I have a computer that serves as a home server as well as a desktop machine. It has an encrypted home directory to protect user files and, in the default configuration, that unfortunately interferes with unattended reboots since someone needs to be present to enter the encryption password.

Here's how I added a timeout and made /home optional on that machine.

I started by adding a one-minute timeout on the password prompt by adding timeout=60 in my /etc/crypttab:

crypt  UUID=7e12c123-abcd-5555-8c40-900d1f8cc281  none  luks,timeout=60

then I made /home optional by adding nofail to the appropriate mount point in /etc/fstab:

/dev/mapper/crypt  /home  ext4  nodev,noatime,nosuid,nofail  0  2

Before that, the password prompt would timeout but the system would be unable to boot since one of the required partitions had failed to mount.

Now, to ensure that I don't accidentally re-create home directories for users when the system is mounted without a /home, I made the /home directory on the non-encrypted drive read-only:

umount /home
cd /home
chmod a-w .

Finally, with all of this in place, I was now happy to configure the machine to automatically reboot after a kernel panic by putting the following in /etc/sysctl.d/local.conf:

# Automatic reboot 10 seconds after a kernel panic
kernel.panic = 10

since I know that the machine will come back up just fine and that all services will be running. I simply won't be able to log into that machine as any other user than root until I manually unlock and mount /home.