SWAPCTL(8) | System Manager's Manual | SWAPCTL(8)

# NAME

`swapctl`, `swapon` — system swap management tool

# SYNOPSIS

`swapctl` | `-A` [`-p` priority] [`-t` `blk` | `noblk`]

`swapctl` | `-a` [`-p` priority] path

`swapctl` | `-c` `-p` priority path

`swapctl` | `-d` path

`swapctl` | [[`-l`] | `-s`] [`-k`]

`swapon` | `-a` | path

# DESCRIPTION

The `swapctl` program adds, removes, lists and prioritizes swap devices and files for the system. The `swapon` program acts the same as `swapctl -a`, except if `swapon` itself is called with `-a`, in which case it acts as `swapctl -A`.

The options are as follows:

`-A`
  This option causes `swapctl` to read the /etc/fstab file for devices and files with an “sw” type, and adds all these entries as swap devices. If no swap devices are configured, `swapctl` will exit with an error code.
`-a`
  The `-a` option requires that a path also be in the argument list. The path is added to the kernel's list of swap devices using the swapctl(2) system call. When using the `swapon` form of this command, the `-a` option is treated the same as the `-A` option, for backwards compatibility.
`-c`
  The `-c` option changes the priority of the listed swap device or file.
`-d` path
  The `-d` option removes the listed path from the kernel's list of swap devices or files.
`-k`
  The `-k` option uses 1024 byte blocks instead of the default 512 byte.
`-l`
  The `-l` option lists the current swap devices and files, and their usage statistics.
`-p` priority
  The `-p` option sets the priority of swap devices or files to the priority argument.
`-s`
  The `-s` option displays a single line summary of current swap statistics.
`-t` `blk` | `noblk`
  This flag modifies the function of the `-A` option. The `-t` option allows the type of device to add to be specified. An argument of `blk` causes all block devices in /etc/fstab to be added. An argument of `noblk` causes all non-block devices in /etc/fstab to be added. This option is useful in early system startup, where swapping may be needed before all file systems are available, such as during disk checks of large file systems.

# SWAP OPTIONS

Lines such as the following specify swap devices in /etc/fstab:

    /dev/sd1b none swap sw
    d48d0e3fc1c39531.k none swap sw

The initial swap device (root disk, partition b) need not appear in /etc/fstab, though it is not an error for it to do so.

Additional flags include:

priority=N
  Swap devices and files may be assigned different priorities, to allow faster resources to be used first. Swap devices at the same priority are used in a round-robin fashion until there is no more space available at this priority, when the next priority level will be used. The default priority is 0, the highest. This value can be any valid integer, with higher values receiving less priority.
nfsmntpt=/path
  This option is useful for swapping to NFS files. It specifies an existing directory /path to be used as the local mount point for an NFS file system. Typically, once this mount has succeeded, the file to be used for swapping on will be available under this mount point. For example:

      server:/export/swap/client none swap sw,nfsmntpt=/swap

# EXIT STATUS

The `swapctl` utility exits 0 on success, and >0 if an error occurs.

# SEE ALSO

swapctl(2), vnd(4), fstab(5), mount_nfs(8), mount_vnd(8)

# HISTORY

The `swapctl` program was originally developed in NetBSD 1.3. It was ported to OpenBSD 2.6 by Tobias Weingartner. The original `swapon` program, provided for backwards compatibility, appeared in 4.0BSD.

# AUTHORS

The `swapctl` program was written by Matthew R. Green <mrg@eterna.com.au>.

# BUGS

Local and remote swap files cannot be configured until the file systems they reside on are mounted read/write. The system startup scripts need to fsck(8) all local file systems before this can happen. This process requires substantial amounts of memory on some systems. If one configures no local block swap devices on a machine that has local file systems to check and rely only on swap files, the machine will have no swap space at all during system fsck(8) and may run out of real memory, causing fsck to abnormally exit and startup scripts to fail.

August 8, 2025 | Debian