The procfs Interface

Another way to modify kernel parameters is to use the file system interface through procfs. The /proc file system (procfs) is a special file system. It is a virtual file system; it is not associated with a block device, but exists only in memory. The /proc/ directory shows a hierarchical view of the parameters. You can view the parameters by looking at the file's contents. The parameters can be modified by echoing the value in the file. However, changes made this way do not persist across machine reboots.

/proc is organized into the following directories:

/proc/bus	Bus-specific information
/proc/driver	Driver-specific information
/proc/fs	File system parameters
/proc/irq	Masks for IRQ-to-CPU affinity
/proc/net	Networking information
/proc/scsi	SCSI-related information
/proc/sys	Kernel parameters
/proc/sys/fs	Generic file system data
/proc/sys/kernel	General kernel parameters
/proc/sys/vm	Memory management parameters
/proc/sys/dev	Device-specific information
/proc/sys/sunrpc	RPC information
/proc/sys/net	Networking information
/proc/sysvipc	System V IPC information
/proc/tty	TTY driver information
/proc/pid	Per-process information

Using procfs

The parameters can be viewed or changed by writing to the appropriate file in the /proc/ directory.

For example, to view the current value of shmmax, enter the following:

 $ cat  /proc/sys/kernel/shmmax 

Similarly, you can change the value of shmmax by entering this command:

 $ echo "32" > /proc/sys/kernel/shmmax 

Note that this change is temporary and does not persist across reboots.