swapon

swapon

The swapon command in Linux is used to activate swap space on the system. Here’s a detailed explanation:

  1. Purpose:

    • swapon is used to enable and activate swap partitions or swap files on a Linux system. Swap space serves as virtual memory, allowing the system to use disk space when physical RAM is fully utilized.

  2. Usage:

    • Syntax: swapon [options] device

    • Example: swapon /dev/sda2

    • Options:

      • -a: Activate all swap devices listed in /etc/fstab.

      • -v: Verbose mode, providing detailed output about the activation process.

  3. Device Specification:

    • Device: Typically, you specify a device file representing a swap partition (e.g., /dev/sda2) or a swap file (e.g., /swapfile).

    • Swap File Creation: If using a swap file, it needs to be created and initialized with dd and mkswap commands before using swapon.

  4. Considerations:

    • Performance: Activating swap (swapon) helps alleviate memory pressure and prevents out-of-memory situations by utilizing disk space as additional virtual memory.

    • Monitoring: Use tools like free, top, or vmstat to monitor memory and swap usage.

    • Permanent Activation: Modify /etc/fstab to ensure swap devices or files are activated automatically at system boot.

  5. Managing Swap Configuration:

    • Temporary Activation: Use swapon command to activate swap space temporarily during runtime.

    • Permanent Configuration: Update /etc/fstab to include entries for swap devices or files for automatic activation at boot time.

  6. Best Practices:

    • Ensure sufficient swap space relative to physical RAM for optimal system performance.

    • Regularly monitor and adjust swap usage based on system workload and memory demands.

Conclusion

Understanding swapon is essential for Linux administrators and users managing system resources effectively. It provides flexibility in utilizing swap space to improve system performance and manage memory efficiently. Always consider system requirements and workload demands when configuring and monitoring swap usage on Linux systems.

help

Usage:
 swapon [options] [<spec>]

Enable devices and files for paging and swapping.

Options:
 -a, --all                enable all swaps from /etc/fstab
 -d, --discard[=<policy>] enable swap discards, if supported by device
 -e, --ifexists           silently skip devices that do not exist
 -f, --fixpgsz            reinitialize the swap space if necessary
 -o, --options <list>     comma-separated list of swap options
 -p, --priority <prio>    specify the priority of the swap device
 -s, --summary            display summary about used swap devices (DEPRECATED)
     --show[=<columns>]   display summary in definable table
     --noheadings         don't print table heading (with --show)
     --raw                use the raw output format (with --show)
     --bytes              display swap size in bytes in --show output
 -v, --verbose            verbose mode

 -h, --help               display this help
 -V, --version            display version

The <spec> parameter:
 -L <label>             synonym for LABEL=<label>
 -U <uuid>              synonym for UUID=<uuid>
 LABEL=<label>          specifies device by swap area label
 UUID=<uuid>            specifies device by swap area UUID
 PARTLABEL=<label>      specifies device by partition label
 PARTUUID=<uuid>        specifies device by partition UUID
 <device>               name of device to be used
 <file>                 name of file to be used

Available discard policy types (for --discard):
 once    : only single-time area discards are issued
 pages   : freed pages are discarded before they are reused
If no policy is selected, both discard types are enabled (default).

Available output columns:
 NAME   device file or partition path
 TYPE   type of the device
 SIZE   size of the swap area
 USED   bytes in use
 PRIO   swap priority
 UUID   swap uuid
 LABEL  swap label

breakdown

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