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

166

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
2

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
3

@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
1

@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 55 · Answer 2 · edited May 23 '17 at 12:41

55

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
4

"$TERM" = "screen" seems to be preserved when entering sudo environment, unlike the $STY option. – Melebius Dec 13 '16 at 10:00

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

39

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

slava

161

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
1

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

24

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
I'd like to add $STY in it. caption always "%{= kc}Screen $STY on %H (system load: %l)%-28=%{= .m}%D %d.%m.%Y %0c" – John Lee Dec 22 '22 at 01:25

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

1,733

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

4

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
1

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

1

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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