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.Dd December 8, 2021 .Dt SWAPON 2 .Os .Sh NAME .Nm swapon , swapoff .Nd control devices for interleaved paging/swapping .Sh LIBRARY .Lb libc .Sh SYNOPSIS t vm/vm_param.h t vm/swap_pager.h n unistd.h .Ft int .Fn swapon "const char *special" .Ft int .Fn swapoff "const char *special" "u_int flags" .Sh DESCRIPTION The .Fn swapon system call makes the block device .Fa 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 .Fa special is calculated at the time the device is first made available for swapping.
p The .Fn 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.
p The .Fa special argument points to the name of the device or file used for swapping. .The .Va flags argument takes the following flags: l -tag -width SWAPOFF_FORCE t Dv 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. .El .Sh RETURN VALUES If an error has occurred, a value of -1 is returned and .Va errno is set to indicate the error. .Sh ERRORS Both .Fn swapon and .Fn swapoff can fail if: l -tag -width Er t Bq Er ENOTDIR A component of the path prefix is not a directory. t Bq Er ENAMETOOLONG A component of a pathname exceeded 255 characters, or an entire path name exceeded 1023 characters. t Bq Er ENOENT The named device does not exist. t Bq Er EACCES Search permission is denied for a component of the path prefix. t Bq Er ELOOP Too many symbolic links were encountered in translating the pathname. t Bq Er EPERM The caller is not the super-user. t Bq Er EFAULT The .Fa special argument points outside the process's allocated address space. .El
p Additionally, .Fn swapon can fail for the following reasons: l -tag -width Er t Bq Er ENOTBLK The .Fa special argument is not a block device. t Bq Er EBUSY The device specified by .Fa special has already been made available for swapping t Bq Er ENXIO The major device number of .Fa special is out of range (this indicates no device driver exists for the associated hardware). t Bq Er EIO An I/O error occurred while opening the swap device. t Bq Er EINTEGRITY Corrupted data was detected while reading from the file system to open the swap device. .El
p Lastly, .Fn swapoff can fail if: l -tag -width Er t Bq Er EINVAL The system is not currently swapping to .Fa special . t Bq Er ENOMEM Not enough virtual memory is available to safely disable paging and swapping to the given device. .El .Sh SEE ALSO .Xr config 8 , .Xr swapon 8 , .Xr sysctl 8 .Sh HISTORY The .Fn swapon system call appeared in x 4.0 . The .Fn swapoff system call appeared in .Fx 5.1 .