Add and Remove Byobu's Timed Bash Prompt Safely

You will finish with Byobu's colour Bash prompt enabled, showing the previous command's approximate runtime and non-zero exit status, with a clean way to remove the change. These examples use the installed Byobu package version 6.11-0ubuntu1.1.

Allow about ten minutes. You need Byobu installed, Bash as your current shell, and a writable ~/.bashrc. The commands change your user shell configuration only. They do not need sudo, and using elevated privileges would target the wrong home directory in most cases.

1. Check the shell and installed version

The prompt helper is compatible with Bash, not with an arbitrary shell. Check both the shell selected for this session and the package version before changing anything:

$ printf 'shell: %s\n' "$SHELL"
shell: /bin/bash
$ command -v byobu-prompt byobu-enable-prompt byobu-disable-prompt
/usr/bin/byobu-prompt
/usr/bin/byobu-enable-prompt
/usr/bin/byobu-disable-prompt
$ dpkg-query -W -f='${Package} ${Version}\n' byobu
byobu 6.11-0ubuntu1.1

2. Inspect the existing prompt line

Before enabling anything, look for a previous Byobu prompt entry. This is read-only and lets you spot a custom configuration that should be backed up first:

$ grep -nF '#byobu-prompt#' ~/.bashrc || echo 'no Byobu prompt line found'
no Byobu prompt line found

If the command prints a line, do not keep running the enable command to solve a duplicate. The helper writes a new marker line after removing its own older marker, but it does not understand unrelated prompt customisations. Copy the file before making a deliberate change:

$ cp --preserve=all ~/.bashrc ~/.bashrc.before-byobu-prompt
$ ls -l ~/.bashrc ~/.bashrc.before-byobu-prompt

That backup is your recovery point. It contains your personal shell settings, so keep its permissions and do not paste it into a public issue or chat.

3. Enable the prompt

Run the enable helper as your ordinary user:

$ byobu-enable-prompt

You will need to reload your shell configuration for this to take effect...
  . ~/.bashrc

The installed helper creates or updates Byobu's user prompt file and appends a guarded source line ending in #byobu-prompt# to ~/.bashrc. It does not replace your whole Bash configuration. The user configuration directory is normally ~/.byobu when that directory already exists, otherwise Byobu follows XDG_CONFIG_HOME or uses ~/.config/byobu.

Reload the file in the current Bash process:

$ . ~/.bashrc
$ grep -nF '#byobu-prompt#' ~/.bashrc
N:[ -r .../byobu/prompt ] && . .../byobu/prompt   #byobu-prompt#

The exact path and line number are host-specific. If you are inside a tmux session, this package version attempts to reload the configuration through tmux when enabling; an explicit . ~/.bashrc is still a clear verification step.

4. Verify timing and failure status

Run a short command and then a deliberately failing command. The prompt is interactive, so the bracketed timing text appears immediately before the next prompt rather than as ordinary command output:

$ sleep 1
[1.00Xs] andy@host:~/work$ false
[1] [0.00Xs] andy@host:~/work$

The runtime is approximate and its exact digits depend on scheduling. A non-zero status is shown when the previous command failed. The prompt also uses separate colours for the user, host and working directory, although terminal themes may make those colours look different. The prompt symbol is $ for a normal user and # for root.

5. Understand the Bash boundary

The prompt file uses Bash features, including PS0 and Bash's EPOCHREALTIME. Do not source it from Zsh, Dash or a script that is not running Bash. If a tool launches a non-interactive shell, its prompt may not be displayed even though the marker remains in ~/.bashrc.

If a new terminal shows no change, check the simple causes in order:

1. Confirm that the new terminal is Bash with printf '%s\n' "$0" and printf '%s\n' "$SHELL".
2. Confirm that ~/.bashrc contains the marker line and that the referenced prompt file exists.
3. Run . ~/.bashrc again, then run true and false to create fresh prompt results.

If enabling exits with status 1, inspect the shell value and the write permission of the file:

$ printf 'shell=%s\n' "$SHELL"
$ test -w ~/.bashrc && echo 'bashrc writable' || echo 'bashrc is not writable'
$ printf 'status=%s\n' "$?"

Do not make ~/.bashrc writable by everyone just to get past this check. Fix ownership or permissions through your normal account-repair process, and preserve the backup made earlier.

6. Disable it and undo the change

When you no longer want the prompt, use the matching helper:

$ byobu-disable-prompt

You will need to reload your shell configuration for this to take effect...
  . ~/.bashrc
$ . ~/.bashrc
$ grep -nF '#byobu-prompt#' ~/.bashrc || echo 'Byobu prompt disabled'
Byobu prompt disabled

Disable removes lines ending with the Byobu marker. It does not remove the rest of your Bash configuration. If you need to restore the exact pre-change state, stop first and compare the backup rather than overwriting blindly:

$ diff -u ~/.bashrc.before-byobu-prompt ~/.bashrc
$ cp --preserve=all ~/.bashrc.before-byobu-prompt ~/.bashrc
$ . ~/.bashrc

The final copy is a deliberate replacement of your current shell configuration. Use it only after reviewing the diff; any unrelated edits made after the backup will be lost. If you did not make a backup, disable the prompt and remove only a line that you have confirmed ends in #byobu-prompt#.

7. Use the interactive wrapper when preferred

byobu-prompt is an interactive wrapper around the enable and disable helpers. It asks a yes-or-no question; an empty answer or any answer other than n selects enable, while n or N selects disable:

$ byobu-prompt

Do you want to enable Byobu's bash color prompt? [Y/n]: n

You will need to reload your shell configuration for this to take effect...
  . ~/.bashrc

For repeatable administration, the explicit commands are easier to audit. The wrapper still requires an interactive input stream, so it is a poor fit for an unattended script.