How to check, view, create and remove a swap file on Linux

1_how-to-check-swap-space.md

How to Check Swap Space

There are several ways to check swap space in Linux.

• The free command with the -h tag shows the total, available, and used swap space in a human-readable format.

$ free -h

• The /proc/meminfo file shows the total, free, and used swap space in kilobytes.

$ cat /proc/meminfo | grep Swap

• The /proc/swaps file shows active swap devices.

$ cat /proc/swaps

• The swapon command with the --show tag displays swap information. The output shows the active swap devices, including the path, file type, size, and usage.

$ swapon --show

To monitor swap space, use a monitoring tool such as the vmstat command.

2_how-to-view-swap-file-on-linux.md

How to View a Swap File on Linux

To view the contents of a swap file, use the strings command and save the contents to another file.

$ sudo strings /swapfile > output.txt

3_how-to-create-a-new-swap-file-on-linux.md

How to Create a New Swap File on Linux

Creating a swap file on Linux is a simple process.

Create Storage File

Use the dd tool to create a new storage file.

$ sudo dd if=/dev/zero of=/swapfile bs=1M count=2048

The command contains the following parameters:

• if=/dev/zero is the input file. The /dev/zero file is a special file that returns as many null characters as a read operation requests.
• of=/swapfile is the output swap storage file. The common practice is to place the file in the root directory.
• The bs parameter is the block size.
• The count parameter determines how many blocks to copy.

The total data size is bs*count, which in this case is 2GB.

Set Swap Permissions

Set the swap file permissions to root read and write.

$ sudo chmod 600 /swapfile

The command shows no output. Check the permissions with the following:

$ ls / | grep swapfile

Set Up Swap Area

The swap file requires formatting the reserved file size into a swap area.

$ sudo mkswap /swapfile

The command formats the swap file into a swap space and outputs the size, label, and UUID.

Enable Swap

Enable the swap area for use.

$ sudo swapon /swapfile

Verify the swap is active.

$ swapon --show

The output shows a list of swapping devices and files, including the newly created swap file.

Persist Swap

The swap file does not persist after a restart by default. To make the changes permanent:

1. Open the /etc/fstab file with a text editor.

$ sudo vim /etc/fstab

2. Append the swap information in the following format.

/swapfile swap swap defaults 0 0

3. Save the file and close the editor.

4_how-to-adjust-swappiness-on-linux.md

How to Adjust Swappiness on Linux

Swappiness determines how often a Linux system uses the swap space. The swappiness value is a number between 0 and 200.

1. To check the current system swappiness value, run:

$ cat /proc/sys/vm/swappiness

The command prints a number between 0 and 200. A low value avoids swapping, while a high value increases swap usage.

2. To change the swappiness value to 10, run:

$ sudo sysctl vm.swappiness=10

The optimal value depends on the system, workload, and memory usage. Production servers typically require lower values.

3. To persist the change after a restart, open the /etc/sysctl.conf file:

$ sudo vim /etc/sysctl.conf

4. Append the following information to the file:

vm.swappiness = 10

5. Save the file and close vim.

5_how-to-remove-a-swap-file-on-linux.md

How to Remove a Swap File on Linux

Removing a swap file requires deactivating the swap space before removal.

1. To deactivate the swap, run:

$ sudo swapoff -v /swapfile

2. Use the rm command to delete the swap file:

$ sudo rm /swapfile

3. Open the /etc/fstab file:

$ sudo vim /etc/fstab

4. Remove the following swap information.

/swapfile swap swap defaults 0 0

5. Save the file and close vim.