How to check if I'm in screen session?

Question

I need it to determine if hitting ctrl+d would disconnect me from server or just close current screen.

Is it somehow possible to check if I'm right now in screen session?

score 143 · Accepted Answer · edited Apr 06 '18 at 21:00

143

You can look at the $STY variable (a variable set by the screen command). If it is not "" then you are in a screen session.

I am in screen

$ echo $STY 
29624.pts-1.iain-10-04
$

I am not in screen

$ echo $STY

$

edited Apr 06 '18 at 21:00

rogerdpack

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answered Apr 10 '11 at 16:36

user9517

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This presumes that you are still within a running session on the local computer. If you start up screen and then SSH somewhere else, this won't work. – David Mackintosh Apr 11 '11 at 03:05
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`if test -n "$STY"; then printf "This is a screen session named '$STY'.\n"; else printf "This is NOT a screen session.\n"; fi` – aggregate1166877 Sep 19 '15 at 17:08
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@DavidMackintosh if you're SSH'd into somewhere else, hitting ctrl-D will "disconnect me from server", which is exactly what the question asks about. – womble Aug 11 '16 at 08:24
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@aggregate1166877 I have this if you posted as an alias in every single machine that I use now. – Eduardo Bezerra Sep 10 '16 at 12:32
This doesn't work in a `sudo` script run inside a screen – ceztko Nov 07 '21 at 14:14

score 51 · Answer 2 · edited May 23 '17 at 12:41

51

You can look at the $TERM variable.

echo $TERM

If it's a screen session, the term variable should return "screen".

root@deore:/volumes# echo $TERM
screen

Ctrl-a -d (to exit screen)

root@deore:/volumes# echo $TERM
xterm

Also check: https://stackoverflow.com/questions/3472287/how-do-you-tell-if-the-current-terminal-session-is-in-gnu-screen

edited May 23 '17 at 12:41

Community

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answered Apr 10 '11 at 16:34

ewwhite

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This presumes that you are not deliberately messing with your TERM value for some reason. – David Mackintosh Apr 11 '11 at 03:04
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If you're changing your TERM variable while inside screen, you're inviting all sorts of trouble on yourself. – womble Aug 11 '16 at 08:24
Well my Solaris 2.6 nodes don't play nice with TERM values set to screen values. – David Mackintosh Aug 11 '16 at 17:56
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`"$TERM" = "screen"` seems to be preserved when entering `sudo` environment, unlike the `$STY` option. – Melebius Dec 13 '16 at 10:00

score 35 · Answer 3 · edited Jan 17 '19 at 12:39

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Unless you have changed the default key bindings, you can do Ctrl+a -> Ctrl+t, which will show the time, if you are in screen. This will work even if you have ssh:d away somewhere else, unlike the other suggestions.

edited Jan 17 '19 at 12:39

mature

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answered Jan 31 '14 at 14:38

Gurgeh

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Why are we not upvoting this. – AndreKR Mar 06 '14 at 02:36
This is definitely the best solution here. – Felix Jen Aug 11 '16 at 07:22
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How is this the best solution? What if you're *not* in screen, and `^A^T` is the key sequence for "nuke your homedir" in the program you're currently running? – womble Aug 11 '16 at 08:25
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@womble If you are in an unknown program that may do random destructive things as a response to key sequences and commands, then nothing is safe. – Gurgeh Aug 12 '16 at 08:55
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@AndreKR: It doesn't work in a script – Frank Meulenaar Jan 19 '19 at 20:38
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im not upvoting because in in a screen, and screening into another screen, and i literally need to see if $STY is even set. which for some reason its coming back empty. – Brian Thomas Apr 23 '19 at 01:18
Furthermore, this is not the best solution because this doesn't allow you to check this programmatically. – scubbo Nov 08 '19 at 08:43

score 22 · Answer 4 · answered Jan 05 '15 at 12:03

22

The caption command in the ~/.screenrc is a nice way to differentiate a screen session.

I'm personally using this:

$ cat ~/.screenrc
caption always "%{= kc}Screen session on %H (system load: %l)%-28=%{= .m}%D %d.%m.%Y %0c"

It adds a line like this one at the bottom of the screen:

Screen session on gbook (system load: 1,75 1,74 1,68)                   Lun 05.01.2015 13:01

With the first part (system name + load) in green and the date in pink. Useful and hard to miss!

answered Jan 05 '15 at 12:03

Gaëtan Lehmann

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This is perfect! It does not get in the way (bottom position), it is always visible (and colored) and provides useful info about system. I posted this here also http://stackoverflow.com/a/43571028/2450431 – hrvoj3e Apr 23 '17 at 12:22

score 7 · Answer 5 · answered Aug 24 '11 at 10:21

7

I have found another solution:
Modify your .screenrc, so my screen session looks completely different from normal terminal.

answered Aug 24 '11 at 10:21

wlk

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I think I know what you're suggesting, and it could *in some situations* avoid this problem entirely. It might be more helpful if you describe what you mean by showing (e.g.) an example `.screenrc` file. – jvriesem Apr 29 '19 at 18:42

GingkoFr · Answer 6 · 2021-08-27T14:27:12.663

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Better answer (in my opinion), inspired by this, just type the following:

pstree -s $$

If you get something like this:

systemd───sshd───sshd───bash───screen───screen───bash───pstree

… then you are in screen.

This is true not only for screen, but also for any kind of process (like script, nested bash or other shells) opening a nested shell, and this can even also show nested screen calls (if several not consecutive occurrences exists).

edited Aug 27 '21 at 14:27

answered Aug 27 '21 at 14:21

GingkoFr

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This would be a good answer but it should be worked on further to allow scripting – ceztko Nov 07 '21 at 14:22
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Scripting was not asked inside initial question, but if really required: `if [[ $(pstree -s $$) =~ screen ]] ; then echo 'yes' ; else echo 'no' ; fi` – GingkoFr Nov 08 '21 at 15:40
I would suggest `[[ $(pstree -sA $$) =~ ---screen--- ]]`, this will reduce the risk of a false positive. – Glushiator Jun 10 '22 at 15:25

score 0 · Answer 7 · answered Apr 30 '20 at 19:20

0

If you are looking at a command line prompt, you can just type something, anything, and hit Ctrl+A. If your cursor jumps to the beginning of the prompt, you're not inside a screen. If you additionally have to hit A, then you are.

answered Apr 30 '20 at 19:20

Gabriel Schulhof

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score -1 · Answer 8 · answered Apr 29 '15 at 09:04

-1

Do a screen -ls. It's going to explicitly indicate Attached versus Detached status.

Example attached:

$ screen -ls | grep tached
3132.pts-0.esavo00      (Attached)

Example detached:

$ screen -ls |grep tached
3132.pts-0.esavo00  (Detached)

answered Apr 29 '15 at 09:04

Marcus Junius Brutus

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if there are screens attached somewhere else this might be an issue. – Dennis Nolte Apr 29 '15 at 09:15

score -1 · Answer 9 · answered Aug 11 '16 at 06:43

-1

screen -ls

to view your sessions and

screen -r sessioninfo

to reconnect to a disconnected one, if detached.

screen -D -r sessioninfo

to reconnect to a disconnected one.

answered Aug 11 '16 at 06:43

Kevin

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This doesn't answer the question. – womble Aug 11 '16 at 08:22

How to check if I'm in screen session?

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