Screen

From Wikitech

screen is a terminal multiplexer.

Once logged in on a server, use 'screen bash' and you will have another bash in a virtual window. From there you can add other windows with different program and move from a window to another. Ultimatly, you can send screen in the background & logout : screen will detach and run in the background.

Example: 

hashar@bihash:$ ssh aserver
$ screen bash

A new bash is invoked, my xterm title show: 

[screen 0: bash] hashar@zwinger:~

This means I am in the screen window #0 and running bash. 

$ vmstat 1
procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in    cs us sy id wa
 2  0  65508  51500 106756 430740    2    1     3     4    6     6  7 14 65 14
 0  0  65508  51372 106764 430732    0    0    12    24    0     0  2 15 82  2
 0  0  65508  51404 106768 430728    0    0     8     0    0     0  1 10 88  1
and so on ...

Multiple windows inside one screen

I am monitoring the server. Now let's create another window to edit a file. This is done by using CTRL + A then C (for create).

A new bash is invoked, my xterm title show: 

[screen 1: bash] hashar@zwinger:~

I can do whatever I want there. To move back to the window with vmstat use CTRL + A then P (for previous), to switch again CTRL + A then N (for next).

Splitting windows

You can also split a screen to see more than one window at once. Use CTRL + A then S (yes, that's a capital S, so SHIFT + s, for Split), then use CTRL + A then <Tab> to switch between them. Now you can create a new window, using CTRL + A then C as described above and keep switching betweem them using Tab.

Detaching and Re-attaching

Finally it's dinner time or you need to reboot your computer, or whatever. You can send screen in the background and logout, that will keep all your program running. This is done with CTRL + A then D (for detach). 

$ screen bash
[detached]
$ ps fx
13178 ?        S      0:00 SCREEN bash
13179 pts/1235 S      0:00  \_ bash
13249 pts/1236 S      0:00  \_ /bin/bash

Screen is in the background. Now you can logout. Once logged back, you want to resume your backgrounded screen: 

$ screen -r

You are back to the vmstat stuff which is still spamming values :)

Finally log out of all windows, when there is none left, screen exit: 

[screen is terminating]
$

Attaching a shared screen

If you want to share a screen with somebody else who is logged in as the same user, or you have forgotten to detach from somewhere else, and screen -r does not appear to work use: 

$ screen -x

(Attach to a not detached screen session.)

Troubleshooting

From inside "become", screen currently (cf. bugzilla:50248) outputs an error: 

local-dbreps@tools-login:~$ screen
Cannot open your terminal '/dev/pts/50' - please check.

You can work around this by running "script /dev/null" (you can first read "man script" to figure out what script does).

A second workaround is running screen first and then running become from inside screen.

External link

Retrieved from "https://labtestwikitech.wikimedia.org/w/index.php?title=Screen&oldid=1523"