If you need additional swap space to improve your system performance. You have two different ways: add/upgrade a swap partition or create a swap file. But changing the size or create a new swap partition is not easy, the best solution is to create a new swap file. This articles help you add/create swap file very quickly.

Creating swap file on Linux

Login as root and type the following command to create 512MB swap file

[root@lifelinux ~]# dd if=/dev/zero of=/swapfile bs=1024 count=524288

Where,
if=/dev/zero: read from /dev/zero instead of stdin
of=/swapfile: write to /swapfile instead of stdout
bs=1024: blocksize = 1024 bytes
count=524288: number of blocks are 524288

Setup the swap file with the command: mkswap. Type following command to setup your swap file:

[root@lifelinux ~]# mkswap /swapfile

To enable the swap file immediately but not automatically at boot time

[root@lifelinux ~]# swapon /swapfile

To activate the new swap file automatically at the boot, you need to edit the file /etc/fstab, enter

[root@lifelinux ~]# vi /etc/fstab

Add the following line at end of the file

/swapfile         swap             swap        defaults         0   0

To verify the swap file is working fine with these commands:

[root@lifelinux ~]# free -m

Or

[root@lifelinux ~]# cat /proc/swaps

Recommended size of linux swap

1 GB RAM —> 2 GB of Swap file
2 GB RAM —> 4 GB of Swap file
4 GB RAM —> 8 GB of Swap file
8 GB RAM —> 12 GB of Swap file
16 GB RAM —> 24 GB of Swap file
32 GB RAM —> 32 GB of Swap file

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To check avilable memory in Linux type free -m command. free displays the total amount of free and used physical and swap memory in the system, as well as the buffers used by the kernel.

free -m
free -h
free -b

Output:

             total       used       free     shared    buffers     cached
Mem:          2025       1961         64          0        172       1035
-/  buffers/cache:        753       1272
Swap:         1906          0       1906

1. The -b switch displays the amount of memory in bytes
2. The -k switch (set by default) displays it in kilobytes
3. The -m switch displays it in megabytes
4. The -g switch displays it in gigabytes.

vmstat

Output:

procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa
 0  0      0  63316 176624 1062340    0    0    25    18   39  592  5  1 94  0

1. swpd: the amount of virtual memory used.
2. free: the amount of idle memory.
3. buff: the amount of memory used as buffers.
4. cache: the amount of memory used as cache.

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