sysctl

View and modify kernel parameters

TLDR

Show all available variables and their values

$ sysctl -a

Set a changeable kernel state variable

$ sysctl -w [section.tunable]=[value]

Get currently open file handlers

$ sysctl fs.file-nr

Get limit for simultaneous open files

$ sysctl fs.file-max

Apply changes from /etc/sysctl.conf

$ sysctl -p

SYNOPSIS

sysctl [options] [variable[=value]] ...

sysctl is used to examine and modify kernel parameters at runtime. Parameters available are listed under /proc/sys/ and can be read or written using this tool.Common categories include kernel. (core kernel settings), net. (networking), vm. (virtual memory), and fs. (filesystem). Changes made with sysctl are temporary unless persisted to configuration files.

PARAMETERS

-a, --all

Display all available variables

-w, --write

Write value to variable

-p, --load [_file_]

Load settings from file (default: /etc/sysctl.conf)

-n, --values

Print only values, not variable names

-e, --ignore

Ignore unknown variables

-q, --quiet

Suppress error messages

--system

Load settings from all system configuration files

CONFIGURATION

/etc/sysctl.conf

Main configuration file for persistent kernel parameter settings, loaded at boot.

**/etc/sysctl.d/*.conf**

Drop-in directory for modular kernel parameter configuration files.

INSTALL

sudo apt install procps

sudo dnf install procps-ng

sudo pacman -S procps-ng

sudo apk add procps-ng

sudo zypper install procps

brew install procps

nix profile install nixpkgs#procps

CAVEATS

Changes are lost on reboot unless saved to /etc/sysctl.conf or files in /etc/sysctl.d/. Some parameters are read-only. Incorrect values can destabilize the system. Requires root privileges to modify values.

HISTORY

sysctl is part of procps (now procps-ng). It provides a convenient interface to the /proc/sys virtual filesystem for reading and writing kernel parameters at runtime.