.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
.\"
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.\" preserved on all copies.
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.\"
.\" References consulted:
.\"     Linux libc source code
.\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
.\"     386BSD man pages
.\" Modified Sat Jul 24 19:29:54 1993 by Rik Faith (faith@cs.unc.edu)
.TH GETGRENT 3  2017-09-15 "" "Linux Programmer's Manual"
.SH NAME
getgrent, setgrent, endgrent \- get group file entry
.SH SYNOPSIS
.nf
.B #include <sys/types.h>
.B #include <grp.h>
.PP
.B struct group *getgrent(void);
.PP
.B void setgrent(void);
.PP
.B void endgrent(void);
.fi
.PP
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.PP
.PD 0
.ad l
.BR setgrent ():
.RS 4
_XOPEN_SOURCE\ >=\ 500
.\"    || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
    || /* Glibc since 2.19: */ _DEFAULT_SOURCE
    || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
.RE
.PP
.BR getgrent (),
.BR endgrent ():
.RS 4
Since glibc 2.22:
    _XOPEN_SOURCE\ >=\ 500 ||
.\"        || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
        _DEFAULT_SOURCE
.br
Glibc 2.21 and earlier
    _XOPEN_SOURCE\ >=\ 500
.\"        || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
        || /* Since glibc 2.12: */ _POSIX_C_SOURCE\ >=\ 200809L
        || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
.RE
.PD
.ad b
.SH DESCRIPTION
The
.BR getgrent ()
function returns a pointer to a structure containing
the broken-out fields of a record in the group database
(e.g., the local group file
.IR /etc/group ,
NIS, and LDAP).
The first time
.BR getgrent ()
is called,
it returns the first entry; thereafter, it returns successive entries.
.PP
The
.BR setgrent ()
function rewinds to the beginning
of the group database, to allow repeated scans.
.PP
The
.BR endgrent ()
function is used to close the group database
after all processing has been performed.
.PP
The \fIgroup\fP structure is defined in \fI<grp.h>\fP as follows:
.PP
.in +4n
.EX
struct group {
    char   *gr_name;        /* group name */
    char   *gr_passwd;      /* group password */
    gid_t   gr_gid;         /* group ID */
    char  **gr_mem;         /* NULL-terminated array of pointers
                               to names of group members */
};
.EE
.in
.PP
For more information about the fields of this structure, see
.BR group (5).
.SH RETURN VALUE
The
.BR getgrent ()
function returns a pointer to a
.I group
structure,
or NULL if there are no more entries or an error occurs.
.PP
Upon error,
.I errno
may be set.
If one wants to check
.I errno
after the call, it should be set to zero before the call.
.PP
The return value may point to a static area, and may be overwritten
by subsequent calls to
.BR getgrent (),
.BR getgrgid (3),
or
.BR getgrnam (3).
(Do not pass the returned pointer to
.BR free (3).)
.SH ERRORS
.TP
.B EAGAIN
The service was temporarily unavailable; try again later.
For NSS backends in glibc this indicates a temporary error talking to the backend.
The error may correct itself, retrying later is suggested.
.TP
.B EINTR
A signal was caught; see
.BR signal (7).
.TP
.B EIO
I/O error.
.TP
.B EMFILE
The per-process limit on the number of open file descriptors has been reached.
.TP
.B ENFILE
The system-wide limit on the total number of open files has been reached.
.TP
.\" not in POSIX
.B ENOENT
A necessary input file cannot be found.
For NSS backends in glibc this indicates the backend is not correctly configured.
.TP
.B ENOMEM
.\" not in POSIX
Insufficient memory to allocate
.I group
structure.
.TP
.B ERANGE
Insufficient buffer space supplied.
.SH FILES
.TP
.I /etc/group
local group database file
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lbw11 lb lb
l l l.
Interface	Attribute	Value
T{
.BR getgrent ()
T}	Thread safety	T{
MT-Unsafe race:grent
.br
race:grentbuf locale
T}
T{
.BR setgrent (),
.BR endgrent ()
T}	Thread safety	MT-Unsafe race:grent locale
.TE
.PP
In the above table,
.I grent
in
.I race:grent
signifies that if any of the functions
.BR setgrent (),
.BR getgrent (),
or
.BR endgrent ()
are used in parallel in different threads of a program,
then data races could occur.
.SH CONFORMING TO
POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
.SH SEE ALSO
.BR fgetgrent (3),
.BR getgrent_r (3),
.BR getgrgid (3),
.BR getgrnam (3),
.BR getgrouplist (3),
.BR putgrent (3),
.BR group (5)