Provided by: util-linux_2.40.2-1ubuntu2_amd64 
NAME
agetty - alternative Linux getty
SYNOPSIS
agetty [options] port [baud_rate...] [term]
DESCRIPTION
agetty opens a tty port, prompts for a login name and invokes the /bin/login command. It
is normally invoked by init(8).
agetty has several non-standard features that are useful for hardwired and for dial-in
lines:
• 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 --erase-chars and
--kill-chars options.
• Optionally deduces the baud rate from the CONNECT messages produced by
Hayes(tm)-compatible modems.
• Optionally does not hang up when it is given an already opened line (useful for
call-back applications).
• Optionally does not display the contents of the /etc/issue file.
• Optionally displays an alternative issue files or directories instead of /etc/issue or
/etc/issue.d.
• Optionally does not ask for a login name.
• Optionally invokes a non-standard login program instead of /bin/login.
• Optionally turns on hardware flow control.
• Optionally forces the line to be local with no need for carrier detect.
This program does not use the /etc/gettydefs (System V) or /etc/gettytab (SunOS 4) files.
ARGUMENTS
port
A path name relative to the /dev directory. If a "-" is specified, agetty 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 "-" port argument should be preceded by a "--".
baud_rate,...
A comma-separated list of one or more baud rates. Each time agetty 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 virtual terminals.
The default for serial terminals is keep the current baud rate (see --keep-baud) and
if unsuccessful then default to '9600'.
term
The value to be used for the TERM environment variable. This overrides whatever
init(1) 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.
OPTIONS
-8, --8bits
Assume that the tty is 8-bit clean, hence disable parity detection.
-a, --autologin username
Automatically log in the specified user without asking for a username or password.
Using this option causes an -f username option and argument to be added to the
/bin/login command line. See --login-options, which can be used to modify this
option’s behavior.
Note that --autologin may affect the way in which getty initializes the serial line,
because on auto-login agetty does not read from the line and it has no opportunity
optimize the line setting.
-c, --noreset
Do not reset terminal cflags (control modes). See termios(3) for more details.
-E, --remote
Typically the login(1) command is given a remote hostname when called by something
such as telnetd(8). This option allows agetty to pass what it is using for a hostname
to login(1) for use in utmp(5). See --host, login(1), and utmp(5).
If the --host fakehost option is given, then an -h fakehost option and argument are
added to the /bin/login command line.
If the --nohostname option is given, then an -H option is added to the /bin/login
command line.
See --login-options.
-f, --issue-file path
Specifies a ":" delimited list of files and directories to be displayed instead of
/etc/issue (or other). All specified files and directories are displayed, missing or
empty files are silently ignored. If the specified path is a directory then display
all files with .issue file extension in version-sort order from the directory. This
allows custom messages to be displayed on different terminals. The --noissue option
will override this option.
--show-issue
Display the current issue file (or other) on the current terminal and exit. Use this
option to review the current setting, it is not designed for any other purpose. Note
that output may use some default or incomplete information as proper output depends on
terminal and agetty command line.
-h, --flow-control
Enable hardware (RTS/CTS) flow control. It is left up to the application to disable
software (XON/XOFF) flow protocol where appropriate.
-H, --host fakehost
Write the specified fakehost into the utmp file. Normally, no login host is given,
since agetty 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 /etc/issue (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 initstring
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 \12.
-J, --noclear
Do not clear the screen before prompting for the login name. By default the screen is
cleared.
-l, --login-program login_program
Invoke the specified login_program instead of /bin/login. This allows the use of a
non-standard login program. Such a program could, for example, ask for a dial-up
password or use a different password file. See --login-options.
-L, --local-line[=mode]
Control the CLOCAL line flag. The optional mode argument is auto, always or never. If
the mode argument is omitted, then the default is always. If the --local-line option
is not given at all, then the default is auto.
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.
never
Explicitly clears the CLOCAL flag from the line setting and the carrier-detect
signal is expected on the line.
auto
The 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>". agetty assumes that the modem emits its status message at the
same speed as specified with (the first) baud_rate value on the command line.
Since the --extract-baud feature may fail on heavily-loaded systems, you still should
enable BREAK processing by enumerating all expected baud rates on the command line.
--list-speeds
Display supported baud rates. These are determined at compilation time.
-n, --skip-login
Do not prompt the user for a login name. This can be used in connection with the
--login-program option to invoke a non-standard login process such as a BBS system.
Note that with the --skip-login option, agetty gets no input from the user who logs in
and therefore will not 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 agetty starts (usually
/bin/login) is run as root.
-N, --nonewline
Do not print a newline before writing out /etc/issue.
-o, --login-options login_options
Options and arguments that are passed to login(1). Where \u is replaced by the login
name. For example:
--login-options '-h darkstar -- \u'
See --autologin, --login-program and --remote.
Please read the SECURITY NOTICE below before using this option.
-p, --login-pause
Wait for any key before dropping to the login prompt. Can be combined with --autologin
to save memory by lazily spawning shells.
-r, --chroot directory
Change root to the specified directory.
-R, --hangup
Call vhangup(2) 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. If another baud rates specified then the original
baud rate is also saved to the end of the wanted baud rates list. This can be used to
return to the original baud rate after unexpected BREAKs.
-t, --timeout timeout
Terminate if no user name could be read within timeout seconds. Use of this option
with hardwired terminal lines is not recommended.
-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 /etc/issue file (or others) and the login prompt. This is useful
with the --init-string option.
--nohints
Do not print hints about Num, Caps and Scroll Locks.
--nohostname
By default the hostname will be printed. With this option enabled, no hostname at all
will be shown. This setting is also possible to able by LOGIN_PLAIN_PROMPT option in
the /etc/login.defs configuration file (see below for more details).
--long-hostname
By default the hostname is only printed until the first dot. With this option enabled,
the fully qualified hostname by gethostname(3P) or (if not found) by getaddrinfo(3) is
shown.
--erase-chars string
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 string
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 directory
Change directory before the login.
--delay number
Sleep seconds before open tty.
--nice number
Run login with this priority.
--reload
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 inotify(7).
-h, --help
Display help text and exit.
-V, --version
Print version and exit.
CONFIG FILE ITEMS
agetty reads the /etc/login.defs configuration file (see login.defs(5)). Note that the
configuration file could be distributed with another package (usually shadow-utils). The
following configuration items are relevant for agetty:
LOGIN_PLAIN_PROMPT (boolean)
Tell agetty that printing the hostname should be suppressed in the login: prompt. This
is an alternative to the --nohostname command line option. The default value is no.
EXAMPLE
This section shows examples for the process field of an entry in the /etc/inittab file.
You’ll have to prepend appropriate values for the other fields. See inittab(5) 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: prompt):
/sbin/agetty --local-line 9600 ttyS1 vt100
For an old-style dial-in line with a 9600/2400/1200 baud modem:
/sbin/agetty --extract-baud --timeout 60 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 --wait-cr --init-string 'ATE0Q1&D2&C1S0=1\015' 115200 ttyS1
SECURITY NOTICE
If you use the --login-program and --login-options 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 cannot be abused this way.
Some programs use "--" to indicate that the rest of the command line should not be
interpreted as options. Use this feature if available by passing "--" before the username
gets passed by \u.
ISSUE FILES
The default issue file is /etc/issue. If the file exists, then agetty also checks for
/etc/issue.d directory. The directory is optional extension to the default issue file and
content of the directory is printed after /etc/issue content. If the /etc/issue does not
exist, then the directory is ignored. All files with .issue extension from the directory
are printed in version-sort order. The directory can be used to maintain 3rd-party
messages independently on the primary system /etc/issue file.
Since version 2.35 additional locations for issue file and directory are supported. If the
default /etc/issue does not exist, then agetty checks for /run/issue and /run/issue.d,
thereafter for /usr/lib/issue and /usr/lib/issue.d. The directory /etc is expected for
host specific configuration, /run is expected for generated stuff and /usr/lib for static
distribution maintained configuration.
The default path maybe overridden by --issue-file option. In this case specified path has
to be file or directory and all the default issue file and directory locations are
ignored.
The issue file feature can be completely disabled by --noissue option.
It is possible to review the current issue file by agetty --show-issue on the current
terminal.
The issue files may contain certain escape codes to display the system name, date, time et
cetera. All escape codes consist of a backslash (\) immediately followed by one of the
characters listed below.
4 or 4{interface}
Insert the IPv4 address of the specified network interface (for example: \4{eth0}). If
the interface argument is not specified, then select the first fully configured (UP,
non-LOCALBACK, RUNNING) interface. If no configured interface is found, fall back to
the IP address of the machine’s hostname.
6 or 6{interface}
The same as \4 but for IPv6.
b
Insert the baudrate of the current line.
d
Insert the current date.
e or e{name}
Translate the human-readable name to an escape sequence and insert it (for example:
\e{red}Alert text.\e{reset}). If the name argument is not specified, then insert \033.
The currently supported names are: black, blink, blue, bold, brown, cyan, darkgray,
gray, green, halfbright, lightblue, lightcyan, lightgray, lightgreen, lightmagenta,
lightred, magenta, red, reset, reverse, yellow and white. All unknown names are
silently ignored.
s
Insert the system name (the name of the operating system). Same as 'uname -s'. See
also the \S escape code.
S or S{VARIABLE}
Insert the VARIABLE data from /etc/os-release. If this file does not exist then fall
back to /usr/lib/os-release. If the VARIABLE argument is not specified, then use
PRETTY_NAME from the file or the system name (see \s). This escape code can be used to
keep /etc/issue distribution and release independent. Note that \S{ANSI_COLOR} is
converted to the real terminal escape sequence.
l
Insert the name of the current tty line.
m
Insert the architecture identifier of the machine. Same as uname -m.
n
Insert the nodename of the machine, also known as the hostname. Same as uname -n.
o
Insert the NIS domainname of the machine. Same as hostname -d.
O
Insert the DNS domainname of the machine.
r
Insert the release number of the OS. Same as uname -r.
t
Insert the current time.
u
Insert the number of current users logged in.
U
Insert the string "1 user" or "<n> users" where <n> is the number of current users
logged in.
v
Insert the version of the OS, that is, the build-date and such.
An example. On my system, the following /etc/issue file:
This is \n.\o (\s \m \r) \t
displays as:
This is thingol.orcan.dk (Linux i386 1.1.9) 18:29:30
FILES
/var/run/utmp
the system status file.
/etc/issue
printed before the login prompt.
/etc/os-release /usr/lib/os-release
operating system identification data.
/dev/console
problem reports (if syslog(3) is not used).
/etc/inittab
init(8) configuration file for SysV-style init daemon.
CREDENTIALS
agetty supports configuration via systemd credentials (see
https://systemd.io/CREDENTIALS/). agetty reads the following systemd credentials:
agetty.autologin (string)
If set, configures agetty to automatically log in the specified user without asking
for a username or password, similarly to the --autologin option.
BUGS
The baud-rate detection feature (the --extract-baud option) requires that agetty 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 --extract-baud option in combination
with a multiple baud rate command-line argument, so that BREAK processing is enabled.
The text in the /etc/issue file (or other) and the login prompt are always output with
7-bit characters and space parity.
The baud-rate detection feature (the --extract-baud option) requires that the modem emits
its status message after raising the DCD line.
DIAGNOSTICS
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 port
argument does not specify a terminal device; if there is no utmp entry for the current
process (System V only); and so on.
AUTHORS
Werner Fink <werner@suse.de>, Karel Zak <kzak@redhat.com>
The original agetty for serial terminals was written by W.Z. Venema
<wietse@wzv.win.tue.nl> and ported to Linux by Peter Orbaek <poe@daimi.aau.dk>.
REPORTING BUGS
For bug reports, use the issue tracker at https://github.com/util-linux/util-linux/issues.
AVAILABILITY
The agetty command is part of the util-linux package which can be downloaded from Linux
Kernel Archive <https://www.kernel.org/pub/linux/utils/util-linux/>.