3.3.11. /proc/tty/

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               /dev/cua        5  64-127 serial:callout 
serial               /dev/ttyS       4  64-127 serial 
pty_slave            /dev/pts      136   0-255 pty:slave 
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 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.

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