tmux: terminal multiplexing made simple

Three hours into a database migration. SSH session to a remote server in Jakarta. The migration was halfway done, processing a few million rows. My laptop went to sleep for a coffee break. When I came back, the WiFi had reconnected but the SSH session was dead. The migration was still running on the server (I checked), but I had no way to see the output or know when it finished.

That was the last time I ran anything important outside of tmux.

tmux keeps your terminal sessions alive when you disconnect. Not just the processes, the entire session: your shell, your output, your scrollback. You detach, walk away, come back, attach, and everything is exactly where you left it.

The basics

Start tmux:

tmux

You’re now inside a tmux session. It looks like a normal terminal. The difference is that this session is independent of your SSH connection.

Detach (leave tmux running, go back to your regular terminal):

Ctrl+b d

That’s the prefix key (Ctrl+b) followed by d (detach). Every tmux shortcut starts with the prefix.

Reattach:

tmux attach
# or shorter:
tmux a

If you have multiple sessions:

tmux ls           # list sessions
tmux attach -t 0  # attach to session 0

Named sessions are easier to keep track of:

tmux new -s deploy
tmux attach -t deploy

Windows

Windows are like browser tabs. Each one is a separate terminal.

Action	Shortcut
New window	Ctrl+b c
Next window	Ctrl+b n
Previous window	Ctrl+b p
Switch by number	Ctrl+b 0 (or 1, 2, …)
List windows	Ctrl+b w
Rename window	Ctrl+b ,
Close window	Ctrl+b &

I name my windows after what they’re doing: “logs”, “deploy”, “db”. Makes switching fast with Ctrl+b w.

Panes

Split the current window into panes. Two or more terminals in one screen.

Action	Shortcut
Split horizontally	Ctrl+b %
Split vertically	Ctrl+b "
Switch to next pane	Ctrl+b o
Switch by direction	Ctrl+b ←↑↓→
Close pane	Ctrl+b x
Zoom pane (toggle fullscreen)	Ctrl+b z
Resize pane	Ctrl+b Ctrl+←↑↓→

My typical setup: left pane running tail -f on logs, right pane for typing commands. When I need more space for the logs, Ctrl+b z to zoom the left pane fullscreen, same shortcut to go back.

Copy mode

When you need to scroll back through output:

Ctrl+b [

Navigate with arrow keys (or j/k if you’ve enabled vi keys). Start selection with Space, copy with Enter, paste with Ctrl+b ]. Exit copy mode with q.

This is tmux’s weakest feature honestly. For serious scrolling and searching, I usually pipe output to less instead.

Configuration

Create ~/.tmux.conf:

# Mouse support (scroll, click to switch panes)
set -g mouse on

# Start counting from 1 (0 is far from the prefix key)
set -g base-index 1
setw -g pane-base-index 1

# More scrollback history
set -g history-limit 50000

# Vi keys in copy mode
setw -g mode-keys vi

# Reload config without restarting tmux
bind r source-file ~/.tmux.conf \; display "Config reloaded"

After editing, either restart tmux or use Ctrl+b r if you added the reload binding.

Practical patterns

The long-running task:

tmux new -s migration
# start your migration script
# Ctrl+b d to detach
# come back later:
tmux attach -t migration

Your process never stopped. Your output is still there. This is the entire reason I use tmux.

Side-by-side monitoring:

tmux
# Ctrl+b % to split vertically
# in the left pane:
tail -f /var/log/nginx/access.log
# Ctrl+b o to switch to right pane:
tail -f /var/log/nginx/error.log

Multiple projects, one SSH session:

tmux new -s frontend
tmux new -s backend
tmux new -s ops
tmux switch -t backend

Each “session” is a separate workspace. Switch between them without opening new SSH connections.

Pair programming:

Two people can attach to the same tmux session. Both see the same terminal. Both can type. It’s the CLI equivalent of screen sharing.

# Person 1:
tmux new -s pair

# Person 2 (on the same server):
tmux attach -t pair

tmux vs screen

GNU screen does the same thing, roughly. tmux has better pane support, cleaner config, and more active development. Screen is older and simpler. If you’re choosing today, tmux. If you already know screen and it works for you, no reason to switch.

One gotcha with either tool: if you SSH from inside a tmux session to another server that also runs tmux, the keybindings conflict. The inner tmux captures Ctrl+b before the outer one sees it. Fix this by changing the prefix key on one of them:

# In the outer tmux:
set -g prefix C-a

Quick reference

tmux                         # new session
tmux new -s name             # named session
tmux ls                      # list sessions
tmux attach -t name          # attach
tmux kill-session -t name    # kill session
tmux kill-server             # kill everything

Inside tmux: Ctrl+b d to detach, Ctrl+b c for new window, Ctrl+b % to split, Ctrl+b z to zoom pane.

The basics take about 10 minutes to learn. You’ll use them every day. The advanced stuff (scripting layouts, custom status bars, nested sessions) you can pick up as needed. Start with tmux, split a pane, detach and reattach. That alone will change how you work over SSH.