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** [tickets:#62] Lines missing in terminal scrollback (smcup@:rmcup@)**
**Status:** open
**Created:** Fri Sep 06, 2013 08:42 AM UTC by Joachim Breuer
**Last Updated:** Fri Sep 06, 2013 08:42 AM UTC
**Owner:** nobody
The 'workaround' to have terminal scrollback is enabled:
`set -g terminal-overrides 'xterm*:smcup@:rmcup@'`
This causes terminal scrollback to work in principle.
BUT there is a grave problem:
If a program outputs a lot of text, only "most" of the text will be pushed
through to the terminal's scrollback buffer.
(I did not touch the tmux terminal at all while observing and reproducing this,
so no window switches etc.).
"Most" of the text means something like this:
- Assume the physical terminal is 3 lines high (to keep this example
manageable), or if you prefer assume that each line in the example stands for
20 lines of actual output. Lines "above" those three are available from
scrollback. tmux is running with 2 or 3 windows, I'm in window 0. There already
is some text in it (including the scrollback buffer):
...
A01
A02
A03
A04
A05
A06
A07
A08
A09
A10
- I run something that generates a lot of output quickly (think build log):
P01
P02
P03
...
P17
P18
P19
P20
- Now, I see the last three lines in the physical terminal:
P18
P19
P20
- When I use the terminal's scrollback to scroll up through the lines, I see
output like this:
...
A04
A05
P15
P16
P17
...
=> A chunk of output is missing "in the middle".
- If/When I notice this and use tmux's built in scrollback, all output lines
are available as expected.
Since the above procedure using the terminal scrollback (Shift-PgUp) is my
"hardwired in the spinal cord" way of skimming / looking for problems in build
logs, that's a HUGE problem for me.
Sometimes it's obvious that lines are missing, and then switching to tmux's own
scrollback (<prefix> PgUp) shows all output correctly. Sometimes, of course,
it's not obvious that a chunk is missing.
System details:
- tmux 1.8
- ncurses 5.9.20110404
- KDE 4.10.5 / Konsole 2.10.5
- current gentoo 13.0 kde profile, on amd64
Control:
I've been using screen since about 1995 before tmux, also with terminal
scrollback enabled:
`termcapinfo xterm*|xs ti@:te=\E[2J`
I've never observed missing lines using screen; on the same system with both of
them installed in parallel it's only tmux that's affected; screen does not
exhibit this problem.
Conjecture:
It feels like some layer decides that "for efficiency" the terminal scrollback
should not be updated with all of the fast-arriving output.
Here, both tmux and screen use ncurses 5.9; with tmux linked against
`libncurses.so.5` and screen against `libncursesw.so.5`.
I'll be happy to help with any analysis or testing.
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