NAME¶

screen - screen manager with VT100/ANSI terminal emulation

SYNOPSIS¶

screen [ -options ] [ cmd [ args ] ]
screen -r [[pid.]tty[.host]]
screen -r sessionowner/[[pid.]tty[.host]]

DESCRIPTION¶

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. Shells usually distinguish between running as login-shell or sub-shell. Screen runs them as sub-shells, unless told otherwise (See shell .screenrc command).

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, although this notation is used in this manual for readability. 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:

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 (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. - Note that you cannot transport environment variables from the invoking shell to the application (emacs in this case), because it is forked from the parent screen process, not from the invoking shell.

If /run/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 terminal's own record is removed from the utmp file. See also C-a L.

GETTING STARTED¶

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 test 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 using 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.

COMMAND-LINE OPTIONS¶

Screen has the following 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 current terminal. By default, screen tries to restore its old window sizes when attaching to resizable terminals (those with WS in its description, e.g. suncmd or some xterm).

-c file

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

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

does not start screen, but detaches 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. In combination with the -r/-R option more powerful effects can be achieved:

-d -r

Reattach a session and if necessary detach it first.

-d -R

Reattach a session and if necessary detach or even create it first.

-d -RR

Reattach a session and if necessary detach or create it. Use the first session if more than one session is available.

-D -r

Reattach a session. If necessary detach and logout remotely first.

-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.

-D -RR

Attach here and now. Whatever that means, just do it.

Note: It is always a good idea to check the status of your sessions 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. When creating a screen session, this option sets the default command character. In a multiuser session all users added will start off with this command character. But when attaching to an already running session, this option changes only the command character of the attaching user. This option is equivalent to either the commands defescape or escape respectively.

-f, -fn, and -fa

turns flow-control on, off, or automatic switching mode. This can also be defined through the defflow .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 defflow .screenrc command for details. The use of this option is discouraged.

-l and -ln

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

-ls [match]

-list [match]

does not start screen, but prints a list of pid.tty.host strings and creation timestamps identifying your screen sessions. Sessions marked `detached' can be resumed with screen -r. Those marked `attached' are running and have a controlling terminal. If the session runs in multiuser mode, it is marked `multi'. Sessions marked as `unreachable' either live on a different host or are `dead'. An unreachable session is considered dead, when its name matches either the name of the local host, or the specified parameter, if any. See the -r flag for a description how to construct matches. 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.

-L

tells screen to turn on automatic output logging for the windows.

-Logfile file

By default logfile name is screenlog.0. You can set new logfile name with the -Logfile option.

-m

causes screen to ignore the $STY environment variable. With screen -m creation of a new session is enforced, regardless whether screen is called from within another screen session or not. This flag has a special meaning in connection with the `-d' option:

-d -m

Start screen in detached mode. This creates a new session but doesn't attach to it. This is useful for system startup scripts.

-D -m

This also starts screen in detached mode, but doesn't fork a new process. The command exits if the session terminates.

-O

selects an 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.

-p number_or_name|-|=|+

Preselect a window. This is useful when you want to reattach to a specific window or you want to send a command via the -X option to a specific window. As with screen's select command, - selects the blank window. As a special case for reattach, = brings up the windowlist on the blank window, while a + will create a new window. The command will not be executed if the specified window could not be found.

-q

Suppress printing of error messages. In combination with -ls the exit value is as follows: 9 indicates a directory without sessions. 10 indicates a directory with running but not attachable sessions. 11 (or more) indicates 1 (or more) usable sessions. In combination with -r the exit value is as follows: 10 indicates that there is no session to resume. 12 (or more) indicates that there are 2 (or more) sessions to resume and you should specify which one to choose. In all other cases -q has no effect.

-Q

Some commands now can be queried from a remote session using this flag, e.g. screen -Q windows. The commands will send the response to the stdout of the querying process. If there was an error in the command, then the querying process will exit with a non-zero status.

The commands that can be queried now are:
echo
info
lastmsg
number
select
time
title
windows

-r [pid.tty.host]

-r sessionowner/[pid.tty.host]

resumes a detached screen session. No other options (except combinations with -d/-D) may be specified, though an optional prefix of [pid.]tty.host may be needed to distinguish between multiple detached screen sessions. The second form is used to connect to another user's screen session which runs in multiuser mode. This indicates that screen should look for sessions in another user's directory. This requires setuid-root.

-R

resumes screen only when it's unambiguous which one to attach, usually when only one screen is detached. Otherwise lists available sessions. -RR attempts to resume the youngest (in terms of creation time) 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 had not been specified. The option is set by default if screen is run as a login-shell (actually screen uses -xRR in that case). For combinations with the -d/-D option see there. Note: Time-based session selection is a Debian addition.

-s program

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. See also there.

-S sessionname

When creating a new session, this option can be used to specify a meaningful name for the session. This name identifies the session for screen -list and screen -r actions. It substitutes the default [tty.host] suffix. This name should not be longer then 80 symbols.

-t name

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

-T term

Set the $TERM environment variable using the specified term as opposed to the default setting of screen.

-U

Run screen in UTF-8 mode. This option tells screen that your terminal sends and understands UTF-8 encoded characters. It also sets the default encoding for new windows to `utf8'.

-v

Print version number.

-wipe [match]

does the same as screen -ls, but removes destroyed sessions instead of marking them as `dead'. An unreachable session is considered dead, when its name matches either the name of the local host, or the explicitly given parameter, if any. See the -r flag for a description how to construct matches.

-x

Attach to a not detached screen session. (Multi display mode). Screen refuses to attach from within itself. But when cascading multiple screens, loops are not detected; take care.

-X

Send the specified command to a running screen session. You may use the -S option to specify the screen session if you have several screen sessions running. You can use the -d or -r option to tell screen to look only for attached or detached screen sessions. Note that this command doesn't work if the session is password protected.

-4

Resolve hostnames only to IPv4 addresses.

-6

Resolve hostnames only to IPv6 addresses.

DEFAULT KEY BINDINGS¶

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. The trailing commas in boxes with multiple keystroke entries are separators, not part of the bindings.

CUSTOMIZATION¶

The socket directory defaults either to $HOME/.screen or simply to /tmp/screens or preferably to /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 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 "$VAR " or "${VAR}". Note that this causes incompatibility with previous 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

aclchg usernames permbits list

chacl usernames permbits list

acldel username

aclgrp username [groupname]

aclumask [[ users ] +bits | [ users ] -bits... ]

umask [[ users ] +bits | [ users ] -bits... ]

activity message

	'Activity in window %n'

allpartial [ on | off ]

altscreen [ on | off ]

at [identifier][#|*|%] command [args ... ]

attrcolor attrib [attribute/color-modifier]

autodetach [ on | off ]

autonuke [ on | off ]

backtick id lifespan autorefresh cmd args...

backtick id

bce [ on | off ]

bell_msg [message]

	'Bell in window %n'

bind [class] key [command [args]]

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

	bind -c demo1 0 select 10
	bind -c demo1 1 select 11
	bind -c demo1 2 select 12
	bindkey "^B" command -c demo1

	bind -c demo2 0 select 10
	bind -c demo2 1 select 11
	bind -c demo2 2 select 12
	bind - command -c demo2

bindkey [-d] [-m] [-a] [[-k|-t] string [cmd-args]]

        bindkey -d

        bindkey -k k1 select 1

        bindkey -t foo stuff barfoo

        bindkey "\024" mapdefault

        bindkey -k F1 command

break [duration]

blanker

blankerprg [program-args]

breaktype [tcsendbreak|TIOCSBRK|TCSBRK]

bufferfile [exchange-file]

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

bumpright

c1 [ on | off ]

caption [ top | bottom ] always|splitonly[string]

caption string [string]

charset set

chdir [directory]

cjkwidth [ on | off ]

clear

collapse

colon [prefix]

command [ -c class"]"

compacthist [ on | off ]

console [ on | off ]

copy

copy_reg [key]

crlf [ on | off ]

debug [ on | off ]

defc1 [ on | off ]

defautonuke [ on | off ]

defbce [ on | off ]

defbreaktype [tcsendbreak|TIOCSBRK|TCSBRK]

defcharset [set]

defdynamictitle [ on | off ]

defescape xy

defflow [ on | off | auto [ interrupt ]]

defgr [ on | off ]

defhstatus [status]

defencoding enc

deflog [ on | off ]

deflogin [ on | off ]

defmode mode

defmonitor [ on | off]

defmousetrack [ on | off ]

defnonblock [ on | off | numsecs]

defobuflimit limit

defscrollback num

defshell command

defsilence [ on | off ]

defslowpaste msec

defutf8 [ on | off ]

defwrap [ on | off ]

defwritelock [ on | off | auto ]

detach [-h]

dinfo

displays

xterm 80x42 jnweiger@/dev/ttyp4     0(m11)   &rWx
facit 80x24 mlschroe@/dev/ttyhf nb 11(tcsh)   rwx
xterm 80x42 jnhollma@/dev/ttyp5     0(m11)   &R.x


 (A)   (B)     (C)     (D)     (E) (F)(G)   (H)(I)

    bind h focus left


    bind j focus down


    bind k focus up


    bind l focus right


    bind t focus top


    bind b focus bottom

	C-a : layout dump /home/user/.screenrc

	C-a : readreg p /etc/passwd
	C-a : paste p

screen [-opts] [n] [cmd [args]|//group]

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

scrollback num

select [WindowID]

sessionname [name]

setenv [var [string]]

setsid [ on | off ]

shell command

shelltitle title

silence [ on | off | sec ]

silencewait sec

termcap vt*  LP

THE MESSAGE LINE¶

Screen displays informational messages and other diagnostics in a message line. While this line is distributed to appear at the bottom of the screen, it can be defined to appear at the top of the screen during compilation. If your terminal has a status line defined in its termcap, screen will use this for displaying its messages, otherwise a line of the current screen will be temporarily overwritten and output will be momentarily interrupted. The message line is automatically removed after a few seconds delay, but it can also be removed early (on terminals without a status line) by beginning to type.

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 from window '$WINDOW'<esc>\\'

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

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.

• 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):

•

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.

STRING ESCAPES¶

Screen provides an escape mechanism to insert information like the current time into messages or file names. The escape character is '%' with one exception: inside of a window's hardstatus '^%' ('^E') is used instead.

Here is the full list of supported escapes:

%

the escape character itself

E

sets %? to true if the escape character has been pressed.

e

encoding

f

flags of the window, see windows for meanings of the various flags

F

sets %? to true if the window has the focus

h

hardstatus of the window

H

hostname of the system

n

window number

P

sets %? to true if the current region is in copy/paste mode

S

session name

s

window size

t

window title

u

all other users on this window

w

all window numbers and names. With '-' qualifier: up to the current window; with '+' qualifier: starting with the window after the current one.

W

all window numbers and names except the current one

x

the executed command including arguments running in this windows

X

the executed command without arguments running in this windows

?

the part to the next '%?' is displayed only if a '%' escape inside the part expands to a non-empty string

:

else part of '%?'

=

pad the string to the display's width (like TeX's hfill). If a number is specified, pad to the percentage of the window's width. A '0' qualifier tells screen to treat the number as absolute position. You can specify to pad relative to the last absolute pad position by adding a '+' qualifier or to pad relative to the right margin by using '-'. The padding truncates the string if the specified position lies before the current position. Add the 'L' qualifier to change this.

<

same as '%=' but just do truncation, do not fill with spaces

>

mark the current text position for the next truncation. When screen needs to do truncation, it tries to do it in a way that the marked position gets moved to the specified percentage of the output area. (The area starts from the last absolute pad position and ends with the position specified by the truncation operator.) The 'L' qualifier tells screen to mark the truncated parts with '...'.

{

attribute/color modifier string terminated by the next }

`

Substitute with the output of a 'backtick' command. The length qualifier is misused to identify one of the commands.

The 'c' and 'C' escape may be qualified with a '0' to make screen use zero instead of space as fill character. The '0' qualifier also makes the '=' escape use absolute positions. The 'n' and '=' escapes understand a length qualifier (e.g. '%3n'), 'D' and 'M' can be prefixed with 'L' to generate long names, 'w' and 'W' also show the window flags if 'L' is given.

An attribute/color modifier is used to change the attributes or the color settings. Its format is [attribute modifier] [color description]. The attribute modifier must be prefixed by a change type indicator if it can be confused with a color description. The following change types are known:

+

add the specified set to the current attributes

-

remove the set from the current attributes

!

invert the set in the current attributes

=

change the current attributes to the specified set

The attribute set can either be specified as a hexadecimal number or a combination of the following letters:

d

dim

u

underline

b

bold

r

reverse

s

/standout

B

blinking

Colors are coded either as a hexadecimal number or two letters specifying the desired background and foreground color (in that order). The following colors are known:

k

black

r

red

g

green

y

yellow

b

blue

m

magenta

c

cyan

w

white

d

default color

.

leave color unchanged

The capitalized versions of the letter specify bright colors. You can also use the pseudo-color 'i' to set just the brightness and leave the color unchanged.
A one digit/letter color description is treated as foreground or background color dependent on the current attributes: if reverse mode is set, the background color is changed instead of the foreground color. If you don't like this, prefix the color with a .. If you want the same behavior for two-letter color descriptions, also prefix them with a ..
As a special case, %{-} restores the attributes and colors that were set before the last change was made (i.e., pops one level of the color-change stack).

Examples:

G

set color to bright green

+b r

use bold red

= yd

clear all attributes, write in default color on yellow background.

%-Lw%{= BW}%50>%n%f* %t%{-}%+Lw%<

The available windows centered at the current window and truncated to the available width. The current window is displayed white on blue. This can be used with hardstatus alwayslastline.

%?%F%{.R.}%?%3n %t%? [%h]%?

The window number and title and the window's hardstatus, if one is set. Also use a red background if this is the active focus. Useful for caption string.

FLOW-CONTROL¶

Each window has a flow-control setting that determines how screen deals with the XON and XOFF characters (and perhaps the interrupt character). When flow-control is turned off, screen ignores the XON and XOFF characters, which allows the user to send them to the current program by simply typing them (useful for the emacs editor, for instance). The trade-off is that it will take longer for output from a normal program to pause in response to an XOFF. With flow-control turned on, XON and XOFF characters are used to immediately pause the output of the current window. You can still send these characters to the current program, but you must use the appropriate two-character screen commands (typically C-a q (xon) and C-a s (xoff)). The xon/xoff commands are also useful for typing C-s and C-q past a terminal that intercepts these characters.

Each window has an initial flow-control value set with either the -f option or the defflow .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 'automatic' interactively with the flow command bound to "C-a f".

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.

TITLES (naming windows)¶

You can customize each window's name in the window display (viewed with the windows command (C-a w)) by setting it with one of the title commands. Normally the name displayed is the actual command name of the program created in the window. However, it is sometimes useful to distinguish various programs of the same name or to change the name on-the-fly to reflect the current state of the window.

The default name for all shell windows can be set with the shelltitle 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 title-string escape-sequence (<esc>kname<esc>\) and the title 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 title command to set things quickly without prompting. Changing title by this escape sequence can be controlled by defdynamictitle and dynamictitle commands.

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 title 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 title-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 title. Once this is set up, screen will use the title-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 nice-d version of the top command in window 2 named top rather than nice.

	shelltitle '> |csh'
	screen 1

These commands would start a shell with the given shelltitle. The title specified is an auto-title 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-title name of root:. For this auto-title 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 title
	bind E title ""
	bind u title (unknown)

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

One thing to keep in mind when adding a null title-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='printf "\033k\033\134"'

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

THE VIRTUAL TERMINAL¶

Each window in a screen session emulates a VT100 terminal, with some extra functions added. The VT100 emulator is hard-coded, no other terminal types can be emulated.
Usually screen tries to emulate as much of the VT100/ANSI standard as possible. But if your terminal lacks certain capabilities, the emulation may not be complete. In these cases screen has to tell the applications that some of the features are missing. This is no problem on machines using termcap, because screen can use the $TERMCAP variable to customize the standard screen termcap.

But if you do a rlogin on another machine or your machine supports only terminfo this method fails. Because of this, screen offers a way to deal with these cases. Here is how it works:

When screen tries to figure out a terminal name for itself, it first looks for an entry named screen.<term>, where <term> is the contents of your $TERM variable. If no such entry exists, screen tries screen (or screen-w if the terminal is wide (132 cols or more)). If even this entry cannot be found, vt100 is used as a substitute.

The idea is that if you have a terminal which doesn't support an important feature (e.g. delete char or clear to EOS) you can build a new termcap/terminfo entry for screen (named screen.<dumbterm>) in which this capability has been disabled. If this entry is installed on your machines you are able to do a rlogin and still keep the correct termcap/terminfo entry. The terminal name is put in the $TERM variable of all new windows. Screen also sets the $TERMCAP variable reflecting the capabilities of the virtual terminal emulated. Notice that, however, on machines using the terminfo database this variable has no effect. Furthermore, the variable $WINDOW is set to the window number of each window.

The actual set of capabilities supported by the virtual terminal depends on the capabilities supported by the physical terminal. If, for instance, the physical terminal does not support underscore mode, screen does not put the `us' and `ue' capabilities into the window's $TERMCAP variable, accordingly. However, a minimum number of capabilities must be supported by a terminal in order to run screen; namely scrolling, clear screen, and direct cursor addressing (in addition, screen does not run on hardcopy terminals or on terminals that over-strike).

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 is 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. The info command displays a line starting `PRIN' while the printer is active.

Screen maintains a hardstatus line for every window. If a window gets selected, the display's hardstatus will be updated to match the window's hardstatus line. If the display has no hardstatus the line will be displayed as a standard screen message. The hardstatus line can be changed with the ANSI Application Program Command (APC): ESC_<string>ESC\. As a convenience for xterm users the sequence ESC]0..2;<string>^G is also accepted.

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 "alternate screen" capability is not enabled by default. Set the altscreen .screenrc command to enable it.

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 Z

Send VT100 Identification String

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 g

Visual Bell

ESC Pn p

Cursor Visibility (97801)

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 !

Global 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 (Hardstatus)

ESC ] 0 ; string ^G (A)

Operating System Command (Hardstatus, xterm title hack)

ESC ] 83 ; cmd ^G (A)

Execute screen command. This only works if multi-user support is compiled into screen. The pseudo-user :window: is used to check the access control list. Use addacl :window: -rwx #? to create a user with no rights and allow only the needed commands.

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

same as above

ESC [ Pn J

Erase in Display

ESC [ Pn K

Erase in Line

ESC [ Pn X

Erase character

ESC [ Pn A

Cursor Up

ESC [ Pn B

Cursor Down

ESC [ Pn C

Cursor Right

ESC [ Pn D

Cursor Left

ESC [ Pn E

Cursor next line

ESC [ Pn F

Cursor previous line

ESC [ Pn G

Cursor horizontal position

ESC [ Pn `

same as above

ESC [ Pn d

Cursor vertical position

ESC [ Ps ;...; Ps m

Select Graphic Rendition

ESC [ Pn g

Tab Clear

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 [ Pn S

Scroll Scrolling Region Up

ESC [ Pn T

Scroll Scrolling Region Down

ESC [ Pn ^

same as above

ESC [ Ps ;...; Ps h

Set Mode

ESC [ Ps ;...; Ps l

Reset Mode

ESC [ 5 i (A)

Start relay to printer (ANSI Media Copy)

ESC [ 4 i (A)

Stop relay to printer (ANSI Media Copy)

ESC [ 8 ; Ph ; Pw t

Resize the window to `Ph' lines and `Pw' columns (SunView special)

ESC [ c

Send VT100 Identification String

ESC [ x

Send Terminal Parameter Report

ESC [ > c

Send VT220 Secondary Device Attributes String

ESC [ 6 n

Send Cursor Position Report

INPUT TRANSLATION¶

In order to do a full VT100 emulation screen has to detect that a sequence of characters in the input stream was generated by a keypress on the user's keyboard and insert the VT100 style escape sequence. Screen has a very flexible way of doing this by making it possible to map arbitrary commands on arbitrary sequences of characters. For standard VT100 emulation the command will always insert a string in the input buffer of the window (see also command stuff in the command table). Because the sequences generated by a keypress can change after a reattach from a different terminal type, it is possible to bind commands to the termcap name of the keys. Screen will insert the correct binding after each reattach. See the bindkey command for further details on the syntax and examples.

Here is the table of the default key bindings. The fourth is what command is executed if the keyboard is switched into application mode.

SPECIAL TERMINAL CAPABILITIES¶

The following table describes all terminal capabilities that are recognized by screen and are not in the termcap(5) manual. You can place these capabilities in your termcap entries (in `/etc/termcap') or use them with the commands `termcap', `terminfo' and `termcapinfo' in your screenrc files. It is often not possible to place these capabilities in the terminfo database.

LP (bool)

Terminal has VT100 style margins (`magic margins'). Note that this capability is obsolete because screen uses the standard 'xn' instead.

Z0 (str)

Change width to 132 columns.

Z1 (str)

Change width to 80 columns.

WS (str)

Resize display. This capability has the desired width and height as arguments. SunView(tm) example: '\E[8;%d;%dt'.

NF (bool)

Terminal doesn't need flow control. Send ^S and ^Q direct to the application. Same as 'flow off'. The opposite of this capability is 'nx'.

G0 (bool)

Terminal can deal with ISO 2022 font selection sequences.

S0 (str)

Switch charset 'G0' to the specified charset. Default is '\E(%.'.

E0 (str)

Switch charset 'G0' back to standard charset. Default is '\E(B'.

C0 (str)

Use the string as a conversion table for font '0'. See the 'ac' capability for more details.

CS (str)

Switch cursor-keys to application mode.

CE (str)

Switch cursor-keys back to normal mode.

AN (bool)

Turn on autonuke. See the 'autonuke' command for more details.

OL (num)

Set the output buffer limit. See the 'obuflimit' command for more details.

KJ (str)

Set the encoding of the terminal. See the 'encoding' command for valid encodings.

AF (str)

Change character foreground color in an ANSI conform way. This capability will almost always be set to '\E[3%dm' ('\E[3%p1%dm' on terminfo machines).

AB (str)

Same as 'AF', but change background color.

AX (bool)

Does understand ANSI set default fg/bg color (\E[39m / \E[49m).

XC (str)

Describe a translation of characters to strings depending on the current font. More details follow in the next section.

XT (bool)

Terminal understands special xterm sequences (OSC, mouse tracking).

C8 (bool)

Terminal needs bold to display high-intensity colors (e.g. Eterm).

TF (bool)

Add missing capabilities to the termcap/info entry. (Set by default).

CHARACTER TRANSLATION¶

Screen has a powerful mechanism to translate characters to arbitrary strings depending on the current font and terminal type. Use this feature if you want to work with a common standard character set (say ISO8851-latin1) even on terminals that scatter the more unusual characters over several national language font pages.

Syntax:

    XC=<charset-mapping>{,,<charset-mapping>}


    <charset-mapping> := <designator><template>{,<mapping>}


    <mapping> := <char-to-be-mapped><template-arg>

The things in braces may be repeated any number of times.

A <charset-mapping> tells screen how to map characters in font <designator> ('B': Ascii, 'A': UK, 'K': German, etc.) to strings. Every <mapping> describes to what string a single character will be translated. A template mechanism is used, as most of the time the codes have a lot in common (for example strings to switch to and from another charset). Each occurrence of '%' in <template> gets substituted with the <template-arg> specified together with the character. If your strings are not similar at all, then use '%' as a template and place the full string in <template-arg>. A quoting mechanism was added to make it possible to use a real '%'. The '\' character quotes the special characters '\', '%', and ','.

Here is an example:

termcap hp700 'XC=B\E(K%\E(B,\304[,\326\\\\,\334]'

This tells screen how to translate ISOlatin1 (charset 'B') upper case umlaut characters on a hp700 terminal that has a German charset. '\304' gets translated to '\E(K[\E(B' and so on. Note that this line gets parsed *three* times before the internal lookup table is built, therefore a lot of quoting is needed to create a single '\'.

Another extension was added to allow more emulation: If a mapping translates the unquoted '%' char, it will be sent to the terminal whenever screen switches to the corresponding <designator>. In this special case the template is assumed to be just '%' because the charset switch sequence and the character mappings normally haven't much in common.

This example shows one use of the extension:

termcap xterm 'XC=K%,%\E(B,[\304,\\\\\326,]\334'

Here, a part of the German ('K') charset is emulated on an xterm. If screen has to change to the 'K' charset, '\E(B' will be sent to the terminal, i.e. the ASCII charset is used instead. The template is just '%', so the mapping is straightforward: '[' to '\304', '\' to '\326', and ']' to '\334'.

ENVIRONMENT¶

COLUMNS

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

HOME

Directory in which to look for .screenrc.

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). See also shell .screenrc command.

STY

Alternate socket name.

SYSSCREENRC

Alternate system screenrc file.

TERM

Terminal name.

TERMCAP

Terminal description.

WINDOW

Window number of a window (at creation time).

FILES¶

.../screen-4.?.??/etc/screenrc

.../screen-4.?.??/etc/etcscreenrc

Examples in the screen distribution package for private and global initialization files.

$SYSSCREENRC

/etc/screenrc

screen initialization commands

$SCREENRC

$HOME/.screenrc

Read in after /etc/screenrc

$SCREENDIR/S-<login>

/run/screen/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

/run/utmp

Login records

$LOCKPRG

Program that locks a terminal.

AUTHORS¶

Originally created by Oliver Laumann. For a long time maintained and developed by Juergen Weigert, Michael Schroeder, Micah Cowan and Sadrul Habib Chowdhury. Since 2015 maintained and developed by Amadeusz Slawinski <amade@asmblr.net> and Alexander Naumov <alexander_naumov@opensuse.org>.

COPYLEFT¶

Copyright (c) 2018-2023
	Alexander Naumov <alexander_naumov@opensuse.org>
	Amadeusz Slawinski <amade@asmblr.net>
Copyright (c) 2015-2017
	Juergen Weigert <jnweiger@immd4.informatik.uni-erlangen.de>
	Alexander Naumov <alexander_naumov@opensuse.org>
	Amadeusz Slawinski <amade@asmblr.net>
Copyright (c) 2010-2015
	Juergen Weigert <jnweiger@immd4.informatik.uni-erlangen.de>
	Sadrul Habib Chowdhury <sadrul@users.sourceforge.net>
Copyright (c) 2008, 2009
	Juergen Weigert <jnweiger@immd4.informatik.uni-erlangen.de>
	Michael Schroeder <mlschroe@immd4.informatik.uni-erlangen.de>
	Micah Cowan <micah@cowan.name>
	Sadrul Habib Chowdhury <sadrul@users.sourceforge.net>
Copyright (C) 1993-2003
	Juergen Weigert <jnweiger@immd4.informatik.uni-erlangen.de>
	Michael Schroeder <mlschroe@immd4.informatik.uni-erlangen.de>
Copyright (C) 1987 Oliver Laumann

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program (see the file COPYING); if not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA

CONTRIBUTORS¶

Vincent Lefevre <vincent@vinc17.net>,
Carl Drougge <bearded@longhaired.org>,
Maarten ter Huurne <maarten@treewalker.org>,
Jussi Kukkonen <jussi.kukkonen@intel.com>,
Eric S. Raymond <esr@thyrsus.com>,
Thomas Renninger <treen@suse.com>,
Axel Beckert <abe@deuxchevaux.org>,
Ken Beal <kbeal@amber.ssd.csd.harris.com>,
Rudolf Koenig <rfkoenig@immd4.informatik.uni-erlangen.de>,
Toerless Eckert <eckert@immd4.informatik.uni-erlangen.de>,
Wayne Davison <davison@borland.com>,
Patrick Wolfe <pat@kai.com, kailand!pat>,
Bart Schaefer <schaefer@cse.ogi.edu>,
Nathan Glasser <nathan@brokaw.lcs.mit.edu>,
Larry W. Virden <lvirden@cas.org>,
Howard Chu <hyc@hanauma.jpl.nasa.gov>,
Tim MacKenzie <tym@dibbler.cs.monash.edu.au>,
Markku Jarvinen <mta@{cc,cs,ee}.tut.fi>,
Marc Boucher <marc@CAM.ORG>,
Doug Siebert <dsiebert@isca.uiowa.edu>,
Ken Stillson <stillson@tsfsrv.mitre.org>,
Ian Frechett <frechett@spot.Colorado.EDU>,
Brian Koehmstedt <bpk@gnu.ai.mit.edu>,
Don Smith <djs6015@ultb.isc.rit.edu>,
Frank van der Linden <vdlinden@fwi.uva.nl>,
Martin Schweikert <schweik@cpp.ob.open.de>,
David Vrona <dave@sashimi.lcu.com>,
E. Tye McQueen <tye%spillman.UUCP@uunet.uu.net>,
Matthew Green <mrg@eterna.com.au>,
Christopher Williams <cgw@pobox.com>,
Matt Mosley <mattm@access.digex.net>,
Gregory Neil Shapiro <gshapiro@wpi.WPI.EDU>,
Johannes Zellner <johannes@zellner.org>,
Pablo Averbuj <pablo@averbuj.com>.

AVAILABILITY¶

The latest official release of screen available via anonymous ftp from ftp.gnu.org/gnu/screen/ or any other GNU distribution site. The home page of screen is https://savannah.gnu.org/projects/screen/ and the git repo is https://git.savannah.gnu.org/cgit/screen.git. If you want to help, send a note to screen-devel@gnu.org.

BUGS¶

• `dm' (delete mode) and `xs' are not handled correctly (they are ignored). `xn' is treated as a magic-margin indicator.
• Screen has no clue about double-high or double-wide characters. But this is the only area where vttest is allowed to fail.
• 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 on most systems 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 /run/utmp.
• Entries in /run/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.
• Screen may give a strange warning when your tty has no utmp entry.
• When the modem line was hung up, screen may not automatically detach (or quit) unless the device driver is configured to send a HANGUP signal. To detach a screen session use the -D or -d command line option.
• If a password is set, the command line options -d and -D still detach a session without asking.
• Both breaktype and defbreaktype change the break generating method used by all terminal devices. The first should change a window specific setting, where the latter should change only the default for new windows.
• When attaching to a multiuser session, the user's .screenrc file is not sourced. Each user's personal settings have to be included in the .screenrc file from which the session is booted, or have to be changed manually.
• A weird imagination is most useful to gain full advantage of all the features.

Send bug-reports, fixes, enhancements, t-shirts, money, beer & pizza to screen-devel@gnu.org.

SEE ALSO¶

termcap(5), utmp(5), vi(1), captoinfo(1), tic(1), tty(4), pty(7)