Proc/Sysvipc; Proc/Tty; Using The Sysctl Command - Red Hat ENTERPRISE LINUX 5 - DEPLOYMENT Deployment Manual

3.3.10. /proc/sysvipc/

This directory contains information about System V IPC resources. The files in this directory relate to
System V IPC calls for messages (msg), semaphores (sem), and shared memory (shm).

3.3.11. /proc/tty/

This directory contains information about the available and currently used tty devices on the system.
Originally called teletype devices, any character-based data terminals are called tty devices.
In Linux, there are three different kinds of tty devices. Serial devices are used with serial connections,
such as over a modem or using a serial cable. Virtual terminals create the common console
connection, such as the virtual consoles available when pressing Alt+<F-key> at the system
console. Pseudo terminals create a two-way communication that is used by some higher level
applications, such as XFree86. The drivers file is a list of the current tty devices in use, as in the
following example:
serial
serial
pty_slave
pty_master
pty_slave
pty_master
/dev/vc/0
/dev/ptmx
/dev/console
/dev/tty
unknown
The /proc/tty/driver/serial file lists the usage statistics and status of each of the serial tty
lines.
In order for tty devices to be used as network devices, the Linux kernel enforces 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 a 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, and more detailed information is available
within the ldisc/ directory.

3.4. Using the sysctl Command

The /sbin/sysctl command is used to view, set, and automate kernel settings in the /proc/sys/
directory.
For a quick overview of all settings configurable in the /proc/sys/ directory, type the /sbin/
sysctl -a command as root. This creates a large, comprehensive list, a small portion of which looks
something like the following:
net.ipv4.route.min_delay = 2 kernel.sysrq = 0 kernel.sem = 250
This is the same information seen if each of the files were viewed individually. The only difference
is the file location. For example, the /proc/sys/net/ipv4/route/min_delay file is listed as
/dev/cua 5 64-127 serial:callout
/dev/ttyS 4 64-127 serial
/dev/pts 136 0-255 pty:slave
/dev/ptm 128 0-255 pty:master
/dev/ttyp 3 0-255 pty:slave
/dev/pty 2 0-255 pty:master
/dev/vc/0 4
/dev/ptmx 5
/dev/console 5
/dev/tty 5
/dev/vc/%d 4
0 system:vtmaster
2 system
1 system:console
0 system:/dev/tty
1-63 console
/proc/sysvipc/
32000 32 128
51