[arch-general] Timing issues when decrypting a USB drive during boot (/etc/crypttab)

[Julius Adorf]

Hello,

Recently, I tried to automatically unlock an encrypted external USB
hard drive on Arch Linux. I have done this by inserting an appropriate
entry into /etc/crypttab. I chose the device to be unlocked by
cryptsetup with a key file by UUID.

Unfortunately, the unlocking failed at boot time ("device does not
exist or access denied"). After some debugging via /etc/rc.sysinit, I
found out that it is a timing issue and the USB drive which is a
couple of years old was not ready yet at the time the /etc/crypttab
was read and processed. A similar issue has been reported here:
https://bbs.archlinux.org/viewtopic.php?id=137467

For now, I have inserted a workaround into /etc/rc.local which unlocks
the disk after an initial delay. This is still programming by
coincidence; I wonder whether there is any better (i.e. reliable)
solution to this problem?

Best,
Julius