution
command from the
.IR ed
utility. As there was no reason for only a subset to be supported, the
.BR \-s
option is now compatible with the current
.IR ed
specification. Since the delimiter can be any non-null character, the
following usage with single
<space>
characters is valid:
.sp
.RS 4
.nf

pax -s " foo bar " ...
.fi
.P
.RE
.P
The
.BR \-t
description is worded so as to note that this may cause the access time
update caused by some other activity (which occurs while the file is
being read) to be overwritten.
.P
The default behavior of
.IR pax
with regard to file modification times is the same as historical
implementations of
.IR tar .
It is not the historical behavior of
.IR cpio .
.P
Because the
.BR \-i
option uses
.BR /dev/tty ,
utilities without a controlling terminal are not able to use this
option.
.P
The
.BR \-y
option, found in early proposals, has been deleted because a line
containing a single
<period>
for the
.BR \-i
option has equivalent functionality. The special lines for the
.BR \-i
option (a single
<period>
and the empty line) are historical practice in
.IR cpio .
.P
In early drafts, a
.BR \-e \c
.IR charmap
option was included to increase portability of files between systems
using different coded character sets. This option was omitted because
it was apparent that consensus could not be formed for it. In this
version, the use of UTF\(hy8 should be an adequate substitute.
.P
The ISO\ POSIX\(hy2:\|1993 standard and ISO\ POSIX\(hy1 standard requirements for
.IR pax ,
however, made it very difficult to create a single archive containing
files created using extended characters provided by different locales.
This version adds the
.BR hdrcharset
keyword to make it possible to archive files in these cases without
dropping files due to translation errors.
.P
Translating filenames and other attributes from a locale's encoding to
UTF\(hy8 and then back again can lose information, as the resulting
filename might not be byte-for-byte equivalent to the original. To
avoid this problem, users can specify the
.BR \-o
.BR hdrcharset=binary
option, which will cause the resulting archive to use binary
format for all names and attributes. Such archives are not portable
among hosts that use different native encodings (e.g., EBCDIC
\fIversus\fR ASCII-based encodings), but they will allow interchange
among the vast majority of POSIX file systems in practical use. Also,
the
.BR \-o
.BR hdrcharset=binary
option will cause
.IR pax
in
.BR copy
mode to behave more like other standard utilities such as
.IR cp .
.P
If the values specified by the
.BR \-o
.BR exthdr.name=value ,
.BR \-o
.BR globexthdr.name=value ,
or by
.BR $TMPDIR
(if
.BR \-o
.BR globexthdr.name
is not specified) require a character encoding other than that
described in the ISO/IEC\ 646:\|1991 standard, a
.BR path
extended header record will have to be created for the file. If a
.BR hdrcharset
extended header record is active for such headers, it will determine
the codeset used for the value field in these extended
.BR path
header records. These
.BR path
extended header records always need to be created when writing an
archive even if
.BR hdrcharset=binary
has been specified and would contain the same (binary) data that
appears in the
.BR ustar
header record prefix and
.IR name
fields. (In other words, an extended header
.BR path
record is always required to be generated if the
.IR prefix
or
.IR name
fields contain non-ASCII characters even when
.BR hdrcharset=binary
is also in effect for that file.)
.P
The
.BR \-k
option was added to address international concerns about the dangers
involved in the character set transformations of
.BR \-e
(if the target character set were different from the source, the
filenames might be transformed into names matching existing files) and
also was made more general to protect files transferred between file
systems with different
{NAME_MAX}
values (truncating a filename on a smaller system might also
inadvertently overwrite existing files). As stated, it prevents any
overwriting, even if the target file is older than the source. This
version adds more granularity of options to solve this problem by
introducing the
.BR \-o \c
.BR invalid=option \c
\(emspecifically the
.BR UTF\(hy8
and
.BR binary
actions. (Note that an existing file is still subject to overwriting in
this case. The
.BR \-k
option closes that loophole.)
.P
Some of the file characteristics referenced in this volume of POSIX.1\(hy2017 might not be
supported by some archive formats. For example, neither the
.BR tar
nor
.BR cpio
formats contain the file access time. For this reason, the
.BR e
specification character has been provided, intended to cause all file
characteristics specified in the archive to be retained.
.P
It is required that extracted directories, by default, have their
access and modification times and permissions set to the values
specified in the archive. This has obvious problems in that the
directories are almost certainly modified after being extracted and
that directory permissions may not permit file creation. One possible
solution is to create directories with the mode specified in the
archive, as modified by the
.IR umask
of the user, with sufficient permissions to allow file creation. After
all files have been extracted,
.IR pax
would then reset the access and modification times and permissions as
necessary.
.P
The list-mode formatting description borrows heavily from the one
defined by the
.IR printf
utility. However, since there is no separate operand list to get
conversion arguments, the format was extended to allow specifying the
name of the conversion argument as part of the conversion
specification.
.P
The
.BR T
conversion specifier allows time fields to be displayed in any of
the date formats. Unlike the
.IR ls
utility,
.IR pax
does not adjust the format when the date is less than six months in the
past. This makes parsing the output more predictable.
.P
The
.BR D
conversion specifier handles the ability to display the major/minor
or file size, as with
.IR ls ,
by using \fR%\-8(\fIsize\fR)D\fR.
.P
The
.BR L
conversion specifier handles the
.IR ls
display for symbolic links.
.P
Conversion specifiers were added to generate existing known types used
for
.IR ls .
.SS "pax Interchange Format"
.P
The new POSIX data interchange format was developed primarily to
satisfy international concerns that the
.BR ustar
and
.BR cpio
formats did not provide for file, user, and group names encoded in
characters outside a subset of the ISO/IEC\ 646:\|1991 standard. The standard developers
realized that this new POSIX data interchange format should be very
extensible because there were other requirements they foresaw in the
near future:
.IP " *" 4
Support international character encodings and locale information
.IP " *" 4
Support security information (ACLs, and so on)
.IP " *" 4
Support future file types, such as realtime or contiguous files
.IP " *" 4
Include data areas for implementation use
.IP " *" 4
Support systems with words larger than 32 bits and timers with
subsecond granularity
.P
The following were not goals for this format because these are better
handled by separate utilities or are inappropriate for a portable
format:
.IP " *" 4
Encryption
.IP " *" 4
Compression
.IP " *" 4
Data translation between locales and codesets
.IP " *" 4
.IR inode
storage
.P
The format chosen to support the goals is an extension of the
.BR ustar
format. Of the two formats previously available, only the
.BR ustar
format was selected for extensions because:
.IP " *" 4
It was easier to extend in an upwards-compatible way. It offered version
flags and header block type fields with room for future
standardization. The
.BR cpio
format, while possessing a more flexible file naming methodology, could
not be extended without breaking some theoretical implementation
or using a dummy filename that could be a legitimate filename.
.IP " *" 4
Industry experience since the original ``\c
.IR tar
wars'' fought in developing the ISO\ POSIX\(hy1 standard has clearly been in favor of the
.BR ustar
format, which is generally the default output format selected for
.IR pax
implementations on new systems.
.P
The new format was designed with one additional goal in mind:
reasonable behavior when an older
.IR tar
or
.IR pax
utility happened to read an archive. Since the POSIX.1\(hy1990 standard mandated that a
``format-reading utility'' had to treat unrecognized
.IR typeflag
values as regular files, this allowed the format to include all the
extended information in a pseudo-regular file that preceded each real
file. An option is given that allows the archive creator to set up
reasonable names for these files on the older systems. Also, the
normative text suggests that reasonable file access values be used for
this
.BR ustar
header block. Making these header files inaccessible for convenient
reading and deleting would not be reasonable. File permissions of 600
or 700 are suggested.
.P
The
.BR ustar
.IR typeflag
field was used to accommodate the additional functionality of the new
format rather than magic or version because the POSIX.1\(hy1990 standard (and, by
reference, the previous version of
.IR pax ),
mandated the behavior of the format-reading utility when it encountered
an unknown
.IR typeflag ,
but was silent about the other two fields.
.P
Early proposals for the first version of this standard contained a proposed
archive format that was based on compatibility with the standard for
tape files (ISO\ 1001, similar to the format used historically on many
mainframes and minicomputers). This format was overly complex and required
considerable overhead in volume and header records. Furthermore, the
standard developers felt that it would not be acceptable to the community
of POSIX developers, so it was later changed to be a format more closely
related to historical practice on POSIX systems.
.P
The prefix and name split of pathnames in
.BR ustar
was replaced by the single path extended header record for simplicity.
.P
The concept of a global extended header (\c
.IR typeflag \c
.BR g )
was controversial. If this were applied to an archive being recorded on
magnetic tape, a few unreadable blocks at the beginning of the tape
could be a serious problem; a utility attempting to extract as many
files as possible from a damaged archive could lose a large percentage
of file header information in this case. However, if the archive were
on a reliable medium, such as a CD\(hyROM, the global extended header
offers considerable potential size reductions by eliminating redundant
information. Thus, the text warns against using the global method for
unreliable media and provides a method for implanting global
information in the extended header for each file, rather than in the
.IR typeflag
.BR g
records.
.P
No facility for data translation or filtering on a per-file basis is
included because the standard developers could not invent an interface
that would allow this in an efficient manner. If a filter, such as
encryption or compression, is to be applied to all the files, it is
more efficient to apply the filter to the entire archive as a single
file. The standard developers considered interfaces that would invoke a
shell script for each file going into or out of the archive, but the
system overhead in this approach was considered to be too high.
.P
One such approach would be to have
.BR filter=
records that give a pathname for an executable. When the program is
invoked, the file and archive would be open for standard input/output
and all the header fields would be available as environment variables
or command-line arguments. The standard developers did discuss such
schemes, but they were omitted from POSIX.1\(hy2008 due to concerns about
excessive overhead. Also, the program itself would need to be in the
archive if it were to be used portably.
.P
There is currently no portable means of identifying the character
set(s) used for a file in the file system. Therefore,
.IR pax
has not been given a mechanism to generate charset records
automatically. The only portable means of doing this is for the user to
write the archive using the
.BR \-o \c
.BR charset=string
command line option. This assumes that all of the files in the archive
use the same encoding. The ``implementation-defined'' text is
included to allow for a system that can identify the encodings used for
each of its files.
.P
The table of standards that accompanies the charset record description
is acknowledged to be very limited. Only a limited number of character
set standards is reasonable for maximal interchange. Any character set
is, of course, possible by prior agreement. It was suggested that
EBCDIC be listed, but it was omitted because it is not defined by a
formal standard. Formal standards, and then only those with reasonably
large followings, can be included here, simply as a matter of
practicality. The <\fIvalue\fP>s represent names of officially
registered character sets in the format required by the ISO\ 2375:\|1985 standard.
.P
The normal
<comma>
or
<blank>-separated
list rules are not followed in the case of keyword options to allow
ease of argument parsing for
.IR getopts .
.P
Further information on character encodings is in
.IR "pax Archive Character Set Encoding/Decoding".
.P
The standard developers have reserved keyword name space for vendor
extensions. It is suggested that the format to be used is:
.sp
.RS 4
.nf

\fIVENDOR.keyword\fR
.fi
.P
.RE
.P
where
.IR VENDOR
is the name of the vendor or organization in all uppercase letters. It
is further suggested that the keyword following the
<period>
be named differently than any of the standard keywords so that it could
be used for future standardization, if appropriate, by omitting the
.IR VENDOR
prefix.
.P
The <\fIlength\fP> field in the extended header record was included to
make it simpler to step through the records, even if a record contains
an unknown format (to a particular
.IR pax )
with complex interactions of special characters. It also provides a
minor integrity checkpoint within the records to aid a program
attempting to recover files from a damaged archive.
.P
There are no extended header versions of the
.IR devmajor
and
.IR devminor
fields because the unspecified format
.BR ustar
header field should be sufficient. If they are not, vendor-specific
extended keywords (such as
.IR VENDOR.devmajor )
should be used.
.P
Device and
.IR i -number
labeling of files was not adopted from
.IR cpio ;
files are interchanged strictly on a symbolic name basis, as in
.BR ustar .
.P
Just as with the
.BR ustar
format descriptions, the new format makes no special arrangements for
multi-volume archives. Each of the
.IR pax
archive types is assumed to be inside a single POSIX file and splitting
that file over multiple volumes (diskettes, tape cartridges, and so
on), processing their labels, and mounting each in the proper sequence
are considered to be implementation details that cannot be described
portably.
.P
The
.BR pax
format is intended for interchange, not only for backup on a single
(family of) systems. It is not as densely packed as might be possible
for backup:
.IP " *" 4
It contains information as coded characters that could be coded in
binary.
.IP " *" 4
It identifies extended records with name fields that could be omitted
in favor of a fixed-field layout.
.IP " *" 4
It translates names into a portable character set and identifies
locale-related information, both of which are probably unnecessary for
backup.
.P
The requirements on restoring from an archive are slightly different
from the historical wording, allowing for non-monolithic privilege to
bring forward as much as possible. In particular, attributes such as
``high performance file'' might be broadly but not universally granted
while set-user-ID or
\fIchown\fR()
might be much more restricted. There is no implication in POSIX.1\(hy2008 that
the security information be honored after it is restored to the file
hierarchy, in spite of what might be improperly inferred by the silence
on that topic. That is a topic for another standard.
.P
Links are recorded in the fashion described here because a link can be
to any file type. It is desirable in general to be able to restore part
of an archive selectively and restore all of those files completely. If
the data is not associated with each link, it is not possible to do
this. However, the data associated with a file can be large, and when
selective restoration is not needed, this can be a significant burden.
The archive is structured so that files that have no associated data
can always be restored by the name of any link name of any link, and
the user may choose whether data is recorded with each instance of a
file that contains data. The format permits mixing of both types of
links in a single archive; this can be done for special needs, and
.IR pax
is expected to interpret such archives on input properly, despite the
fact that there is no
.IR pax
option that would force this mixed case on output. (When
.BR \-o
.BR linkdata
is used, the output must contain the duplicate data, but the
implementation is free to include it or omit it when
.BR \-o
.BR linkdata
is not used.)
.P
The time values are included as extended header records for those
implementations needing more than the eleven octal digits allowed by
the
.BR ustar
format. Portable file timestamps cannot be negative. If
.IR pax
encounters a file with a negative timestamp in
.BR copy
or
.BR write
mode, it can reject the file, substitute a non-negative timestamp, or
generate a non-portable timestamp with a leading
.BR '\-' .
Even though some implementations can support finer file-time
granularities than seconds, the normative text requires support only
for seconds since the Epoch because the ISO\ POSIX\(hy1 standard states them that way. The
.BR ustar
format includes only
.IR mtime ;
the new format adds
.IR atime
and
.IR ctime
for symmetry. The
.IR atime
access time restored to the file system will be affected by the
.BR \-p
.BR a
and
.BR \-p
.BR e
options. The
.IR ctime
creation time (actually
.IR inode
modification time) is described with appropriate privileges so that
it can be ignored when writing to the file system. POSIX does not
provide a portable means to change file creation time. Nothing is
intended to prevent a non-portable implementation of
.IR pax
from restoring the value.
.P
The
.IR gid ,
.IR size ,
and
.IR uid
extended header records were included to allow expansion beyond the
sizes specified in the regular
.IR tar
header. New file system architectures are emerging that will exhaust
the 12-digit size field. There are probably not many systems requiring
more than 8 digits for user and group IDs, but the extended header
values were included for completeness, allowing overrides for all of
the decimal values in the
.IR tar
header.
.P
The standard developers intended to describe the effective results of
.IR pax
with regard to file ownerships and permissions; implementations are not
restricted in timing or sequencing the restoration of such, provided
the results are as specified.
.P
Much of the text describing the extended headers refers to use in ``\c
.BR write
or
.BR copy
modes''. The
.BR copy
mode references are due to the normative text: ``The effect of the
copy shall be as if the copied files were written to an archive file
and then subsequently extracted .\|.\|.''. There is certainly no way to
test whether
.IR pax
is actually generating the extended headers in
.BR copy
mode, but the effects must be as if it had.
.SS "pax Archive Character Set Encoding/Decoding"
.P
There is a need to exchange archives of files between systems of
different native codesets. Filenames, group names, and user names must
be preserved to the fullest extent possible when an archive is read on
the receiving platform. Translation of the contents of files is not
within the scope of the
.IR pax
utility.
.P
There will also be the need to represent characters that are not
available on the receiving platform. These unsupported characters
cannot be automatically folded to the local set of characters due to
the chance of collisions. This could result in overwriting previous
extracted files from the archive or pre-existing files on the system.
.P
For these reasons, the codeset used to represent characters within the
extended header records of the
.IR pax
archive must be sufficiently rich to handle all commonly used character
sets. The fields requiring translation include, at a minimum,
filenames, user names, group names, and link pathnames. Implementations
may wish to have localized extended keywords that use non-portable
characters.
.P
The standard developers considered the following options:
.IP " *" 4
The archive creator specifies the well-defined name of the source
codeset. The receiver must then recognize the codeset name and perform
the appropriate translations to the destination codeset.
.IP " *" 4
The archive creator includes within the archive the character mapping
table for the source codeset used to encode extended header records.
The receiver must then read the character mapping table and perform the
appropriate translations to the destination codeset.
.IP " *" 4
The archive creator translates the extended header records in the
source codeset into a canonical form. The receiver must then perform
the appropriate translations to the destination codeset.
.P
The approach that incorporates the name of the source codeset poses the
problem of codeset name registration, and makes the archive useless to
.IR pax
archive decoders that do not recognize that codeset.
.P
Because parts of an archive may be corrupted, the standard developers
felt that including the character map of the source codeset was too
fragile. The loss of this one key component could result in making the
entire archive useless. (The difference between this and the global
extended header decision was that the latter has a
workaround\(emduplicating extended header records on unreliable
media\(embut this would be too burdensome for large character set
maps.)
.P
Both of the above approaches also put an undue burden on the
.IR pax
archive receiver to handle the cross-product of all source and
destination codesets.
.P
To simplify the translation from the source codeset to the canonical
form and from the canonical form to the destination codeset, the
standard developers decided that the internal representation should be
a stateless encoding. A stateless encoding is one where each codepoint
has the same meaning, without regard to the decoder being in a specific
state. An example of a stateful encoding would be the Japanese
Shift-JIS; an example of a stateless encoding would be the ISO/IEC\ 646:\|1991 standard
(equivalent to 7-bit ASCII).
.P
For these reasons, the standard developers decided to adopt a canonical
format for the representation of file information strings. The obvious,
well-endorsed candidate is the ISO/IEC\ 10646\(hy1:\|2000 standard (based in part on Unicode), which
can be used to represent the characters of virtually all standardized
character sets. The standard developers initially agreed upon using
UCS2 (16-bit Unicode) as the internal representation. This repertoire
of characters provides a sufficiently rich set to represent all
commonly-used codesets.
.P
However, the standard developers found that the 16-bit Unicode
representation had some problems. It forced the issue of standardizing
byte ordering. The 2-byte length of each character made the extended
header records twice as long for the case of strings coded entirely
from historical 7-bit ASCII. For these reasons, the standard developers
chose the UTF\(hy8 defined in the ISO/IEC\ 10646\(hy1:\|2000 standard. This multi-byte representation
encodes UCS2 or UCS4 characters reliably and deterministically,
eliminating the need for a canonical byte ordering. In addition, NUL
octets and other characters possibly confusing to POSIX file systems do
not appear, except to represent themselves. It was realized that
certain national codesets take up more space after the encoding, due to
their placement within the UCS range; it was felt that the usefulness
of the encoding of the names outweighs the disadvantage of size
increase for file, user, and group names.
.P
The encoding of UTF\(hy8 is as follows:
.sp
.RS 4
.nf

UCS4 Hex Encoding  UTF-8 Binary Encoding
.P
00000000-0000007F  0xxxxxxx
00000080-000007FF  110xxxxx 10xxxxxx
00000800-0000FFFF  1110xxxx 10xxxxxx 10xxxxxx
00010000-001FFFFF  11110xxx 10xxxxxx 10xxxxxx 10xxxxxx
00200000-03FFFFFF  111110xx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx
04000000-7FFFFFFF  1111110x 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx
.fi
.P
.RE
.P
where each
.BR 'x' 
represents a bit value from the character being translated.
.SS "ustar Interchange Format"
.P
The description of the
.BR ustar
format reflects numerous enhancements over pre-1988 versions of the
historical
.IR tar
utility. The goal of these changes was not only to provide the
functional enhancements desired, but also to retain compatibility
between new and old versions. This compatibility has been retained.
Archives written using the old archive format are compatible with the
new format.
.P
Implementors should be aware that the previous file format did not
include a mechanism to archive directory type files. For this reason,
the convention of using a filename ending with
<slash>
was adopted to specify a directory on the archive.
.P
The total size of the
.IR name
and
.IR prefix
fields have been set to meet the minimum requirements for
{PATH_MAX}.
If a pathname will fit within the
.IR name
field, it is recommended that the pathname be stored there without the
use of the
.IR prefix
field. Although the name field is known to be too small to contain
{PATH_MAX}
characters, the value was not changed in this version of the archive
file format to retain backwards-compatibility, and instead the prefix
was introduced. Also, because of the earlier version of the format,
there is no way to remove the restriction on the
.IR linkname
field being limited in size to just that of the
.IR name
field.
.P
The
.IR size
field is required to be meaningful in all implementation extensions,
although it could be zero. This is required so that the data blocks can
always be properly counted.
.P
It is suggested that if device special files need to be represented
that cannot be represented in the standard format, that one of the
extension types (\c
.BR A \(hy\c
.BR Z )
be used, and that the additional information for the special file be
represented as data and be reflected in the
.IR size
field.
.P
Attempting to restore a special file type, where it is converted to
ordinary data and conflicts with an existing filename, need not be
specially detected by the utility. If run as an ordinary user,
.IR pax
should not be able to overwrite the entries in, for example,
.BR /dev
in any case (whether the file is converted to another type or not). If
run as a privileged user, it should be able to do so, and it would be
considered a bug if it did not. The same is true of ordinary data files
and similarly named special files; it is impossible to anticipate the
needs of the user (who could really intend to overwrite the file), so
the behavior should be predictable (and thus regular) and rely on the
protection system as required.
.P
The value 7 in the
.IR typeflag
field is intended to define how contiguous files can be stored in a
.BR ustar
archive. POSIX.1\(hy2008 does not require the contiguous file extension, but does
define a standard way of archiving such files so that all conforming
systems can interpret these file types in a meaningful and consistent
manner. On a system that does not support extended file types, the
.IR pax
utility should do the best it can with the file and go on to the next.
.P
The file protection modes are those conventionally used by the
.IR ls
utility. This is extended beyond the usage in the ISO\ POSIX\(hy2 standard to support the
``shared text'' or ``sticky'' bit. It is intended that the conformance
document should not document anything beyond the existence of and
support of such a mode. Further extensions are expected to these bits,
particularly with overloading the set-user-ID and set-group-ID flags.
.SS "cpio Interchange Format"
.P
The reference to appropriate privileges in the
.BR cpio
format refers to an error on standard output; the
.BR ustar
format does not make comparable statements.
.P
The model for this format was the historical System V
.IR cpio \c
.BR \-c
data interchange format. This model documents the portable version of
the
.BR cpio
format and not the binary version. It has the flexibility to transfer
data of any type described within POSIX.1\(hy2008, yet is extensible to transfer
data types specific to extensions beyond POSIX.1\(hy2008 (for example, contiguous
files). Because it describes existing practice, there is no question of
maintaining upwards-compatibility.
.SS "cpio Header"
.P
There has been some concern that the size of the
.IR c_ino
field of the header is too small to handle those systems that have very
large
.IR inode
numbers. However, the
.IR c_ino
field in the header is used strictly as a hard-link resolution
mechanism for archives. It is not necessarily the same value as the
.IR inode
number of the file in the location from which that file is extracted.
.P
The name
.IR c_magic
is based on historical usage.
.SS "cpio Filename"
.P
For most historical implementations of the
.IR cpio
utility,
{PATH_MAX}
octets can be used to describe the pathname without the addition of
any other header fields (the NUL character would be included in this
count).
{PATH_MAX}
is the minimum value for pathname size, documented as 256 bytes.
However, an implementation may use
.IR c_namesize
to determine the exact length of the pathname. With the current
description of the
.IR <cpio.h> 
header, this pathname size can be as large as a number that is
described in six octal digits.
.P
Two values are documented under the
.IR c_mode
field values to provide for extensibility for known file types:
.IP "\fB0110\ 000\fP" 10
Reserved for contiguous files. The implementation may treat the rest of
the information for this archive like a regular file. If this file type
is undefined, the implementation may create the file as a regular
file.
.P
This provides for extensibility of the
.BR cpio
format while allowing for the ability to read old archives. Files of an
unknown type may be read as ``regular files'' on some implementations.
On a system that does not support extended file types, the
.IR pax
utility should do the best it can with the file and go on to the next.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "Chapter 2" ", " "Shell Command Language",
.IR "\fIcp\fR\^",
.IR "\fIed\fR\^",
.IR "\fIgetopts\fR\^",
.IR "\fIls\fR\^",
.IR "\fIprintf\fR\^"
.P
The Base Definitions volume of POSIX.1\(hy2017,
.IR "Section 3.169" ", " "File Mode Bits",
.IR "Chapter 5" ", " "File Format Notation",
.IR "Chapter 8" ", " "Environment Variables",
.IR "Section 12.2" ", " "Utility Syntax Guidelines",
.IR "\fB<cpio.h>\fP",
.IR "\fB<tar.h>\fP"
.P
The System Interfaces volume of POSIX.1\(hy2017,
.IR "\fIchown\fR\^(\|)",
.IR "\fIcreat\fR\^(\|)",
.IR "\fIfstatat\fR\^(\|)",
.IR "\fImkdir\fR\^(\|)",
.IR "\fImkfifo\fR\^(\|)",
.IR "\fIutime\fR\^(\|)",
.IR "\fIwrite\fR\^(\|)"
.\"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
.PP
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .