This document is a WORK IN PROGRESS.
This is just a quick personal cheat sheet: treat its contents with caution!

sysctl¶

sysctl is a tool for examining and changing kernel parameters at runtime (package procps-ng). sysctl is implemented in procfs, the virtual process file system at /proc/.

Reference(s)

Config¶

Possible locations for sysctl configuration files are:

/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

Use¶

List all current kernel parameters:
```
$ sysctl -a
```
> See https://www.kernel.org/doc/html/latest/admin-guide/sysctl/index.html for the > documentation about all parameters.
List all current kernel parameters of a specific parameters group (e.g. net.ipv6):
```
$ sysctl -a --pattern '^net.ipv6'
```
> See https://www.kernel.org/doc/html/latest/admin-guide/sysctl/net.html for the > documentation about the whole net group.

Print a single/specific parameter (e.g. fs.file-max):

$ sysctl fs.file-max
    > fs.file-max = 3270749

Apply changes from sysctl config file:
```
$ sudo sysctl -p
```
Modify a specific kernel parameter (e.g. vm.swappiness):
```
$ sysctl -w vm.swappiness=10
```
The change takes effect immediately, but it is not persistent. After a system reboot, the default value is loaded.

To set a parameter permanently, you will need to write the settings to the configuration file.

Another way to change parameters is to write the settings to the files in the /proc/sys directory, e.g.:
```
$ echo 1 > /proc/sys/net/ipv4/ip_forward
```

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