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Unix Dweeb

How to use tmux to create a multi-pane Linux terminal window

May 26, 20206 mins

The tmux tool is one of a number of Linux terminal window splitters that allow you to run commands in adjacent (up/down, right/left or both) panes so that you can easily use the output in one pane to help with work you’re doing in another. You can even disconnect a multi-pane tmux session and reattach to it when you need it again.

What’s more, processes running within tmux will continue running even when you detach, making tmux an excellent tool to use when you’re not sure your connection to a remote server is solid and don’t want to be dropped in the middle of an important task.

The “mux” in the name tmux stands for multiplexer. This term generally refers to sharing digital connection or an information stream. So, “tmux” stands for “terminal multiplexer”. The tool is similar to terminator and konsole. However, tmux is also available on some OSes other than Linux including MacOS.

The primary drawback of tmux is that you have to learn some mildly awkward command sequences to use it. However, if you can adjust to just about everything you need to do starting with Ctrl-b (hold the Ctrl key and press b), you’re off to a good start.

Starting tmux is easy. Just type “tmux” in a terminal window. If you plan to detach and return to a session later, it’s a good idea to give the session a meaningful name.

To start a session type:

$ tmux

To start a named session type:

$ tmux new -s perf

Once tmux is started, a bar along the bottom of the tmux session will display the session name (if used), server name, and current (updating) time and date.

[perf] 0:bash*                         "dragonfly" 15:45 25-May-20

Opening new panes is quite easy with commands likes these below. You just have to remember that % means “to the right” and means “below”:

Ctrl-b %     open a pane to the right of the current pane
Ctrl-b “     open a pane below the current pane

Moving from pane to pane then requires the use of arrow keys. If you want to move to a pane to the right, use Ctrl-b followed by pressing the right arrow key and, if you want to move down a pane, use Ctrl-b following by the down arrow key. In other words, use whichever arrow key points in the direction you want to move – right, left, up or down.

To close a pane, first ensure that you’re positioned in it. Then type “exit” or Ctrl-d. Note that there is no need for Ctrl-b in this step. Once you type “exit” or Ctrl-d in the last remaining pane, tmux will close.

You can also exit tmux by pressing : to go to the bottom bar of the tmux window. Then type kill-session. Note that the session will be gone and will not be reattachable.

If you want to detach a session instead of simply closing it, use Ctrl-b d (d for “detach”). You can detach with all of the panes still open.

To list detached sessions, use the command tmux ls on the command line or within a tmux session. Sessions without given names will be called 0, 1, 2 etc., in the order in which they were created. Only detached sessions will show up in the output of the tmux ls command.

You can rename a session with a command like this:

$ tmux rename-session -t 0 acct-mgt
$ tmux ls
1: 1 windows (created Sat May 23 16:10:26 2020)
acct-mgt: 1 windows (created Mon May 25 16:09:52 2020) (attached)

You can reattach to a session using a command like one of these that includes the session name you assigned or was automatically provided:

$ tmux attach -t acct-mgt


$ tmux attach -t 0.

Note that, if you reattach a session and then exit instead of detaching, it will no longer be available for reattaching.

Recipe for a 3-pane tmux session

Want a recipe for setting up a tmux window like this that you can reuse any time you want?

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Here goes. First start your session and give it a name. In this example, we’re calling the session  “tmux3” because it will have three panes.

$ tmux new -s tmux3

After it opens, type these character sequences:

Ctrl-b “		

Next, list your saved session to make sure you did everything right:

$ tmux ls
tmux3: 1 windows (created Mon May 25 13:46:14 2020)

Reattach to your session:

$ tmux attach -t tmux3

Your session will start each time with your cursor in whatever pane it was sitting in when you detached. On that note, don't forget to detach each time you use it by typing Ctrl-b d.

You can even create an alias to make reattaching to your session that much easier.. In the commands below, we create the alias and save it to our .bashrc file to ensure it's available each time we log in:

alias tmux3="tmux attach -t tmux3"; echo 'alias tmux3="tmux attach -t tmux3"' >> ~/.bashrc

Got that? You will have to detach every time you use the tmux session by typing Ctrl-b d. Otherwise, the session will no longer be saved. And don’t forget that the session will always pick up where you left off, displaying the output of any commands that are still running.

For example, if you left top running when you last used the session, it will still be running after you have detached and adding output to the pane in which it's active. If you kill that top process outside of tmux (which you can), it will no longer be running when you reattach your session. After all, tmux is not a separate system, just a way of splitting your terminal connection. Detaching doesn't disrupt the running processes, whick is one of the key benefits of using tmux in the first place.

There are lots of other options available for use with tmux. We've only touched on the basics in this post. Refer to the tmux man page for more information, but be aware that C-b is sometimes used to represent Ctrl-b.

Unix Dweeb

Sandra Henry-Stocker has been administering Unix systems for more than 30 years. She describes herself as "USL" (Unix as a second language) but remembers enough English to write books and buy groceries. She lives in the mountains in Virginia where, when not working with or writing about Unix, she's chasing the bears away from her bird feeders.

The opinions expressed in this blog are those of Sandra Henry-Stocker and do not necessarily represent those of IDG Communications, Inc., its parent, subsidiary or affiliated companies.

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