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GNU screen [man:window_types]

Window Types

Screen provides three different window types. New windows are created with screen's screen command (see also the entry in chapter customization). The first parameter to the screen command defines which type of window is created. The different window types are all special cases of the normal type. They have been added in order to allow screen to be used efficiently as a console multiplexer with 100 or more windows.

Normal Windows

The normal window contains a shell (default, if no parameter is given) or any other system command that could be executed from a shell (e.g. slogin, etc…).


screen – Creates a new window and starts the default shell in that window.

screen /bin/bash – Creates a new window and starts bash in that window.

screen pine – Creates a new window and starts pine in that window.

TTY Windows

If a tty (character special device) name (e.g. ”/dev/ttya”) is specified as the first parameter, then the window is directly connected to this device. This window type is similar to ”screen cu -l /dev/ttya”. Read and write access is required on the device node, an exclusive open is attempted on the node to mark the connection line as busy. An optional parameter is allowed consisting of a comma separated list of flags in the notation used by stty(1):

<baud_rate> Usually 300, 1200, 9600, or 19200. This affects transmission as well as receive speed.
cs8 or cs7 Specify the transmission of eight (or seven) bits per byte.
ixon or -ixon Enables (or disables) software flow-control (CTRL-S/CTRL-Q) for sending data.
ixoff or -ixoff Enables (or disables) software flow for receiving data.
istrip or -istrip Clear (or keep) the eight bit in each received byte.

You may want to specify as many of the options as possible. Unspecified options cause the terminal driver to make up the parameter values of the connection. These values are system dependent and may be in defaults or values saved from a previous connection.

For tty windows, the info command shows some of the modem control lines in the status line. These may include 'RTS', 'CTS', 'DTR', 'DSR', 'CD', and more. This depends on the available ioctl()s and system header files as well as on the physical capabilities of the serial board. Signals that are logical low (inactive) have their name preceded by an exclamation mark (!), otherwise the signal is logical high (active). Signals not supported by the hardware but available to the ioctl() interface are usually shown low. When the CLOCAL status bit is true, the whole set of modem signals is placed inside curly braces ({ and }). When the CRTSTS or TIOCSOFTCAR bit is set, the signals 'CTS' or 'CD' are shown in parentheses.

For tty windows, the command break causes the Data transmission line (TxD) to go low for a specified period of time. This is expected to be interpreted as a break signal on the other side. No data is sent and no modem control line is changed when a break is issued.


screen /dev/ttyS0 – Creates a new window and connects it to /dev/ttyS0 with the default settings from the terminal driver.

screen /dev/ttyUSB1 19200,cs8 – Creates a new window and connects it to /dev/ttyUSB1 at 19200 baud with 8-bit bytes.

Telnet Windows

If the first parameter is ”//telnet”, the second parameter is expected to be a host name, and an optional third parameter may specify a TCP port number (default decimal 23). Screen will connect to a server listening on the remote host and use the telnet protocol to communicate with that server.

For telnet windows, the command info shows details about the connection in square brackets ([ and ]) at the end of the status line:

b BINARY The connection is in binary mode.
e ECHO Local echo is disabled.
c SGA The connection is in 'character mode' (default: 'line mode').
t TTYPE The terminal type has been requested by the remote host. Screen sends the name “screen” unless instructed otherwise (see also the command term).
w NAWS The remote site is notified about window size changes.
F LFLOW The remote host will send flow control information. (Ignored at the moment.)

Additional flags are x, t, and n (XDISPLOC, TSPEED, and NEWENV).

For telnet windows, the command break sends the telnet code IAC BREAK (decimal 243) to the remote host.

This window type is only available if screen was compiled with the BUILTIN_TELNET option defined.


screen //telnet otherhost – Creates a new window and opens a telnet session to otherhost in it.

screen //telnet 25 – Creates a new window and opens a connection to port 25 on in it.

man/window_types.txt · Last modified: 2014/07/12 12:18 by
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