Using the zramctl Command (with examples)

Introduction

The zramctl command is used to set up and control zram devices in Linux. Zram is a compressed block device in the kernel that creates a virtual drive in RAM, allowing for faster I/O operations. This article provides examples of various use cases of the zramctl command, explaining the code, motivation, and output for each use case.

Use Case 1: Checking if zram is enabled

To check if zram is enabled, you can use the following command:

lsmod | grep -i zram

Motivation

This use case allows users to confirm whether the zram module is loaded and enabled in the Linux kernel. It is essential to verify this before using zram functionalities.

Explanation

The command lsmod lists all loaded modules in the kernel, and grep -i zram searches for the keyword “zram” in the module list (case-insensitive).

Example Output

zram                   40960  1

In the example output, the “zram” module is listed, indicating that zram is enabled.

Use Case 2: Enabling zram with dynamic number of devices

To enable zram with a dynamic number of devices, use the command:

sudo modprobe zram

Motivation

This use case enables the zram module in the Linux kernel without specifying the number of devices. By default, zram creates one device per CPU core, making it advantageous for multi-core systems.

Explanation

The modprobe command is used to load kernel modules. In this case, modprobe zram loads the zram module.

Example Output

No output is displayed if the command successfully loads the zram module.

Use Case 3: Enabling zram with a specific number of devices

To enable zram with a specific number of devices, use the following command:

sudo modprobe zram num_devices=2

Motivation

This use case allows users to customize the number of zram devices created in their system. Specifying the number of devices can be beneficial for resource management or specific use cases.

Explanation

Similar to the previous use case, this command uses modprobe to load the zram module. The additional argument num_devices=2 sets the desired number of zram devices to 2.

Example Output

No output is displayed if the command successfully loads the zram module.

Use Case 4: Finding and initializing the next free zram device

To find and initialize the next free zram device, use the following command:

sudo zramctl --find --size 2GB --algorithm lz4

Motivation

This use case allows users to create a new zram device with a specific size and compression algorithm. It is useful for creating additional zram devices for specific tasks or optimizing resource utilization.

Explanation

The zramctl command is used to interact with zram devices. The --find option finds the next available zram device. The --size 2GB argument specifies the desired size for the zram device (in this case, 2 GB). The --algorithm lz4 argument sets the compression algorithm to LZ4.

Example Output

/dev/zram0                                  [SWAP]
Size:                         2G
Used:                         5.1M
Priority:                     -2
Disk identifier:               0x00000000

The example output shows that a new zram device, /dev/zram0, has been initialized with a size of 2 GB. The device’s current usage is minimal, with only 5.1 MB used.

Use Case 5: Listing currently initialized zram devices

To list all currently initialized zram devices, use the following command:

zramctl

Motivation

This use case allows users to view the status and details of all initialized zram devices. It is useful for monitoring and managing existing zram devices.

Explanation

The zramctl command, without any arguments, displays information about all initialized zram devices.

Example Output

NAME       ALGORITHM DISKSIZE DATA COMPR TOTAL STREAMS MOUNTPOINT
/dev/zram0 lz4           2G  5.1M  1.1M  1.8M       1 [SWAP]

The example output shows that there is one initialized zram device, /dev/zram0, using LZ4 compression. The device has a disk size of 2 GB, with only 5.1 MB of data written.