====== Proc - System file ======

Certain aspects of kernel behavior can be modified at runtime, without the need to recompile the kernel, or even to reboot the system.  The files in the **/proc/sys** tree can not only be read, but also modified.  You can use the **echo** command to write value into these files, thereby changing the default settings of the kernel.

<WRAP warning>
**WARNNG:**  Be very careful when attempting any writes.  You can optimize your system, but you can also cause it to crash.  Never  alter kernel parameters on a production system.  Set up a development machine and test to make sure that everything works the way you want it to.  You may have no alternative but to reboot the machine once an error has been made.
</WRAP>

<WRAP info>
**NOTE:**  The general rule is that the contents, or even the existence of the **/proc/sys** directory, depends on your kernel configuration.  The /proc/sys directory may not exist.
</WRAP>


To change a value, simply echo the new value into the file.  An example is given below in the section on the file system data.  You need to be root to do this.  You can create your own boot script to perform this every time your system boots.

The files in /proc/sys can be used to fine tune and monitor miscellaneous and general things in the operation of the Linux kernel.  Since some of the files can inadvertently disrupt your system, it is advisable to read both documentation and source before actually making adjustments.  In any case, be very careful when writing to any of these files.  The entries in /proc may change slightly between different versions of the Kernel, so if there is any doubt review the kernel documentation in the directory /usr/src/linux/Documentation.

Please see: Documentation/sysctls/ directory for descriptions of these entries.