NAME
swapon, swapoff - start/stop swapping to file/device
SYNOPSIS
#include <unistd.h> #include <sys/swap.h> int swapon(const char *path, int swapflags); int swapoff(const char *path);
DESCRIPTION
swapon() sets the swap area to the file or block device specified by path. swapoff() stops swapping to the file or block device specified by path. If the SWAP_FLAG_PREFER flag is specified in the swapon() swapflags argument, the new swap area will have a higher priority than default. The priority is encoded within swapflags as: (prio << SWAP_FLAG_PRIO_SHIFT) & SWAP_FLAG_PRIO_MASK If the SWAP_FLAG_DISCARD flag is specified in the swapon() swapflags argument, freed swap pages will be discarded before they are reused, if the swap device supports the discard or trim operation. (This may improve performance on some Solid State Devices, but often it does not.) See also NOTES. These functions may be used only by a privileged process (one having the CAP_SYS_ADMIN capability). Priority Each swap area has a priority, either high or low. The default priority is low. Within the low-priority areas, newer areas are even lower priority than older areas. All priorities set with swapflags are high-priority, higher than default. They may have any nonnegative value chosen by the caller. Higher numbers mean higher priority. Swap pages are allocated from areas in priority order, highest priority first. For areas with different priorities, a higher-priority area is exhausted before using a lower-priority area. If two or more areas have the same priority, and it is the highest priority available, pages are allocated on a round-robin basis between them. As of Linux 1.3.6, the kernel usually follows these rules, but there are exceptions.
RETURN VALUE
On success, zero is returned. On error, -1 is returned, and errno is set appropriately.
ERRORS
EBUSY (for swapon()) The specified path is already being used as a swap area. EINVAL The file path exists, but refers neither to a regular file nor to a block device; EINVAL (swapon()) The indicated path does not contain a valid swap signature or resides on an in-memory filesystem such as tmpfs(5). EINVAL (since Linux 3.4) (swapon()) An invalid flag value was specified in flags. EINVAL (swapoff()) path is not currently a swap area. ENFILE The system-wide limit on the total number of open files has been reached. ENOENT The file path does not exist. ENOMEM The system has insufficient memory to start swapping. EPERM The caller does not have the CAP_SYS_ADMIN capability. Alternatively, the maximum number of swap files are already in use; see NOTES below.
CONFORMING TO
These functions are Linux-specific and should not be used in programs intended to be portable. The second swapflags argument was introduced in Linux 1.3.2.
NOTES
The partition or path must be prepared with mkswap(8). There is an upper limit on the number of swap files that may be used, defined by the kernel constant MAX_SWAPFILES. Before kernel 2.4.10, MAX_SWAPFILES has the value 8; since kernel 2.4.10, it has the value 32. Since kernel 2.6.18, the limit is decreased by 2 (thus: 30) if the kernel is built with the CONFIG_MIGRATION option (which reserves two swap table entries for the page migration features of mbind(2) and migrate_pages(2)). Since kernel 2.6.32, the limit is further decreased by 1 if the kernel is built with the CONFIG_MEMORY_FAILURE option. Discard of swap pages was introduced in kernel 2.6.29, then made conditional on the SWAP_FLAG_DISCARD flag in kernel 2.6.36, which still discards the entire swap area when swapon() is called, even if that flag bit is not set.
SEE ALSO
mkswap(8), swapoff(8), swapon(8)
COLOPHON
This page is part of release 4.09 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.
More Linux Commands
manpages/keytool-java-1.8.0-openjdk.1.html
keytool-java-1.8.0-openjdk(1) Manages a keystore (database)
The keytool command is a key and certificate management utility. It enables users to administer their own public/private key pairs and associated certificates f
manpages/NetworkManager.8.html
NetworkManager(8) - network management daemon (Man Page)....
The NetworkManager daemon attempts to make networking configuration and operation as painless and automatic as possible by managing the primary network connecti
manpages/partprobe.8.html
partprobe(8) - inform the OS of partition table changes.....
This manual page documents briefly the partprobe command. partprobe is a program that informs the operating system kernel of partition table changes, by request
manpages/Tcl_GetHashValue.3.html
Tcl_GetHashValue(3) - procedures to manage hash tables......
A hash table consists of zero or more entries, each consisting of a key and a value. Given the key for an entry, the hashing routines can very quickly locate th
manpages/chroot.1.html
chroot(1) - run command or interactive shell with special ro
Run COMMAND with root directory set to NEWROOT. --groups=G_LIST specify supplementary groups as g1,g2,..,gN --userspec=USER:GROUP specify user and group (ID or
manpages/iswalpha.3.html
iswalpha(3) - test for alphabetic wide character (Man Page)
The iswalpha() function is the wide-character equivalent of the isalpha(3) function. It tests whether wc is a wide character belonging to the wide-character cla
manpages/qiflush_sp.3ncurses.html
qiflush_sp(3ncurses) - curses screen-pointer extension......
This implementation can be configured to provide a set of functions which improve the ability to manage multiple screens. This feature can be added to any of th
manpages/XDrawRectangles.3.html
XDrawRectangles(3) - draw rectangles and rectangles structur
The XDrawRectangle and XDrawRectangles functions draw the outlines of the specified rectangle or rectangles as if a five-point PolyLine protocol request were sp
manpages/make_sha1.8.html
make_sha1(8) - Generate SHA1 checksums for given set of user
Generate SHA1 checksums for messages given set of users. Works as incremental update: reads in existing set of SHA1 checksums from sha1_dir/u/userid (hashed on
manpages/Xsecurity.7.html
Xsecurity(7) - X display access control - Linux manual page
X provides mechanism for implementing many access control systems. The sample implementation includes five mechanisms. Any client on a host in the host acces...
manpages/XML::DOM::Comment.3pm.html
XML::DOM::Comment(3pm) - An XML comment in XML::DOM.........
XML::DOM::Comment extends XML::DOM::CharacterData which extends XML::DOM::Node. This node represents the content of a comment, i.e., all the characters between
manpages/futimesat.2.html
futimesat(2) - change timestamps of a file relative to a dir
This system call is obsolete. Use utimensat(2) instead. The futimesat() system call operates in exactly the same way as utimes(2), except for the differences de
