Red Hat LINUX 7.2 - OFFICIAL LINUX CUSTOMIZATION GUIDE Guida di Installazione Scaricare il pdf (Pagina 52)

52 Chapter 2. The /proc File System

Registered line disciplines are stored in the ldiscs ﬁle, with detailed information available in the

ldisc directory.

2.4. Using sysctl

The sysctl command is used to view, set, and automated kernel settings in the /proc/sys/ direc-

tory.

To get a quick overview of all settings conﬁgurable in the /proc/sys/ directory, type the sysctl

-a command as root. This will create a large, comprehensive list, a small portion of which looks

something like this:

net.ipv4.route.min_delay = 2

kernel.sysrq = 0

kernel.sem = 250 32000 32 128

This is the same basic information you would see if you viewed each of the ﬁles individually. The

only difference is the ﬁle location. The /proc/sys/net/ipv4/route/min_delay ﬁle is signiﬁed

by net.ipv4.route.min_delay, with the directory slashes replaced by dots and the proc.sys

portion assumed.

The sysctl command can be use in place of echo to assign values to writable ﬁles in the

/proc/sys/ directory. For instance instead of using this command:

echo 1 > /proc/sys/kernel/sysrq

You can use this sysctl command:

sysctl -w kernel.sysrq="1"

kernel.sysrq = 1

While quickly setting single values like this in /proc/sys/ is helpful during testing, it does not work

as well on a production system, as all /proc/sys/ special settings are lost when the machine is

rebooted. To preserve the settings that you like to make permanently to your kernel, add them to the

/etc/sysctl.conf ﬁle.

Every time the system boots, the /etc/rc.d/rc.sysinit script is executed by init. This script

contains a command to execute sysctl using /etc/sysctl.conf as the values to set. Therefore,

any values added to /etc/sysctl.conf will take effect after the system boots.

2.5. Additional Resources

Below are additional sources of information about /proc.

2.5.1. Installed Documentation

Most of the best /proc documentation is available on your system.

• /usr/src/linux-2.4/Documentation/filesystems/proc.txt — Contains assorted, but

limited, information about all aspects of the /proc directory.

• /usr/src/linux-2.4/Documentation/sysrq.txt — An overview of System Request Key

options.

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Red Hat LINUX 7.2 - OFFICIAL LINUX CUSTOMIZATION GUIDE Guida di Installazione Pagina 52