---
name: "sysctl"
section: "8"
platform: "linux"
package: "procps-ng"
version: "4.0.7-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux", "freebsd", "openbsd", "macos"]
url: "https://new.carta.tech/sysctl"
---

# sysctl(8)

configure kernel parameters at runtime

## NAME

sysctl - configure kernel parameters at runtime

## SYNOPSIS

**sysctl** \[*option* ...\] *variable*\[ **=***value* \] ...

**sysctl -p** *file-or-regexp* ...

## DESCRIPTION

**sysctl** is used to modify kernel parameters at runtime.  The parameters available are those listed under */proc/sys/*.  Procfs is required for **sysctl** support in Linux.  You can use **sysctl** to both read and write sysctl data.

## PARAMETERS

- *variable*

  The name of a key to read from.  An example is kernel.ostype.  The '/' separator is also accepted in place of a '.'.

- *variable*=*value*

  To set a key, use the form *variable*=*value* where *variable* is the key and *value* is the value to set it to.  If the value contains quotes or characters which are parsed by the shell, you may need to enclose the value in double quotes.

- **-n**, **--values**

  Use this option to disable printing of the key name when printing values.

- **-e**, **--ignore**

  Use this option to ignore errors about unknown keys.

- **-N**, **--names**

  Use this option to only print the names.  It may be useful with shells that have programmable completion.

- **-q**, **--quiet**

  Use this option to not display the values set to stdout.

- **-w**, **--write**

  Force all arguments to be write arguments and print an error if they cannot be parsed this way.

- **-p**\[*FILE*\], **--load**\[=*FILE*\]

  Load in **sysctl** settings from the file specified or */etc/sysctl.conf* if none given.  Specifying - as filename means reading data from standard input. Using this option will mean arguments to **sysctl** are files, which are read in the order they are specified. The file argument may be specified as regular expression.

- **-a**, **--all**

  Display all values currently available except deprecated and verboten parameters.

- **--deprecated**

  Include deprecated parameters to **--all** values listing.

- **-b**, **--binary**

  Print value without new line.

- **--system**

  Load settings from all system configuration files. See the **SYSTEM FILE PRECEDENCE** section below.

- **-r**, **--pattern** *pattern*

  Only apply settings that match *pattern*. The *pattern* uses extended regular expression syntax.

- **-A**

  Alias of **-a**

- **-d**

  Alias of **-h**

- **-f**

  Alias of **-p**

- **-X**

  Alias of **-a**

- **-o**

  Does nothing, exists for BSD compatibility.

- **-x**

  Does nothing, exists for BSD compatibility.

- **-h**, **--help**

  Display help text and exit.

- **-V**, **--version**

  Display version information and exit.

## FILES

| |
| --- |
| */proc/sys* |
| */etc/sysctl.d/\*.conf* |
| */run/sysctl.d/\*.conf* |
| */usr/local/lib/sysctl.d/\*.conf* |
| */usr/lib/sysctl.d/\*.conf* |
| */lib/sysctl.d/\*.conf* |
| */etc/sysctl.conf* |

## NOTES

### System file precedence

When using the **--system** option, **sysctl** will read files from directories in the following list in given order from top to bottom. Once a file of a given filename is loaded, any file of the same name in subsequent directories is ignored.

| |
| --- |
| */etc/sysctl.d/\*.conf* |
| */run/sysctl.d/\*.conf* |
| */usr/local/lib/sysctl.d/\*.conf* |
| */usr/lib/sysctl.d/\*.conf* |
| */lib/sysctl.d/\*.conf* |

All configuration files are sorted in lexicographic order, regardless of the directory they reside in. Configuration files can either be completely replaced (by having a new configuration file with the same name in a directory of higher priority) or partially replaced (by having a configuration file that is ordered later).

The file */etc/sysctl.conf* is read last which means it can replace/override any parameters previously set in files in the listed directories.

### Deprecated parameters

The **base\_reachable\_time** and **retrans\_time** are deprecated.  The **sysctl** command does not allow changing values of these parameters.  Users who insist to use deprecated kernel interfaces should push values to **/proc** file system by other means.  For example:

echo 256 \> /proc/sys/net/ipv6/neigh/eth0/base\_reachable\_time

### Verboten parameters

Certain kernel parameters should not be read due to side-effects and will be skipped by **sysctl** using the **--all** option.

- **stat\_refresh**

  This parameter returns no value but flushes per-cpu vm statistics.

## EXAMPLES

/sbin/sysctl -a\
 /sbin/sysctl -n kernel.hostname\
 /sbin/sysctl -w kernel.domainname="example.com"\
 /sbin/sysctl -p/etc/sysctl.conf\
 /sbin/sysctl -a --pattern forward\
 /sbin/sysctl -a --pattern forward$\
 /sbin/sysctl -a --pattern 'net.ipv4.conf.(eth\|wlan)0.arp'\
 /sbin/sysctl --pattern '^net.ipv6' --system

## SEE ALSO

[**proc**(5)](/proc/5.md), [**sysctl.conf**(5)](/sysctl.conf/5.md), [**regex**(7)](/regex/7.md)

## REPORTING BUGS

Please send bug reports to ⟨procps@freelists.org⟩.