Why Tmux

When working on the Mac Terminal, I used to create multiple tabs. Then I can switch quickly between tabs using Ctrl + Shift + [ and Ctrl + Shift + ]. While this works smoothly, one annoying problem is all the tabs will lose their content after reboot. So I've been looking for a solution that supports:

• Multiple tabs. Easily switch between tabs
• Able to restore sessions

From my search, it's quite obvious that tmux is the solution to my problem. Another candidate is screen, which I used for running some scripts on servers, but screen is pretty much a dead project now and its functions are far inferior to tmux.

My tmux settings

Tmux configuration is stored inside ~/.tmux.conf. On startup, tmux will pick up the content on this file and run it. We will put our customization code in this file.

First, we will remap reload key to r so that we can reload tmux.conf quickly.

# Set reload key to r
bind r source-file ~/.tmux.conf

Now, when we press <prefix> r, tmux.conf will be reloaded to reflect our new settings. The current <prefix> is still Ctrl B.

Remap prefix key

Prefix key is one of the most commonly used keys, so it's super important to map it to a single key instead of Ctrl B or Ctrl A as some people might prefer.

On Mac, one popular solution is to change the prefix to Capslock key because it's rarely used and very well positioned. We have 2 approaches to do this.

• Approach 1: Remap Capslock to Esc and remap tmux <prefix> to Esc

  • Go to System Preferences => Keyboard => Modifier keys to remap Capslock to Esc
  • One annoying problem is now we have to press Esc or Capslock twice in Vim. This is quite unacceptable as I use Vim a lot

• Approach 2: Remap Capslock to Home and remap tmux <prefix> to Home

  • Normally you don't have Home in Mac keyboard, but fortunately there is a software called Karabiner-Elements that allows you to completely customize your Mac keyboard.

  • After that, remap tmux prefix key to Home:

    set -g prefix Home
    bind-key Home send-prefix
    unbind C-b
    

  • I learnt this from https://blog.guilhermegarnier.com/2017/12/increasing-productivity-in-tmux-with-a-single-prefix-key/

Fast window switching

Windows in tmux are the same concept as tabs in Terminal. I want to be able to switch between windows quickly without having to lift up all fingers.

Fortunately, there's an easy way to do this by mapping next-window and previous-window commands to Shift Right and Shift Left

# Shift arrow to switch windows
bind-key -r -T root         S-Left            previous-window
bind-key -r -T root         S-Right           next-window

You just have to hold Shift and press Left or Right arrows accordingly, which makes switching very fast.

Next, we also want to be able to move a window to the left and right. We'll do this by mapping <prefix> n and <prefix> p to swapping a window with the one of the left or right

# Prefix n/p to move window to the left or right
bind-key -r -T prefix n { swap-window -t +1; next-window }
bind-key -r -T prefix p { swap-window -t -1; previous-window }

In effect, you will press Capslock n or Capslock p. However, unlike Shift Left key combination, you cannot hold Capslock. Instead, you will have to lift all your fingers and press 2 keys Capslock and n at the same time again. This is not a big problem since I'll don't usually move windows around a lot.

Restore Tmux and Vim sessions

When it comes to restoring tmux environment after system restart, the best solution is no other than tmux-resurrect. The installation instruction in their website is rather easy to follow.

After installing tmux-resurrect, we can use <prefix> Ctrl s to save, and <prefix> Ctrl r to restore tmux sessions.

Next and equally important, we also need a way to restore Vim session. I found vim-obsession works well with tmux-resurrect.

The part for tmux-resurrect in my .tmux.conf looks like this:

# tmux-resurrect
set -g @resurrect-processes '"~sudo pmset" "~Vim"'
set -g @resurrect-capture-pane-contents 'on'
set -g @resurrect-strategy-vim 'session'

Pay attention to the line set -g @resurrect-processes '"~sudo pmset" "~Vim"'. There are a number of default commands such as vi vim nvim emacs man less more tail top htop irssi weechat mutt that tmux-resurrect will automatically restore, but other commands outside of this list will not be restored automatically. So this line tells tmux-resurrect to restores extra commands if the command string match what is specified in the @resurrect-processes variable. In this case, since MacVim uses the command Vim and not vim, we have to specify "~Vim" so tmux-resurrect know that it should restore Vim window. Another command I use is sudo pmset, so I specify "~sudo pmset" here. For more details, read https://github.com/tmux-plugins/tmux-resurrect/blob/master/docs/restoring_programs.md

Finally, there are 2 problems when you restore tmux sessions. First, if you create temporary tmux session first, so that you can run the command <prefix> Ctrl r to restore previous sessions, you will have to kill the temporary session manually, which is annoying. Second, the restored windows will not have automatic-rename set to on, so their titles will not be updated automatically, which is equally annoying. To deal with these 2 problem, I use the following bash function:

mux() {
    tmux new -d -s delete-me && (tmux run-shell ~/.tmux/plugins/tmux-resurrect/scripts/restore.sh && tmux kill-session -t delete-me) &&\
    (for session_window in $(tmux list-windows -a -F '#{session_name}:#{window_index}'); do
        tmux set-window-option -t $session_window automatic-rename on
    done) &&\
    tmux attach || tmux attach
}

This function is modified from https://gist.github.com/rootulp/93f67511ae97c20c4d32b600a5ab6a8d. To use it, simply type mux in the terminal and it will restore previous session and reattach to it automatically. If there are multiple previous sessions, you can use tmux a -t <name> to attach to the session you want.

Vim binding in copy mode

Similar to screen, tmux has a copy mode to let you scroll through the content of your window, and copy/paste the parts you like.

Below is the setting to make this easier

# Use vim bindings in copy mode too
set -g status-keys  vi    # in the status/command prompt
setw -g mode-keys vi

# Setup 'v' to begin selection as in Vim
bind-key -T copy-mode-vi v send-keys -X begin-selection
bind-key -T copy-mode-vi y send-keys -X copy-pipe-and-cancel "reattach-to-user-namespace pbcopy"
unbind -T copy-mode-vi Enter ; bind-key -T copy-mode-vi Enter send-keys -X copy-pipe-and-cancel "reattach-to-user-namespace pbcopy"

You can start the copy mode with <prefix> [. Then you navigate the window content with Vim-mode keys h j k l. v to start selecting. y or Enter to copy.

Customize Status bar

The default tmux status bar position is at the top, which is ideal for showing tab-like window titles. I want to maximize the space for showing window title, so I limit the left part and right part of the status bar to very basic information.

# Set Colors
set -g default-terminal "screen-256color"
setw -g window-status-style fg=colour254,bg=colour102
setw -g window-status-format '#I:#W '
setw -g window-status-current-style fg=colour254,bg=colour30,bright
setw -g window-status-current-format '#I:#W '

# Set status bar
set -g status-bg colour252
set -g status-fg black
set -g status-left-length 90
set -g status-right-length 60
set -g status-left "#[fg=green]#S "
set -g status-justify left
set -g status-right ' #[fg=green]%a %d %b %R'

The left part of status bar, specified by status-left, only shows session title. The right part shows current date and time. Other colors and background colors are customized based on personal preferences.

Customize window title

For me, one important feature is a good window title, so that I can understand what's in a window just by glancing at the title. One format that works quite well for me has these features:

• Show full path of the current directory if possible. Replace home directory with ~ for brevity.
• Limit the length of the path to 20 characters so that the title is not too long
• But always try to show at least the full name of the current directory. This will deal with very long directory name that if truncated to 20 characters, will be hard to guess the full name.

The code to achieve these features is listed below. It uses awk because awk is best for one-liner kinds of programs.

# Set window title
set -g automatic-rename on
set -g automatic-rename-format "#(echo '#{pane_current_path}' | awk '{split($0, a, \"/\");basename=a[length(a)];cmd=\"pwd\"; cmd | getline homepath; close(cmd);baselength=length(basename);i=index($0,homepath);path=$0;if (i==1) { path=\"~\"substr(path,length(homepath)+1,length(path)); };maxlength=15; if (length(basename) > maxlength-3) { print \"../\"basename; } else if (length(path) > maxlength) {print \"..\"substr(path, length(path)-maxlength+3, length(path)) } else print path }') - #{pane_current_command}"

If you want to customize this code, you can change maxlength=15 to whatever you like. If you want to customize further, then you need to get a bit more involved with awk

The result is pretty good as far as I'm concerned. Here are some examples:

• ~/work: Shorter than 15 characters, so it shows full path
• ..rk/webarchive: full path is ~/work/webarchive, so it truncates to 13 characters and replaces the rest with ..
• ../a-very-long-folder-name: The folder name itself is longer than 15 characters, so it's kept in tact and then prefixed with ../

Conclusion

Those are my main points of customization of tmux. Granted there are other functions that can be customized such as pane splitting, pane switching, mouse mode, etc, but I don't use those functions much if at all in my every day activities.

My tmux settings can be found at https://github.com/minhhh/dotfiles/blob/master/tmux/.tmux.conf