A guide to GNU Screen
by the editorial team
written by Steve ‘Ashcrow’ Milner and Anderson Silva
The same way tabbed browsing revolutionized the web experience, GNU Screen can do the same for your experience in the command line. GNU Screen allows you to manage several interactive shell instances within the same “window.” By using different keyboard shortcuts, you are able to shuffle through the shell instances, access any of them directly, create new ones, kill old ones, attach and detach existing ones.
Instead of opening up several terminal instances on your desktop or using those ugly GNOME/KDE-based tabs, Screen can do it better and simpler.
Not only that, with GNU Screen, you can share sessions with others and detach/attach terminal sessions. It is a great tool for people who have to share working environments between work and home.
By adding a status bar to your screen environment, you are able to name your shell instances on the fly or via a configuration file called .screenrc that can be created on the user’s home directory.
Installing
Installing Screen on a Fedora or Red Hat® Enterprise Linux® 5 system is quite easy with yum, assuming you have sudo access.
- Login as root:
su # enter root password - Use yum to install it:
yum install screen
Enter your password. After a few minutes (depending on your network connection), Screen will be installed. But before you start playing around with it, let’s look at how to do some basic configuration.
Customizing the configuration file
Screen keeps its configuration file in the same vein that many applications do: in a dot file in your user’s home directory. This file is aptly named .screenrc. In my experience, most people use ~/.screenrc to do two things:
- Make a hardstatus line. This is basically a line at the bottom of the screen that lists your current terminal and all opened ones. It can also display the system clock and the hostname.
- Default screens on startup. It’s quite nice to have your IRC connection, mail client, and default SSH connections auto-start for you!
The lines below are numbered for reference. Your config file should not have numbered lines.
1 hardstatus alwayslastline
2 hardstatus string '%{= kG}[ %{G}%H %{g}][%= %{=kw}%?%-Lw%?%{r}(%{W}%n*%f%t%?(%u)%?%{r})%{w}%?%+Lw%?%?%= %{g}][%{B}%Y-%m-%d %{W}%c %{g}]'
3
4 # Default screens
5 screen -t shell1 0
6 screen -t shell2 1
7 screen -t server 2 ssh me@myserver
On lines 1 and 2, you are setting the hardstatus. Line 1 makes the hardstatus always show up as the last line. Line 2 is about what will be shown in the hardstatus line. In this case you will see something like so at the bottom:
As you change screens, you will see the parentheses move around the active screen.
Line 4 is a comment, as it starts with #. Lines 5-7 are all screen statements in the following format:
screen -t NameOfScreen ScreenNumber ShellCommand
Shortcuts
The following are some of the most used shortcuts that lets you navigate through your screen environment. Note that unless modified by your .screenrc, by default every screen shortcut is preceded by Ctrl+a. Note that these shortcuts are case-sensitive.
- 0 through 9 – Switches between windows
- Ctrl+n – Switches to the next available window
- Backspace – Switches to the previous available
- Ctrl+a – Switches back to the last window you were on
- A – Changes window session name
- K – Kills a window session
- c – Creates a new window
- [ - Then use arrows to scroll up and down terminal
Find out about more shortcuts in Screen’s man pages. In your terminal, run: man screen.
Sharing a session with others
Another great application of Screen is to allow other people to login to your station and to watch the work you are doing. It is a great way to teach someone how to do things on the shell.
Setup to allow screen to be shared
- As root:
chmod u+s /usr/bin/screen(Screen has to be SUID if you want to share a term between two users.)
Note: SUID allows an executable to be run by the owner of that file, instead of with the user’s own permission. There are some security concerns when doing this, so use this tip at your own discretion. chmod 755 /var/run/screen- Log out of root, and run Screen as the user who is going to share the session:
screen - Press Ctrl+a, then type :multiuser on and press Enter.
- Press Ctrl+a, then type :acladd steve (”steve” is the username of the person who will connect to your screen session).
Connecting to the shared screen:
- SSH into the workstation that you are going to watch the screen session on.
- On your terminal type: screen -x anderson/ (”anderson” is the username of the person who is sharing the screen session. You need the / at the end.).
And now both users (from the host and guest) will be sharing a screen session and can run commands on the terminal.
Working from multiple locations
Let’s say you have a screen session open at work with X number of windows on it. Within those screens you may be running an IRC client, an SSH connection to the web server, and your favorite text-based email client. It’s 5 p.m. and you have to go home, but you still have work left to do.
Without Screen you would probably go home, VPN into your company’s network, and fire up all the shells you need to keep working from home. With Screen, life gets a little easier.
You can simply SSH into your workstation at work and list your available screen sessions with the command:
screen -ls
And connect to the sessions you were running at work with the command:
screen -x screen_session_name
This way screen will let you pick things up exactly from where you left off.
Applications to make Screen your window manager
Now that you have seen what Screen can do for you, you probably are wondering how to make it your main interaction point, like a terminal window manager.
Let’s start with IRC, a very common and popular chat system. Instead of using a graphical client like Pidgin, install Irssi. Irssi sports a slick console interface, tons of add-ons and scripts, and can be enhanced with Perl. It’s even theme-able!
Another important part of any user’s setup is email. Today most people use graphical clients such as Thunderbird, Evolution, or Sylpheed. My favorite client happens to run in a terminal: Mutt. While Mutt isn’t the easiest client in the world to set up, it sure is a joy to use. You can even use your favorite console text editor for doing emails.
Speaking of favorite text editors, there is a good chance that you work on some code projects or configurations. Instead of using gedit/kedit or powering up a heavy IDE such as Eclipse, you can pick up on Vim. Vim is a powerful text editor which, as is stated on the Vim website, could be considered an entire IDE in itself and sports syntax coloring in over 200 programming languages. If Vim doesn’t fit your style, there is always emacs, nano, or JOE.
Now all you need you need to do is edit your ~/.screenrc to meet your needs.
My ~/.screenrc looks like the following:
1 hardstatus alwayslastline
2 hardstatus string '%{= kG}[ %{G}%H %{g}][%= %{=
kw}%?%-Lw%?%{r}(%{W}%n*%f %t%?(%u)%?%{r})%{w}%?%+Lw%?%?%= %{g}][%{B}
%Y-%m-%d %{W}%c %{g}]'
3
4 # Default screens
5 screen -t shell1 0
6 screen -t shell2 1
7 screen -t server 2 sh me@myserver
8 screen -t IRC 7 irssi
9 screen -t Mail 8 mutt
Once you get used to the shortcuts in GNU screen, not only will your desktop become more organized (due to the lower number of open windows), but your efficiency as a developer or system administrator will increase not only at work but at your home office as well.
September 27th, 2007 at 8:44 am
[…] veryvera wrote an interesting post today onHere’s a quick excerptIf Vim doesn’t fit your style, there is always emacs, nano, or JOE. Now all you need you need to do is edit your ~/.screenrc to meet your needs. My ~/.screenrc looks like the following: 1 hardstatus alwayslastline 2 hardstatus string … […]
September 27th, 2007 at 9:57 am
[…] unknown wrote an interesting post today on A guide to GNU ScreenHere’s a quick excerpt […]
September 27th, 2007 at 11:37 am
Yeah, I gave screen a try several times. The problem is, I use CTRL-A for “go to beginning of the line” a lot and all the screen shortcuts seem to utilize CTRL-A.
September 27th, 2007 at 12:48 pm
Dmitriy, you can use Ctrl-a by hitting Ctrl-a-a.
I also use “set -o vi” which works in bash, ksh, and pretty much any shell with POSIX mode. vi mode lets you operate your shell using keyboard commands similar to the vi editor. To get back to the default emacs-style, use “set -o emacs”.
September 27th, 2007 at 12:59 pm
Dmitriy Kropivnitskiy,
Add the following line to your .screenrc
escape ^gg
Now, you can use Ctrl+g instead of Ctrl+a, Steve uses ~
You can customize it to whatever key you want.
I hope this helps.
AS
September 27th, 2007 at 4:27 pm
[…] mauzenne wrote an interesting post today onHere’s a quick excerptveryvera wrote an interesting post today onHere’sa quick excerptIf Vim doesn’t fit your style, there is always emacs, nano, or JOE. Now all you need you need to do is edit your ~/.screenrc to meet your needs. My ~/.screenrc looks like … […]
September 28th, 2007 at 12:02 am
[…] jstruan wrote an interesting post today onHere’s a quick excerptmauzenne wrote an interesting post today onHere’sa quick excerptveryvera wrote an interesting post today onHere’sa quick excerptIf Vim doesn’t fit your style, there is always emacs, nano, or JOE. Now all you need you need to do is edit … […]
September 28th, 2007 at 8:12 am
[…] A handy reference, A guide to GNU Screen, appears inRed Hat Magazine: The same way tabbed browsing revolutionized the web experience, GNU Screen can do the same for your experience in the command line. GNU Screen allows you to manage several interactive shell instances within the same “window.” […]
September 28th, 2007 at 9:52 am
I have customized my bash shell fairly heavily - changed prompt, vi style keystrokes, bash completion etc etc etc.
How do I get screen to pick up on all those settings?
September 28th, 2007 at 10:14 pm
[…] I’ve been meaning to write a guide to using GNU screen for months now, but it seems that Steve ‘Ashcrow’ Milner and Anderson Silva beat me to it. [?] Share This […]
September 29th, 2007 at 12:57 am
[…] Red Hat Magazine | A guide to GNU Screen Screen is a great tool, a valuable addition to your Linux toolbox (tags: open-source linux programming-tools via:lxer) […]
September 30th, 2007 at 10:20 pm
[…] read more | digg story […]
October 1st, 2007 at 3:22 am
> I have customized my bash shell fairly heavily - changed
> prompt, vi style keystrokes, bash completion etc etc etc.
> How do I get screen to pick up on all those settings?
You don’t need to - screen doesn’t replace your shell so any changes you make to the shell environment via e.g. bashrc or bash_profile will still be applied inside screen.
October 1st, 2007 at 10:17 am
> You don’t need to - screen doesn’t replace your shell so
> any changes you make to the shell environment via e.g.
> bashrc or bash_profile will still be applied inside screen.
Unfortunately that doesn’t hold true here… On my OSX box it doesn’t pick up anything, on my typical linux boxes it brings forward the bash prompt but not the vi style keybindings.
October 1st, 2007 at 3:50 pm
Any way to send one command to all screens at once?
In other words, open sessions to a bunch of separate machines and instead of C-a,n “ps”, C-a,n “ps”, … Issue the command once, and C-a,n to view the output in each?
October 1st, 2007 at 5:20 pm
Hardly revolutionary. Yawn! Ugly tabs? Is that a line from a marketing brochure?
October 1st, 2007 at 7:02 pm
Beside dettach and reattach feature, I also love the “split” feature. Even better, latest development version, can do vertical split too. With the feature, I can monitor several items at the same time, example, irssi at the top pane, top at the middle and mutt at bottom. Oh, wait, nethack is hiding behind :)
October 3rd, 2007 at 1:27 am
I was introduced to screen about 4 years ago, and haven’t looked back. It’s brilliant, and has more features than I could imagine using, but am gradually finding new ways to use them.
I don’t think BigFill ‘gets it’. Sure, you could open up multiple windows in X11 (or in PuTTY if you’re a Windows user) to do your job. But consider this: What do you do if your network connection between your laptop/workstation and the machines you’re working on gets interrupted (eg, working from home over VPN)? Basically you have to set everything up again.
But with screen, you ssh to a remote host, set up screen with as many virtual windows as you need, and if the connection between you and the screen session gets interrupted, no problem, just get your VPN going again, ssh to the remote host, then “screen -rd” (or “screen -rd “) and you’re back where you were moments earlier. This may not make complete sense until you’ve actually tried it.
This approach is also handy if you want to disconnect at 5pm and head home to continue from there. Or simply to reconnect and resume the next morning without having to do session setup situps.
If you prefer the GUI approach, there’s always VNC, but quite often the command line is where all the goodness happens.
Earlier tonight I realized that I’d like to write a couple scripts, each one which will fire up a new screen session (completely separate from any other I might be running), but from the context of the script in question, there will be multiple commands where each command connects to a different screen windows. I think I’ve figured out a way to do this from reading the man page earlier tonight, although it’s not explicitly called out as such.
Anyway, happy screening all!
October 3rd, 2007 at 9:42 am
I have RH3 and screen install fine from RH rpm. Screen works except multiuser mode. The instructions require that for multiuser mode we must do “chmod 755 /var/run/screen” however this file/directory does not exist on my system.
Next I activate multiuser mode and acladd the desired user. When this user tries to connect to my screen they get the error to the effect that “/tmp/screen-[my user name]” does not exist, which is correct, this file/directory does not exist. Creating it as a file simply results in the error “here is no screen to be attached matching [my user name]”
Any assistance appreciated
October 5th, 2007 at 5:08 am
Screen is great, but please don’t use it for sharing sessions.
Use “kibitz” from the “expect” package instead. None of the one-time (SUID, etc) or every-time (multiuser, acladd, screen -x) complexities described above.
When userA types “kibitz userB”, userB will see:
Message from userA@our.dom.ain on pts/1 at 15:59 …
Can we talk? Run: kibitz -28996
All he has to do is type the command and they are sharing userA’s session. Either of them hits a Ctrl-D to end the shared session.
Can’t get simpler than that…
October 5th, 2007 at 9:32 am
Just like abeowitz, I’m wondering whether it is possible
to use screen to send commands to multiple screens.
According the documentation this should be possible with
the “at” command, but I don’t get it to work.
So the command sequence:
C-a :at # date
Should result in a date executed on all windows (to my
understanding, but the result I get is:
“: at: at least two arguments required”)
OTOH according the TODO file at:
ftp://ftp.uni-erlangen.de/pub/utilities/screen/screen-4.0.3.tar.gz
states: “- type into several windows at once (for cluster admins)”
That file has been changed in august 2003 for the last time… :(
Hopefully someone reading this article knows how to use the
at command???
October 8th, 2007 at 4:07 am
With the ‘at’ command, you can send commands to other windows that have to be typed when you press C-a :
This changes the title of a window in a certain screen session:
screen -X at 1 title blublublu
October 11th, 2007 at 11:03 am
kibitz is great for sharing a screen and work session. Tks to Sitaram Chamarty. Much simpler to implement than screen if your interest is primarily sharing sessions.
October 14th, 2007 at 1:03 am
Brian: If bash isn’t starting up how you expect it to when invoked by screen, it’s likely because bash reads different initialization files depending on how it’s started. Setting up a link from .bashrc to your favorite rc file [.bash_login, .bash_profile, .profile] might make it behave how you like.
Maybe something like this: ln -s .bash_login .bashrc
bash’s manpage has the details.
October 20th, 2007 at 4:18 pm
A way to broadcast commands to all windows is the following:
^a:at \# stuff “ls12″
Thanks goes to Michael, (one of the screen devs) who provided this information to me.
October 20th, 2007 at 4:20 pm
The command above should read: double quote ls backslash zero twelve double quote. Somehow the parser removes the blackslash zero. One more try:
^a:at \# stuff “ls\\12″
November 9th, 2007 at 3:42 am
i use screent to run rtorrent on our homeserver.
i also would like to provide a read only display of rtorrents screen output.
i dont want press buttons to make a hardcopy, can i automate this on a timer?
i want hardcopy to run every 5min.
November 13th, 2007 at 8:30 am
Hi, I am very interested in the “chat to all tabs” function from secureCRT if it would be possible to do with screen it would be wonderfull but the command above doesn’t work. I am using screen under solaris I don’t know if it is any different but I have 50 sessions opened to 50 machines and sometimes I need to change a word in a file on all machines and it is very time consuming without this option.
Can anyone help?
January 18th, 2008 at 2:05 pm
Hi, all!
If I understand it correctly what Jim C said: You can use screen to ‘recover’ sessions even if there are on a remote computer?
Is the following scenario possible:
1. ssh to a remote computer
2. start screen (or should I start it on my local machine?)
3. run a big task
4. detach from this session
5. ## shutdown the local computer ## e.g. go sleeping :-)
6. restart the local computer
7. re-attach to the remote computer to see the progress of the task
Is this possbible? I tried it but I always get:
XIO: fatal IO error 104 (Connection reset by peer) on X server “localhost:10.0
after 0 requests (0 known processed) with 0 events remaining
if I shut down the local machine. If not - all is fine.
Any suggestions?
January 19th, 2008 at 11:29 am
Okay I got it: it was the specific big task which was the problem.
PS: it is imortant to start screen on the remote machine, of course!
January 22nd, 2008 at 12:23 am
[…] There’s a nice little howto that included this and some other tips (like, starting programs automatically and setting a status bar) at Redhat Magazine. Posted by bob Filed in tech […]
April 21st, 2008 at 8:03 pm
[…] So I did some research on how to optimize use of vim and screen together. The first thing I came up with was getting screen to display a nice bar at the bottom by adding this to my .screenrc: (Thanks, Red Hat Magazine!) […]
May 3rd, 2008 at 5:18 pm
[…] http://www.redhatmagazine.com/2007/09/27/a-guide-to-gnu-screen/ […]
June 9th, 2008 at 10:35 pm
[…] If you’re not familiar with Screen, Red Hat Magazine has a nice little introduction […]
July 2nd, 2008 at 3:56 am
[…] There’s a great Red Hat Magazine article showing the basics plus how to set up a .screenrc config file to automatically start sessions or add a status bar to the bottom. […]
September 16th, 2008 at 10:39 pm
[…] Red Hat Magazine | A guide to GNU Screen […]