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agetty command in Linux with Examples

Last Updated : 15 Oct, 2024

agetty is a Linux version of getty. getty short for "get tty" is a Unix program running on a host computer that manages physical or virtual terminals to allow multi-user access. Linux provides a virtual terminal(tty) which is similar to the regular Linux terminal. agetty command opens a virtual terminal(tty port), prompts for a login name, and invokes the /bin/login command.

Syntax

agetty [options] port [baud_rate...] [term]

where,

port: It is a pathname relative to the /dev directory. If a "-" is specified, then this command considers that its standard input is already connected to a tty port and that a connection to a remote user has already been established.
baud_rate, ...: It is a comma-separated list of one or more baud rates. It should be specified in the descending order.
term: It is the value to be used for the TERM environment variable.

Common Options used with the agetty command Option Description -8, --8bits Assume 8-bit tty, meaning full 8-bit data transmission. -a, --autologin Automatically logs in the specified user without a password prompt. -c, --noreset Do not reset control mode upon start. -E, --remote Allows passing a hostname to login for remote connections (e.g., via telnetd). -h, --flow-control Enables hardware flow control using CTS/RTS handshaking for smoother communication. -i, --noissue Do not display the issue file (custom login message). -J, --noclear Do not clear the screen before displaying the login prompt. -m, --extract-baud Extract the baud rate from the terminal device during connection. -n, --skip-login Skip the login prompt and go directly to session (useful for auto-login setups). -p, --login-pause Wait for the user to press any key before showing the login prompt. -R, --hangup Perform a virtual hangup (vhangup) to disconnect the specified terminal. -s, --keep-baud Attempt to keep the previously used baud rate for the terminal connection. -t, --timeout Sets a timeout (in seconds) to terminate the session if the login prompt is not completed in time. -U, --detect-case Detect uppercase-only terminals and adjust login accordingly. --help Display a help message with a list of all available options. --version Display the current version of the agetty command.

For more details about the options you can run the following command on the terminal:

agetty --help

Linux agetty command Examples 1. agetty -8 - linux

-8 option for 8-bit tty.
'-' for specifies that standard input is already connected to a tty port.
baud rate is optional so not used here.
'linux' is value of TERM environment variable.

2. agetty -8 -t 5 - linux

-t 5 is the login process timeout.

3. agetty -h -t 60 tty 9600 vtxxx

tty refers to the device /dev/tty.
9600 is the bits per second bound rate.
vtxxx is the TERM environment variable to indicate that a VTxxx terminal is connecting, in the previous example 'linux' is used as TERM env.
-h activates CTS/RTS handshaking (flow control).
-t 60 allows 60 seconds for someone to attempt to log in before the modem is hung up.

4. agetty -a -h -t 60 tty 9600 vt102

-a specifies autologin.

5. agetty --version

To display the version information.

6. agetty -a -h -t 60 -U -s -m tty 9600 vt100

-U detects the uppercase terminal.
-s try to use existing baud rate.
-m use exact baud rate specified in the command.

Conclusion

The agetty command is an essential tool for managing terminal sessions in Linux, particularly for embedded systems, servers, and environments requiring serial connections. With its numerous options, such as autologin, flow control, timeout settings, and baud rate management, agetty provides robust control over terminal and user session management.

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