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6.6 Window Types

Screen provides three different window types. New windows are created with screen’s ‘screen’ command (see Screen Command). 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 with 100 or more 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...).
• 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-control for receiving data.

  istrip or -istrip

  Clear (or keep) the eight bit in each received byte.

  You may want to specify as many of these options as applicable. 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’, ‘CD’ and more. This depends rather on on the available ioctl()’s and system header files than on the physical capabilities of the serial board. The name of a logical low (inactive) signal is preceded by an exclamation mark (‘!’), otherwise the signal is logical high (active). Unsupported but shown signals 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 CRTSCTS or TIOCSOFTCAR bit is true, the signals ‘CTS’ or ‘CD’ are shown in parenthesis, respectively.

  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 break signal on the other side. No data is sent and no modem control line is changed when a break is issued.

• 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 for debugging 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.