check to see if you have swap partitions defined by consulting /etc/fstab. If you do then

grep swap /etc/fstab 

Returns something like this.

UUID=14a0f7b9-dabb-4296-b0e7-013527a7d82d none swap sw 0 0

If one is defined you can check that it is being used by the system:

swapon -s

returns:

Filename Type Size Used Priority
/dev/sda6 partition 1004020 215532 -1

If one is defined but not in use the obvious thing to do is check that it is formatted as a swap partition:

sudo fdisk -l /dev/sda

returns

[..snipped..]
/dev/sda5 3842 6595 22121473+ 83 Linux
/dev/sda6 6596 6720 1004031 82 Linux swap / Solaris

If it is a swap partition, ready it for use and turn it on. At this point, you might see any errors that prevented its use.

su -
mkswap /dev/sda6
swapon /dev/sda6

You can now check that the partition is being used using the “swapon -s” command we saw above.

Add an entry to /etc/fstab to have this swap partition loaded at bootup. You can replace the “UUID=xxx” part from above with “/dev/sda6”; so the entry would look like this:

/dev/sda6 none swap sw 0 0

If you didn't define a swap partition earlier, then you'd have to create one, or point swap to a regular file (which is a little less efficient, but probably sufficient).

Using a static partition for swap is wasteful - so I tend to configure my systems with LVM, and allocate a swap partition in that.

If I'm not using LVM then a simple file is sufficient, since a system actually using swap is probably already broken. This is how I'd set it up:

su -
dd if=/dev/zero of=/swap.file bs=1024k count=1
mkswap -f /swap.file
echo "/swap.file none swap sw 0 0 " >> /etc/fstab
swapon -a