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.TH AGETTY 8 "May 2011" "util-linux" "System Administration"
agetty \- alternative Linux getty
.B agetty
.IR port " [" baud_rate "...] [" term ]
\fBagetty\fP opens a tty port, prompts for a login name and invokes
the /bin/login command. It is normally invoked by \fBinit\fP(8).
\fBagetty\fP has several \fInon-standard\fP features that are useful
for hardwired and for dial-in lines:
.IP \(bu
Adapts the tty settings to parity bits and to erase, kill,
end-of-line and uppercase characters when it reads a login name.
The program can handle 7-bit characters with even, odd, none or space
parity, and 8-bit characters with no parity. The following special
characters are recognized: Control-U (kill); DEL and
backspace (erase); carriage return and line feed (end of line).
See also the \fB\-\-erase\-chars\fP and \fB\-\-kill\-chars\fP options.
.IP \(bu
Optionally deduces the baud rate from the CONNECT messages produced by
Hayes(tm)-compatible modems.
.IP \(bu
Optionally does not hang up when it is given an already opened line
(useful for call-back applications).
.IP \(bu
Optionally does not display the contents of the \fI/etc/issue\fP file.
.IP \(bu
Optionally displays an alternative issue file instead of \fI/etc/issue\fP.
.IP \(bu
Optionally does not ask for a login name.
.IP \(bu
Optionally invokes a non-standard login program instead of
.IP \(bu
Optionally turns on hardware flow control
.IP \(bu
Optionally forces the line to be local with no need for carrier detect.
This program does not use the \fI/etc/gettydefs\fP (System V) or
\fI/etc/gettytab\fP (SunOS 4) files.
A path name relative to the \fI/dev\fP directory. If a "\-" is
specified, \fBagetty\fP assumes that its standard input is
already connected to a tty port and that a connection to a
remote user has already been established.
Under System V, a "\-" \fIport\fP argument should be preceded
by a "\-\-".
A comma-separated list of one or more baud rates. Each time
\fBagetty\fP receives a BREAK character it advances through
the list, which is treated as if it were circular.
Baud rates should be specified in descending order, so that the
null character (Ctrl\-@) can also be used for baud-rate switching.
This argument is optional and unnecessary for \fBvirtual terminals\fP.
The default for \fBserial terminals\fP is keep the current baud rate
(see \fB\-\-keep\-baud\fP) and if unsuccessful then default to '9600'.
The value to be used for the TERM environment variable. This overrides
whatever init(8) may have set, and is inherited by login and the shell.
The default is 'vt100', or 'linux' for Linux on a virtual terminal,
or 'hurd' for GNU Hurd on a virtual terminal.
\-8, \-\-8bits
Assume that the tty is 8-bit clean, hence disable parity detection.
\-a, \-\-autologin \fIusername\fP
Log the specified user automatically in without asking for a login name and
password. The \-f \fIusername\fP option is added to the \fB/bin/login\fP
command line by default. The \-\-login\-options option changes this default
behavior and then only \\u is replaced by the \fIusername\fP and no other
option is added to the login command line.
\-c, \-\-noreset
Don't reset terminal cflags (control modes). See \fBtermios\fP(3) for more
\-E, \-\-remote
If an \fB\-H\fP \fIfakehost\fP option is given, then an \fB\-r\fP
\fIfakehost\fP option is added to the \fB/bin/login\fP command line.
\-f, \-\-issue\-file \fIissue_file\fP
Display the contents of \fIissue_file\fP instead of \fI/etc/issue\fP.
This allows custom messages to be displayed on different terminals.
The \-i option will override this option.
\-h, \-\-flow\-control
Enable hardware (RTS/CTS) flow control. It is left up to the
application to disable software (XON/XOFF) flow protocol where
\-H, \-\-host \fIlogin_host\fP
Write the specified \fIlogin_host\fP into the utmp file. (Normally,
no login host is given, since \fBagetty\fP is used for local hardwired
connections and consoles. However, this option can be useful for
identifying terminal concentrators and the like.)
\-i, \-\-noissue
Do not display the contents of \fI/etc/issue\fP (or other) before writing the
login prompt. Terminals or communications hardware may become confused
when receiving lots of text at the wrong baud rate; dial-up scripts
may fail if the login prompt is preceded by too much text.
\-I, \-\-init\-string \fIinitstring\fP
Set an initial string to be sent to the tty or modem before sending
anything else. This may be used to initialize a modem. Non-printable
characters may be sent by writing their octal code preceded by a
backslash (\\). For example, to send a linefeed character (ASCII 10,
octal 012), write \\012.
Do not clear the screen before prompting for the login name
(the screen is normally cleared).
\-l, \-\-login\-program \fIlogin_program\fP
Invoke the specified \fIlogin_program\fP instead of /bin/login.
This allows the use of a non-standard login program (for example,
one that asks for a dial-up password or that uses a different
password file).
\-L, \-\-local\-line[=\fImode\fP]
Control the CLOCAL line flag. The optional \fImode\fP argument is 'auto', 'always' or 'never'.
If the \fImode\fP argument is omitted, then the default is 'always'. If the
\-\-local\-line option is not given at all, then the default is 'auto'.
The \fImode\fP 'always' forces the line to be a local line with no need for carrier detect.
This can be useful when you have a locally attached terminal where the serial line
does not set the carrier-detect signal.
The \fImode\fP 'never' explicitly clears the CLOCAL flag from the line setting and
the carrier-detect signal is expected on the line.
The \fImode\fP 'auto' (agetty default) does not modify the CLOCAL setting
and follows the setting enabled by the kernel.
\-m, \-\-extract\-baud
Try to extract the baud rate from the CONNECT status message
produced by Hayes(tm)\-compatible modems. These status
messages are of the form: "<junk><speed><junk>".
\fBagetty\fP assumes that the modem emits its status message at
the same speed as specified with (the first) \fIbaud_rate\fP value
on the command line.
Since the \fB\-m\fP feature may fail on heavily-loaded systems,
you still should enable BREAK processing by enumerating all
expected baud rates on the command line.
\-n, \-\-skip\-login
Do not prompt the user for a login name. This can be used in
connection with the \fB\-l\fP option to invoke a non-standard login process such
as a BBS system. Note that with the \-n option, \fBagetty\fR gets no input from
the user who logs in and therefore won't be able to figure out parity,
character size, and newline processing of the connection. It defaults to
space parity, 7 bit characters, and ASCII CR (13) end-of-line character.
Beware that the program that \fBagetty\fR starts (usually /bin/login)
is run as root.
\-N, \-\-nonewline
Do not print a newline before writing out /etc/issue.
\-o, \-\-login\-options "\fIlogin_options\fP"
Options that are passed to the login program. \\u is replaced
by the login name. The default \fB/bin/login\fP command line
is "/bin/login -- <username>".
Please read the SECURITY NOTICE below if you want to use this.
\-p, \-\-login\-pause
Wait for any key before dropping to the login prompt. Can be combined
with \fB\-\-autologin\fP to save memory by lazily spawning shells.
\-r, \-\-chroot \fIdirectory\fP
Change root to the specified directory.
\-R, \-\-hangup
Call vhangup() to do a virtual hangup of the specified terminal.
\-s, \-\-keep\-baud
Try to keep the existing baud rate. The baud rates from
the command line are used when agetty receives a BREAK character.
\-t, \-\-timeout \fItimeout\fP
Terminate if no user name could be read within \fItimeout\fP
seconds. This option should probably not be used with hardwired
\-U, \-\-detect\-case
Turn on support for detecting an uppercase-only terminal. This setting
will detect a login name containing only capitals as indicating an
uppercase-only terminal and turn on some upper-to-lower case conversions.
Note that this has no support for any Unicode characters.
\-w, \-\-wait\-cr
Wait for the user or the modem to send a carriage-return or a
linefeed character before sending the \fI/etc/issue\fP (or other) file
and the login prompt. Very useful in connection with the \-I option.
Do not print hints about Num, Caps and Scroll Locks.
By default the hostname will be printed. With this option enabled,
no hostname at all will be shown.
By default the hostname is only printed until the first dot. With
this option enabled, the fully qualified hostname by gethostname()
or (if not found) by getaddrinfo() is shown.
\-\-erase\-chars \fIstring\fP
This option specifies additional characters that should be interpreted as a
backspace ("ignore the previous character") when the user types the login name.
The default additional \'erase\' has been \'#\', but since util-linux 2.23
no additional erase characters are enabled by default.
\-\-kill\-chars \fIstring\fP
This option specifies additional characters that should be interpreted as a
kill ("ignore all previous characters") when the user types the login name.
The default additional \'kill\' has been \'@\', but since util-linux 2.23
no additional kill characters are enabled by default.
\-\-chdir \fIdirectory\fP
Change directory before the login.
\-\-delay \fInumber\fP
Sleep seconds before open tty.
\-\-nice \fInumber\fP
Run login with this priority.
Ask all running agetty instances to reload and update their displayed prompts,
if the user has not yet commenced logging in. After doing so the command will
exit. This feature might be unsupported on systems without Linux
.BR inotify (7).
Display version information and exit.
Display help text and exit.
This section shows examples for the process field of an entry in the
\fI/etc/inittab\fP file. You'll have to prepend appropriate values
for the other fields. See \fIinittab(5)\fP for more details.
For a hardwired line or a console tty:
/sbin/agetty 9600 ttyS1
For a directly connected terminal without proper carrier-detect wiring
(try this if your terminal just sleeps instead of giving you a password:
/sbin/agetty \-L 9600 ttyS1 vt100
For an old-style dial-in line with a 9600/2400/1200 baud modem:
/sbin/agetty \-mt60 ttyS1 9600,2400,1200
For a Hayes modem with a fixed 115200 bps interface to the machine
(the example init string turns off modem echo and result codes, makes
modem/computer DCD track modem/modem DCD, makes a DTR drop cause a
disconnection, and turns on auto-answer after 1 ring):
/sbin/agetty \-w \-I 'ATE0Q1&D2&C1S0=1\\015' 115200 ttyS1
If you use the \fB\-\-login\-program\fP and \fB\-\-login\-options\fP options,
be aware that a malicious user may try to enter lognames with embedded options,
which then get passed to the used login program. Agetty does check
for a leading "\-" and makes sure the logname gets passed as one parameter
(so embedded spaces will not create yet another parameter), but depending
on how the login binary parses the command line that might not be sufficient.
Check that the used login program can not be abused this way.
Some programs use "\-\-" to indicate that the rest of the commandline should
not be interpreted as options. Use this feature if available by passing "\-\-"
before the username gets passed by \\u.
The issue-file (\fI/etc/issue\fP or the file set with the \fB\-f\fP option)
may contain certain escape codes to display the system name, date, time
etcetera. All escape codes consist of a backslash (\\) immediately
followed by one of the letters explained below.
4 or 4{interface}
Insert the IPv4 address the specified network interface (e.g. \\4{eth0})
and if the interface argument is not specified then select the first fully
configured (UP, non-LOCALBACK, RUNNING) interface. If not found any
configured interface fall back to IP address of the machine hostname.
6 or 6{interface}
The same as \\4 but for IPv6.
Insert the baudrate of the current line.
Insert the current date.
Insert the system name, the name of the operating system. Same as `uname \-s'.
See also \\S escape code.
Insert the VARIABLE data from \fI/etc/os-release\fP, if the file does not exist
then fallback to \fI/usr/lib/os-release\fP. If the VARIABLE argument is not
specified then use PRETTY_NAME from the file or the system name (see \\s).
This escape code allows to keep \fI/etc/issue\fP distribution and release
independent. Note that \\S{ANSI_COLOR} is converted to the real terminal
escape sequence.
Insert the name of the current tty line.
Insert the architecture identifier of the machine. Same as `uname \-m'.
Insert the nodename of the machine, also known as the hostname. Same as `uname \-n'.
Insert the NIS domainname of the machine. Same as `hostname \-d'.
Insert the DNS domainname of the machine.
Insert the release number of the OS. Same as `uname \-r'.
Insert the current time.
Insert the number of current users logged in.
Insert the string "1 user" or "<n> users" where <n> is the number of current
users logged in.
Insert the version of the OS, eg. the build-date etc.
Example: On my system, the following \fI/etc/issue\fP file:
This is \\n.\\o (\\s \\m \\r) \\t
displays as:
This is (Linux i386 1.1.9) 18:29:30
.B /var/run/utmp
the system status file.
.B /etc/issue
printed before the login prompt.
.B /etc/os-release /usr/lib/os-release
operating system identification data.
.B /dev/console
problem reports (if syslog(3) is not used).
.B /etc/inittab
\fIinit\fP(8) configuration file for SysV-style init daemon.
The baud-rate detection feature (the \fB\-m\fP option) requires that
\fBagetty\fP be scheduled soon enough after completion of a dial-in
call (within 30 ms with modems that talk at 2400 baud). For robustness,
always use the \fB\-m\fP option in combination with a multiple baud
rate command-line argument, so that BREAK processing is enabled.
The text in the \fI/etc/issue\fP file (or other) and the login prompt
are always output with 7-bit characters and space parity.
The baud-rate detection feature (the \fB\-m\fP option) requires that
the modem emits its status message \fIafter\fP raising the DCD line.
Depending on how the program was configured, all diagnostics are
written to the console device or reported via the syslog(3) facility.
Error messages are produced if the \fIport\fP argument does not
specify a terminal device; if there is no utmp entry for the
current process (System V only); and so on.
Werner Fink
Karel Zak
The original
.B agetty
for serial terminals was written by W.Z. Venema <>
and ported to Linux by Peter Orbaek <>.
The agetty command is part of the util-linux package and is available from\-linux/.