# mkswap

## NAME



           mkswap - set up a Linux swap area
    


## SYNOPSIS



           **mkswap**[options] _device_ [_blocks_]
    
           **mkswap**[options] --size _size_ --file _file_
    


## DESCRIPTION



           **mkswap** sets up a Linux swap area on a device or in a file.
    
           The _device_ argument will usually be a disk partition (something
           like _/dev/sdb7_) but can also be a file. The Linux kernel does not
           look at partition IDs, but many installation scripts will assume
           that partitions of hex type 82 (LINUX_SWAP) are meant to be swap
           partitions. (**Warning: Solaris also uses this type. Be careful not**
           **to kill your Solaris partitions.**)
    
           The _blocks_ parameter is superfluous but retained for backwards
           compatibility. (It specifies the desired size of the swap area in
           1024-byte blocks. **mkswap** will use the entire partition or file if
           it is omitted. Specifying it is unwise - a typo may destroy your
           disk.)
    
           After creating the swap area, you need the swapon(8) command to
           start using it. Usually swap areas are listed in _/etc/fstab_ so
           that they can be taken into use at boot time by a **swapon -a**
           command in some boot script.
    


## WARNING



           The swap header does not touch the first block. A boot loader or
           disk label can be there, but it is not a recommended setup. The
           recommended setup is to use a separate partition for a Linux swap
           area.
    
           **mkswap** , like many others mkfs-like utils, **erases the first**
           **partition block to make any previous filesystem invisible.**
    
           However, **mkswap** refuses to erase the first block on a device with
           a disk label (SUN, BSD, ...).
    


## OPTIONS



           **-c** , **--check**
               Check the device (if it is a block device) for bad blocks
               before creating the swap area. If any bad blocks are found,
               the count is printed.
    
           **-F** , **--file**
               Create a swap file with the appropriate file permissions and
               populated blocks on disk.
    
           **-f** , **--force**
               Go ahead even if the command is stupid. This allows the
               creation of a swap area larger than the file or partition it
               resides on.
    
               Also, without this option, **mkswap** will refuse to erase the
               first block on a device with a partition table.
    
           **-q** , **--quiet**
               Suppress output and warning messages.
    
           **-L** , **--label** _label_
               Specify a _label_ for the device, to allow swapon(8) by label.
    
           **--lock**[**=**_mode_]
               Use an exclusive BSD lock for the device or file that is
               operated upon. The optional argument _mode_ can be **yes**(**1**), **no**
               (**0**), or **nonblock**. If the _mode_ argument is omitted, it defaults
               to **yes**. This option overrides the environment variable
               **$LOCK_BLOCK_DEVICE**. The default is to not use any lock at all,
               but using a lock is recommended to avoid collisions with
               systemd-udevd(8) or other tools.
    
           **-p** , **--pagesize** _size_
               Specify the page _size_ (in bytes) to use. This option is
               usually unnecessary; **mkswap** reads the size from the kernel.
    
           **-U** , **--uuid** _UUID_
               Specify the _UUID_ to use. The default is to generate a UUID.
               The format of the UUID is a series of hex digits separated by
               hyphens, like this: "c1b9d5a2-f162-11cf-9ece-0020afc76f16".
               The UUID parameter may also be one of the following:
    
               **clear**
                   clear the filesystem UUID
    
               **random**
                   generate a new randomly-generated UUID
    
               **time**
                   generate a new time-based UUID
    
           **-e** , **--endianness** _ENDIANNESS_
               Specify the _ENDIANNESS_ to use, valid arguments are **native** ,
               **little** or **big**. The default is **native**.
    
           **-o** , **--offset** _offset_
               Specify the _offset_ to write the swap area to.
    
           **-s** , **--size** _size_
               Specify the size of the created swap file in bytes and may be
               followed by a multiplicative suffix: KiB (=1024), MiB
               (=1024*1024), and so on for GiB, TiB, PiB, EiB, ZiB and YiB
               (the "iB" is optional, e.g., "K" has the same meaning as
               "KiB"). If the file exists and is larger than _size_ , it will be
               truncated to this size. This option only makes sense when used
               with **--file**.
    
           **-v** , **--swapversion 1**
               Specify the swap-space version. (This option is currently
               pointless, as the old **-v 0** option has become obsolete and now
               only **-v 1** is supported. The kernel has not supported v0
               swap-space format since 2.5.22 (June 2002). The new version v1
               is supported since 2.1.117 (August 1998).)
    
           **--verbose**
               Verbose execution. With this option **mkswap** will output more
               details about detected problems during swap area set up.
    
           **-h** , **--help**
               Display help text and exit.
    
           **-V** , **--version**
               Display version and exit.
    


## ENVIRONMENT



           LIBBLKID_DEBUG=all
               enables libblkid debug output.
    
           LOCK_BLOCK_DEVICE=<mode>
               use exclusive BSD lock. The mode is "1" or "0". See **--lock** for
               more details.
    


## NOTES



           The maximum useful size of a swap area depends on the architecture
           and the kernel version.
    
           The maximum number of the pages that is possible to address by
           swap area header is 4294967295 (32-bit unsigned int). The
           remaining space on the swap device is ignored.
    
           Presently, Linux allows 32 swap areas. The areas in use can be
           seen in the file _/proc/swaps_.
    
           **mkswap** refuses areas smaller than 10 pages.
    
           If you don’t know the page size that your machine uses, you can
           look it up with **getconf PAGESIZE**.
    
           Aside from **mkswap --file** , it is also possible to create the
           swapfile manually before initializing it with **mkswap** , e.g. using a
           command like
    
           Since version 2.41, **mkswap --file** sets the nocow attribute for
           newly created files to support swapfiles on Btrfs.
    
               # dd if=/dev/zero of=swapfile bs=1MiB count=$((8*1024))
    
           to create 8GiB swapfile.
    
           In such a case, please read notes from swapon(8) about **the swap**
           **file use restrictions**(holes, preallocation and copy-on-write
           issues).
    


## AVAILABILITY



           The **mkswap** 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                      _MKSWAP_(8)
    


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