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swapon, swapoff - control devices for interleaved paging/swapping
Standard C Library (libc, -lc)
swapon(const char *special);
swapoff(const char *special);
The swapon() system call makes the block device special available to the
system for allocation for paging and swapping. The names of potentially
available devices are known to the system and defined at system
configuration time. The size of the swap area on special is calculated
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.
If an error has occurred, a value of -1 is returned and errno is set to
indicate the error.
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
[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
[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.
config(8), swapon(8), sysctl(8)
The swapon() system call appeared in 4.0BSD. The swapoff() system call
appeared in FreeBSD 5.0.