swapon(2) [osf1 man page]
swapon(2) System Calls Manual swapon(2) NAME
swapon - Adds a swap device for interleaved paging and swapping SYNOPSIS
swapon( char *path, int flags, int lowat, int hiwat ); PARAMETERS
Specifies the block special device to be made available. Specifies a flag. Only the MS_PREFER flag is currently supported, and it causes the specified path to be the preferred paging device. (Ignored on Tru64 UNIX.) Specifies the low water mark. (Ignored on Tru64 UNIX.) Specifies the high water mark. (Ignored on Tru64 UNIX.) DESCRIPTION
The swapon() function makes a block special device available to the system for allocation of paging and swapping space. (The operating system does not currently support paging and swapping to a normal file. All swapping and pages areas must be block special devices.) The calling process must have superuser privilege to call the swapon() function. RETURN VALUES
Upon successful completion, the swapon() function returns a value of 0 (zero). If an error has occurred, -1 is returned and errno is set to indicate the error. ERRORS
If the swapon() function fails, errno may be set to one of the following values: A component of the path prefix is not a directory. The pathname contains a character with the high-order bit set, the device was not specified, the device configured by the path parameter was not configured into the system as a swap device, or the device does not allow paging. A component of a pathname exceeded NAME_MAX charac- ters, or an entire pathname exceeded PATH_MAX characters. The named device does not exist. Search permission is denied for a component of the path prefix. Too many symbolic links were encountered in translating the pathname. The caller does not have appropriate privilege. The device specified by the path parameter has already been made available for swapping. The major device number of the path parameter is out of range (this indicates no device driver exists for the associated hardware). An I/O error occurred while opening the swap device. The path parameter points outside the process' allocated address space. An attempt was made to activate a paging file on a read-only file system. RELATED INFORMATION
Commands: swapon(8), config(8) delim off swapon(2)
Check Out this Related Man Page
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)