SWAPON(2)                 FreeBSD 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, u_int flags);

DESCRIPTION
     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.

     The special argument points to the name of the device or file used for
     swapping.  flags argument takes the following flags:

     SWAPOFF_FORCE  Overrides a very conservative check that prevents swapoff
                    if the total amount of free memory and remaining swap
                    devices space might be unsufficient for the system to
                    continue operating.

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:

     [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.

     [EINTEGRITY]       Corrupted data was detected while reading from the
                        file system to open 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.

FreeBSD 13.1-RELEASE-p6        December 8, 2021        FreeBSD 13.1-RELEASE-p6