Screen -X isn't working (“No screen found”)

Question

I have this php code:

echo shell_exec(\'sh /backups/turnon.sh\');

The /backups/turnon.sh code is:

scree

Answer 1

Not sure why one would do this, but as a sample of one way to do it.

---

www-data

One way to solve this case would be to attach to correct user session. For Apache that is normally www-data which is a user with stripped down privileges. Use ps on apache or,

in PHP you can run this to show you which user PHP (Apache) run as:

Output:

www-data

Note that if you run the script using PHP from command-line you will get current user, which you do not want.

---

Initiate screen session for www-data

www-data is normally not set up with password, as such we cannot log in with that user. To run a screen session for www-data one can do the following:

$ sudo su - www-data
$ script /dev/null
$ screen

Or as a one-liner:

sudo su - www-data -c 'script -c screen /dev/null'

This will start a new shell in www-data's home directory, typically /var/www/. The script command is one way to prevent access error to terminal when running screen due to the use of sudo su.

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Execute script from PHP

Now that we have a screen session for www-data we can continue with the Bash script.

/usr/bin/screen -X stuff '/usr/bin/java -cp /some/path/ Test

'

and execute it from PHP.

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Capturing output

If you want the buffer from screen in PHP there is various ways:

First create a log-file for www-data's screen session.

touch /tmp/www-data-scr.log
chown www-data:www-data /tmp/www-data-scr.log

• Use logfile option in .screenrc and run screen with -L.

• Run script -f /tmp/www-data-scr.log inside screen.

• Start www-data script screen session with log-file, -f to flush.

    sudo su - www-data -c 'script -fc screen /tmp/www-data-scr.log'
  

• Copy buffer to file to get a snapshot.

    /usr/bin/screen -X hardcopy /tmp/www-data-scr.log
  

• etc.

You would typically add a

sleep N

in your bash script after issuing the command producing some output and before reading the log file.

---

To sum up

As privileged user:

touch /tmp/screen.log
sudo chown www-data:www-data /tmp/screen.log
sudo su - www-data -c 'script -c screen /dev/null'

Bash script:

#!/bin/bash

/usr/bin/screen -X stuff 'java -cp /some/class/path/ Test

'
sleep 1
/usr/bin/screen -X hardcopy /tmp/screen.log
sed '/^$/d' /tmp/screen.log

PHP: