Terminal multiplexers

“Terminal Multiplexers”, like screen and tmux, are extremely useful tools for running jobs on the department servers. The primary reason to use them is so you can run a job on the server and not need to keep your connection with the server open (e.g. you can close your computer, go to sleep, etc. while your job runs). It’s often the case that your connection to the server might disconnect even if your computer just goes to sleep or disconnects from the internet for a minute.

There are two major terminal multiplexer options: screen and tmux. The Internet recommends tmux (but some people in the department use screen).

In terms of usage, the most important commands 1. creating a new session 2. detaching but not closing as session 3. reattaching a session and 4. closing a session.

With these four options you can start up a session (1), step away from a session / the server without killing a job you’re running (2), come back to the session you left (3) and close a session once you’re done with it (4). The rest of the commands are icing on the cake.

In the following sections below, we’ll present pros of both, then present sections on standard commands for both approaches. This article is currently more a place to remind yourself of what commands to use than a new introduction to the ideas. We recommend reading either of the introductions (at the end of either tool’s subsection) for get exposure to the power of these tools.

Comparisons

1. tmux:
   • more consistent syntax (but screen is still pretty good)
   • preserves panels / windows even when you detach the session
   • maybe a little safer in closing sessions (confirms request)

1. screen:
   • a stable tool (tmux is a little more in flux)

screen

Basic commands

Action	Command	Notes
Start new session [important]	screen
Starting a named session	screen -S _session_name_
List current sessions	screen -list
Detach session [important]	(Ctrl+a)+d
Attach/ reopen session [important]	screen -r _session_name_	If only one session is open you can just use screen -r
Close session [important]	Ctrl+d
Kill a session you are not currently in	screen -XS _session_name_ quit
enter scrollback/copy mode	Ctrl+a+[
end scrollback/paste buff	Ctrl+a+]

Window/panel based commands

Having multiple panels / windows going in a single session at the same time.

Action	Command	Notes
Create new window	(Ctrl+a)+c
split terminal horizontally, and create a new window	(Ctrl+a)+S  +  (Ctrl+a)+c	Note the capital S.
split terminal vertically, and create a new window	(Ctrl+a)+| +  (Ctrl+a)+c	This only works if the screen is a high enough version.
move between windows	(Ctrl+a)+ …
- next window	+n
- previous window	+p
- pick from list	+"
Move between splits	(Ctrl+a)+ Tab

External Links

• Introduction: howtogeek.com, linuxize.com
• Cheat sheets: pixelbeat.org.

tmux

Basic commands

Action	Command	Notes
Start session [important]	tmux
Start named session	tmux new -s _session_name_
Rename session	(Ctrl+b)+: -> then rename-session -t _current_name_ _new_name_	You don’t have to include -t _current_name_ if you want to rename a session you are in.
Detach session [important]	(Ctrl+b)+d
Attach/ reopen session [important]	tmux attach-session -t _session_name_
Close session [important]	tmux kill-session -t _session_name_
List current sessions	tmux ls

Window/panel based commands

Having multiple panels / windows going in a single session at the same time.

Action	Command	Notes
new window	(Ctrl+b)+c
see window numbering	(Ctrl+b)+q	flashes number of each panel open
close current window	(Ctrl+b)+& -> then y close current window
create panel splitting	(Ctrl+b)+ …
- horizontal splitting	+”	this is capital"
- vertical splitting	+%	this is also a capital %
- move between panels	+ arrow keys
move between windows	(Ctrl+b)+ …
- next window	+n
- previous window	+p

External Links

• Introduction: howtogeek.org
• Cheat sheets: howtogeek.org (see the bottom of the article).