`sysctl` - configure kernel parameters at runtime

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

Options you will use

variable: read one: vm.swappiness is /proc/sys/vm/swappiness
-w variable=value: set it (root) - lost at reboot
-p [FILE]: apply the settings in FILE (default /etc/sysctl.conf) now
--system: apply every /usr/lib, /run and /etc sysctl.d/*.conf file, like at boot
-n: print only the value
-a: every variable

Examples

$ sysctl vm.swappiness

vm.swappiness = 60

$ sudo sysctl -w vm.swappiness=10

until reboot; make it permanent in /etc/sysctl.d/99-local.conf

Gotchas

sysctl is only a front end: cat /proc/sys/vm/swappiness and echo 10 | sudo tee /proc/sys/vm/swappiness do the same thing.

Taught in

Try sysctl in a real terminal Free, in your browser - a real Ubuntu terminal to try it in, with missions that check your work.