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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
- .It vm/vm_param.h
- .It vm/swap_pager.h
- .In 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.
- .Pp
- 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.
- .Pp
- The
- .Fa special
- argument points to the name of the device or file used for swapping.
- .The
- .Va flags
- argument takes the following flags:
- .Bl -tag -width SWAPOFF_FORCE
- .It 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:
- .Bl -tag -width Er
- .It Bq Er ENOTDIR
- A component of the path prefix is not a directory.
- .It Bq Er ENAMETOOLONG
- A component of a pathname exceeded 255 characters,
- or an entire path name exceeded 1023 characters.
- .It Bq Er ENOENT
- The named device does not exist.
- .It Bq Er EACCES
- Search permission is denied for a component of the path prefix.
- .It Bq Er ELOOP
- Too many symbolic links were encountered in translating the pathname.
- .It Bq Er EPERM
- The caller is not the super-user.
- .It Bq Er EFAULT
- The
- .Fa special
- argument
- points outside the process's allocated address space.
- .El
- .Pp
- Additionally,
- .Fn swapon
- can fail for the following reasons:
- .Bl -tag -width Er
- .It Bq Er ENOTBLK
- The
- .Fa special
- argument
- is not a block device.
- .It Bq Er EBUSY
- The device specified by
- .Fa special
- has already
- been made available for swapping
- .It Bq Er ENXIO
- The major device number of
- .Fa special
- is out of range (this indicates no device driver exists
- for the associated hardware).
- .It Bq Er EIO
- An I/O error occurred while opening the swap device.
- .It Bq Er EINTEGRITY
- Corrupted data was detected while reading from the file system to open the
- swap device.
- .El
- .Pp
- Lastly,
- .Fn swapoff
- can fail if:
- .Bl -tag -width Er
- .It Bq Er EINVAL
- The system is not currently swapping to
- .Fa special .
- .It 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
- .Bx 4.0 .
- The
- .Fn swapoff
- system call appeared in
- .Fx 5.1 .
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