This article is about how to create swap space on a live RHEL/CentOS Linux system. However you can still follow that procedure in case you messed up your filesystem and swap is now non-existent (e.g.: swap show 0M).
First, use fdisk to edit the partition table and create a partition (this step might be skipped if you already have one) :
fdisk /dev/sda
Useful fdisk commands are :
m = help
p = show the partition layout
n = create a partition
t = change partition type
w = write changes
q = quit fdisk utility
Then, show your current partition layout (hit “p” key) :
Device Boot Start End Blocks Id System /dev/sda1 * 1 32 256000 83 Linux /dev/sda2 32 424 3145728 83 Linux /dev/sda3 424 45168 359403520 83 Linux
(We can see we have no swap area here!)
Let’s create a partition (hit “n” key) :
Command action e extended p primary partition (1-4)
(Select extended or primary depending on your situation. We’ll use extended here)
Device Boot Start End Blocks Id System /dev/sda1 * 1 32 256000 83 Linux /dev/sda2 32 424 3145728 83 Linux /dev/sda3 424 45168 359403520 83 Linux /dev/sda4 45168 45689 4190620+ 5 Extended /dev/sda5 45168 45689 4190589 83 Linux
Change the type of your brand new partition for swap use (hit “t” key and enter “82” as hex code) :
Command (m for help): t Partition number (1-5): 5 Hex code (type L to list codes): 82 Changed system type of partition 5 to 82 (Linux swap / Solaris)
Now write the changes to the partition table (hit “w” key and then “q”).
We are now ready to format the partition as swap, use “mkswap” command :
mkswap /dev/sda5
Will return :
# mkswap /dev/sda5 Setting up swapspace version 1, size = 4190584 KiB no label, UUID=d52c8bdb-96a8-4244-a300-b753b08570d6
The last step is to set (or modify if the swap where accidental removed) the partition UUID in fstab :
vi /etc/fstab
Config line shoud looks like :
UUID=d52c8bdb-96a8-4244-a300-b753b08570d6 swap swap defaults 0 0
Final step, enable the swap!
swapon -a