TTY Autologin
What follows is one from many different ways to get autologin.
How
- Writing a wrapper, 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
Prerequisites
- A C compiler
- The musl-dev package which contains the C standard library
Example on how to assolve the prerequisites:
# apk add --repository https://dl-cdn.alpinelinux.org/alpine/edge/testing tcc # apk add musl-dev
Writing the autologin.c program
Create a file; in this example called autologin.c
# vi autologin.c
Write into it the following C program.
#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:
- -f flag which stands for "Do not authenticate (user already authenticated)"
- username in this example is root but if you created a new user, the user username can be used instead.
Compiling the autologin.c program
If using tcc:
# tcc -o autologin autologin.c
Move the binary autologin to /usr/sbin
# mv autologin /usr/sbin/
Editing /etc/inittab
# sed -i 's@:respawn:/sbin/getty@:respawn:/sbin/getty -n -l /usr/sbin/autologin@g' /etc/inittab
The above command:
- replaces ":respawn:/sbin/getty" with ":respawn:/sbin/getty -n -l /usr/sbin/autologin"
- "@" is used as a delimiter
- The -i flag edits the file in-place
- 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
Cleaning up
It is possible to remove the autologin.c file, the C compiler and the musl-dev package
# rm autologin.c # apk del tcc # apk del musl-dev