Sysctl

sysctl is a *nix concept, which tweaks parameters of in-kernel systems.

Linux also exposes sysctl as a virtual file system at /proc/sys, so e.g. reading out

sysctl net.ipv4.ip_forward
sysctl -w net.ipv4.ip_forward=1

can also be done like

cat /proc/sys/net/ipv4/ip_forward
echo 1>/proc/sys/net/ipv4/ip_forward

There is also an on-filesystem set of files that present what should be set at boot

Best known is probably

/etc/sysctl.conf

To see what kind of parameters, see current values using:

sysctl -a