Sysctl is used to view and modify kernel parameters at run time. It is slightly more elegant than copying values directly to /proc.

The /etc/sysctl.conf file is the sysctl default file that often contains multiple parameter settings to be loaded at once. It is sometimes used by start up scripts so be careful making changes to it. To modify multiple parameters at once, it is safer to create a new file.

To view all kernel parameters:

sysctl -a

To set a new value for a kernel parameter:

sysctl -w variable.name=xxxx

For example:
sysctl -w net.ipv4.ip_forward=1

To load multiple parameters from a file:

sysctl -p filename