Question: I would like to add more swap space to my Linux system. Can you explain with clear examples on how to increase the swap space?
Answer: You can either use a dedicated hard drive partition to add new swap space, or create a swap file on an existing filesystem and use it as swap space.
Table of Contents
How much swap space is currently used by the system?
Free command displays the swap space. free -k shows the output in KB.
# free -k
total used free shared buffers cached
Mem: 3082356 2043700 1038656 0 50976 1646268
-/+ buffers/cache: 346456 2735900
Swap: 4192956 0 4192956
Swapon command with option -s, displays the current swap space in KB.
# swapon -s Filename Type Size Used Priority /dev/sda2 partition 4192956 0 -1
Swapon -s, is same as the following.
# cat /proc/swaps Filename Type Size Used Priority /dev/sda2 partition 4192956 0 -1
Method 1: Use a Hard Drive Partition for Additional Swap Space
If you have an additional hard disk, (or space available in an existing disk), create a partition using fdisk command. Let us assume that this partition is called /dev/sdc1
Now setup this newly created partition as swap area using the mkswap command as shown below.
# mkswap /dev/sdc1
Enable the swap partition for usage using swapon command as shown below.
# swapon /dev/sdc1
To make this swap space partition available even after the reboot, add the following line to the /etc/fstab file.
# cat /etc/fstab /dev/sdc1 swap swap defaults 0 0
Verify whether the newly created swap area is available for your use.
# swapon -s
Filename Type Size Used Priority
/dev/sda2 partition 4192956 0 -1
/dev/sdc1 partition 1048568 0 -2
# free -k
total used free shared buffers cached
Mem: 3082356 3022364 59992 0 52056 2646472
-/+ buffers/cache: 323836 2758520
Swap: 5241524 0 5241524
Note: In the output of swapon -s command, the Type column will say “partition” if the swap space is created from a disk partition.
Method 2: Use a File for Additional Swap Space
If you don’t have any additional disks, you can create a file somewhere on your filesystem, and use that file for swap space.
The following dd command example creates a swap file with the name “myswapfile” under /root directory with a size of 1024MB (1GB).
# dd if=/dev/zero of=/root/myswapfile bs=1M count=1024 1024+0 records in 1024+0 records out # ls -l /root/myswapfile -rw-r--r-- 1 root root 1073741824 Aug 14 23:47 /root/myswapfile
Change the permission of the swap file so that only root can access it.
# chmod 600 /root/myswapfile
Make this file as a swap file using mkswap command.
# mkswap /root/myswapfile Setting up swapspace version 1, size = 1073737 kB
Enable the newly created swapfile.
# swapon /root/myswapfile
To make this swap file available as a swap area even after the reboot, add the following line to the /etc/fstab file.
# cat /etc/fstab /root/myswapfile swap swap defaults 0 0
Verify whether the newly created swap area is available for your use.
# swapon -s
Filename Type Size Used Priority
/dev/sda2 partition 4192956 0 -1
/root/myswapfile file 1048568 0 -2
# free -k
total used free shared buffers cached
Mem: 3082356 3022364 59992 0 52056 2646472
-/+ buffers/cache: 323836 2758520
Swap: 5241524 0 5241524
Note: In the output of swapon -s command, the Type column will say “file” if the swap space is created from a swap file.
If you don’t want to reboot to verify whether the system takes all the swap space mentioned in the /etc/fstab, you can do the following, which will disable and enable all the swap partition mentioned in the /etc/fstab
# swapoff -a # swapon -a