In Ubuntu, I can get the desired behavior by adding the following line to $ {HOME} /. byobu / .tmuxrc:
set-option -g default-path $HOME
This parameter is a document on the tmux man page:
set-option [-agoqsuw] [-t target-session | target-window] option value
(alias: set)
Set a window option with -w (equivalent to the set-window-option
command), a server option with -s, otherwise a session option.
If -g is specified, the global session or window option is set.
With -a, and if the option expects a string, value is appended
to the existing setting. The -u flag unsets an option, so a session
inherits the option from the global options. It is not possible to
unset a global option.
The -o flag prevents setting an option that is already set.
The -q flag suppresses the informational message (as if the quiet
server option was set).
Available window options are listed under set-window-option.
value depends on the option and may be a number, a string, or a flag
(on, off, or omitted to toggle).
Available server options are:
<snip>
default-path path
Set the default working directory for new panes. If empty (the
default), the working directory is determined from the process running
in the active pane, from the command line environment or from the
working directory where the session was created. Otherwise the same
options are available as for the -c flag to new-window.
I tried with at first set-option -g default-path ~, but it looks like tmux does not understand this alias.
Update: the above does not work with byobu 5.92 (possibly other versions) and tmux 1.9, since tmux removed the parameter default-path. It looks like byobu dev used this to get a behavior in which new windows open in CWD, while I and the poll wanted it to be open in the default HOME directory. In the new default bindings in /usr/share/byobu/keybindings/f-keys.tmuxI found this:
bind-key -n F2 new-window -c "#{pane_current_path}" \; rename-window "-"
bind-key -n C-F2 display-panes \; split-window -h -c "#{pane_current_path}"
bind-key -n S-F2 display-panes \; split-window -v -c "#{pane_current_path}"
To get the desired behavior, always making byobu open new screens in your home directory, add the following to ~/.byobu/keybindings.tmux:
bind-key -n F2 new-window -c "$HOME" \; rename-window "-"
bind-key -n C-F2 display-panes \; split-window -h -c "$HOME"
bind-key -n S-F2 display-panes \; split-window -v -c "$HOME"