Manual: agetty
AGETTY(8) System Administration AGETTY(8)
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: "". 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
Display 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 the issue file and directory are supported. agetty
checks for the files /run/issue and /run/issue.d, and then for /usr/lib/issue and /usr/lib/issue.d.
The directory /etc is expected for host-specific configuration, /run is expected for generated
content, and /usr/lib is used for static configuration maintained by the distribution.
Note that in versions 2.35 to 2.40, the additional locations were only read if the default /etc/issue
file did not exist. However, since version 2.41, the additional locations are always read, regardless
of the existence of the /etc/issue file. This change allows for the generation of issue files by
default.
The default paths maybe completely 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 " users" where 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 , Karel Zak
The original agetty for serial terminals was written by W.Z. Venema and
ported to Linux by Peter Orbaek .
REPORTING BUGS
For bug reports, use the issue tracker .
AVAILABILITY
The agetty command is part of the util-linux package which can be downloaded from Linux Kernel
Archive .
util-linux 2.41.3 2025-12-15 AGETTY(8)