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.TH AGETTY 8 "May 2011" "util-linux" "System Administration"
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agetty \- alternative Linux getty
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.BR "agetty " [\-8chiLmnsUw]
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.RI "[\-f " issue_file ]
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.RI "[\-H " login_host ]
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.RI "[\-l " login_program ]
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\fBagetty\fP opens a tty port, prompts for a login name and invokes
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the /bin/login command. It is normally invoked by \fIinit(8)\fP.
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\fBagetty\fP has several \fInon-standard\fP features that are useful
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for hard-wired and for dial-in lines:
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Adapts the tty settings to parity bits and to erase, kill,
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end-of-line and uppercase characters when it reads a login name.
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The program can handle 7-bit characters with even, odd, none or space
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parity, and 8-bit characters with no parity. The following special
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characters are recognized: @ and Control-U (kill); #, DEL and
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back space (erase); carriage return and line feed (end of line).
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Optionally deduces the baud rate from the CONNECT messages produced by
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Hayes(tm)-compatible modems.
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Optionally does not hang up when it is given an already opened line
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(useful for call-back applications).
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Optionally does not display the contents of the \fI/etc/issue\fP file.
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Optionally displays an alternative issue file instead of \fI/etc/issue\fP.
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Optionally does not ask for a login name.
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Optionally invokes a non-standard login program instead of
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Optionally turns on hard-ware flow control
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Optionally forces the line to be local with no need for carrier detect.
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This program does not use the \fI/etc/gettydefs\fP (System V) or
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\fI/etc/gettytab\fP (SunOS 4) files.
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A path name relative to the \fI/dev\fP directory. If a "\-" is
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specified, \fBagetty\fP assumes that its standard input is
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already connected to a tty port and that a connection to a
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remote user has already been established.
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Under System V, a "\-" \fIport\fP argument should be preceded
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A comma-separated list of one or more baud rates. Each time
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\fBagetty\fP receives a BREAK character it advances through
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the list, which is treated as if it were circular.
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Baud rates should be specified in descending order, so that the
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null character (Ctrl\-@) can also be used for baud rate switching.
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The value to be used for the TERM environment variable. This overrides
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whatever init(8) may have set, and is inherited by login and the shell.
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Assume that the tty is 8-bit clean, hence disable parity detection.
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\-a, \-\-autologin \fIusername\fP
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Log the specified user automatically in without asking for a login name and
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password. The \-f \fIusername\fP option is added to the \fB/bin/login\fP
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command line by default. The \-\-login-options option changes this default
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behaviour and then only \\u is replaced by the \fIusername\fP and no other
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option is added to the login command line.
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Don't reset terminal cflags (control modes). See \fItermios(3)\fP for more
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\-f, \-\-issue\-file \fIissue_file\fP
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Display the contents of \fIissue_file\fP instead of \fI/etc/issue\fP.
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This allows custom messages to be displayed on different terminals.
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The \-i option will override this option.
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\-h, \-\-flow\-control
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Enable hardware (RTS/CTS) flow control. It is left up to the
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application to disable software (XON/XOFF) flow protocol where
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\-H, \-\-host \fIlogin_host\fP
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Write the specified \fIlogin_host\fP into the utmp file. (Normally,
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no login host is given, since \fBagetty\fP is used for local hardwired
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connections and consoles. However, this option can be useful for
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identifying terminal concentrators and the like.
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Do not display the contents of \fI/etc/issue\fP (or other) before writing the
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login prompt. Terminals or communications hardware may become confused
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when receiving lots of text at the wrong baud rate; dial-up scripts
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may fail if the login prompt is preceded by too much text.
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\-I, \-\-init\-string \fIinitstring\fP
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Set an initial string to be sent to the tty or modem before sending
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anything else. This may be used to initialize a modem. Non printable
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characters may be sent by writing their octal code preceded by a
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backslash (\\). For example to send a linefeed character (ASCII 10,
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octal 012) write \\012.
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\-l, \-\-login\-program \fIlogin_program\fP
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Invoke the specified \fIlogin_program\fP instead of /bin/login.
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This allows the use of a non-standard login program (for example,
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one that asks for a dial-up password or that uses a different
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Force the line to be a local line with no need for carrier detect. This can
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be useful when you have a locally attached terminal where the serial line
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does not set the carrier detect signal.
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\-m, \-\-extract\-baud
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Try to extract the baud rate the CONNECT status message
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produced by Hayes(tm)\-compatible modems. These status
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messages are of the form: "<junk><speed><junk>".
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\fBagetty\fP assumes that the modem emits its status message at
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the same speed as specified with (the first) \fIbaud_rate\fP value
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Since the \fI\-m\fP feature may fail on heavily-loaded systems,
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you still should enable BREAK processing by enumerating all
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expected baud rates on the command line.
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Do not prompt the user for a login name. This can be used in
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connection with \-l option to invoke a non-standard login process such
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as a BBS system. Note that with the \-n option, \fBagetty\fR gets no input from
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user who logs in and therefore won't be able to figure out parity,
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character size, and newline processing of the connection. It defaults to
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space parity, 7 bit characters, and ASCII CR (13) end-of-line character.
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Beware that the program that \fBagetty\fR starts (usually /bin/login)
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\-o, \-\-login\-options \fI"login_options"\fP
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Options that are passed to the login program. \\u is replaced
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by the login name. The default \fB/bin/login\fP command line
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is "/bin/login -- <username>".
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Please read the SECURITY NOTICE below if you want to use this.
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\-p, \-\-login\-pause
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Wait for any key before dropping to the login prompt. Can be combined
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with \fB\-\-autologin\fP to save memory by lazily spawning shells.
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Do call vhangup() for a virtually hangup of the specified terminal.
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Try to keep the existing baud rate. The baud rates from
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the command line are used when agetty receives a BREAK character.
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\-t, \-\-timeout \fItimeout\fP
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Terminate if no user name could be read within \fItimeout\fP
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seconds. This option should probably not be used with hard-wired
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\-U, \-\-detect\-case
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Turn on support for detecting an uppercase only terminal. This setting will
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detect a login name containing only capitals as indicating an uppercase
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only terminal and turn on some upper to lower case conversions. Note that
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this has no support for any unicode characters.
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Wait for the user or the modem to send a carriage-return or a
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linefeed character before sending the \fI/etc/issue\fP (or other) file
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and the login prompt. Very useful in connection with the \-I option.
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Do not clear the screen before prompting for the login name
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(the screen is normally cleared).
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Do not print a newline before writing out /etc/issue.
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By default the hostname will be printed. With this option enabled,
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no hostname at all will be shown.
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By default the hostname is only printed until the first dot. With
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this option enabled, the full qualified hostname by gethostname()
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or if not found by gethostbyname() is shown.
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Output version information and exit.
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Output help screen and exit.
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This section shows examples for the process field of an entry in the
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\fI/etc/inittab\fP file. You'll have to prepend appropriate values
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for the other fields. See \fIinittab(5)\fP for more details.
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For a hard-wired line or a console tty:
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/sbin/agetty 9600 ttyS1
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For a directly connected terminal without proper carriage detect wiring:
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(try this if your terminal just sleeps instead of giving you a password:
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/sbin/agetty \-L 9600 ttyS1 vt100
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For a old style dial-in line with a 9600/2400/1200 baud modem:
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/sbin/agetty \-mt60 ttyS1 9600,2400,1200
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For a Hayes modem with a fixed 115200 bps interface to the machine:
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(the example init string turns off modem echo and result codes, makes
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modem/computer DCD track modem/modem DCD, makes a DTR drop cause a
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dis-connection and turn on auto-answer after 1 ring.)
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/sbin/agetty \-w \-I 'ATE0Q1&D2&C1S0=1\\015' 115200 ttyS1
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If you use the \fB\-\-login\-program\fP and \fB\-\-login\-options\fP options,
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be aware that a malicious user may try to enter lognames with embedded options,
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which then get passed to the used login program. Agetty does check
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for a leading "\-" and makes sure the logname gets passed as one parameter
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(so embedded spaces will not create yet another parameter), but depending
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on how the login binary parses the command line that might not be sufficient.
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Check that the used login program can not be abused this way.
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Some programs use "\-\-" to indicate that the rest of the commandline should
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not be interpreted as options. Use this feature if available by passing "\-\-"
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before the username gets passed by \\u.
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The issue-file (\fI/etc/issue\fP or the file set with the \-f option)
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may contain certain escape codes to display the system name, date and
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time etc. All escape codes consist of a backslash (\\) immediately
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followed by one of the letters explained below.
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Insert the baudrate of the current line.
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Insert the current date.
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Insert the system name, the name of the operating system. Same as `uname \-s'.
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Insert the name of the current tty line.
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Insert the architecture identifier of the machine. Same as `uname \-m'.
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Insert the nodename of the machine, also known as the hostname. Same as `uname \-n'.
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Insert the NIS domainname of the machine. Same as `hostname \-d'.
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Insert the DNS domainname of the machine.
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Insert the release number of the OS. Same as `uname \-r'.
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Insert the current time.
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Insert the number of current users logged in.
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Insert the string "1 user" or "<n> users" where <n> is the number of current
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Insert the version of the OS, eg. the build-date etc.
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Example: On my system, the following \fI/etc/issue\fP file:
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This is \\n.\\o (\\s \\m \\r) \\t
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This is thingol.orcan.dk (Linux i386 1.1.9) 18:29:30
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/var/run/utmp, the system status file.
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/etc/issue, printed before the login prompt.
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/dev/console, problem reports (if syslog(3) is not used).
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/etc/inittab, \fIinit\fP(8) configuration file.
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The baud-rate detection feature (the \fI\-m\fP option) requires that
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\fBagetty\fP be scheduled soon enough after completion of a dial-in
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call (within 30 ms with modems that talk at 2400 baud). For robustness,
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always use the \fI\-m\fP option in combination with a multiple baud
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rate command-line argument, so that BREAK processing is enabled.
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The text in the \fI/etc/issue\fP file (or other) and the login prompt
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are always output with 7-bit characters and space parity.
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The baud-rate detection feature (the \fI\-m\fP option) requires that
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the modem emits its status message \fIafter\fP raising the DCD line.
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Depending on how the program was configured, all diagnostics are
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written to the console device or reported via the syslog(3) facility.
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Error messages are produced if the \fIport\fP argument does not
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specify a terminal device; if there is no utmp entry for the
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current process (System V only); and so on.
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W.Z. Venema <wietse@wzv.win.tue.nl>
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Eindhoven University of Technology
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Department of Mathematics and Computer Science
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Den Dolech 2, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
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Peter Orbaek <poe@daimi.aau.dk>
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Linux port and more options. Still maintains the code.
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Eric Rasmussen <ear@usfirst.org>
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Added \-f option to display custom login messages on different terminals.
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The agetty command is part of the util-linux package and is available from
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ftp://ftp.kernel.org/pub/linux/utils/util\-linux/.
added
removed
term-utils/agetty.8
