# swapon

## NAME



           swapon, swapoff - enable/disable devices and files for paging and
           swapping
    


## SYNOPSIS



           **swapon**[options] [_specialfile_...]
    
           **swapoff**[**-va**] [_specialfile_...]
    


## DESCRIPTION



           **swapon** is used to specify devices on which paging and swapping are
           to take place.
    
           The device or file used is given by the _specialfile_ parameter. It
           may be of the form **-L** _label_ or **-U** _uuid_ to indicate a device by
           label or uuid.
    
           Calls to **swapon** normally occur in the system boot scripts making
           all swap devices available, so that the paging and swapping
           activity is interleaved across several devices and files.
    
           **swapoff** disables swapping on the specified devices and files. When
           the **-a** flag is given, swapping is disabled on all known swap
           devices and files (as found in _/proc/swaps_ or _/etc/fstab_).
    


## OPTIONS



           **-a** , **--all**
               All devices marked as "swap" in _/etc/fstab_ are made available,
               except for those with the "noauto" option. Devices that are
               already being used as swap are silently skipped.
    
           **-T** , **--fstab** _path_
               Specifies an alternative fstab file for compatibility with
               mount(8). If _path_ is a directory, then the files in the
               directory are sorted by strverscmp(3); files that start with
               "." or without an .fstab extension are ignored. The option can
               be specified more than once. This option is mostly designed
               for initramfs or chroot scripts where additional configuration
               is specified beyond standard system configuration.
    
           **-d** , **--discard**[**=**_policy_]
               Enable swap discards, if the swap backing device supports the
               discard or trim operation. This may improve performance on
               some Solid State Devices, but often it does not. The option
               allows one to select between two available swap discard
               policies:
    
               **--discard=once**
                   to perform a single-time discard operation for the whole
                   swap area at swapon; or
    
               **--discard=pages**
                   to asynchronously discard freed swap pages before they are
                   available for reuse.
    
               If no policy is selected, the default behavior is to enable
               both discard types. The _/etc/fstab_ mount options **discard** ,
               **discard=once** , or **discard=pages** may also be used to enable
               discard flags.
    
           **-e** , **--ifexists**
               Silently skip devices that do not exist. The _/etc/fstab_ mount
               option **nofail** may also be used to skip non-existing device.
    
           **-f** , **--fixpgsz**
               Reinitialize (exec mkswap) the swap space if its page size
               does not match that of the current running kernel. mkswap(8)
               initializes the whole device and does not check for bad
               blocks.
    
           **-L** _label_
               Use the partition that has the specified _label_. (For this,
               access to _/proc/partitions_ is needed.)
    
           **-o** , **--options** _opts_
               Specify swap options by an _fstab_ -compatible comma-separated
               string. For example:
    
               **swapon -o pri=1,discard=pages,nofail /dev/sda2**
    
               The _opts_ string is evaluated last and overrides all other
               command line options.
    
           **-p** , **--priority** _priority_
               Specify the priority of the swap device. _priority_ is a value
               between 0 and 32767. Higher numbers indicate higher priority.
               See swapon(2) for a full description of swap priorities. Add
               **pri=**_value_ to the option field of _/etc/fstab_ for use with
               **swapon -a**. When no priority is defined, Linux kernel defaults
               to negative numbers.
    
           **-s** , **--summary**
               Display swap usage summary by device. Equivalent to **cat**
               **/proc/swaps**. This output format is DEPRECATED in favour of
               **--show** that provides better control on output data.
    
           **--show**[**=**_column_...]
               Display a definable table of swap areas. See the **--help** output
               for a list of available columns.
    
           **--output-all**
               Output all available columns.
    
           **--noheadings**
               Do not print headings when displaying **--show** output.
    
           **--raw**
               Display **--show** output without aligning table columns.
    
           **--bytes**
               Display swap size in bytes in **--show** output instead of in
               user-friendly units.
    
           **-U** _uuid_
               Use the partition that has the specified _uuid_.
    
           **-v** , **--verbose**
               Be verbose.
    
           **-h** , **--help**
               Display help text and exit.
    
           **-V** , **--version**
               Display version and exit.
    


## EXIT STATUS



           **swapoff** has the following exit status values since v2.36:
    
           **0**
               success
    
           **2**
               system has insufficient memory to stop swapping (OOM)
    
           **4**
               swapoff(2) syscall failed for another reason
    
           **8**
               non-swapoff(2) syscall system error (out of memory, ...)
    
           **16**
               usage or syntax error
    
           **32**
               all swapoff failed on **--all**
    
           **64**
               some swapoff succeeded on **--all**
    
           The command **swapoff --all** returns 0 (all succeeded), 32 (all
           failed), or 64 (some failed, some succeeded).
    
           + The old versions before v2.36 has no documented exit status, 0
           means success in all versions.
    


## ENVIRONMENT



           **LIBMOUNT_DEBUG** =all
               enables **libmount** debug output.
    
           **LIBBLKID_DEBUG** =all
               enables **libblkid** debug output.
    


## FILES



           _/dev/sd??_
               standard paging devices
    
           _/etc/fstab_
               ascii filesystem description table
    


## NOTES



       **Files with holes**
           The swap file implementation in the kernel expects to be able to
           write to the file directly, without the assistance of the
           filesystem. This is a problem on files with holes or on
           copy-on-write files on filesystems like Btrfs.
    
           Commands like cp(1) or truncate(1) create files with holes. These
           files will be rejected by **swapon**.
    
           Preallocated files created by fallocate(1) may be interpreted as
           files with holes too depending of the filesystem. Preallocated
           swap files are supported on XFS since Linux 4.18.
    
           The most portable solution to create a swap file is to use dd(1)
           and _/dev/zero_.
    
       **Btrfs**
           Swap files on Btrfs are supported since Linux 5.0 on files with
           **nocow** attribute. See the **btrfs**(5) manual page for more details.
    
           Since version 2.41, the command **mkswap --file** can create a new
           swap file with the **nocow** attribute.
    
       **NFS**
           Swap over **NFS** may not work.
    
       **Suspend**
           **swapon** automatically detects and rewrites a swap space signature
           with old software suspend data (e.g., **S1SUSPEND** , **S2SUSPEND** , ...).
           The problem is that if we don’t do it, then we get data corruption
           the next time an attempt at unsuspending is made.
    


## AVAILABILITY



           The **swapon** command is part of the util-linux package which can be
           downloaded from Linux Kernel Archive
           <https://www.kernel.org/pub/linux/utils/util-linux/>. This page is
           part of the _util-linux_ (a random collection of Linux utilities)
           project. Information about the project can be found at 
           ⟨https://www.kernel.org/pub/linux/utils/util-linux/⟩. If you have a
           bug report for this manual page, send it to
           util-linux@vger.kernel.org. This page was obtained from the
           project's upstream Git repository
           ⟨git://git.kernel.org/pub/scm/utils/util-linux/util-linux.git⟩ on
           2025-08-11. (At that time, the date of the most recent commit that
           was found in the repository was 2025-08-05.) If you discover any
           rendering problems in this HTML version of the page, or you
           believe there is a better or more up-to-date source for the page,
           or you have corrections or improvements to the information in this
           COLOPHON (which is _not_ part of the original manual page), send a
           mail to man-pages@man7.org
    
    util-linux 2.42-start-521-ec46  2025-08-09                      _SWAPON_(8)
    


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