[SOLVED]Choose different autologin-user depending on luks-keyslot used

Question

I got two users on this system and both have a passphrase for the system encryption with luks. Now I want to build a script that changes the gdm settings at boot time to change the user that is going to be logged in automatically depending on which slot was unlocked.
I already changed /lib/initcpio/hooks/encrypt to include a "-v" when cryptsetup is called (so it gives the number of the slot to the output) and also changed the appropriate lines to
while ! CRYPTSLOT=$(/sbin/cryptsetup -v luksOpen ${cryptdev} ${cryptname} ${cryptargs} ${CSQUIET}); do
sleep 2;
done
which saves the output in the variable CRYPTSLOT.
Now I just need to export this variable somehow in a way that i can pick it up in some rc.d script (at a time when the filesystems are mounted etc.). I tried just
export CRYPTSLOT
, which did not work. Saving it to a file will also not be possible since the hook is run before / is mounted, in the initramdisk. Is there any other possibility? Can I write it to some file in /boot? (is it mounted?)
I also tried it without a variable, extracting the information from dmesg or /etc/messages.log, but it wasn't there. If I do not save it in the variable I see it in the boot screen, but I can not pass it to some later script.
Last edited by viktordick (2012-03-25 15:34:34)

Answer 1

The output is put to stdout, not stderr. Is msg some function inside the initramfs? Because bash does not find the command, but if I put it into the hook, it acts the same way as echo. Its argument still does not appear in dmesg.
Well, I found another way: I wrote the output to /dev/cryptslot. /dev is already there and it seems it is also writeable. So in /lib/initcpio/hooks/encrypt I have
while ! /sbin/cryptsetup -v luksOpen ${cryptdev} ${cryptname} ${cryptargs} ${CSQUIET} > /dev/cryptslot; do
sleep 2;
done
and then I created a script in /etc/rc.d/changeuser:
#!/bin/bash
case "$1" in
start)
SLOT=$(cat /dev/cryptslot | cut -d ' ' -f 3)
case $SLOT in
0) cp /etc/gdm/custom-user1.conf /etc/gdm/custom.conf;;
1) cp /etc/gdm/custom-user2.conf /etc/gdm/custom.conf;;
esac
stop)
restart)
$0 stop
sleep 1
$0 start
echo "usage: $0 {start|stop|restart}"
esac
exit 0
Of course, this has to be added to /etc/rc.conf, too. Preferably before gdm and not in background.
Maybe this ist not such a good solution since /dev is not the right place for this. /proc might be better, but I cannot write anything there.
And yeah, the changes in /lib will probably be overwritten, but they are few, I can redo them when neccessary.