====== Ubuntu - Swap - Enabling swap ======

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

<code bash>
grep swap /etc/fstab 
</code>

Returns something like this.

<code bash>
UUID=14a0f7b9-dabb-4296-b0e7-013527a7d82d none swap sw 0 0
</code>

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

<code bash>
swapon -s
</code>

returns:

<code bash>
Filename Type Size Used Priority
/dev/sda6 partition 1004020 215532 -1
</code>

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

<code bash>
sudo fdisk -l /dev/sda
</code>

returns

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

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.

<code bash>
su -
mkswap /dev/sda6
swapon /dev/sda6
</code>

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:

<code>
/dev/sda6 none swap sw 0 0
</code>

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 file for swap =====

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:

<code bash>
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
</code>