Let's say you want to do some cooperative hacking with another user. Here is how:
0. Screen needs the setuid flag set:
```
ls -l $(which screen)
-rwxr-sr-x 1 root screen 383096 May 11 2016 /usr/bin/screen
```
If yours *doesn't* have an `s` in the mode field, set it:
```
sudo chmod +s $(which screen)
```
1. Start a screen session (here the session is called "hacking"):
```
screen -S hacking
```
2. Set multiuser
**Ctrl-A**
`:multiuser on`
4. Add the other username to the ACL list of the session (allows them to join, here the other username is "bob"):
**Ctrl-A**
`:acladd bob`
5. Now the other user can join your session (here the *sharing* user is called "alice" and bob is joining the "hacking" session):
```
screen -x alice/hacking
```