TTY Autologin: Difference between revisions

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{{tip|You can change the `tty1` or `ttyS0` to a different serial port or virtual terminal as you please. `root` can be changed to a different user as well. Finally the terminal type (`linux` and `vt100` in our examples) can be changed to a wide variety of serial terminals.}}
{{tip|You can change the `tty1` or `ttyS0` to a different serial port or virtual terminal as you please. `root` can be changed to a different user as well. Finally the terminal type (`linux` and `vt100` in our examples) can be changed to a wide variety of serial terminals.}}


=By compiling your own autologin wrapper=
=By making your own autologin wrapper=


== How ==
== How ==
# Writing a wrapper, called autologin, around {{path|/bin/login}} and moving it in {{path|/usr/sbin/}}
# Writing a wrapper script, called autologin, around {{path|/bin/login}} and moving it in {{path|/usr/sbin/}}
# Editing {{path|/etc/inittab}} specifying the use of {{path|/usr/sbin/autologin}} instead of {{path|/bin/login}}
# Editing {{path|/etc/inittab}} specifying the use of {{path|/usr/sbin/autologin}} instead of {{path|/bin/login}}


== Prerequisites ==
== Writing the autologin script ==
* A C compiler
* The '''''{{pkg|musl-dev}}''''' package which contains the C standard library


==== Example on how to assolve the prerequisites: ====
Edit and create the script in this example in the location {{path|/usr/sbin/autologin}}:
{{Cmd|# apk add gcc
# apk add musl-dev}}


== Writing the autologin.c program ==
{{cat|/usr/sbin/autologin|#!/bin/sh
exec login -f root}}


Create a file; in this example called autologin.c
Remember to make the scripts executable:
{{Cmd|# vi autologin.c }}
{{cmd|# chmod +x /usr/sbin/autologin}}


Write into it the following C program.
The script executes the ''login'' binary (part of busybox) which will be searched in $PATH.
 
{{cat|autologin.c|&#35;include <unistd.h>
 
int main()
{
    execlp( "login", "login", "-f", "root", 0);
}
}}
 
The only thing it does is a system call to execute the ''login'' binary (part of busybox) which will be searched in $PATH.


As parameters are passed:
As parameters are passed:
* '''-f'''  flag which stands for "Do not authenticate (user already authenticated)"
* '''-f'''  flag which stands for "Do not authenticate (user already authenticated)"
* ''username'' in this example is ''root'' but if you created a new user, its username can be used instead.
* ''username'' in this example is ''root'' but if you created a new user, its username can be used instead.
== Compiling the autologin.c program ==
If using gcc:
{{Cmd|&#35; gcc -o autologin autologin.c }}
Move the binary autologin to {{path|/usr/sbin}}
{{Cmd|&#35; mv autologin /usr/sbin/}}


== Editing /etc/inittab ==
== Editing /etc/inittab ==


Open {{path|/etc/inittab}}
Open {{path|/etc/inittab}}
{{Cmd|&#35; vi /etc/inittab }}


replace "'':respawn:/sbin/getty''" with "'':respawn:/sbin/getty -n -l /usr/sbin/autologin''" for each TTY you want to enable autologin.
replace "'':respawn:/sbin/getty''" with "'':respawn:/sbin/getty -n -l /usr/sbin/autologin''" for each TTY you want to enable autologin.
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==== Note ====
==== Note ====
To perform such a replacement on all TTYs, the following command can be used:
To perform such a replacement on all TTYs, the following command can be used:
{{Cmd|&#35; sed -i 's@:respawn:/sbin/getty@:respawn:/sbin/getty -n -l /usr/sbin/autologin@g' /etc/inittab }}
{{Cmd|# sed -i 's@:respawn:/sbin/getty@:respawn:/sbin/getty -n -l /usr/sbin/autologin@g' /etc/inittab }}
* "'''@'''" is used as a delimiter
* "'''@'''" is used as a delimiter
* The '''-i''' flag edits the file in-place
* The '''-i''' flag edits the file in-place
== Cleaning up ==
It is possible to remove the autologin.c file, the C compiler and the {{pkg|musl-dev}} package
{{Cmd|&#35; rm autologin.c
&#35; apk del gcc musl-dev}}


== References ==
== References ==
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* [https://busybox.net/downloads/BusyBox.html#getty Busybox getty arguments]
* [https://busybox.net/downloads/BusyBox.html#getty Busybox getty arguments]
* [https://github.com/util-linux/util-linux/blob/master/term-utils/agetty.8.adoc agetty(8) Manual Page]
* [https://github.com/util-linux/util-linux/blob/master/term-utils/agetty.8.adoc agetty(8) Manual Page]
[[Category:Display Managers]]
[[Category:Desktop]]

Latest revision as of 04:05, 24 September 2024

By using agetty

How

Install agetty:

# apk add agetty

Edit /etc/inittab to use agetty
Example for the virtual terminal tty1:
tty1::respawn:/sbin/agetty --autologin root tty1 linux

Example inittab entry for a serial terminal on ttys01:
ttyS0::respawn:/sbin/agetty --autologin root ttyS0 vt100

Tip: You can change the `tty1` or `ttyS0` to a different serial port or virtual terminal as you please. `root` can be changed to a different user as well. Finally the terminal type (`linux` and `vt100` in our examples) can be changed to a wide variety of serial terminals.

By making your own autologin wrapper

How

  1. Writing a wrapper script, called autologin, around /bin/login and moving it in /usr/sbin/
  2. Editing /etc/inittab specifying the use of /usr/sbin/autologin instead of /bin/login

Writing the autologin script

Edit and create the script in this example in the location /usr/sbin/autologin:

Contents of /usr/sbin/autologin

#!/bin/sh exec login -f root

Remember to make the scripts executable:

# chmod +x /usr/sbin/autologin

The script executes the login binary (part of busybox) which will be searched in $PATH.

As parameters are passed:

  • -f flag which stands for "Do not authenticate (user already authenticated)"
  • username in this example is root but if you created a new user, its username can be used instead.

Editing /etc/inittab

Open /etc/inittab

replace ":respawn:/sbin/getty" with ":respawn:/sbin/getty -n -l /usr/sbin/autologin" for each TTY you want to enable autologin.

  • The getty's -n flag do not prompt the user for a login name
  • The getty's -l flag invokes a custom login instead of /bin/login; in our case it is set to invoke /usr/sbin/autologin

Note

To perform such a replacement on all TTYs, the following command can be used:

# sed -i 's@:respawn:/sbin/getty@:respawn:/sbin/getty -n -l /usr/sbin/autologin@g' /etc/inittab

  • "@" is used as a delimiter
  • The -i flag edits the file in-place

References

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