6 Managing Kernel Parameters at Runtime

Some virtual files under /proc, and especially under /proc/sys, are writable. You can adjust settings in the running kernel through these files. For example, to change the hostname, you can revise the /proc/sys/kernel/hostname file as follows: 

echo www.mydomain.com | sudo tee /proc/sys/kernel/hostname

Other files take binary or Boolean values, such as the setting of IP forwarding, which is defined in /proc/sys/net/ipv4/ip_forward: 

cat /proc/sys/net/ipv4/ip_forward
0
echo 1 | sudo tee /proc/sys/net/ipv4/ip_forward
cat /proc/sys/net/ipv4/ip_forward
1

Use the sysctl command to view or change values under the /proc/sys directory.

Note:

Even root can't bypass the file access permissions of virtual file entries under /proc. If you change the value of a read-only entry such as /proc/partitions, no kernel code exists to service the write() system call.

For more information, see the sysctl(8) and sysctl.d(5) manual pages.