Accessing other user's screen session

This need usually arises, when in a multi user machine, you as an admin wanted to check what is other user is running using screen. The best you can see even as root using ps, is just the name of the command, like below:

michael@vbox:~$ sudo ps awxuf | grep -i screen

root      1135  0.0  0.0  13636   976 pts/1    S+   13:27   0:00                          \_ grep --color=auto -i screen

john   4245  0.0  0.0 387364 16668 ?        Sl   Feb02   0:06  |       \_ gnome-screensaver

1001      6762  0.0  0.0 347384 10428 ?        Sl   Feb02   0:00              \_ gnome-screensaver

john    625  0.0  0.0  31320  1568 ?        Ss   11:57   0:00 SCREEN -S test

michael@vbox:~$ pstree -Gap 625

screen,625 -S test

  └─bash,626

When you try to access the screen session using other user, this is usually the error:

michael@vbox:~$ sudo -u john screen -r 625

Cannot open your terminal '/dev/pts/1' - please check.

This is because, your terminal: /dev/pts/1 is only readable and writable to the owner of the terminal:

michael@vbox:~$ ls -lh /dev/pts/1

crw--w---- 1 john tty 136, 1 Feb  12 13:30 /dev/pts/1

To overcome this, simply allow read and write to the terminal, to all users:

john@vbox:~$ chmod o+rw /dev/pts/1

john@vbox:~$ ls -lh /dev/pts/1

crw--w-rw- 1 john tty 136, 1 Feb  12 13:32 /dev/pts/1

Once that done, you can use sudo to access the screen of the other user:

michael@vbox:~$ sudo -u john screen -r 625

Hope this help :).