SCREEN

NAME

SYNOPSIS

DESCRIPTION

The name of this program was changed to iScreen to be able to distinguish it from Oliver Laumann's original screen program. Despite that fact, this manual will continue to use the name screen. This is, because often the binary is installed as 'screen'.

When screen is called, it creates a single window with a shell in it (or the specified command) and then gets out of your way so that you can use the program as you normally would. Then, at any time, you can create new (full-screen) windows with other programs in them (including more shells), kill existing windows, view a list of the current windows, turn output logging on and off, copy-and-paste text between windows, view the scrollback history, switch between windows in whatever manner you wish, etc. When a program terminates, screen kills the window that contained it. If this window was in the foreground, the display switches to the previous window; if none are left, screen exits.

Everything you type is sent to the program running in the current window. The only exception to this is the one keystroke that is used to initiate a command to the window manager. By default, each command begins with a control-a (abbreviated C-a from now on), and is followed by one other keystroke. The command character and all the key bindings can be fully customized to be anything you like, though they are always two characters in length.

The standard way to create a new window is to type "C-a c". This creates a new window running a shell and switches to that window immediately, regardless of the state of the process running in the current window. Similarly, you can create a new window with a custom command in it by first binding the command to a keystroke (in your .screenrc file) and then using it just like the "C-a c" command. In addition, new windows can be created by running a command like:

screen emacs prog.c

from a shell prompt within a previously created window. This will not run another copy of screen, but will instead supply the command name and its arguments to the window manager who will use it to create the new window. The above example would start the emacs editor (editing prog.c) and switch to its window.

If "/etc/utmp" is writable by screen, an appropriate record will be written to this file for each window, and removed when the window is terminated. This is useful for working with "talk", "script", "shutdown", "rsend", "sccs" and other similar programs that use the utmp file to determine who you are. As long as screen is active on your terminal, the terminals own record is removed from the utmp file. See also "C-a L".  

GETTING STARTED

If you're impatient and want to get started without doing a lot more reading, you should remember this one command: "C-a ?". Typing these two characters will display a list of the available screen commands and their bindings. Each keystroke is discussed in the section "COMMAND KEYS". The manual section "CUSTOMIZATION" deals with the contents of your .screenrc.

If possible, choose a version of your terminal's termcap that has automatic margins turned off. This will ensure an accurate and optimal update of the screen in all circumstances. The next best thing is an auto-margin terminal that allows the last position on the screen to be updated without scrolling the screen (such as a vt100). This also allows the entire screen to be updated. Lastly, if all you've got is a "true" auto-margin terminal screen will be content to use it, but updating a character put into the last position on the screen may not be possible until the screen scrolls or the character is moved into a safe position in some other way. This delay can be shortened by using a terminal with insert-character capability.

If your terminal is of the second type (firm-margined `am'), you will want to let screen know about this, since a normal termcap doesn't distinguish this type of automatic margins from a "true" `am' terminal. You do this by specifying the `LP' capability in your termcap (see the "termcap" .screenrc command), or by using the -L command-line option. Screen needs this information to correctly update the screen.

If you are using a "true" auto-margin terminal (no `LP') at low baud rates, you may want to turn on a more optimal output mode by including the flag `OP' in your termcap entry, or by specifying the -O command-line option. The trade-off is that screen will no-longer accurately emulate the vt100's line-end quirks (e.g. the screen will scroll after putting one character in the last screen position).  

COMMAND KEYS

The following keystroke commands are available:

C-a 0 - C-a 9 (select0 - select9)

Switch to the window with the number 0 through 9. When a new window is established, the first available number from the range 0..9 is assigned to this window. Thus, the first window can be activated by "C-a 0" (there can be no more than 10 windows present at any one time).

C-a C-a (other)

Switch to the window displayed previously. Note that this function defaults to the command character typed twice, unless overridden; for instance, if you use the option "-e]x", this function becomes "]]", not "]C-a".

C-a a     

Send the command character (C-a) to the processes in the current window.

C-a A (aka)

Allow the user to enter an a.k.a (also-known-as). for the current window.

C-a c or C-a C-c (shell)

Create a new window with a shell and switch to that window.

C-a C (clear)

Clear the screen (saves image to scrollback buffer).

C-a d or C-a C-d (detach)

Detach screen (disconnect it from the terminal and put it into the background). A detached screen can be resumed by invoking screen with the -r option. (See also section "COMMAND-LINE OPTIONS".)

C-a D (pow_detach)

Power detach. Mainly the same as above, but also sends a HANGUP signal to the parent process of screen. CAUTION: This will result in a logout, when screen was started from your login shell.

C-a f or C-a C-f (flow)

Cycles the current window's flow-control setting from "automatic" to "on" to "off", see the section titled FLOW-CONTROL for details.

C-a C-g (vbell)

Toggles screen's visual bell mode. If your terminal does not support a visual bell, a `vbell-message' is displayed in the status line.

C-a h or C-a C-h (hardcopy)

Write a hardcopy of the current window to the file "hardcopy.n" in the window's default directory, where n is the number of the current window.

C-a H (log)

Begins/ends logging of the current window to the file "screenlog.n" in the window's default directory, where n is the number of the current window. The session log is appended to the previous contents of the file if it already exists. The current contents and the contents of the scrollback history are not included in the session log.

C-a i or C-a C-i (info)

Uses the message line to display some information about the current window: the cursor position in the form "(column,row)" starting with "(1,1)", the terminal width and height plus the size of the scrollback buffer in lines, like in "(80,24)+50", various flag settings (flow-control, insert mode, origin mode, wrap mode, application-keypad mode, output logging, activity monitoring, and redraw (`+' indicates enabled, `-' not)), the currently active character set (G0, G1, G2, or G3), and in square brackets the terminal character sets that are currently designated as G0 through G3. For system information use "C-a t".

C-a k or C-a C-k (kill)

Kill the current window and switch to the previously displayed window. Note: Emacs users should keep this command in mind, when killing a line. It is recommended not to use "C-a" as the screen escape key or that kill is rebound to "C-a K".

C-a l or C-a C-l (redisplay)

Redisplay the current window.

C-a L (login)

Adds or removes the entry in /etc/utmp file for the current window. This controls if the window is `logged in'. See also above. Additionally to that toggle, it is convenient having a `log in' and a `log out' key. E.g. `bind I set login on' and `bind O set login off' will map these keys to be C-a I and C-a O.

C-a m or C-a C-m (lastmsg)

Repeat the last message displayed in the message line. Useful if you're typing when a message appears, because (unless your terminal has a status line) the message goes away when you press a key.

C-a M (monitor)

Toggles monitoring of the current window. When monitoring is turned on and the affected window is switched into the background, you will receive the activity notification message in the status line at the first sign of output and the window will also be marked with an `@' in the window-status display. Monitoring is initially off for all windows.

C-a space or C-a n or C-a C-n (next)

Switch to the next window. This function can be used repeatedly to cycle through the list of windows. (Some terminals require you to release the control key before pressing space.)

C-a p or C-a C-p (prev)

Switch to the previous window (the opposite of C-a n).

C-a q or C-a C-q (xon)

Send a control-q to the program in the current window.

C-a r or C-a C-r (wrap)

Toggle the current window's line-wrap setting (turn the current window's automatic margins on and off).

C-a s or C-a C-s (xoff)

Send a control-s to the program in the current window.

C-a t or C-a C-t (time)

Uses the message line to display the time of day, the host name, and the load averages over 1, 5, and 15 minutes (if this is available on your system). For window specific information use "C-a i".

C-a v or C-a C-v (version)

Display the version and compilation date.

C-a w or C-a C-w (windows)

Uses the message line to display a list of all the windows. Each window is listed by number with the name of process that has been started in the window (or its a.k.a.); the current window is marked with a `*'; the previous window is marked with a `-'; all the windows that are "logged in" are marked with a `$'; a background window that has received a bell is marked with a `!'; a background window that is being monitored and has had activity occur is marked with an `@'; a window which has output logging turned on is marked with `(L)'.

C-a W (width)

Toggle the window width between 80 and 132 columns. As this command became a toggle, "C-a N" is no longer supported. This requires a capable terminal and the termcap entries "Z0" and "Z1". See the "termcap" command in section "CUSTOMIZATION" for more information.

C-a x or C-a C-x (lock)

Call a screenlock program (/local/bin/lck or /usr/bin/lock or a builtin, if no other is available). Screen does not accept any command keys until this program terminates. Meanwhile processes in the windows may continue, as the windows are in the `detached' state. The screenlock program may be changed through the environment variable $LOCKPRG (which must be set in the shell from which screen is started) and is executed with the user's uid and gid.

C-a z or C-a C-z (suspend)

Suspend screen. The windows are in the `detached' state, while screen is suspended.

C-a Z (reset)

Reset the virtual terminal to its "power-on" values.

C-a . (termcap)

Write the termcap entry for the virtual terminal of the currently active window to the file ".termcap" in the user's "$HOME/.screen" directory (or wherever screen stores its sockets. See the "FILES" section below). This termcap entry is identical to the value of the environment variable $TERMCAP that is set up by screen for each window. For terminfo based systems you will need to run a converter like captoinfo and then compile the entry with tic.

C-a ? (help)

Displays a help screen showing you all the key bindings. The first pages list all the internal commands followed by their bindings. Subsequent pages will display the custom commands, one command per key. Press space when you're done reading each page, or return to exit early. All other characters are ignored, except for the command character, which will exit the help display and begin a command.

C-a C-\ (quit)

Kill all windows and terminate screen. Note that on vt100-style terminals the keys C-4 and C-\ are identical. So be careful not to write C-a C-4 when selecting window no. 4. Use the empty bind command (as in "bind '^'") to remove a key binding.

C-a : (colon)

Allows you to enter ".screenrc" command lines as well as names of key-bound-functions. Useful for on-the-fly modification of key bindings, specific window creation and changing settings. Settings of the current window can be changed by prepending the command (if appropriate) with the keyword "set". If you consider this as the `Ex command mode' of screen, you may regard "C-a esc" as its `Vi command mode'.

C-a [ or C-a C-[ or C-a esc (copy)

Enter copy/scrollback mode. This allows you to copy text from the current window and its history into the paste buffer. In this mode a vi-like `full screen editor' is active:
Movement keys:
h, j, k, l move the cursor line by line or column by column.
0, ^ and $ move to the leftmost column, to the first or last non-whitespace character on the line.
H, M and L move the cursor to the leftmost column of the top, center or bottom line of the window.
+ and - positions one line up and down.
G moves to the specified absolute line (default: end of buffer).
| moves to the specified absolute column.
w, b, e move the cursor word by word.
C-u and C-d scroll the display up/down by the specified amount of lines while preserving the cursor position. (Default: half screenfull).
C-b and C-f scroll the display up/down a full screen.
g moves to the beginning of the buffer, whereas
% jumps to the specified percentage.
Note: Emacs style movement keys can be customized by a .screenrc command. (E.g. markkeys "h=^B:l=^F:$=^E") There is no simple method for a full emacs-style keymap, as this involves multi-character codes.
Marking:
The copy range is specified by setting two marks. The text between these marks will be highlighted. Press space to set the first or second mark respectively.
Y and y can be used to mark one whole line or to mark from start of line.
W marks exactly one word.
Repeat count:
Any of these commands can be prefixed with a number (by pressing digits 0..9) which is taken as a repeat count. Example: "C-a C-[ H 10 j 5 Y" will copy lines 11 to 15 into the pastebuffer.
Specials:
There are however some keys that act differently here and in vi. Vi does not allow to yank rectangular blocks of text, but screen does. Press
c or C to set the left or right margin respectively. If no repeat count is given, both default to the current cursor position. Try this on a rather full text screen as an example: "C-A [ S-M 20 l SPACE c 10 l 5 j S-C SPACE".
J joins lines. It toggles between 3 modes: lines separated by a newline character (012), lines glued seamless, lines separated by a single whitespace. Note that you can prepend the newline character with a carriage return character, by issuing a "set crlf on".
v is for all the vi users with ":set numbers" - it toggles the left margin between column 9 and 1.
Press a before the final space key to toggle in append mode. Thus the contents of the pastebuffer will not be overwritten, but appended to.
A toggles in append mode and sets a (second) mark.
> sets the (second) mark and writes the contents of the copybuffer to the screen-exchange file (/tmp/screen-exchange per default) once copy-mode is finished. This example demonstrates how to dump the whole scrollback buffer to that file: "C-A [ g SPACE G $ >".
? gives information about the current line and column.

C-a ] or C-a C-] (paste)

Paste. Write the contents of the paste buffer to the stdin queue of the current window.

C-a { (history)

Usually users work with a shell that allows easy access to previous commands. E.g. csh has the command "!!" to repeat the last command executed. Screen allows you to have a primitive way of re-calling "the command that started ...": You just type the first letter of that command, then hit `C-a {' and screen tries to find a previous line that matches with the `prompt character' to the left of the cursor. This line is pasted into this window's input queue. Thus you have a crude command history (made up by the visible window and its scrollback buffer).

C-a > (write_buffer)

Writes the contents of the paste buffer to a public accessible screen-exchange file. This is thought of as a primitive means of communication between screen users on the same host. See also "C-a esc".

C-a < (read_buffer)

Reads the screen-exchange file into the pastebuffer. See also "C-a ]".

C-a = (kill_buffer)

Removes the exchange file used by "C-a <" and "C-a >".

COMMAND-LINE OPTIONS

-a

include all capabilities (with some minor exceptions) in each window's termcap, even if screen must redraw parts of the display in order to implement a function.

-A

Adapt the sizes of all windows to the size of the display. By default, screen may try to restore its old window sizes.

-c file

override the default configuration file from "$HOME/.screenrc" to file.

-d|-D [pid.tty.host]

does not start screen, but detach the elsewhere running screen session. It has the same effect as typing "C-a d" from screen's controlling terminal. -D is the equivalent to the power detach key. If no session can be detached, this option is ignored. The combination "screen -D -r" can be used to `transport' the elsewhere running session to this terminal and logout there. Note: It is a good idea to have the status of your sessions checked by means of "screen -list".

-e xy

specifies the command character to be x and the character generating a literal command character to y (when typed after the command character). The default is "C-a" and `a', which can be specified as "-e^Aa". See the "escape" .screenrc command for more details.

-f, -fn, and -fa

turns flow-control on, off, or "automatic switching mode". This can also be defined through the "flow" .screenrc command.

-h num

Specifies the history scrollback buffer to be num lines high.

-i

will cause the interrupt key (usually C-c) to interrupt the display immediately when flow-control is on. See the "flow" .screenrc command for details.

-l and -ln

turns login mode on or off (for /etc/utmp updating). This can also be defined through the "login" .screenrc command.

-ls and -list

does not start screen, but prints a list of pid.tty.host strings identifying your screen sessions. Sessions marked `detached' can be resumed with "screen -r". Those marked `attached' are running and have a controlling terminal. Sessions marked as `dead' should be thoroughly checked and removed. Ask your system administrator if you are not sure. Remove sessions with the -wipe option.

5

-m disables looking in environment variable $STY for an alternate socket name.

-t name or -k name

sets the title (a.k.a.) for the default shell or specified program. See also the "shellaka" .screenrc command.

-wipe

does the same as "screen -ls", but removes destroyed sessions instead of marking them as `dead'.

-L

tells screen your auto-margin terminal has a writable last-position on the screen. This can also be set in your .screenrc by specifying `LP' in a "termcap" command.

-O

selects a more optimal output mode for your terminal rather than true vt100 emulation (only affects auto-margin terminals without `LP'). This can also be set in your .screenrc by specifying `OP' in a "termcap" command.

-r [pid.tty.host]

resumes a detached screen session. No other options (except "-d -r" or "-D -r") may be specified, though an optional prefix of [pid.]tty.host may be needed to distinguish between multiple detached screen sessions.

-R

attempts to resume the first detached screen session it finds. If successful, all other command-line options are ignored. If no detached session exists, starts a new session using the specified options, just as if -R were not specified.

-s

sets the default shell to the program specified, instead of the value in the environment variable $SHELL (or "/bin/sh" if not defined). This can also be defined through the "shell" .screenrc command.

CUSTOMIZATION

When screen is invoked, it executes initialization commands from the files "/local/etc/screenrc" and ".screenrc" in the user's home directory. These are the "programmer's defaults" that can be overridden in the following ways: For the global screenrc file screen searches for the environment variable $SYSSCREENRC. The user specific screenrc file is searchend in $ISCREENRC, then $SCREENRC, then $HOME/.iscreenrc and finally defaults to $HOME/.screenrc. The command line option -c takes precedence over the user specific screenrc file. Commands in these files are used to set options, bind functions to keys, and to automatically establish one or more extra windows at the beginning of your screen session. Commands are listed one per line, with empty lines being ignored. A command's arguments are separated by tabs or spaces, and may be surrounded by single or double quotes. A `#' turns the rest of the line into a comment, except in quotes. Unintelligible lines are warned about and ignored. Commands may contain references to environment variables. The syntax is the shell-like "$VAR " or "${VAR}". Note that this causes incompatibilities with previous screen versions, as now the '$'-sign has to be protected with '' if no variable substitution shall be performed.

Customization can also be done 'on-line'. To enter the command mode type `C-a :'. Setting flags (like scrollback, login, etc.) on-line may not have the desired effect, as e.g. the command "C-a : login on" will affect only the settings for the creation of new windows (just like within .screenrc). If you intend to change flags of the current window, then prepend the command with the keyword "set". E.g. "C-a : set login on" will log this window in.

The following initialization commands are available:

activity message

When any activity occurs in a background window that is being monitored, screen displays a notification in the message line. The notification message can be re-defined by means of the "activity" command. Each occurrence of `%' in message is replaced by the number of the window in which activity has occurred, and each occurrence of `~' is replaced by the definition for bell in your termcap (usually an audible bell). The default message is

    'Activity in window %'

Note that monitoring is off for all windows by default, but can be altered by use of the "monitor" command (C-a M).

autodetach on|off

Sets whether screen will automatically detach upon hangup, which saves all your running programs until they are resumed with a screen -r command. When turned off, a hangup signal will terminate screen and all the processes it contains. Autodetach is on by default.

bell message

When a bell character is sent to a background window, screen displays a notification in the message line. The notification message can be re-defined by means of the "bell" command. Each occurrence of `%' in message is replaced by the number of the window to which a bell has been sent, and each occurrence of `~' is replaced by the definition for bell in your termcap (usually an audible bell). The default message is

    'Bell in window %'

An empty message can be supplied to the "bell" command to suppress output of a message line (bell "").

bind key [function [args]]

Bind a function to a key. By default, each function provided by screen is bound to one or more keys as indicated by the above table, e.g. the function to create a new window is bound to "C-c" and "c". The "bind" command can be used to redefine the key bindings and to define new bindings. The key argument is either a single character, a two-character sequence of the form "^x" (meaning "C-x"), a backslash followed by an octal number (specifying the ASCII code of the character), or a backslash followed by a second character, such as "\^" or "\\". The argument can also be quoted, if you like. If no further argument is given, any previously established binding for this key is removed. The function argument can be one of the following keywords:

     select0      Switch to window #0
       ...
     select9      Switch to window #9
     aka          Change the current window's a.k.a.
     clear        Clear the screen
     colon        Enter one ".screenrc" command on-the-fly.
     copy         Select a piece of text.
     detach       Detach screen
     flow         Toggle the current window's flow-control setting
     hardcopy     Make hardcopy of current window
     history      Use cut&paste to fetch a recently displayed line.
     help         Display a list of the key bindings in effect
     info         Display the current window's status information
     kill         Kill the current window
     lastmsg      Redisplay the last message line
     lock         Run a screenlock program. 
     log          Begin/end logging of the current window's output
     login        Toggle the window's "login" setting (/etc/utmp entry)
     monitor      Toggle activity monitoring of the current window
     next         Switch to the next window
     other        Switch to the window displayed previously
     paste        Paste in a selected piece of text.
     pow_detach   Detach screen and logout.
     prev         Switch to the previous window
     quit         Kill all windows and terminate
     readbuffer   Take text from the exchange file.
     redisplay    Redisplay current window
     reset        Reset the window to its "power-on" settings
     screen       Create a new window with the specified command
     shell        Create a new window with a shell
     suspend      Suspend screen
     termcap      Write screen's termcap entry to $HOME/.screencap
     vbell        Toggle the window's "vbell" setting.
     version      Display the version numbers and date last modified
     width        Toggle the terminal width between 80 and 132 columns
     windows      Display a list of all windows
     wrap         Toggle the current window's line-wrap setting
     writebuffer  Store the selected text in the exchange file.
     xoff         Send a control-s to the current program
     xon          Send a control-q to the current program

Some examples:

     bind ' ' windows
     bind ^f screen telnet foobar
     bind \033 screen -ln -t root -h 1000 9 su

would bind the space key to the function that displays a list of windows (so that the function usually invoked by "C-a C-w" would also be available as "C-a space"), bind "C-f" to the function "create a window with a TELNET connection to foobar", and bind "escape" to the function that creates an non-login window with a.k.a. "root" in slot #9, with a super-user shell and a scrollbackbuffer of 1000 lines.

bufferfile exchange-file

Change the filename used for reading and writing with the copybuffer. The default is "/tmp/screen-exchange". The following example will paste the system's password file into the screen window:

     C-a : bufferfile /etc/passwd
     C-a < C-a ]

chdir [directory]

Change the current directory of screen to the specified directory or, if called without an argument, to your home directory (the value of the environment variable $HOME). All windows that are created by means of the "screen" command from within ".screenrc" or by means of "C-a : screen ..." or "C-a c" use this as their default directory. Without a chdir command, this would be the directory from which screen was invoked. Hardcopy and log files are always written to the window's default directory, not the current directory of the process running in the window. You can use this command multiple times in your .screenrc to start various windows in different default directories, but the last chdir value will affect all the windows you create interactively.

crlf on|off

This affects the copying of text regions with the `C-a [' command. If it is set to `on', lines will be separated by the two character sequence `CR' - `LF'. Otherwise only `LF' is used.

echo [-n] message

The echo command may be used to annoy screen users with a 'message of the day'. Typically installed in a global /local/etc/screenrc. See also "sleep". Echo is also useful for online checking of environment variables.

escape xy

Set the command character to x and the character generating a literal command character to y (just like in the -e option). Each argument is either a single character, a two-character sequence of the form "^x" (meaning "C-x"), a backslash followed by an octal number (specifying the ASCII code of the character), or a backslash followed by a second character, such as "\^" or "\\". The default is "^Aa", but "``" is recommended by one of the authors.

flow on|off|auto [interrupt]

Sets the default flow-control mode for new windows. Specifying "flow auto interrupt" is the same as the command-line options -fa and -i. See the discussion on FLOW-CONTROL later on in this document for full details and note, that this is subject to change in future releases.

hardcopy_append on|off

If set to "on", screen will append to the "hardcopy.n" files created by the command "C-a h", otherwise these files are overwritten each time.

hardstatus on|off

Toggles the use of the terminals hardware status line. If "on", screen will use this facility to display one line messages. Otherwise these messages are overlayed in reverse video mode at the display line. Note that the hardstatus feature should only be used, if the termcap/terminfo capabilities "hs", "ts", "fs" and "ds" are set properly.

login on|off

Sets the login flag which determines if new windows should have /etc/utmp entries added for them. The login state is also changeable on-the-fly by using the bindable version of the "login" command (C-a L) of by means of "C-a : set login on|off". The default should be "on" for a screen that runs under suid-root.

markkeys string

This is a method of changing the keymap used for copy/history mode. The string is made up of oldchar=newchar pairs which are separated by `:'. Example: The string "B=^B:F=^F" will change the keys `C-b' and `C-f' from their (original emacs-style bindings) to the vi style binding (scroll up/down full page), which is the default meaning of `B' and `F'.

mode mode

The mode of each newly allocated pseudo-tty is set to mode. Mode is an octal number. When no "mode" command is given, mode 0622 is used.

monitor on|off

Toggles activity monitoring of windows. When monitoring is turned on and an affected window is switched into the background, you will receive the activity notification message in the status line at the first sign of output and the window will also be marked with an `@' in the window-status display. Monitoring is initially off for all windows.

msgminwait sec

Defines the time screen delays all activity after a message was dispayled. The default is 1 second.

msgwait sec

Defines the time a message is displayed, if screen is not disturbed by other activity. The default is 5 seconds.

nethack on|off

Changes the kind of error messages used by screen. When you are familiar with the game "nethack", you may enjoy the nethack-style messages which will often blur the facts a little, but are much funnier to read. Anyway, standard messages often tend to be unclear as well.
This option is only available if screen was compiled with the NETHACK flag defined. The default setting is then determined by the presence of the environment variable $NETHACKOPTIONS.

password [crypted_pw]

Present a crypted password in your ".screenrc" file and screen will ask for it, whenever a detached session is tried to be resumed. This is useful, if you have privileged programs running under screen and you want to protect your session from reattach attempts by users that managed to have your uid. (I.e. any superuser.)

pow_detach_msg message

The message specified here is output whenever a `Power detach' was performed. It may be used as a replacement for a logout message or to reset baud rate, etc.

screen [-opts] [n] [cmd [args]]

Establish a new window. The flow-control options (-f, -fn and -fa), title (a.k.a.) option (-t), login options (-l and -ln) , terminal type option (-T <term>) and scrollback option (-h <num>) may be specified for each command. If an optional number n in the range 0..9 is given, the window number n is assigned to the newly created window (or, if this number is already in-use, the next available number). If a command is specified after "screen", this command (with the given arguments) is started in the window; otherwise, a shell is created. Thus, if your ".screenrc" contains the lines

     # example for .screenrc:
     screen 1
     screen -fn -t foobar 2 telnet foobar

screen creates a shell window (in window #1) and a window with a TELNET connection to the machine foobar (with no flow-control using the a.k.a. "foobar" in window #2). If you do not include any screen commands in your ".screenrc" file, then screen defaults to creating a single shell window, number zero. When the initialization is completed, screen switches to the last window specified in your .screenrc file or, if none, it opens default window #0.

scrollback num

Set the size of the scrollback buffer for new windows to num lines. The default scrollback is 50 lines. Use "C-a : set scrollback num" to change the scrollback size of the current window and use "C-a i" to view the current setting.

redraw on|off

Define whether the display should be refreshed (as done with "C-a l") after switching to the current window. As usual when the "set" keyword is given, this command only affects the current window. But unlike other commands, "redraw off" (without "set") affects all windows, the window specific settings come into effect again when "redraw on" (without "set") is entered.

shell command

Set the command to be used to create a new shell. This overrides the value of the environment variable $SHELL, or "/bin/sh" if undefined. This is useful if you'd like to run a tty-enhancer which is expecting to execute the program specified in $SHELL.

shellaka a.k.a.

Set the a.k.a. for all shells created during startup or by the C-A C-c command. For details about what a.k.a.'s are, see the discussion entitled ALSO KNOWN AS.

sleep num This command will pause the execution of a .screenrc file for num seconds. It may be used to give users a chance to read the messages output by "echo".

slowpaste usec

Define the speed text is inserted by the paste ("C-a ]") command. For each 80 characters (IOSIZE) pasted screen will make a pause of usec milliseconds to allow the application the processing of input. Use that, if you have to fear that your underlying system chokes on large pastes.

startup_message on|off

Select whether to display the copyright notice when screen starts up.

term term

In each window's environment screen opens, it sets the $TERM variable to "screen" by default, unless no description for "screen" is installed in the local termcap or terminfo data base. In that case it pretends that the terminal emulator is "vt100". This won't do much harm, as screen is VT100/ANSI compatible. The use of the "term" command is discouraged for non-default purpose. That is, one may want to specify special $TERM settings (e.g. vt100) for the next "screen rlogin othermachine" command. Use the command "screen -T vt100 rlogin othermachine" rather than setting ("term vt100") and resetting ("term screen") the default before and after the "screen" command.

termcap term terminal-tweaks [window-tweaks]
terminfo term terminal-tweaks [window-tweaks]

Use this command to modify your terminal's termcap entry without going through all the hassles involved in creating a custom termcap entry. Plus, you can optionally customize the termcap generated for the windows. If your system works with terminfo-database rather than with termcap screen will understand the `terminfo' command which has the same effects as the `termcap' command. Thus users can write one .screenrc file that handles both cases, although terminfo syntax is slightly different from termcap syntax.

The first argument specifies which terminal(s) should be affected by this definition. You can specify multiple terminal names by separating them with `|'s. Use `*' to match all terminals and `vt*' to match all terminals that begin with "vt".

Each tweak argument contains one or more termcap defines (separated by `:'s) to be inserted at the start of the appropriate termcap entry, enhancing it or overriding existing values. The first tweak modifies your terminal's termcap, and contains definitions that your terminal uses to perform certain functions. Specify a null string to leave this unchanged (e.g. ''). The second (optional) tweak modifies all the window termcaps, and should contain definitions that screen understands (see the "VIRTUAL TERMINAL" section).

Some examples:

termcap xterm* LP:hs@

Informs screen that all terminals that begin with `xterm' have firm auto-margins that allow the last position on the screen to be updated (LP), but they don't really have a status line (no 'hs' -- append `@' to turn entries off). Note that we assume `LP' for all terminal names that start with "vt", but only if you don't specify a termcap command for that terminal.

     termcap vt*  LP
     termcap vt102|vt220  Z0=\E[?3h:Z1=\E[?3l

Specifies the firm-margined `LP' capability for all terminals that begin with `vt', and the second line will also add the escape-sequences to switch into (Z0) and back out of (Z1) 132-character-per-line mode if this is a vt102 or vt220. (You must specify Z0 and Z1 in your termcap to use the width-changing commands.)

termcap vt100 "" l0=PF1:l1=PF2:l2=PF3:l3=PF4

This leaves your vt100 termcap alone and adds the function key labels to each window's termcap entry.

termcap h19|z19 am@:im=\E@:ei=\EO dc=\E[P

Takes a h19 or z19 termcap and turns off auto-margins (am@) and enables the insert mode (im) and end-insert (ei) capabilities (the `@' in the `im' string is after the `=', so it is part of the string). Having the `im' and `ei' definitions put into your terminal's termcap will cause screen to automatically advertise the character-insert capability in each window's termcap. Each window will also get the delete-character capability (dc) added to its termcap, which screen will translate into a line-update for the terminal (we're pretending it doesn't support character deletion).

If you would like to fully specify each window's termcap entry, you should instead set the $SCREENCAP variable prior to running screen. See the discussion on the "VIRTUAL TERMINAL" in this manual, and the termcap(5) man page for more information on termcap definitions.

vbell on|off

Sets the visual bell setting for new windows. If your terminal does not support a visual bell a message is printed to the status line. The default message is "Wuff, Wuff!!".

vbell_msg message

Sets the visual bell message. message is printed to the status line if the window receives a bell character (^G) and vbell is set to "on".

vbellwait sec

Define a delay in seconds after each display of screen 's visual bell message. The default is 0 seconds.

wrap on|off

Sets the line-wrap setting for new windows. When line-wrap is on, the second consecutive printable character output at the last column of a line will wrap to the start of the following line. As an added feature, backspace (^H) will also wrap through the left margin to the previous line. Line-wrap is on by default and can be toggled with the "wrap" command ("C-a r") or by means of "C-a : set wrap on|off".  

THE MESSAGE LINE

The message line facility can be used by an application running in the current window by means of the ANSI Privacy message control sequence. For instance, from within the shell, try something like:

echo '<esc>^Hello world<esc>\\'

where '<esc>' is an escape, '^' is a literal up-arrow, and '\\' turns into a single backslash.  

FLOW-CONTROL

Each window has an initial flow-control value set with either the -f option or the "flow" .screenrc command. Per default the windows are set to automatic flow-switching. It can then be toggled between the three states 'fixed on', 'fixed off' and

The automatic flow-switching mode deals with flow control using the TIOCPKT mode (like "rlogin" does). If the tty driver does not support TIOCPKT, screen tries to find out the right mode based on the current setting of the application keypad -- when it is enabled, flow-control is turned off and visa versa. Of course, you can still manipulate flow-control manually when needed.

If you're running with flow-control enabled and find that pressing the interrupt key (usually C-c) does not interrupt the display until another 6-8 lines have scrolled by, try running screen with the "interrupt" option (add the "interrupt" flag to the "flow" command in your .screenrc, or use the -i command-line option). This causes the output that screen has accumulated from the interrupted program to be flushed. One disadvantage is that the virtual terminal's memory contains the non-flushed version of the output, which in rare cases can cause minor inaccuracies in the output. For example, if you switch screens and return, or update the screen with "C-a l" you would see the version of the output you would have gotten without "interrupt" being on. Also, you might need to turn off flow-control (or use auto-flow mode to turn it off automatically) when running a program that expects you to type the interrupt character as input, as it is possible to interrupt the output of the virtual terminal to your physical terminal when flow-control is enabled. If this happens, a simple refresh of the screen with "C-a l" will restore it. Give each mode a try, and use whichever mode you find more comfortable.  

ALSO KNOWN AS (A.K.A.s)

The default name for all shell windows can be set with the "shellaka" command in the .screenrc file, while all other windows are created with a "screen" command and thus can have their name set with the -t option. Interactively, there is the AKA-string escape-sequence (<esc>kname<esc>\) and the "aka" command (C-a A). The former can be output from an application to control the window's name under software control, and the latter will prompt for a name when typed. You can also bind pre-defined names to keys with the "aka" command to set things quickly without prompting.

Finally, screen has a shell-specific heuristic that is enabled by setting the window's name to "search|name" and arranging to have a null aka escape-sequence output as a part of your prompt. The search portion specifies an end-of-prompt search string, while the name portion specifies the default shell name for the window. If the name ends in a `:' screen will add what it believes to be the current command running in the window to the end of the window's shell name (e.g. "name:cmd"). Otherwise the current command name supersedes the shell name while it is running.

Here's how it works: you must modify your shell prompt to output a null aka escape-sequence (<esc>k<esc>\) as a part of your prompt. The last part of your prompt must be the same as the string you specified for the search portion of the a.k.a. Once this is set up, screen will use the aka escape-sequence to clear the previous command name and get ready for the next command. Then, when a newline is received from the shell, a search is made for the end of the prompt. If found, it will grab the first word after the matched string and use it as the command name. If the command name begins with either '!', '%', or '^' screen will use the first word on the following line (if found) in preference to the just-found name. This helps csh users get better command names when using job control or history recall commands.

Here's some .screenrc examples:

screen -t top 2 nice top

Adding this line to your .screenrc would start a niced version of the "top" command in window 2 name "top" rather than "nice".

     shellaka '> |csh'
     screen 1

This file would start a shell using the given shellaka. The a.k.a. specified is an auto-aka that would expect the prompt and the typed command to look something like the following:

/usr/joe/src/dir> trn

(it looks after the '> ' for the command name). The window status would show the name "trn" while the command was running, and revert to "csh" upon completion.

bind R screen -t '% |root:' su

Having this command in your .screenrc would bind the key sequence "C-a R" to the "su" command and give it an auto-aka name of "root:". For this auto-aka to work, the screen could look something like this:

     % !em
     emacs file.c

Here the user typed the csh history command "!em" which ran the previously entered "emacs" command. The window status would show "root:emacs" during the execution of the command, and revert to simply "root:" at its completion.

     bind o aka
     bind E aka ""
     bind u aka (unknown)

The first binding doesn't have any arguments, so it would prompt you for an a.k.a. when you type "C-a o". The second binding would clear an auto-aka's current setting (C-a E). The third binding would set the current window's a.k.a. to "(unknown)" (C-a u).

One thing to keep in mind when adding a null aka escape-sequence to your prompt is that some shells (like the csh) count all the non-control characters as part of the prompt's length. If these invisible characters aren't a multiple of 8 then backspacing over a tab will result in an incorrect display. One way to get around this is to use a prompt like this:

set prompt='^[[0000m^[k^[\% '

The escape-sequence "<esc>[0000m" not only normalizes the character attributes, but all the zeros round the length of the invisible characters up to 8. Bash users will probably want to echo the escape sequence in the PROMPT_COMMAND:

PROMPT_COMMAND='echo -n -e "\033k\033\134"'

(I used "134" to output a `\' because of a bug in v1.04).  

THE VIRTUAL TERMINAL

Also, you can customize the $TERMCAP value used by screen by using the "termcap" .screenrc command, or by defining the variable $SCREENCAP prior to startup. When the latter defined, its value will be copied verbatim into each window's $TERMCAP variable. This can either be the full terminal definition, or a filename where the terminal "screen" (and/or "screen-w") is defined.

Note that screen honors the "terminfo" .screenrc command if the system uses the terminfo database rather than termcap.

When the boolean `G0' capability is present in the termcap entry for the terminal on which screen has been called, the terminal emulation of screen supports multiple character sets. This allows an application to make use of, for instance, the VT100 graphics character set or national character sets. The following control functions from ISO 2022 are supported: lock shift G0 (SI), lock shift G1 (SO), lock shift G2, lock shift G3, single shift G2, and single shift G3. When a virtual terminal is created or reset, the ASCII character set is designated as G0 through G3. When the `G0' capability is present, screen evaluates the capabilities `S0', `E0', and `C0' if present. `S0' is the sequence the terminal uses to enable and start the graphics character set rather than SI. `E0' is the corresponding replacement for SO. `C0' gives a character by character translation string that is used during semi-graphics mode. This string is built like the `acsc' terminfo capability.

When the `po' and `pf' capabilities are present in the terminal's termcap entry, applications running in a screen window can send output to the printer port of the terminal. This allows a user to have an application in one window sending output to a printer connected to the terminal, while all other windows are still active (the printer port is enabled and disabled again for each chunk of output). As a side-effect, programs running in different windows can send output to the printer simultaneously. Data sent to the printer is not displayed in the window.

Some capabilities are only put into the $TERMCAP variable of the virtual terminal if they can be efficiently implemented by the physical terminal. For instance, `dl' (delete line) is only put into the $TERMCAP variable if the terminal supports either delete line itself or scrolling regions. Note that this may provoke confusion, when the session is reattached on a different terminal, as the value of $TERMCAP cannot be modified by parent processes.

The following is a list of control sequences recognized by screen. "(V)" and "(A)" indicate VT100-specific and ANSI- or ISO-specific functions, respectively.

ESC E
     Next Line
ESC D
     Index
ESC M
     Reverse Index
ESC H
     Horizontal Tab Set
ESC 7
(V)  Save Cursor and Attributes
ESC 8
(V)  Restore Cursor and Attributes
ESC [s
(A)  Save Cursor and Attributes
ESC [u
(A)  Restore Cursor and Attributes
ESC c
     Reset to Initial State
ESC =
(V)  Application Keypad Mode
ESC >
(V)  Numeric Keypad Mode
ESC # 8
(V)  Fill Screen with E's
ESC \
(A)  String Terminator
ESC ^
(A)  Privacy Message String (Message Line)
ESC k
     A.k.a. Definition String
ESC P
(A)  Device Control String
     Outputs a string directly to the host
     terminal without interpretation.
ESC _
(A)  Application Program Command (not used)
ESC ]
(A)  Operating System Command (not used)
Control-N
(A)  Lock Shift G1 (SO)
Control-O
(A)  Lock Shift G0 (SI)
ESC n
(A)  Lock Shift G2
ESC o
(A)  Lock Shift G3
ESC N
(A)  Single Shift G2
ESC O
(A)  Single Shift G3
ESC ( Pcs
(A)  Designate character set as G0
ESC ) Pcs
(A)  Designate character set as G1
ESC * Pcs
(A)  Designate character set as G2
ESC + Pcs
(A)  Designate character set as G3
ESC [ Pn ; Pn H
     Direct Cursor Addressing
ESC [ Pn ; Pn f
     Direct Cursor Addressing
ESC [ Pn J
     Erase in Display
Pn = None or 0
     From Cursor to End of Screen
1
     From Beginning of Screen to Cursor
2
     Entire Screen
ESC [ Pn K
     Erase in Line
Pn = None or 0
     From Cursor to End of Line
1
     From Beginning of Line to Cursor
2
     Entire Line
ESC [ Pn A
     Cursor Up
ESC [ Pn B
     Cursor Down
ESC [ Pn C
     Cursor Right
ESC [ Pn D
     Cursor Left
ESC [ Ps ;...; Ps m
     Select Graphic Rendition
Ps = None or 0
     Default Rendition
1
     Bold
2
(A)  Faint
3
(A)  Standout Mode (ANSI: Italicized)
4
     Underlined
5
     Blinking
7
     Negative Image
22
(A)  Normal Intensity
23
(A)  Standout Mode off (ANSI: Italicized off)
24
(A)  Not Underlined
25
(A)  Not Blinking
27
(A)  Positive Image
ESC [ Pn g
     Tab Clear
Pn = None or 0
     Clear Tab at Current Position
3
     Clear All Tabs
ESC [ Pn ; Pn r
(V)  Set Scrolling Region
ESC [ Pn I
(A)  Horizontal Tab
ESC [ Pn Z
(A)  Backward Tab
ESC [ Pn L
(A)  Insert Line
ESC [ Pn M
(A)  Delete Line
ESC [ Pn @
(A)  Insert Character
ESC [ Pn P
(A)  Delete Character
ESC [ Ps ;...; Ps h
     Set Mode
ESC [ Ps ;...; Ps l
     Reset Mode
Ps = 4
(A)  Insert Mode
?3
(V)  Change Terminal Width
?5
(V)  Visible Bell (On followed by Off)
?6
(V)  Origin Mode
?7
(V)  Wrap Mode
ESC [ 5 i
(A)  Start relay to printer (ANSI Media Copy)
ESC [ 4 i
(A)  Stop relay to printer (ANSI Media Copy)

ENVIRONMENT

COLUMNS

Number of columns on the terminal (overrides termcap entry).

HOME

Directory in which to look for .screenrc.

ISCREENRC

Alternate user screenrc file.

LINES

Number of lines on the terminal (overrides termcap entry).

LOCKPRG

Screen lock program.

NETHACKOPTIONS

Turns on nethack option.

PATH

Used for locating programs to run.

SCREENCAP

For customizing a terminal's TERMCAP value.

SCREENDIR

Alternate socket directory.

SCREENRC

Alternate user screenrc file.

SHELL

Default shell program for opening windows (default "/bin/sh").

STY

Alternate socket name.

SYSSCREENRC

Alternate system screenrc file.

TERM

Terminal name.

TERMCAP

Terminal description.

FILES

$SYSSCREENRC


/local/etc/screenrc   screen initialization commands


$ISCREENRC


$SCREENRC


$HOME/.iscreenrc


$HOME/.screenrc       Read in after /local/etc/screenrc


$ISCREENDIR/S-<login>


$SCREENDIR/S-<login>


/local/screens/S-<login>  Socket directories (default)


/usr/tmp/screens/S-<login>  Alternate socket directories.


<socket directory>/.termcap  Written by the "termcap" output function


/usr/tmp/screens/screen-exchange  or


/tmp/screen-exchange  screen `interprocess communication buffer'


hardcopy.[0-9]        Screen images created by the hardcopy function


screenlog.[0-9]       Output log files created by the log function


/usr/lib/terminfo/?/*   or


/etc/termcap          Terminal capability databases


/etc/utmp             Login records


$LOCKPRG              Program that locks a terminal.

SEE ALSO

AUTHORS

CONTRIBUTORS

VERSION

BUGS

The GR set of ISO 2022 is not supported.

There is no keyboard input translation to VT100 sequences.

It is not possible to change the environment variable $TERMCAP when reattaching under a different terminal type.

The support of terminfo based systems is very limited. Adding extra capabilities to $TERMCAP may not have any effects.

Screen does not make use of hardware tabs.

Screen must be installed as set-uid with owner root in order to be able to correctly change the owner of the tty device file for each window. Special permission may also be required to write the file "/etc/utmp".

Entries in "/etc/utmp" are not removed when screen is killed with SIGKILL. This will cause some programs (like "w" or "rwho") to advertise that a user is logged on who really isn't.

Index

NAME

SYNOPSIS

DESCRIPTION

GETTING STARTED

COMMAND KEYS

COMMAND-LINE OPTIONS

CUSTOMIZATION

THE MESSAGE LINE

FLOW-CONTROL

ALSO KNOWN AS (A.K.A.s)

THE VIRTUAL TERMINAL

ENVIRONMENT

FILES

SEE ALSO

AUTHORS

CONTRIBUTORS

VERSION

BUGS