Revision as of 17:23, 23 June 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

Writing a wrapper script, called autologin, around /bin/login and moving it in /usr/sbin/
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

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

@@ Line 11: / Line 11: @@
 {{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 ==
-# 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}}
-== Prerequisites ==
+== Writing the autologin script ==
-* A C compiler (e.g. '''''{{pkg|gcc}}''''' or '''''{{pkg|tcc}}''''')
-* 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 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
+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 program makes a system call to execute 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.
-== Compiling the autologin.c program ==
-If using gcc:
-{{Cmd|# gcc -o autologin autologin.c }}
-Move the binary autologin to {{path|/usr/sbin}}
-{{Cmd|# mv autologin /usr/sbin/}}
 == Editing /etc/inittab ==
@@ Line 62: / Line 43: @@
 * "'''@'''" is used as a delimiter
 * 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
 == References ==