mkswap

Set up a Linux swap area

Description

The mkswap command is used to set up a Linux swap area on a device or in a file. After creating the swap area, use the swapon command to start using it. While an optional parameter allows specifying the swap area size, it is provided for backward compatibility and is usually unnecessary, as the command defaults to using the entire device or file.

Syntax

mkswap [OPTION]... DEVICE [SIZE]

Options

-c：Check for bad blocks before creating the swap area.
-f：Force execution. Required when creating a swap area on SPARC machines.
-v0：Create an old-style swap area (default).
-v1：Create a new-style swap area.

Parameters

Device: The device file or regular file to be used as swap space.

Examples

Check system swap space size:

free -m

View current swap space (files/partitions):

swapon -s
# or
cat /proc/swaps

Add swap space

You can add a swap partition or a swap file. A partition is generally recommended, but a file is useful if you have limited free space.

Steps to add a swap partition:

1. Use fdisk to create a partition (e.g., /dev/sdb2).
2. Set up the swap area:

mkswap /dev/sdb2

3. Enable the swap partition:

swapon /dev/sdb2

4. Add it to /etc/fstab to enable it at boot:

/dev/sdb2 swap swap defaults 0 0

Steps to add a swap file:

1. Create a 512MB file:

dd if=/dev/zero of=/swapfile1 bs=1024 count=524288

2. Set up the swap file:

mkswap /swapfile1

3. Enable the swap file:

swapon /swapfile1

4. Add it to /etc/fstab:

/swapfile1 swap swap defaults 0 0

After adding and enabling the swap space, verify it using free -m or cat /proc/swaps.

Remove swap space:

1. Disable the swap area:

swapoff /dev/sdb2

2. Remove the corresponding entry from /etc/fstab.
3. Use fdisk or other tools to delete the partition or rm to delete the swap file.