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Paddy Landau
Asked: 2014-06-20 12:43:17 +0800 CST

Swap not availlable

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I have noticed that my swap is not available. This could explain why my computer freezes every so often when I am using it heavily.

I installed 14.04 64-bit with an encrypted folder, which automatically encrypts my swap. This used to work perfectly in 12.04 64-bit.

The relevant lines from /etc/fstab are:

# swap was on /dev/sda6 during installation
#UUID=5e37c9cd-ba35-4907-8c77-556a308d1491  none  swap  sw  0  0
/dev/mapper/cryptswap1                      none  swap  sw  0  0

sudo blkid does not list the swap:

/dev/sda1: LABEL="PQSERVICE" UUID="FA3A29383A28F375" TYPE="ntfs" 
/dev/sda2: LABEL="SYSTEM RESERVED" UUID="967CF34F7CF3291F" TYPE="ntfs" 
/dev/sda3: LABEL="Daisy PC" UUID="36027B05027AC97F" TYPE="ntfs" 
/dev/sda5: LABEL="DaisyHome" UUID="4ad946a8-3a8e-41b9-907c-258b2ad9544e" TYPE="ext4" 
/dev/sda7: LABEL="DaisyRoot" UUID="5cb3c1ff-fdd2-458b-9765-b9407d19b469" TYPE="ext4"

System Monitor shows swap as being unavailable.

Swap not available in System Monitor

Gparted shows the swap partition as "unknown".

GIMP swap partition unknown

Disks shows the swap partition as "Linux Swap", but is unable to mount the partition.

Disks Linux partition

I have been Googling, reading Ubuntu Forums and searching this forum, and have been unable to find anything that helps to re-enable the swap.

Can you help, please.

EDIT

The file /etc/crypttab confusingly has two lines:

cryptswap1 UUID=5e37c9cd-ba35-4907-8c77-556a308d1491 /dev/urandom swap,cipher=aes-cbc-essiv:sha256
cryptswap1 UUID=7426472f-9ec1-4e53-b8e1-930e3d6f73fc /dev/urandom swap,cipher=aes-cbc-essiv:sha256

Here is a list of the UUIDs on my system:

$ ls -l /dev/disk/by-uuid/
total 0
lrwxrwxrwx 1 root root 10 Jun 20 08:48 36027B05027AC97F -> ../../sda3
lrwxrwxrwx 1 root root 10 Jun 20 08:48 4ad946a8-3a8e-41b9-907c-258b2ad9544e -> ../../sda5
lrwxrwxrwx 1 root root 10 Jun 20 08:48 5cb3c1ff-fdd2-458b-9765-b9407d19b469 -> ../../sda7
lrwxrwxrwx 1 root root 10 Jun 20 08:48 967CF34F7CF3291F -> ../../sda2
lrwxrwxrwx 1 root root 10 Jun 20 08:48 FA3A29383A28F375 -> ../../sda1

Now my problem is: How do I determine the UUID of /dev/sda6? Is this even possible on an encrypted swap? Finally, how do I fix /etc/crypttab?

encryption

2 Answers

  1. Best Answer

    Thanks to your comments, @saiarcot895, on further investigation I have discovered what to do.

    I have edited /etc/crypttab to remove the extra line (there was also an extra line in /etc/fstab, which I removed), and to replace UUID with the partition reference. Hence:

    cryptswap1 /dev/sda6 /dev/urandom swap,cipher=aes-cbc-essiv:sha256

    I would still like to know how to replace the partition reference with the UUID, but perhaps that's not possible with an encrypted swap.

    EDIT:

    As far as I can tell, the UUID of an encrypted partition is unavailable until that partition has been decrypted. I have discovered that in the case of an encrypted swap using a random key each boot, the UUID changes each time. Therefore, the UUID is not useful in specifying which encrypted partition to mount.

    This can cause a serious problem with removable disks!

    • 3

  2. run cfdisk re-create the swap partition. run command

    # mkswap /dev/sda6

    then

    # swapon /dev/sda6

    mind that sda6 is your swap partition

    • 0