it_tips:screen
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| + | ===== Screen ===== | ||
| + | |||
| + | Screen is the best sysadmin and cluster user companion. It does a magical thing: if you disconnect abruptly from a server, it will keep everything running as is you've never disconnected. Think of it as an open window to your work on a remote machine, to which only you can have access. | ||
| + | |||
| + | To give an idea of what ''screen'' does, follow this simple tutorial in which we will be using the ''top'' utility that shows processes running on a machine. The tutorial shows how, if you start top in a screen session and you disconnect from a server, the top program is still running on the remote machine. | ||
| + | |||
| + | Please read tips at the end on how to use //copy mode// and move in the open window. | ||
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| + | == 1) login via ssh into a server and run screen: == | ||
| + | <code>[pflorido@n12 pp]$ screen</code> | ||
| + | An intro page will appear where you have to press enter or space. At this point you are in a virtual shell running on the server, independent from the ssh connection. If connection drops by during this time you don't loose your session. | ||
| + | |||
| + | == 2) start the top command == | ||
| + | <code>[pflorido@n12 pp]$ top</code> | ||
| + | |||
| + | A lot of info about running processes will fill the terminal. | ||
| + | |||
| + | == 3) press the three keys ''Ctrl a d'' alltogether == | ||
| + | The screen session will be //detached//. you'll see a message like: | ||
| + | <code>[detached]</code> | ||
| + | and you will be sent back to the shell where you wrote ''screen'' before. | ||
| + | |||
| + | == 4) list the existing screen sessions == | ||
| + | With the command | ||
| + | <code>[pflorido@n12 pp]$ screen -list</code> | ||
| + | |||
| + | You'll see a list of running detached or attached screens, like this: | ||
| + | <code> | ||
| + | There is a screen on: | ||
| + | 20440.pts-1.n12 (Detached) | ||
| + | 1 Socket in /var/run/screen/S-pflorido. | ||
| + | </code> | ||
| + | |||
| + | == 5) re-attach the open screen by copy pasting its name: == | ||
| + | <code> | ||
| + | [pflorido@n12 pp]$ screen -DR 20440.pts-1.n12 | ||
| + | </code> | ||
| + | |||
| + | == 6) gaze at top command still running! == | ||
| + | You should now see the running processes as if top command was never stopped. In fact it had never stopped! | ||
| + | |||
| + | Press ''q'' to exit it and keep working on the same screen shell. | ||
| + | |||
| + | == 7) >:-| I don't believe it works! == | ||
| + | You can try ''screen'' effectiveness this way: | ||
| + | - log into the cluster | ||
| + | - running ''screen'' | ||
| + | - close the terminal window wgere you ran it | ||
| + | - relogin via ssh and run ''screen -list'': the screen session is still there!! | ||
| + | |||
| + | |||
| + | === The Copy Mode and other stuff === | ||
| + | Inside a screen session, interaction with the shell changes. In particular, to scroll up and down you should use the combination: | ||
| + | * ''Ctrl a ESC'' to enter //copy mode//. Then you can move the cursor up and down in the screen session. | ||
| + | * ''Ctrl a ?'' will give you a list of commands | ||
| + | * ''man screen'' will give you more info. | ||
| + | * On the same ssh connection you can open multiple screen terminals so that you can have multiple windows open, with ''Ctrl a c'' | ||
| + | * you can move between existing screen terminals with | ||
| + | * ''Ctrl a p'' previous | ||
| + | * ''Ctrl a n'' next | ||
| + | * You can name each session so that you remember what that was about with the ''-S'' flag:<code>[pflorido@n12 pp]$screen -S " Don't screen at me!" | ||
| + | [pflorido@n12 pp]$ screen -list | ||
| + | There are screens on: | ||
| + | 20550.Don't screen at me! (Detached) | ||
| + | 20440.pts-1.n12 (Detached) | ||
| + | 2 Sockets in /var/run/screen/S-pflorido. | ||
| + | </code> | ||
| + | |||
| + | * You can hang the following quick reference card om the wall to remember the commands: | ||
| + | * http://aperiodic.net/screen/quick_reference | ||
| + | |||
| + | == References == | ||
| + | |||
| + | * http://www.gnu.org/software/screen/ | ||
| + | * http://www.gnu.org/software/screen/manual/screen.html | ||
| + | * http://www.rackaid.com/resources/linux-screen-tutorial-and-how-to/ | ||
| + | * Quick reference card: http://aperiodic.net/screen/quick_reference | ||
| + | |||
it_tips/screen.txt ยท Last modified: 2014/03/27 11:08 by florido
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