I had the same problem when using an encrypted swap partition. Neither the general Swap FAQ, Puny Geek's solution to the "cryptswap1 is not ready yet or not present" message nor Braiam's answer to this question solved the problem for me - sometimes the swap was available, sometimes it wasn't. After many reboots and some poking around, I think I have found the underlying reason:
The path to the swap partition like /dev/sda3 is sometimes different, e.g. /dev/sdb3. Since the file /etc/crypttab by default seems to identify the swap partition through this path, sometimes it would find it (if that partition happens to get the same path at boot) or not (if the partition gets a different path assigned at boot).
Seems like I wasn't the only one with that problem becasue as described here, a better solution would be to bind the swap partition through it's drive ID instead of its /dev/sd* path. This can be found by running
ls -l /dev/disk/by-id/
which lists the disk IDs for all partitions including the swap, which in my case was
ata-TOSHIBA_MQ01UBD100_73JATD5GT-part3 -> ../../sdb3
Double check in a program like Disk Utility that the -> ../../sdb* part of this line is indeed the partition you intend to use for swapping, as this (as I said before) can sometimes change names. As always, keep this in mind:
Caution: fiddling with cryptsetup and disk devices is dangerous for
data and OS. I personally made a full backup on a separate disk and
then umplugged it to be sure it wouldn’t be involved in any mishap.
Then edit your /etc/crypttab file by using the ID link instead of the "raw" path, in my case this line is
cryptswap1 /dev/disk/by-id/ata-TOSHIBA_MQ01UBD100_73JATD5GT-part3 /dev/urandom swap,cipher=aes-cbc-essiv:sha256
I think this method should be the default for new installations, as one apparently can never be sure of the /dev/sd* paths... which I find somewhat worrying as I have the feeling that there are way more scripts and software out there which still rely on these paths (instead of IDs, labels or UUIDs) to stay the same across reboots.
TODO:
I haven't checked if resuming out of hibernation still works with this setup, as this seems to rely on a UUID (which my swap partition didn't have), as stated on this page: https://altinukshini.wordpress.com/2012/10/15/devmappercryptswap1-is-not-ready-yet-or-not-present/
Update:
Hibernation seems to work fine so far. Hope this solves these problems for others as well!
Best Answer
From what I'm reading, I don't think that you have removed the swap partition. Getting the swap partition's UUID is easy by typing in a terminal:
blkid. One of the lines should contain the wordswap. That line should look something like this:Now, edit
/etc/fstabby typing in the terminal:sudo gedit /etc/fstab. Add a line saying:So, in my case, it should be:
Save the file, reboot. You should have your swap partition mounted automatically again.
If
blkiddoesn't show a swap partition, you should create a new one. I'd advice you to do that via the toolgparted. Install it viasudo apt-get install gpartedor via the Software Center, then run it. Ingparted, select an unused area, then click on the new partition button (it looks like a document with a green plus sing on it), and make sure you format it aslinux-swaporswap, can't really remember what it's called again. A good swap partition should be 2 times the size of your RAM. So if you've got 2GB of RAM, make sure that your swap partition's size is 4GB. When you've done that,blkidshould show have a line containingswap. Continue using the instructions above.