Using Screen to Keep Unix Sessions Active
In Unix, what is screen, and how do I use it?
The screen program allows you to use multiple windows (virtual VT100 terminals) in Unix.
Note: UITS does not support screen.
- If your local computer crashes, or you are connected via a modem and lose the connection, the processes or login sessions you establish through screen don’t go away. You can resume your screen sessions with the following command:
In some cases you may have to manually “detach” your screen session before resuming it. For more information, see the Knowledge Base document Using screen, why can’t I re-attach to my session after a lost connection?
The screen program creates multiple processes instead of multiple Unix login sessions, which means that it is resource-efficient.
You can cut and paste between different screens without using a mouse. Thus, you don’t need to be on a computer with a windowing environment such as Mac OS, Mac OS X, Windows, or the X Window System.
It has a block copy feature which is similar to the kill rectangle feature of Emacs.
You can copy and paste more than one page at a time, which you cannot do with some clients. You can scroll up more than one page, depending on how many scrolling lines you have set with the -h option.
Using the detach feature, you can save screen processes when logging out and resume where you left off, saving the trouble of restarting them.
To start screen, enter the following command:
Note: Every screen command begins with Ctrl-a .
||Create new window (shell)|
||Kill the current window|
||List all windows (the current window is marked with “*”)|
||Go to a window numbered 0-9|
||Go to the next window|
||Toggle between the current and previous window|
||Start copy mode|
||Paste copied text|
||Help (display a list of commands)|
||Power detach and logout|
||Detach but keep shell window open|
Press the Spacebar or Enter to end a command.
To copy a block
To get into copy mode, press Ctrl-a [ .
To move the cursor, press the h , j , k , and l (the letter l) keys. The 0 (the number 0) or ^ (the caret) moves to the start of the line and $ (the dollar sign) moves to the end of the line. Ctrl-b scrolls the cursor back one page and Ctrl-f scrolls forward one page. To set the left and right margins of copy, press c and C (Shift-c). The Spacebar starts selecting the text and ends selecting the text. To abort copy mode, press Ctrl-g .
To paste a block
To paste the copied text to the current window (as many times as you want), press Ctrl-a ] .
To run a program or execute any Unix command in a new window, at the Unix prompt, enter:
Above, replace unixcommand with the appropriate command name.
To automatically start several windows when you run screen, create a .screenrc file in your home directory and put screen commands in it.
To quit screen (kill all windows in the current session), press Ctrl-a Ctrl-\ .
The man pages for screen are quite readable and make a good tutorial. At the Unix prompt, enter:
Any questions on this, please feel free to ask. We’re here to help…