Reference to rackaid.com
Linux Screen allows you to:
- Use multiple shell windows from a single SSH session.
- Keep a shell acive even through network disruptions.
- Disconnect and re-connect to a shell sessions from multiple locations.
- Run a long running process without maintaining an active shell session.
If this sounds like stuff you can use, check out our 2 minite quick-start video below or read on for more details on how to use screen.
Ps: Youtube is not reachable in china, so…
Screen Tips
We use screen daily, so as we keep adding new tips when we find good ones. If you have something you want to add, just leave it in the comments.
- Installing Screen with Yum
- Starting Linux Screen
- Control Command
- Creating Windows
- Switching Between Windows
- Detaching From Screen
- REattach to a Screen
- Logging Output
- Getting Alerts
- Locking Screen
- Stopping Screen
-
Video Tutorial
- Installing Screen with Yum
Chances are that you already have screen on your system. On most Red Hat and
CentOS distributions you can find Linux screen in /usr/bin/screen. To see if
screen is in your path, you can use the which command:
[root@office ~]# which screen
/usr/bin/screen
If you do not have screen, then ou can install it easily from an PRM or the package file for your system. For example, on CentOS you can install screen with yum:
[root@office ~]# yum install screen
...
Complete!
As you probably already have screen or can use an RPM, I am not going to cover the building of screen from source. Lets get on to how to use screen.
Starting Linux Screen
Screen is started from the command line just like any other command:
[root@office ~]# screen
You are now inside of a window within screen. This functions just like a normail shell except for a few special characters.
Control Command
Command: Ctrl-a
Screen uses the command Ctrl-a that’s the control key and a lowercase “a” as
a signal to send commands to screen instead of the shell.
For example, Ctrl-a then ?. You should now have the screen help page.
Screen key bindings, page 1 of 4.
Command key: ^A Literal ^A: a
break ^B b only Q
clear C other ^A
colon : pow_break B
copy ^[ [ pow-detach D
detach ^D d prev ^P p ^?
digraph ^V readbuf <
displays * redisplay ^L l
fit F removebuf =
flow ^F f reset Z
focus ^I screen ^C c
hardcopy h select '
help ? silence _
Key bindings are the commands the screen accepts after you hit Ctrl-a. You
can reconfigure these keys to your liking using a .screenrc file, but I just
use the defaults.
Creating Windows
Command: Ctrl-a c.
To create a new window, you just use Ctrl-a c
This will create a new window for you with your default prompt. Your old window is still active.
For example, I can be running top and then open a new window to do other things. Top stays running! It is still there. To try this for yourself, start up screen and then run top. (Note: I have truncated some screens to save space.)
Start top
top - 09:1033 up 35 days, 17:25, 1 user, load averag
Tasks: 131 total, 1 running, 130 sleeping, 0 stoppe
Cpu(s): 0.4%us, 0.3%sy, 0.0%ni, 99.4%id, 0.0%wa, 0
Mem: 12302040k total, 6363652k used, 5938388k free,
Swap: 1052248 total, 12k used, 1052236k free,
Now open a new window with: Ctrl-a c
Your top window is still running, you just have to switch back to it.
Switching Between Windows
Command: Ctrl-a n
Screen allows you to move forward and back. In the example above, you could use
Ctrl-a n to get back to top. This command switches you to the next window.
The windows work like a carousel and will loop back around to your first window.
You can create several windows and toggle through them with Ctrl-a n for
the next window or Ctrl-a p for the previous window.
Each process will keep running until you kill that window.
Detaching From Screen
Command: Ctrl-a d
Detaching is the most powerful part of screen. Screen allows you to detach from a window and reattach later.
You can detach from the window using Ctrl-a d.
This will drop you into your shell.
All screen windows are still there and you can re-attach to them later.
This is great when you are using rsync for server migration.
Reattach to Screen
If your connection drops or you have detached from a screen, you can re-attach by just running:
[jeffh@office ~]$ screen -r
This wil re-attach to your scren.
However, if you have multiple screens you may get this:
[jeffh@office ~]$ screen -r
There are several suitable screens on:
31917.pts-5.office (Detached)
31844.pts-0.office (Detached)
Type "screen [-d] -r [pid.]tty.host" to resume one of them.
If you get this, just specify the screen you want.
[jeffh@office ~]$ screen -r 31844.pts-0.office
Logging Your Screen Output
As a consultant, I find it important to keep track of what I do to someone’s server. Fortunately, screen makes this easy.
Using Ctrl-a H, creates a running log of the session.
Screen will keep appending data to the file through multiple sessions. Using the log function is very usefule for capturing what you have done, especially if you are making a lot of changes. If something goes wrong, you can look back through your logs.
Getting Alerts
Screen can monitor a window for activity or inactivity. This is great if you are downloading large files, compiling, or waiting for output.
If you are waitig for output from a long running program, you can use Ctrl-a
M to look for activity. Screen will then flash an alert at the bottom of the
page when output is registered on that screen.
I use this when runing a command that takes a long time to return data. I can just fire up the command, switch to another window and not have to keep switching back to check the status.
You can also monitor for inactivity. Why use this?
If you are downloading a large file or compiling a program, you can be notified
when there is no more output. This is a great signal to when that job is done.
To monitor for silence or no output use Ctrl-A _.
Locking Your Screen Session
If you need to step away from your computer for a minute, you can lock your
screen session using Ctrl-a x. This will require a password to access the
session again.
Screen used by root <jeffh>.
Password:
Stopping Screen
When you are done with your work, I recommend you stop the session instead of saving it for later. To stop screen you can usually just type exit from your shell. This will close that screen window. You have to close all screen windows to terminate the session.
You should get a message about screen being terminated once you close all windows.
[screen is terminating]
Alternatively, you can use Ctrl-a k. You should get a message if you want
to kill the screen.
Screen Video Tutoail (Just 2 Minutes)
Learn how to use screen in this 2 minute video tutorial.
Ps: Youtube is not reachable in china. If you want to check the video, visit rackaid.com
Thx!