---
name: "sysctl"
section: "8"
platform: "openbsd"
package: "man"
version: "8.0-current-20261101"
release: "OpenBSD 8.0-current (2026-11-01)"
platforms: ["linux", "freebsd", "openbsd", "macos"]
url: "https://new.carta.tech/sysctl"
---

# sysctl(8)

get or set kernel state

## NAME

**sysctl** – get or set kernel state

## SYNOPSIS

**sysctl** \[**-Aanq**\] \[**-f** *file*\] \[*name*\[=*value*\] *...*\]

## DESCRIPTION

The **sysctl** utility retrieves kernel state and allows processes with appropriate privilege to set kernel state. The state to be retrieved or set is described using a “Management Information Base” (MIB) style name, using a dotted set of components.

When retrieving a variable, a subset of the MIB name may be specified to retrieve a list of variables in that subset. For example, to list all the machdep variables:

```
$ sysctl machdep
```

The options are as follows:

- **-A**

  List all the known MIB names including tables. Those with string or integer values will be printed as with the **-a** flag; for the table values, the name of the utility to retrieve them is given.

- **-a**

  List all the currently available string or integer values. This is the default, if no parameters are given to **sysctl**.

- **-f** *file*

  Process *name*\[=*value*\] arguments from *file* in [sysctl.conf(5)](/sysctl.conf/5.md) format.

- **-n**

  Suppress printing of the field name, only output the field value. Useful for setting shell variables. For example, to set the psize shell variable to the pagesize of the hardware:

  ```
  # set psize=`sysctl -n hw.pagesize`
  ```

- **-q**

  Suppress all output when setting a variable. This option overrides the behaviour of **-n**.

- *name*\[=*value*\]

  Retrieve the specified variable *name*, or attempt to set it to *value*. Multiple *name*\[=*value*\] arguments may be given. If given, **-f** *file* is processed first.

The information available from **sysctl** consists of integers, strings, and tables. For a detailed description of the variables, see [sysctl(2)](/sysctl/2.md). Tables can only be retrieved by special purpose programs such as [ps(1)](/ps/1.md), [systat(1)](/systat/1.md), and [netstat(1)](/netstat/1.md).

**sysctl** can extract information about the filesystems that have been compiled into the running system. This information can be obtained by using the command:

```
$ sysctl vfs.mounts
```

By default, only filesystems that are actively being used are listed. Use of the **-A** flag lists all the filesystems compiled into the running kernel.

## FILES

- */etc/sysctl.conf*

  sysctl variables to set at system startup

## EXAMPLES

To retrieve the maximum number of processes allowed in the system:

```
$ sysctl kern.maxproc
```

To set the maximum number of processes allowed in the system to 1000:

```
# sysctl kern.maxproc=1000
```

To retrieve information about the system clock rate:

```
$ sysctl kern.clockrate
```

To retrieve information about the load average history:

```
$ sysctl vm.loadavg
```

To set the list of reserved TCP ports that should not be allocated by the kernel dynamically:

```
# sysctl net.inet.tcp.baddynamic=749,750,751,760,761,871
```

```
# sysctl net.inet.udp.baddynamic=749,750,751,760,761,871,1024-2048
```

This can be used to keep daemons from stealing a specific port that another program needs to function. List elements may be separated by commas and/or whitespace; a hyphen may be used to specify a range of ports.

It is also possible to add or remove ports from the current list:

```
# sysctl net.inet.tcp.baddynamic=+748,+6000-6999
# sysctl net.inet.tcp.baddynamic=-871
```

To set the amount of shared memory available in the system and the maximum number of shared memory segments:

```
# sysctl kern.shminfo.shmmax=33554432
# sysctl kern.shminfo.shmseg=32
```

To place core dumps from [issetugid(2)](/issetugid/2.md) programs (in this example [bgpd(8)](/bgpd/8.md)) into a safe place for debugging purposes:

```
# mkdir -m 700 /var/crash/bgpd
# sysctl kern.nosuidcoredump=3
```

## SEE ALSO

[sysctl(2)](/sysctl/2.md), [options(4)](/options/4.md), [sysctl.conf(5)](/sysctl.conf/5.md)

## HISTORY

**sysctl** first appeared in 4.4BSD.