Power Sessions with Screen

Adam explains the many benefits and uses of screen.
Sessions

Now that you're creating new windows and bouncing around between them, you can get many things going in parallel. You could potentially have some editors, an IRC client and a few other things all running in their own windows. But occasionally disaster strikes, and your network connection dies (those of you still playing along at home can kill your SSH client). It looks like it's time to pick up the pieces and relaunch all of your applications on the remote machine, right? Not with screen.

Each time you start up screen without arguments, it creates a new session. This spawns two processes: a terminal management process and a client process. The client process automatically is “attached” to the terminal management process. When you type, the characters you enter go to the client, which sends them to the terminal management process, which then sends them to your application.

When your network connection dies, the client catches the signal and detaches from the terminal management process. The terminal management process continues along managing your terminals as if nothing happened. When you log back in, you can list running sessions by issuing screen -ls at the prompt. It should show something similar to the following:

There are screens on:
        24319.pts-9.hostname (Detached)
1 Sockets in /var/run/screen/S-youruserid.

This shows that your session automatically detached when your connection dropped.

You can re-attach to the session in a few ways. You can give a session name explicitly with screen -r sessionname. You can tell it to re-attach if possible, otherwise start a new session by running screen -R. Or you can go the “do whatever is needed to get a screen session” route and run screen -D -RR. This last option will detach already-attached clients and attach to the first session listed.

When you run one of these commands, you should be right where you left off before your network connection went down. When you're re-attached, you can continue working as if nothing ever happened.

It is also possible to attach to a session multiple times. This is useful if you haven't closed your screen session from another machine, or if you simply want to display windows from the same session side by side. You can multi-attach by adding an -x in the command-line options to screen when attaching.

Finally, when the end of the day rolls around and it's time to go home, you can detach from your session using Ctrl-A D. When you return the next day, you can re-attach, and you will be back where you left off.

Copy and Paste/Scrollback Mode

One of the key features listed in the beginning of the article was screen's searchable scrollback. This is a feature I could not live without. It's not immediately obvious to the new screen user, but screen's scrollback is accessed via the copy command. (You can enter copy mode with Ctrl-A [ or via the copy command.) Navigation works as expected with either the Arrow keys and Page Up/Down or the vi motion equivalents. Searching is accessed via either / and ? for vi-style search or Ctrl-S and Ctrl-R for incremental search. Case-insensitive search can be turned on with the screen command ignorecase yes. If you are using copy mode for scrollback only, it can be exited at any time with the Esc key.

To copy text, maneuver the cursor to the beginning of the desired text, and press the spacebar to mark it. Then position the cursor over the end of the text you'd like and press the spacebar again to mark it. When you mark the end, the text is copied into screen's internal copy buffer, and copy mode is exited. You can paste the text in your copy buffer into the active window with Ctrl-A ].

The final thing you should know about the copy and paste mode is the scrollback buffer is limited to 100 lines by default. This is, in my opinion, not enough. You can tweak this to a higher value (1,024 for example) by adding the command defscrollback 1024 to your .screenrc.

Opening Windows with screenrc

I have already mentioned that you can add a command to your .screenrc to change the behavior of screen. It's not immediately obvious, but you can put any screen command in a screenrc. This is very useful and can be used to spawn windows automatically with the screen command.

A typical application of this tidbit of knowledge is to launch a predefined set of windows at screen startup. Below is a sample screenrc that will do so:

# read in your normal screenrc
# before anything else
source $HOME/.screenrc
# now start opening windows
screen top
# it's possible to set the window title with
# the -t option
screen -t irc epic
# you can also specify the window number
# to launch in
screen -t mail 8 mutt
screen -t daemon 9 tail -f /var/log/daemon.log

If you save this to $HOME/.screenrc.multiwin you can tell screen to use it instead of your normal .screenrc by running screen -c $HOME/.screenrc.multiwin.

You also can launch more systems-oriented screen sessions from a startup script. A common application of a system screen session is a serial console server. Screen is well suited for this task because it has built-in support for serial terminals and logging. A commented example of a screenrc for this purpose is:

# This assumes that serialuser has proper
# permissions to access the serial ports and to
# write to the log files specified in the screenrc.
# turn logging on for all windows
deflog on
# tell screen to log to /var/log/serial.$WINDOW
logfile /var/log/serial.%n
# open windows on the serial ports
screen /dev/ttyS0 38400
screen /dev/ttyS1 19200

If you saved this file in /etc/screenrc.serial, you could launch it at startup with a script that runs:

su serialuser -c \
'screen -dmS serial -c /etc/screenrc.serial'
The -dmS serial options tell screen to launch the session in detached mode and name the session “serial”. User serialuser can log in and attach to this session exactly like any other normal screen session. Launching a detached screen also can be used to start screen from a cron job if this is preferred.

It is possible to set up a single system-wide screenrc that allows multiple users to connect to it. Screen supports multi-user mode with per-window ACLs that define what each user can and cannot do. Multi-user screen sessions, however, require that screen be setuid root. Because of this requirement, I am not going to include examples for multi-user screen sessions in an introductory article. If you would like to set up a multi-user screen session, read the screen docs, put on your “adding setuid root permissions to a complex piece of code” paranoia hat and be prepared to lock things down as tightly as possible.

As a third application, you could merge the two previous examples and launch system-wide interactive programs via screenrc. A good use of this would be launching mutella, a curses-based gnutella client, at startup. With screen, you can launch this program and connect to it on occasion to see the status, run queries, etc.

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screen -- window notification

rask's picture

1. Connect to the remote machine via ssh.

Terminal settings is fine.

2. screen

When I do that, then all my terminal settings change. For example, now I get window notification (not a bell but flash). How can I switch "flash notification" off ?

thanks.

screen. THX

Anonymous's picture

Never heard about screen. THX untile I saw this
very intressting info thank for explaing .
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comment

seo india's picture

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Stucki - u r great

Anonymous's picture

Sorry for being out of context.
Was getting error "can not open /dev/tty", while executing a perl script using ssh.

After "-t" option it went away..incase if its useful for some soul.

Status Bar Line

Michael M.'s picture

Screen quickly becomes confusing for me (since it's by default indistinguishable from a normal terminal), so I use the hardstatusline setting in my .screenrc:

hardstatus alwayslastline
hardstatus string '%{gk}[ %{G}%H %{g}][%= %{wk}%?%-Lw%?%{=b kR}(%{W}%n*%f %t%?(%u)%?%{=b kR})%{= kw}%?%+Lw%?%?%= %{g}][%{Y}%l%{g}]%{=b C}[ %m/%d %c ]%{W}

What that crazy line displays is this: On the last line:

  1. your hostname (the name of the computer you're working on. This is useful if you ssh into many computers, and run a screen in each. You can even do nested screen sessions: Use C-a + a + __ instead of C-a + ___
  2. A listing of all the screen windows you have open, and indication of which you're currently on. This is useful for navigating between windows. By default they aren't helpfully named (e.g. "5$ bash"), but you can rename them with C-a + A, and then something like "python.
  3. System Load (I find it useful, not everyone will.
  4. Date, Time


[mike][ 0-$ emacs (1*$ python) 2-$ vim [0.06 0.12 0.53][ 06/29 5:19]

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Anonymous's picture

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re acai berry during screen session

Anonymous's picture

Weird. When I consumed this acai berry supplement during a screen session, I farted once.
Farting was increased during multiple screen session.

Use wordpress tags

Anonymous's picture

Use Tags There are some other aspects of tagging. Presentation of tags can be influenced by tag similarities and tag hierarchy ( if there is any)

Hi Adam, this is a nice

affenzahn's picture

Hi Adam,

this is a nice article about screen. THX a lot. I have a question and hope you can help me.
I use screen since some time to start ssh session automatic.

- screen -t session1 1 ssh root@system1

It works. But I need a behaviour which didnt' close the screen session when exit. I want stay on the bash after exit and have the ssh command in the bash history.
Is it possible to handle this with screen ?

Cheers

Adam

bind keys in screenrc

Anonymous's picture

How to change CtrA+p for previous and CtrA+n for Next window. I do not want to repeat these option oftenly, i want options just as

Ctr+-> (Right arrow) for Next
Ctr+<- (Left arrow) for Previous.

have you looked at ratpoison?

beyli's picture

very nice images ...........

run same command on multiple sessions

samsixtyone's picture

is there any way, to run same command on all curently opened screen session?

thx

müzik dinle's picture

Is there an easy way of naming a screen session, so that one could use easier-to-remember names with screen -r ? One way is to rename the named socket in /var/run/screen/. Wondering if there's a better way.

of course.. you can use

Lo0m's picture

of course.. you can use screen -S name or (inside running session) - Ctrl+A :sessionname name

why

yarışma's picture

why
?
bell_msg '^GBell in window %n'
activity '^GActivity in window %n'

Personally, I find escape

oyun sitesi's picture

Before i knew screen i would open a putty session for each box i needed to work on. So for 6 servers i would have 6 putty running and it would soon clutter up my taskbar.

Screen is Great!

Jeff at Rackaid's picture

I use screen all of the time. I've long touted the benefits of using it for long running processes. I also use it interactively when reviewing actions of staff. My favorite use is to launch it when I have to run an errand, go home, go to lunch, etc. I can come back and pick up where I left off with worrying about a remote terminal session being open on my system.

Between normal shell escapes

lida's picture

Between normal shell escapes and emacs navigation keys, many of the basic ctl-keys are pretty well utilized.

Ctl-Z for me is critical for suspending processes.

I prefer, 'escape ^Gg' since who really wants to generate a random bell anyway :)

Power submit

John78's picture

To the poser above - Instead of VNC which I have also found really slow, try using chat. It allows users of Microsoft Windows to connect to remote Unix computers, run graphical applications and have the graphics displayed on their desktops.

Oh! Shame!

çok güzel hareketler bunlar's picture

Oh! Shame! I've just found it in the man pages, sorry!!!

These lines in the .screenrc should make it:
bell_msg '^GBell in window %n'
activity '^GActivity in window %n'

RS

Webumut

Webumut's picture

Oh! Shame! I've just found it in the man pages, sorry!!!

These lines in the .screenrc should make it:
bell_msg '^GBell in window %n'
activity '^GActivity in window %n'
http://www.webumut.com

ttt

sagliksorunlari's picture

Does anyone know if it's possible to rename a screen title if it wasn't set initially with the screen -t option?

^A + A (control A then

Anonymous's picture

^A + A

(control A then capital A)

renaming a running session

Nate922's picture

use screen -ls to get the session ID numbers. then just:


screen -X -S sessionname

didnt copy right

Nate922's picture

my above comment didnt complete:

screen -X -S {session#} sessionname {new session name}

Thank you

MorningMist's picture

I just wanted to say thanks for adding that cause you just saved me lol. :D

This is a great

Misafir's picture

This is a great time saver. Though I hope its not resource hungry for the servers to keep the screen session running,

Fwd: GOOD MORNING :)

vector graphics's picture

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hi

amatör's picture

I love screen. But what I want is something that can do stateful sessions with X programs when my X server crashes. VNC is to slow, and Xmove I couldn't get to work. Any suggestions?

session on x

rkms's picture

A very informative article. Loved reading it. In fact I have used screen to connect to my linux machine at my office. One thing though is that it is a console oriented beast.

To the poser above - Instead of VNC which I have also found really slow, try using XLiveCD. It allows users of Microsoft Windows to connect to remote Unix computers, run graphical applications and have the graphics displayed on their desktops.

rkms
Linux and friends

VIM remoting and screen

dkorah's picture

The article is super. Nice one.!

I came across this one while I was looking around for a solution for my vim IDE.

I am trying to create a vim + screen + bash wrap-up to make a vim IDE.

When I open a file, I fire off a delayed-open bash thread that does opening of files on a pre agreed vim server (say VIM_ON_SCREEN). Now while it is stuck in delay, I fire off a screen session with vim starting up the server (screen -R vim_screen vim --servername VIM_ON_SCREEN ) I expect the bash thread to kick in and remote-open files in the vim thats running in screen.

But it doesnt seem to work.

I did a bit of debugging. I started a screen session with vim and tried listing the VIM servers (vim --serverlist), but it didnt show up.

Any idea?

cursor keys and F-keys

y23's picture

I use putty to log into the linux machine and use dosemu to run some old stuff I need...

but using screen stuffs up the keyboard... cursor keys or F keys.
setting putty to application mode.. I tried all combinations, but to no avail. Any light you guys can shed on this?

'Esc' on Vi becomes slower

antz's picture

When I open Vi or VIM while using screen, the 'Esc' takes time to be effective (though it is only a fraction of a second). Without screen, it is instantaneous (unless I have mappings starting with Esc).

Is there any setting I can make in my screenrc or elsewhere? It appears screen intercepts Esc and then perhaps waits for further input. Once that times out, it sends Esc to the running app.

'Esc' on vi becomes slower

tacitdynamite's picture

This is really bugging me too! I'm glad that you left this comment; I run screen + ratpoison, and wasn't sure which one was intercepting it. Vim + slow 'ESC' = sux. Any success ... anyone?

Use Ctrl-C instead of Esc in Vim

Saganist's picture

Another solution is to use Ctrl-C in Vim instead of Esc. It works just the same. It took me a while to get used to it, but I like it a lot better than Esc now.

delay with 'esc' using vim and screen

tacitdynamite's picture

I figured out how to get rid of the delay; put the following:

maptimeout 0

in the .screenrc to make it not wait for more input characters. I added this for good measure:

defc1 off

because screen is essentially waiting for you to enter seven bytes after the 'esc' to enter in extended characters. Huzzah!

Hi dear adam,

Sharad's picture

Hi dear adam,
really you have provided very good information about gnu screen, even then I am facing a problem, So I found this page through Google.

In side screen, if wanted to launch rsh to other machines in window, then the typical command is

screen [-a] [-l] rsh machine # working fine.

but If I wanted to run any other intractive program like vim, emacs, bash or zsh. screen [-a] [-l] rsh machine zsh -il # no Control key working here.

I tried very some other flags also like -fa -fn etc, nothing worked. and I did not got any clue in net. Please let me know if this could be resolved.

thanks
Sharad

screen [-a] [-l] rsh machine zsh -il (NEVER WORKS!)

stucki's picture

Hi!

I stumbled upon your question searching
for another screen-problem :-)

Your problem is NOT 'screen' but 'rsh'!
There are TWO modes of running remote commands:
1) interactive(login) as 'rsh machine'
2) command(one run) as 'rsh machine program'

(1) gets a 'terminal' which can react on control and
other single keystrokes
(2) only gets a 'pipe' (simple input output), so it can
NEVER react correctly on control chars and especially
NEVER run things like an interactive editor.

'rsh' is normally replaced by 'ssh' now,
and THAT has an option '-t' (Terminal)
which exactly solves the problem!

try 'ssh -t machine vim filename' ...

Stucki

Named session

Anonymous's picture

Is there an easy way of naming a screen session, so that one could use easier-to-remember names with screen -r ? One way is to rename the named socket in /var/run/screen/. Wondering if there's a better way.

I just use a shell alias (I

Karthik Gurusamy's picture

I just use a shell alias (I have 'sr' -> for 'screen resume/recover'). At a time I have 1 or utmost two shell sessions (the second one is sr2). So never found the clumsy name as a big issue.

Karthik

Named Session

Anonymous's picture

Is there an easy way of naming a screen session, so that one could use easier-to-remember names with screen -r ? One way is to rename the named socket in /var/run/screen/. Wondering if there's a better way.

screen -S my_session_name

Renaming an existing screen session

David Keech's picture

You certainly can rename an existing screen session.

Type this from within the screen session you want to change:

ctrl-a :
sesionname newsessionname

and you session name will now be whatever you typed for "newsessionname".

The manual states that the $STY variable will not change and that this could cause some confusion. You can always change that variable yourself if it causes you a problem.

Inactive window bell notification

Roomservice's picture

Very good introduction, I suggested my buddies reading it.
I've been using screen for years in every day and there's a feature I would really like and miss the most:
A bell in a not active window should generate a bell (^G) in the active window as well instead of just writing this info out. If I could hear this notification I could react sooner to the problem.
Can this be set through the configuration or not?
I've read all the words in the long manual of this program, but...
Thanks.
RS

Oh! Shame! I've just found

Roomservice's picture

Oh! Shame! I've just found it in the man pages, sorry!!!

These lines in the .screenrc should make it:
bell_msg '^GBell in window %n'
activity '^GActivity in window %n'

RS

Been using this for about 5

Anonymous's picture

Been using this for about 5 years on SCO OpenServer5. Is very handy for serial terminal users who find the multiscreening a productivity improvement. The hot-keying between screens allows them reference back where they left off without laptop battery having to 'back' out then select another option in the menus they use.

Alternative escape character: ^s

Anonymous's picture

If ctrl-a isn't your bag, or you want to run screen in an ssh-ed screen I really enjoy using ctrl-s which AFAIK is mostly a legacy thing, but you've got to disable the default usage by putting the following maybe in a .bashrc or something:

tty > /dev/null && stty -ixon -ixoff

then in your .screenrc:
escape ^Ss

If it ever comes up you can always get an actual ctrl-s by doing two in a row.

Re: Power Sessions with Screen

Anonymous's picture

Been using this for about 5 years on SCO OpenServer5. Is very handy for serial terminal users who find the multiscreening a productivity improvement. The hot-keying between screens allows them reference back where they left off without having to 'back' out then select another option in the menus they use.

One problem I have found is the restricted range of ptys that are allowed in the version I have been supporting. It can only offer a maximum of 48 ptys. Also, if you have LAN connected devices you will find contention in the allocation of ptys. For instance both screen and telnet sessions use the ttyp0 - 8 range so you may find screen 'out of ptys' from time to time

Changing escape key sequence for screen.

Anonymous's picture

There's a typo in the description of changing escape key

sequences.

the line to change it to escape Bb (for emacs users)

should read like this:

escape ^Bb

Personally, I find escape B handy in emacs, so I map the screen key to:

escape ^Zz

Re: Changing escape key sequence for screen.

Anonymous's picture

I personally favor

escape ^Tt

because transpose-chars is a command I've used maybe twice in nearly a decade of Emacs, and everything else is bound to more useful things.

Re: Changing escape key sequence for screen.

Anonymous's picture

Between normal shell escapes and emacs navigation keys, many of the basic ctl-keys are pretty well utilized.

Ctl-Z for me is critical for suspending processes.

I prefer, 'escape ^Gg' since who really wants to generate a random bell anyway :)

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