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I have installed 12.10 on a machine with two disks. The root partition is on one disk, the swap partition on the other. Both disks are encrypted and I have added the corresponding entries to /etc/crypttab.

During boot, it asks for the passphrase for the disk with the root filesystem. Then it continues booting and gets to the login screen before I get a chance to enter the passphrase for the other disk. After logging in, I verified that it was actually waiting for me to enter the passphrase for that second partition (askpass process is running). But at that point, I have no way of entering the passphrase anymore.

The manpage for crypttab suggests that the order in which the volumes are specified matters, so I changed it to have the swap disk first. I updated the initramfs and grub afterwards, but it didn't make any difference.

How can I specify the order in which the encrypted partitions are unlocked? I'm looking for a solution that either asks for the swap passphrase first or tells the system to wait until all encrypted partitions are unlocked before displaying the login screen.

Ideally I want to be able to use hibernation, i.e. neither use a random key for swap nor encode the key in crypttab.

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The method I used to encrypt my system and swap was that I set up an LVM logical disk on a partition encrypted with LUKS. When I enter a single password, the LVM volume appears and each of the partitions pop up in /dev/mapper. Not what you're asking, I know, but if you don't have a ton of time invested in your setup, it's something to consider. –  thirtythreeforty Oct 27 '12 at 22:22
    
Thanks for your suggestion, but in my case it's two physical disks so I can't use one passphrase -- I would actually prefer that though! –  Lars Kotthoff Oct 27 '12 at 22:27
    
@Lars Kotthoff LVM allows you to combine multiple disks together –  Tomasz Zieliński Oct 10 '13 at 0:36
    
Thanks for your comment, but in this case one is an HDD and the other one an SSD and I'd like to control which one is used for what. –  Lars Kotthoff Oct 10 '13 at 11:38
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2 Answers

up vote 2 down vote accepted

After some more digging, I found the decrypt_derived script. It allows to derive the passphrase from another encrypted partition. I set up the swap partition in this way, made the necessary changes to /etc/crypttab and it works! I only need to enter one passphrase, the second partition is unlocked automatically during boot and hibernation works.

More details e.g. here.

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If you don't care about hibernation, you can put the password for the encrypted swap partition into a file on the root partition. /etc/crypttab can then point to that file, and you can bypass this issue altogether. This isn't a security risk, since your root drive is encrypted. As a bonus, since you don't plan on using hibernation, you can actually have the swap file use a random key each time by setting this file to /dev/urandom. If you'll post your crypttab I'd be happy to show you the modifications you need to make.

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Thanks for your suggestion, but I do want hibernation support. I'll modify the question to reflect this. –  Lars Kotthoff Oct 28 '12 at 11:57
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