Originally, "tty" had two definitions: the hardware (now the emulator) and the driver (interfaced through /dev/pty* or /dev/tty*).
The hardware/emulator was/is responsible for:
- Taking a stream of data and presenting it; this included interpreting control sequences like "move cursor left", "blinking cursor", "clear-screen" although these control sequences were often different among manufacturers.
- Sending keycodes for keys typed by the user; most of these were standard ASCII characters, but some terminals sent propriety keycodes for even standard keys.
The 'tty' driver was responsible for:
- Managing the buffering, in raw or canonical mode; for example, buffering a line of characters until Enter is pressed.
- Managing the control flow; e.g. being able to stop/continue with Cntl-s/Cntl-q.
- Translating propriety keycodes to standard ASCII, where applicable.
- Intercepting certain control characters (like Cntl-c and Backspace) and processing them appropriately (send SIGINT on a Cntl-c or signal an EOF on Cntl-d.
- Canonical display of characters, for example, if
echo is turned off, then do not send feedback (character typed) back to the terminal.
The terminfo and termcap databases managed what terminal control characters should be sent for an operation (like 'clear-screen'). These control sequences were/are not interpreted by the driver, but by the hardware/emulator.
There is some information on 256-color support in the tmux FAQ.
Detecting the number of colors that the terminal supports is unfortunately not straightforward, for historical reasons. See Checking how many colors my terminal emulator supports for an explanation. This means that
- tmux cannot reliably determine whether the terminal supports more than 8 colors;
- tmux cannot reliably communicate to the application that it supports more than 8 colors.
When you're in tmux, the terminal you're interacting with is tmux. It doesn't support all of xterm's control sequences. In particular, it doesn't support the OSC 4 ; … control sequence to query or set color values. You need to use that while directly running in xterm, outside tmux.
If you run tmux -2, then tmux starts with 256-color support, even if it doesn't think that your terminal supports 256 colors (which is pretty common).
By default, tmux advertises itself as screen without 256-color support. You can change the value of TERM in .tmux.conf to indicate 256-color support:
set -g default-terminal "screen-256color"
You can use TERM=xterm-256color or TERM=screen-256color on Ubuntu. These values will only cause trouble if you log in to a remote machine that doesn't have a termcap/terminfo entry for these names. You can copy the entries to your home directory on the remote machine; this works with most modern terminfo implementations.
# From the Ubuntu machine to a machine that doesn't have *-256color terminfo entries
ssh somewhere.example.com mkdir -p .terminfo/s .terminfo/x
scp -p /lib/terminfo/s/screen-256color somewhere.example.com:.terminfo/s/
scp -p /lib/terminfo/x/xterm-256color somewhere.example.com:.terminfo/x/
Best Answer
It means that mouse clicks will be reported to whatever is reading the terminal as standard input, the position and click will be encoded in an escape code similar to a special function key. Text mode mouse-aware applications (e.g.
aptitude) can then use that to perform functions like any "real" graphical use interface (GUI) programs use a mouse.Such reporting can be overridden by holding the shift key pressed while performing the mouse action, e.g. if you want to simply select some text instead of passing a drag command to the running application.