NAME
agetty - alternative Linux gettySYNOPSIS
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).•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.
ARGUMENTS
portA 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
"--".
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'.
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, --8bitsAssume that the tty is 8-bit clean, hence
disable parity detection.
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.
Do not reset terminal cflags (control modes).
See termios(3) for more details.
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.
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.
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.
Enable hardware (RTS/CTS) flow control. It is
left up to the application to disable software (XON/XOFF) flow protocol where
appropriate.
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.
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.
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.
Do not clear the screen before prompting for
the login name. By default the screen is cleared.
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.
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
never
auto
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.
Explicitly clears the CLOCAL flag from the
line setting and the carrier-detect signal is expected on the line.
The agetty default. Does not modify the
CLOCAL setting and follows the setting enabled by the kernel.
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.
Display supported baud rates. These are
determined at compilation time.
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.
Do not print a newline before writing out
/etc/issue.
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.
Wait for any key before dropping to the login
prompt. Can be combined with --autologin to save memory by lazily
spawning shells.
Change root to the specified directory.
Call vhangup(2) to do a virtual hangup
of the specified terminal.
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.
Terminate if no user name could be read within
timeout seconds. Use of this option with hardwired terminal lines is
not recommended.
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.
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.
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(3P) or (if not found) by getaddrinfo(3) is
shown.
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.
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.
Change directory before the login.
Sleep seconds before open tty.
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 inotify(7).
Display help text and exit.
Print version and exit.
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.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.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.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.
The same as \4 but for IPv6.
Insert the baudrate of the current line.
Insert the current date.
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.
Insert the system name (the name of the
operating system). Same as 'uname -s'. See also the \S escape code.
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.
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, that is, the
build-date and such.
This is \n.\o (\s \m \r) \t
This is thingol.orcan.dk (Linux i386 1.1.9) 18:29:30
FILES
/var/run/utmpthe system status file.
printed before the login prompt.
operating system identification data.
problem reports (if syslog(3) is not
used).
init(8) configuration file for
SysV-style init daemon.
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.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 <[email protected]>Fink Karel <[email protected]>ZakREPORTING 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/>.2022-08-04 | util-linux 2.38.1 |