Tmux is a terminal multiplexer: it let us run and manage multiple terminal sessions from a single screen. This is specially useful when connecting to remote machines using ssh, since, among the other things, it allows us to keep processes started from those terminals running in the background when we disconnect from the session (or logout and close the remote secure shell altogether), letting us re-attach to it at a later time.
In this tutorial we see how to install Tmux in some of the most used Linux distributions and learn the basic concepts behind its usage.
In this tutorial you will learn:
- How to install Tmux on some of the most used Linux distributions
- How to manage Tmux sessions
- How to manage Tmux windows and panes
Software requirements and conventions used
| Category | Requirements, Conventions or Software Version Used |
|---|---|
| System | Distribution-independent |
| Software | Tmux |
| Other | Root privileges to install software |
| Conventions | # – requires given linux-commands to be executed with root privileges either directly as a root user or by use of sudo command$ – requires given linux-commands to be executed as a regular non-privileged user |
Installation
Free and open source software, Tmux is available in the repositories of all the major Linux distributions, so it can be easily installed by using our package manager of choice. To install Tmux on Fedora, for example, we use dnf:
$ sudo dnf install tmux
To perform the installation on recent versions of Debian and Debian-based distributions, instead, we can use the following command:
$ sudo apt install tmux
Tmux is also available in the “Community” repository of Achlinux. We can install it with pacman:
$ sudo pacman -S tmux
Why Tmux?
The benefits of using Tmux become evident when we connect to a machine via ssh. Suppose we issue a long running command or an interactive application like “htop” in the remote shell. At a certain point we realize we need to run another command; at this point we have two choices: stop the first process, or open another ssh connection from our local machine, in another terminal.
This is where Tmux comes in handy: once connected to a remote shell we can invoke tmux and start a new session which can contain multiple windows, which in turn, can be divided in many sections or panes. This allows us to open several terminals from a single connection. A further advantage is that we can disconnect from a Tmux session while the commands we invoked in it keep running in the background, and re-attach to it later.
Managing Tmux sessions
To start using Tmux, all we have to do is to invoke it from our terminal emulator:
$ tmux
Once Tmux starts, it creates a new session which is composed of a single window. On the bottom of the screen, a status line is displayed. It contains information about the session itself, and can be used to run commands:
In the left side of the status line we can see the session identifier in square brackets, and the names of the windows opened in it. At the moment we have only one window (bash). On the right side of the status bar, instead, we can see the hostname of the machine we are connected to, and the current date and time.
As you can see in the picture above, by sessions are identified by numbers. We can, however, create named sessions by invoking Tmux in the following way:
$ tmux new -s <session-name>
New sessions can be launched also from inside Tmux. In order to achieve this task all we have to do is to press what in the course of this tutorial we will call the “prefix” keys combination, which by default is
Ctrl-b, followed by a : (colon). Doing so, we enter command mode, than, to open a new session, we use the new command:
:new -s <session-name>
An existing session can also be renamed. In order to do so, we press <prefix> followed by the $ key, than we enter the new session name in the status bar, and press enter to confirm it:
Listing existing sessions
Sooner or later we may want to obtain a list of the existing Tmux sessions. We can do it either from command line or from the Tmux interface. In the first case we run:
$ tmux list-sessions
To perform the same operation from inside Tmux, instead, we press <prefix> followed by the s character:
In this case, as you can see from the screenshot above, there is only one session opened.
Attach and detach from a session
Suppose we are attached to a Tmux session as the one we opened in the previous example. Now, from a window, we launch a long running command, than, while it is running, we want to detach from the session. In this case all we have to do is to press <prefix> followed by the d key. Tmux will be closed, and we will will be notified of the detach with a message:
[detached (from session 0)]
When we detached from a session, the session remains alive, and the processes we launched from it, keep running in the background. When it is time to re-attach to a session, we run the following command:
$ tmux attach -t 0
Where the argument passed to the -t option (0 in this case) is the session id or name.
Closing a session
A session is automatically terminated when all its windows are closed, but it can also be closed explicitly by entering command mode and running:
:kill-session
If we are already detached from the session, instead, we can kill it by running the following command:
$ tmux kill-session -t <session-id>
Managing windows
When we first launch Tmux, there is only one window open. Creating a new one, however, is pretty easy: all we have to do is to press <prefix> followed by c character. The name of the new window is reported in the status bar:
The star (*) near a window name is used to identify the one that is currently in use.
Renaming a window
At the moment the name of both windows is just “bash”: that is because it is name of the shell we are using. We may want to use a more meaningful name for a window; in order to do that, once again we press <prefix> this time followed by , (comma). The status bar will change color, and we will be able to set the new name for the window:
Switching windows
To switch between opened windows, as usual, first we need to issue the <prefix> combination, than, we can press p to switch to the previous window in the list or n to switch to the next. Alternatively we can press w to obtain a list of the available windows. We can than select the one we want to switch to and press enter:
Killing a window
Finally, to kill a window we can use the <prefix> combination followed by the & character. We will be prompted to confirm we want to perform the operation:
So to, summarize:
| Action | Keys combinations |
|---|---|
| Create window | <prefix> c |
| Rename window | <prefix> , |
| Switch to previous window | <prefix> p |
| Switch to next window | <prefix> n |
| Obtain navigable windows list | <prefix> w |
| Kill a window | <prefix> & |
Managing panes
Every window in Tmux can be splitted in multiples sections, each one allowing us to use a pseudo-terminal. This sections are called “panes” in the Tmux terminology. To split a window pane vertically we press <prefix> followed by the % sign:
To split a pane horizontally, instead, we use the " key:
Just like sessions and windows, each existing pane is identified by a number. To visualize the numbers associated to the panes we use <prefix> followed by the q key:
Once the numbers are displayed, we can press it on our keyboard to move to the respective pane. The existing panes can be moved to the right and to the left by using
<prefix> followed by the { and } keys respectively, and their layout can be switched by using the spacebar key, instead.
Here is a quick recap of the panes shortcuts:
| Action | Keys combinations |
|---|---|
| Spit vertically | <prefix> % |
| Split horizontally | <prefix> “ |
| Identifying panes | <prefix> q |
| Move pane to the left | <prefix> { |
| Move pane to the right | <prefix> } |
| Switch panes layout | <prefix> spacebar |
Closing thoughts
In this tutorial we learned the basics of Tmux. We saw what are the benefits of using the application when connecting to remote machines via ssh, and we saw how to manage sessions, windows and panes.
