swapoff(2) [debian man page]
SWAPON(2) BSD System Calls Manual SWAPON(2) NAME
swapon, swapoff -- control devices for interleaved paging/swapping LIBRARY
Standard C Library (libc, -lc) SYNOPSIS
#include <unistd.h> int swapon(const char *special); int swapoff(const char *special); DESCRIPTION
The swapon() system call makes the block device special available to the system for allocation for paging and swapping. The names of poten- tially available devices are known to the system and defined at system configuration time. The size of the swap area on special is calcu- lated at the time the device is first made available for swapping. The swapoff() system call disables paging and swapping on the given device. All associated swap metadata are deallocated, and the device is made available for other purposes. RETURN VALUES
If an error has occurred, a value of -1 is returned and errno is set to indicate the error. ERRORS
Both swapon() and swapoff() can fail if: [ENOTDIR] A component of the path prefix is not a directory. [ENAMETOOLONG] A component of a pathname exceeded 255 characters, or an entire path name exceeded 1023 characters. [ENOENT] The named device does not exist. [EACCES] Search permission is denied for a component of the path prefix. [ELOOP] Too many symbolic links were encountered in translating the pathname. [EPERM] The caller is not the super-user. [EFAULT] The special argument points outside the process's allocated address space. Additionally, swapon() can fail for the following reasons: [EINVAL] The system has reached the boot-time limit on the number of swap devices, vm.nswapdev. [ENOTBLK] The special argument is not a block device. [EBUSY] The device specified by special has already been made available for swapping [ENXIO] The major device number of special is out of range (this indicates no device driver exists for the associated hardware). [EIO] An I/O error occurred while opening the swap device. Lastly, swapoff() can fail if: [EINVAL] The system is not currently swapping to special. [ENOMEM] Not enough virtual memory is available to safely disable paging and swapping to the given device. SEE ALSO
config(8), swapon(8), sysctl(8) HISTORY
The swapon() system call appeared in 4.0BSD. The swapoff() system call appeared in FreeBSD 5.0. BSD
June 4, 1993 BSD
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SWAPON(8) Linux Programmer's Manual SWAPON(8) NAME
swapon, swapoff - enable/disable devices and files for paging and swapping SYNOPSIS
Get info: swapon -s [-h] [-V] Enable/disable: swapon [-f] [-p priority] [-v] specialfile... swapoff [-v] specialfile... Enable/disable all: swapon -a [-e] [-f] [-v] swapoff -a [-v] 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). -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. -e, --ifexists Silently skip devices that do not exist. -f, --fixpgsz Reinitialize (exec /sbin/mkswap) the swap space if its page size does not match that of the the current running kernel. mkswap(2) initializes the whole device and does not check for bad blocks. -h, --help Provide help. -L label Use the partition that has the specified label. (For this, access to /proc/partitions is needed.) -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. -s, --summary Display swap usage summary by device. Equivalent to "cat /proc/swaps". Not available before Linux 2.1.25. -U uuid Use the partition that has the specified uuid. -v, --verbose Be verbose. -V, --version Display version. NOTES
You should not use swapon on a file with holes. Swap over NFS may not work. swapon automatically detects and rewrites 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. swapon may not work correctly when using a swap file with some versions of btrfs. This is due to the swap file implementation in the ker- nel expecting to be able to write to the file directly, without the assistance of the file system. Since btrfs is a copy-on-write file system, the file location may not be static and corruption can result. Btrfs actively disallows the use of files on its file systems by refusing to map the file. This can be seen in the system log as "swapon: swapfile has holes." One possible workaround is to map the file to a loopback device. This will allow the file system to determine the mapping properly but may come with a performance impact. SEE ALSO
swapon(2), swapoff(2), fstab(5), init(8), mkswap(8), rc(8), mount(8) FILES
/dev/sd?? standard paging devices /etc/fstab ascii filesystem description table HISTORY
The swapon command appeared in 4.0BSD. AVAILABILITY
The swapon command is part of the util-linux-ng package and is available from ftp://ftp.kernel.org/pub/linux/utils/util-linux-ng/. Linux 1.x 25 September 1995 SWAPON(8)