52

Chapter 2. The

proc

File System

pty_master

/dev/ptm

128

0 255 pty:master

pty_slave

/dev/ttyp

3

0 255 pty:slave

pty_master

/dev/pty

2

0 255 pty:master

/dev/vc/0

/dev/vc/0

4

0 system:vtmaster

/dev/ptmx

/dev/ptmx

5

2 system

/dev/console

/dev/console

5

1 system:console

/dev/tty

/dev/tty

5

0 system:/dev/tty

unknown

/dev/vc/%d

4

1 63 console

The

/proc/tty/driver/serial

file lists the usage statistics and status of each of the serial tty

lines.

In order that tty devices can be used in a similar way as network devices, the Linux kernel will enforce

line discipline on the device. This allows the driver to place a specific type of header with every block

of data transmitted over the device, making it possible for the remote end of the connection to be

able to see that block of data as just one in a stream of data blocks. SLIP and PPP are common line

disciplines, and each are commonly used to connect systems to one other over a serial link.

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 automate kernel settings in the

/proc/sys/

directory.

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

init

program runs the

/etc/rc.d/rc.sysinit

script. This script

contains a command to execute

sysctl

using

/etc/sysctl.conf

to dictate the values passed to

the kernel. Any values added to

/etc/sysctl.conf

will take effect each time the system boots.