# MKSWAP - set up a Linux swap area - man(8) - [phpMan] [_MKSWAP_(8)](https://www.chedong.com/phpMan.php/man/MKSWAP/8/markdown) System Administration [_MKSWAP_(8)](https://www.chedong.com/phpMan.php/man/MKSWAP/8/markdown) ## NAME mkswap - set up a Linux swap area ## SYNOPSIS **mkswap **[options] _device_ [_size_] ## 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 _size_ 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)](https://www.chedong.com/phpMan.php/man/swapon/8/markdown) 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 --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 _ Specify a _label_ for the device, to allow [**swapon**(8)](https://www.chedong.com/phpMan.php/man/swapon/8/markdown) by label. **--lock**[=_mode_] Use exclusive BSD lock for device or file it operates. The optional argument _mode_ can be **yes**, **no **(or 1 and 0) or **nonblock**. If the _mode_ argument is omitted, it defaults to **yes**. This option overwrites environment variable **$LOCK_BLOCK_DEVICE**. The default is not to use any lock at all, but it’s recommended to avoid collisions with [**systemd-udevd**(8)](https://www.chedong.com/phpMan.php/man/systemd-udevd/8/markdown) or other tools. ### -p --pagesize _ Specify the page _size_ (in bytes) to use. This option is usually unnecessary; **mkswap **reads the size from the kernel. ### -U --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 _ Specify the _ENDIANNESS_ to use, valid arguments are **native**, **little **or **big**. The default is **native**. ### -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 Print version and exit. ## ENVIRONMENT LIBBLKID_DEBUG=all enables libblkid debug output. LOCK_BLOCK_DEVICE= 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**. To set up a swap file, it is necessary to create that file before initializing it with **mkswap**, e.g. using a command like # dd if=/dev/zero of=swapfile bs=1MiB count=$((8*1024)) to create 8GiB swapfile. Please read notes from [**swapon**(8)](https://www.chedong.com/phpMan.php/man/swapon/8/markdown) about **the swap file use restrictions **(holes, preallocation and copy-on-write issues). ## SEE ALSO [**fdisk**(8)](https://www.chedong.com/phpMan.php/man/fdisk/8/markdown), [**swapon**(8)](https://www.chedong.com/phpMan.php/man/swapon/8/markdown) ## REPORTING BUGS For bug reports, use the issue tracker at . ## AVAILABILITY The **mkswap **command is part of the util-linux package which can be downloaded from Linux Kernel Archive <>. util-linux 2.39.3 2023-12-01 [_MKSWAP_(8)](https://www.chedong.com/phpMan.php/man/MKSWAP/8/markdown)