Some shift+arrows not working in tmux?

Question

I am attempting customize tmux so that

• Ctrl-Arrows are used for pane selection
• Shift-Arrows are used for pane resizing
• Alt-Arrows (left, right) are used for window selection

... all are working correctly, except for Shift-Up and Shift-Down. (Puzzlingly, Shift-Left and Shift-Right work as expected.)

This is running tmux 2.0 inside xfce4-terminal (although I've also seen this problem on Ubuntu, using Ubuntu's default terminal program.)

Is there something I am not doing correctly? Here is the entire contents of my .tmux.conf file:

# split <h>orizontal and <v>ertical
bind-key h split-window -v
bind-key v split-window -h

# Use Ctrl-arrow keys without prefix key to switch panes
bind -n C-Up    select-pane -U
bind -n C-Down  select-pane -D
bind -n C-Left  select-pane -L
bind -n C-Right select-pane -R

# Use Shift-arrow keys without prefix key to resize panes
bind -n S-Up    resize-pane -U
bind -n S-Down  resize-pane -D
bind -n S-Left  resize-pane -L
bind -n S-Right resize-pane -R

# Use Alt-arrow keys without prefix key to switch windows
bind -n M-Left  previous-window
bind -n M-Right next-window

# No delay for escape key press
set -sg escape-time 0

# Reload tmux config
bind-key r source-file ~/.config/.tmux.conf \; display-message "Configuration reloaded"

Answer 1

The problem is unlikely to be related to some difference in application mode versus normal mode, because xterm sends the same sequence of characters for shifted and unshifted cursor keys.

One clue to the problem is that the various ctrl items are all extended xterm capabilities. tmux uses a couple of tables:

• one lists special keys which are unlikely to be found in a terminal entry
• the other lists terminal capabilities which might be gotten from a regular terminal database entry.

For the latter, these rows from tmux's table are relevant:

    { TTYC_KDN2, TTYCODE_STRING, "kDN" },
    { TTYC_KDN3, TTYCODE_STRING, "kDN3" },
    { TTYC_KDN4, TTYCODE_STRING, "kDN4" },
    { TTYC_KDN5, TTYCODE_STRING, "kDN5" },
    { TTYC_KDN6, TTYCODE_STRING, "kDN6" },
    { TTYC_KDN7, TTYCODE_STRING, "kDN7" },
    { TTYC_KEND, TTYCODE_STRING, "kend" },

    { TTYC_KLFT2, TTYCODE_STRING, "kLFT" },
    { TTYC_KLFT3, TTYCODE_STRING, "kLFT3" },
    { TTYC_KLFT4, TTYCODE_STRING, "kLFT4" },
    { TTYC_KLFT5, TTYCODE_STRING, "kLFT5" },
    { TTYC_KLFT6, TTYCODE_STRING, "kLFT6" },
    { TTYC_KLFT7, TTYCODE_STRING, "kLFT7" },

    { TTYC_KRIT2, TTYCODE_STRING, "kRIT" },
    { TTYC_KRIT3, TTYCODE_STRING, "kRIT3" },
    { TTYC_KRIT4, TTYCODE_STRING, "kRIT4" },
    { TTYC_KRIT5, TTYCODE_STRING, "kRIT5" },
    { TTYC_KRIT6, TTYCODE_STRING, "kRIT6" },
    { TTYC_KRIT7, TTYCODE_STRING, "kRIT7" },
    { TTYC_KUP2, TTYCODE_STRING, "kUP" },
    { TTYC_KUP3, TTYCODE_STRING, "kUP3" },
    { TTYC_KUP4, TTYCODE_STRING, "kUP4" },
    { TTYC_KUP5, TTYCODE_STRING, "kUP5" },
    { TTYC_KUP6, TTYCODE_STRING, "kUP6" },
    { TTYC_KUP7, TTYCODE_STRING, "kUP7" },

    { TTYC_RI, TTYCODE_STRING, "ri" },

Most of these rows (in tty-term.c) are xterm extensions. The strings for the shifted cursor keys might be provided by "kUP", "kDN", "kLFT", "kRGT" — as well as "kri" and "kind".

The last two are problematic:

• tmux has a table entry for "ri" (the string sent to the terminal) but none for "kri" and "kind" (your up/down cursor-keys)
• because (n)curses' wgetch will see only the first capability with a given value in the list of strings, ncurses' database defines only one possibility.
• kUP and kDN are extensions, not standard capabilities, so ncurses defines "kri" and "kind", which are standard.

The problem is not with your configuration, but a simple bug in tmux which could be addressed by adding entries to that table. Something like this (untested) is a way to proceed:

    { TTYC_KUP2, TTYCODE_STRING, "kri" },
    { TTYC_KDN2, TTYCODE_STRING, "kind" },