Screen is a full-screen window manager that multiplexes a physical terminal between several processes (typically interactive shells). Each virtual terminal provides the functions of a DEC VT100 terminal and, in addition, several control functions from the ISO 6429 (ECMA 48, ANSI X3.64) and ISO 2022 standards (e.g. insert/delete line and support for multiple character sets). There is a scrollback history buffer for each virtual terminal and a copy-and-paste mechanism that allows moving text regions between windows.
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 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. All windows run their programs completely independent of each other. Programs continue to run when their window is currently not visible and even when the whole screen session is detached from the user's terminal. When a program terminates, screen (per default) 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.
Screen does not understand the prefix "C-" to mean control. Please use the caret notation ("^A" instead of "C-a") as arguments to e.g. the "escape" command or the "-e" option. Screen will also print out control characters in caret notation.
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 or at the "C-a :" command line) and then using it just like the "C-a c" command. In addition, new windows can be created by running a command like:
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 (specified in the $STY environment variable) 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.
Before you begin to use screen you'll need to make sure you have correctly selected your terminal type, just as you would for any other termcap/terminfo program. (You can do this by using tset for example.)
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 "DEFAULT KEY BINDINGS". The manual section "CUSTOMIZATION" deals with the contents of your .screenrc.
If your terminal is a "true" auto-margin terminal (it doesn't allow the last position on the screen to be updated without scrolling the screen) consider to use 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. Most terminals nowadays have "magic" margins (automatic margins plus usable last column). This is the VT100 style type and perfectly suited for screen. 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.
Screen has the following command-line options:
:-D -R: Attach here and now. In detail this means: If a session is running, then reattach. If necessary detach and logout remotely first. If it was not running create it and notify the user. This is the author's favorite.
As mentioned, each screen command consists of a "C-a" followed by one other character. For your convenience, all commands that are bound to lower-case letters are also bound to their control character counterparts (with the exception of "C-a a"; see below), thus, "C-a c" as well as "C-a C-c" can be used to create a window. See section "CUSTOMIZATION" for a description of the command.
The following table shows the default key bindings:
C-a ' (select)
Prompt for a window name or number to switch to.
C-a (windowlist -b)
Present a list of all windows for selection.
C-a 0 (select 0)
C-a 9 (select 9)
C-a - (select -)
Switch to window number 0 - 9, or to the blank window.
C-a tab (focus)
Switch the input focus to the next region.
C-a C-a (other)
Toggle to the window displayed previously. Note that this binding defaults to the command character typed twice, unless overridden. For instance, if you use the option ``-e]x, this command becomes ``]].
C-a a (meta) Send the command character (C-a) to window. See escape command.
C-a A (title)
Allow the user to enter a name for the current window.
C-a C-b (break)
Send a break to window.
C-a B (pow_break)
Reopen the terminal line and send a break.
C-a C-c (screen)
Create a new window with a shell and switch to that window.
C-a C (clear)
Clear the screen.
C-a C-d (detach)
Detach screen from this terminal.
C-a D D (pow_detach)
Detach and logout.
C-a C-f (flow) Toggle flow on, off or auto.
C-a F (fit) Resize the window to the current region size.
C-a C-g (vbell)
Toggles screen's visual bell mode.
C-a h (hardcopy)
Write a hardcopy of the current window to the file ``hardcopy.n''.
C-a H (log) Begins/ends logging of the current window to the file ``screenlog.n''.
C-a C-i (info) Show info about this window.
C-a C-k (kill) Destroy current window.
C-a C-l (redisplay)
Fully refresh current window.
C-a L (login)
Toggle this windows login slot. Available only if screen is configured to update the utmp database.
C-a C-m (lastmsg)
Repeat the last message displayed in the message line.
C-a M (monitor)
Toggles monitoring of the current window.
C-a C-n (next) Switch to the next window.
C-a N (number)
Show the number (and title) of the current window.
C-a C-p (prev) Switch to the previous window (opposite of C-a n).
C-a C-q (xon) Send a control-q to the current window.
C-a Q (only) Delete all regions but the current one.
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 C-s (xoff) Send a control-s to the current window.
C-a S (split)
Split the current region into two new ones.
C-a C-t (time) Show system information.
C-a v (version)
Display the version and compilation date.
C-a C-v (digraph)
C-a C-w (windows)
Show a list of window.
C-a W (width)
Toggle 80/132 columns.
C-a C-x (lockscreen)
Lock this terminal.
C-a X (remove)
Kill the current region.
C-a C-z (suspend)
Suspend screen. Your system must support BSD-style job-control.
C-a Z (reset)
Reset the virtual terminal to its ``power-on'' values.
C-a . (dumptermcap)
Write out a ``.termcap'' file.
C-a ? (help) Show key bindings.
C-a C-\ (quit) Kill all windows and terminate screen.
C-a : (colon)
Enter command line mode.
C-a esc (copy) Enter copy/scrollback mode.
C-a ] (paste .)
Write the contents of the paste buffer to the stdin queue of the current window.
C-a } (history)
Copy and paste a previous (command) line.
Write paste buffer to a file.
Reads the screen-exchange file into the paste buffer.
C-a = (removebuf)
Removes the file used by C-a and C-a .
C-a , (license)
Shows where screen comes from, where it went to and why you can use it.
C-a _ (silence)
Start/stop monitoring the current window for inactivity.
C-a * (displays)
The ``socket directory defaults either to $HOME/.screen or simply to /tmp/screens or preferably to /var/run/screen chosen at compile-time. If screen is installed setuid-root, then the administrator should compile screen with an adequate (not NFS mounted) socket directory. If screen'' is not running setuid-root, the user can specify any mode 700 directory in the environment variable $SCREENDIR.
When screen is invoked, it executes initialization commands from the files ``/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 (this override feature may be disabled at compile-time). The user specific screenrc file is searched in $SCREENRC, then $HOME/.screenrc. The command line option -c takes precedence over the above user screenrc files.
Commands in these files are used to set options, bind functions to keys, and to automatically establish one or more windows at the beginning of your screen session. Commands are listed one per line, with empty lines being ignored. A command's arguments are separated by tabs or spaces, and may be surrounded by single or double quotes. A `#' turns the rest of the line into a comment, except in quotes. Unintelligible lines are warned about and ignored. Commands may contain references to environment variables. The syntax is the shell-like screen versions, as now the '$'-character has to be protected with '' if no variable substitution shall be performed. A string in single-quotes is also protected from variable substitution.
Two configuration files are shipped as examples with your screen distribution: ``etc/screenrc and ``etc/etcscreenrc. They contain a number of useful examples for various commands.
Customization can also be done 'on-line'. To enter the command mode type `C-a :'. Note that commands starting with ``def'' change default values, while others change current settings.
The following commands are available:
acladd usernames [''crypted-pw''? addacl usernames
Enable users to fully access this screen session. Usernames can be one user or a comma separated list of users. This command enables to attach to the screen session and performs the equivalent of `aclchg usernames +rwx ''
aclchg usernames permbits list chacl usernames permbits list
Change permissions for a comma separated list of users. Permission bits are represented as `r', `w' and `x'. Prefixing `+' grants the permission, `-' removes it. The third parameter is a comma separated list of commands and/or windows (specified either by number or title). The special list `#' refers to all windows, `?' to all commands. if usernames consists of a single `*', all known users are affected. A command can be executed when the user has the `x' bit for it. The user can type input to a window when he has its `w' bit set and no other user obtains a writelock for this window. Other bits are currently ignored. To withdraw the writelock from another user in window 2: `aclchg username -w+w 2'. To allow read-only access to the session: `aclchg username -w screen he can attach to the session and (per default) has full permissions for all command and windows. Execution permission for the acl commands, `at' and others should also be removed or the user may be able to regain write permission. Rights of the special username nobody cannot be changed (see the ``su'' command). `Chacl' is a synonym to `aclchg'. Multi user mode only.
Remove a user from screen's access control list. If currently attached, all the user's displays are detached from the session. He cannot attach again. Multi user mode only.
aclgrp username [''groupname''?
Creates groups of users that share common access rights. The name of the group is the username of the group leader. Each member of the group inherits the permissions that are granted to the group leader. That means, if a user fails an access check, another check is made for the group leader. A user is removed from all groups the special value ``none is used for groupname''. If the second parameter is omitted all groups the user is in are listed.
This specifies the access other users have to windows that will be created by the caller of the command. Users may be no, one or a comma separated list of known usernames. If no users are specified, a list of all currently known users is assumed. Bits is any combination of access control bits allowed defined with the ``aclchg command. The special username ``? predefines the access that not yet known users will be granted to any window initially. The special username ``?? predefines the access that not yet known users are granted to any command. Rights of the special username nobody cannot be changed (see the ``su command). `Umask' is a synonym to `aclumask'.
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 `^G' is replaced by the definition for bell in your termcap (usually an audible bell). The default message is
'Activity in window %n'
Note that monitoring is off for all windows by default, but can be altered by use of the ``monitor'' command (C-a M).
If set to on, only the current cursor line is refreshed on window change. This affects all windows and is useful for slow terminal lines. The previous setting of full/partial refresh for each window is restored with ``allpartial off. This is a global flag that immediately takes effect on all windows overriding the ``partial settings. It does not change the default redraw behavior of newly created windows.
Execute a command at other displays or windows as if it had been entered there. ``At changes the context (the `current window' or `current display' setting) of the command. If the first parameter describes a non-unique context, the command will be executed multiple times. If the first parameter is of the form `identifier' then identifier is matched against user names. The command is executed once for each display of the selected user(s). If the first parameter is of the form `identifier%' identifier is matched against displays. Displays are named after the ttys they attach. The prefix `/dev/' or `/dev/tty' may be omitted from the identifier. If identifier has a `#' or nothing appended it is matched against window numbers and titles. Omitting an identifier in front of the `#', `' or `%'-character selects all users, displays or windows because a prefix-match is performed. Note that on the affected display(s) a short message will describe what happened. Permission is checked for initiator of the ``at command, not for the owners of the affected display(s). Note that the '#' character works as a comment introducer when it is preceded by whitespace. This can be escaped by prefixing a . Permission is checked for the initiator of the ``at command, not for the owners of the affected display(s). Caveat: When matching against windows, the command is executed at least once per window. Commands that change the internal arrangement of windows (like ``other) may be called again. In shared windows the command will be repeated for each attached display. Beware, when issuing toggle commands like ``login! Some commands (e.g. ``stuff, ``process or ``paste) require that a display is associated with the target windows. These commands may not work correctly under ``at looping over windows.
This command can be used to highlight attributes by changing the color of the text. If the attribute attrib is in use, the specified attribute/color modifier is also applied. If no modifier is given, the current one is deleted. See the ``STRING ESCAPES chapter for the syntax of the modifier. Screen understands two pseudo-attributes, ``i stands for high-intensity foreground color and ``I'' for high-intensity background color.
Change the color to bright red if bold text is to be printed.
Use blue text instead of underline.
Use bright colors for bold text. Most terminal emulators do this already.
Make bright colored text also bold.
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.
Sets whether a clear screen sequence should nuke all the output that has not been written to the terminal. See also ``obuflimit''.
Change background-color-erase setting. If ``bce'' is set to on, all characters cleared by an erase/insert/scroll/clear operation will be displayed in the current background color. Otherwise the default background color is used.
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 this 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 `^G' is replaced by the definition for bell in your termcap (usually an audible bell). The default message is
'Bell in window %n'
An empty message can be supplied to the ``bell_msg'' command to suppress output of a message line (bell_msg
Bind a command to a key. By default, most of the commands provided by screen are bound to one or more keys as indicated in the ``DEFAULT KEY BINDINGS section, e.g. the command 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 command argument can be any command listed in this section.
If a command class is specified via the ``-c option, the key is bound for the specified class. Use the ``command command to activate a class. Command classes can be used to create multiple command keys or multi-character bindings.
bind ^k bind k bind K kill bind ^f screen telnet foobar bind 033 screen -ln -t root -h 1000 9 su would bind the space key to the command that displays a list of windows (so that the command usually invoked by ``C-a C-w would also be available as ``C-a space). The next three lines remove the default kill binding from ``C-a C-k and ``C-a k. ``C-a K is then bound to the kill command. Then it binds ``C-f to the command ``create a window with a TELNET connection to foobar, and bind ``escape to the command that creates an non-login window with a.k.a. ``root'' in slot #9, with a superuser shell and a scrollback buffer of 1000 lines.
bind -c demo1 1 select 11 bind -c demo1 2 select 12 bindkey makes ``C-b 0 select window 10, ``C-b 1 window 11, etc.
bind -c demo2 1 select 11 bind -c demo2 2 select 12 bind - command -c demo2 makes ``C-a - 0 select window 10, ``C-a - 1 window 11, etc.
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