Screen

screen is a screen manager with VT100/ANSI terminal emulation.

Basics

• Start a screen session (creates a single window with a shell in it):

screen

• Invoke a screen command (consists of a "Ctrl + a" followed by one other character):

C-a <command_char>

• Detach from this screen terminal (program continues to run when its associated screen session is detached):

C-a d

• Reattach a session (brings foreground a previously detached session):

screen -r

• Invoke a screen customization command (used to set options):

C-a : <customization_command>

Multiuser mode

With multiuser mode, screen reveal itself as a powerfull colaborative administration tool.

Requirements

• screen binary file must be setuid-root:

chmod u+s /usr/bin/screen

• screen socket directory must not be NFS mounted (your default must be changed if it is $HOME/.screen):

SCREENDIR=/tmp/screen-username1

Howto

• User, named username1, initiates a basic screen session name test:

screen -S test

• Then, he enables multiuser mode for this session:

C-a : multiuser on

• After that, he allows the others, like username2, to connect to his session:

C-a : acladd username2

• At last, allowed users, like username2, can attach to the multiuser session initiated by username1:

screen -r username1/test

Note

• The setuid setting can be avoided if the screen -r username1/ is done by root (nothing to configure then on Debian systems, as the SCREENDIR is correctly set on this distro by default)
• a $HOME/.screenrc file can be use the systematicaly setup the multiuser mode. A good one for instance:

caption always "%Y-%m-%d %0c%{=b kW}  %l  %{=r kd}%-Lw%{= bd}%50>%n%f* %t%?(%u)%?%{-}%+Lw%<%{- Wk}"
vbell on
autodetach on
startup_message off
multiuser on
acladd root