---
name: "swapctl"
section: "8"
platform: "freebsd"
package: "base"
version: "16.0-CURRENT-20261027-61c70dc16a79"
release: "FreeBSD 16.0-CURRENT (2026-10-27)"
platforms: ["freebsd", "openbsd"]
url: "https://new.carta.tech/swapctl"
---

# swapctl(8)

specify devices for paging and swapping

## NAME

**swapon**, **swapoff**, **swapctl** – specify devices for paging and swapping

## SYNOPSIS

**swapon** \[**-F** *fstab*\] **-aLq** \| **-E** *file ...*

**swapoff** \[**-F** *fstab*\] **-afLq** \| *file ...*

**swapctl** \[**-AfghklmsU**\]\[ **-a** *file ...* \| **-d** *file ...*\]

## DESCRIPTION

The **swapon**, **swapoff** and **swapctl** utilities are used to control swap devices in the system. At boot time all swap entries in */etc/fstab* are added automatically when the system goes multi-user. Swap devices use a fixed interleave; the maximum number of devices is unlimited. There is no priority mechanism.

The **swapon** utility adds the specified swap devices to the system. If the **-a** option is used, all swap devices in */etc/fstab* will be added, unless their “noauto” or “late” option is also set. If the **-L** option is specified, swap devices with the “late” option will be added as well as ones with no option. If the **-q** option is used, informational messages will not be written to standard output when a swap device is added. The **-E** option causes each of following devices to receive a BIO\_DELETE command. This command marks the device's blocks as unused, except those that might store a disk label. This marking can erase a crash dump. To delay **swapon** for a device until after **savecore** has copied the crash dump to another location, use the “late” option.

The **swapoff** utility removes the specified swap devices from the system. If the **-a** option is used, all swap devices in */etc/fstab* will be removed, unless their “noauto” option is also set. If the **-L** option is specified, only swap devices with the “late” option will be removed. If the **-q** option is used, informational messages will not be written to standard output when a swap device is removed. Note that **swapoff** will fail and refuse to remove a swap device if a very conservative check does not conclude that there is sufficient VM (memory + remaining swap devices) to run the system. The **-f** option turns off this check, which could deadlock the system if there is insufficient swap space remaining.

The **swapoff** utility must move swapped pages out of the device being removed which could lead to high system loads for a period of time, depending on how much data has been swapped out to that device.

Other options supported by both **swapon** and **swapoff** are as follows:

- **-F** *fstab*

  Specify the *fstab* file to use (in conjunction with **-a**).

The **swapctl** utility exists primarily for those familiar with other BSDs and may be used to add, remove, or list swap devices. Note that the **-a** option is used differently in **swapctl** and indicates that a specific list of devices should be added. The **-d** option indicates that a specific list should be removed. The **-A** and **-U** options to **swapctl** operate on all swap entries in */etc/fstab* which do not have their “noauto” option set.

Swap information can be generated using the [swapinfo(8)](/swapinfo/8.md) utility, **pstat** **-s**, or **swapctl** **-l**. The **swapctl** utility has the following options for listing swap:

- **-h**

  Output values in human-readable form.

- **-g**

  Output values in gigabytes.

- **-k**

  Output values in kilobytes.

- **-m**

  Output values in megabytes.

- **-l**

  List the devices making up system swap.

- **-s**

  Print a summary line for system swap.

  The BLOCKSIZE environment variable is used if not specifically overridden. 512 byte blocks are used by default.

## FILES

- */dev/{ada,da}?s?b*

  standard paging devices

- */dev/md?*

  memory disk devices

- */etc/fstab*

  ASCII file system description table

## DIAGNOSTICS

These utilities may fail for the reasons described in [swapon(2)](/swapon/2.md).

## SEE ALSO

[swapon(2)](/swapon/2.md), [fstab(5)](/fstab/5.md), [init(8)](/init/8.md), [mdconfig(8)](/mdconfig/8.md), [pstat(8)](/pstat/8.md), [rc(8)](/rc/8.md)

## HISTORY

The **swapon** utility appeared in 4.0BSD. The **swapoff** and **swapctl** utilities appeared in FreeBSD 5.1.