Screen
GNU screen is a terminal multiplexer, i.e. it lets you run many command-line applications from one console or terminal emulator window.
OverView
Screen allows you to
- detach from a program, leave it running, and attach from another computer. You will not lose any work.
- work collaboratively on a console, every connected person can type or watch the other typing. You can teach others or give support.
- log your session
Another underrated benefit is that you can switch between terminals without resorting to the mouse.
If you want to attach (screen -x) and there are multiple screen sessions available, the program will then list the available screen sessions. For example:
There are screens on:
2463.pts-2.atreus (Attached)
11068.lab (Attached)
2 Sockets in /tmp/screens/S-keithh.
In this case, the user can explicitly specify the desired session using an unambiguous substring of the session name. In the above example, screen -x 11068 and screen -x lab are equivalent and both users will now share the same session. Because each session can contain multiple PTYs, each user can independently switch between the them. They can also share the same PTY in which case they will each see the same display and can each type commands.
Using Screen
To start a new screen, open a console and enter:
screen
If you lose your connection, you can resume your screen by calling
screen -r
If you want to share a screen session with another user, let him log in as your user and call
screen -x
Screen can be controlled while it is running by prefacing commands with the command-key character. By default, this is Control-A. For instance, to view the help screen enter Ctrl-a ? The detach command is Control-a Control-D.
Control-a, Control-c creates a new terminal screen
Control-a, " shows a list of terminal screens
Control-a, n switch to the next screen
Control-a, p switch to the previous screen
Control-a, a switches to the most-recently-used screen
Control-a, d kills the actual shell
Control-a, c creates a new shell
Control-a, A renames the current shell
Control-a, H logs your session to a plain-text file
Customizing Screen
The man page for screen details a large number of options but the following examples will illustrate many of the more useful features. By default, screen checks for a ~/.screenrc file and failing that the /etc/screenrc file. Here is my default screenrc:
defflow auto # Scrollback buffer size in lines defscrollback 5000 # modify the termcap/terminfo when I'm using XTerm. terminfo xterm* LP # Support alternate screens so that, for example, when you # quit out of vi, the display is redrawn as it was before vi # redrew the full screen. altscreen on # don't display the copyright page startup_message off # detach on hangup - if my dial-up session fails, screen will simply # detach and let me re re-attach later. autodetach on msgwait 2 # 1 second messages # Start a number of initial shells and give them titles which show up in the status-line screen -t CCase 0 bash screen -t Sun1 1 bash screen -t Sun2 2 bash screen -t CCase 3 bash screen -t Rich 6 bash screen -t Pine 7 bash screen -t Pine 8 bash screen -t News 9 bash screen # remove some stupid / dangerous key bindings bind k bind W bind ^k bind . bind ^\ bind \\ bind ^h bind h #make them better bind 'K' kill #bind 'I' login on #bind 'O' login off #bind '}' history bind 'W' windowlist
I can create an alternate configuration file as follows:
... sessionname lab # Call this session "lab" caption always # Leave the status line on permanently caption string "LAB %t - %w" msgwait 2 # 1 second messages screen -t CP 0 bash screen -t CAC 1 bash screen -t FTP 2 bash screen -t xterm 3 bash screen ...
This can be made easier to use by defining an alias for the command:
- screen -d -R lab -t LAB -c ~/.screenrc-lab
The -d -R lab option means detach and resume the session named lab and if no such session exists then create it.
The -t LAB option simply puts a title on the status line.
And -c ~/.screenrc-lab specifies the alternate configuration file to use.
External links
- kuro5hin: GNU screen: an introduction and beginner's tutorial (www.kuro5hin.org)
- Screen FAQ (www4.informatik.uni-erlangen.de)