Clean up ncurses mess in terminal after a crash

Question

I am drawing a TUI using ncurses. The trouble is that whenever my program gets seg-fault, my terminal is left in mess. I can not see what I am typing. Its a pain since I am working over ssh. I have mitigated some of the effect by using screen.

I would like to know if there is a command which will refresh my terminal after seg-fault in ncurses so that my terminal starts behaving normally.

Most terminal programs have a "reset" option which puts the terminal back into its initial state - useful for situations like this - check the menus in your program. — Paul R, Aug 01 '12 at 06:50
@PaulR I am using gnome-terminal. Reset doesn't do the job ;-( — Dilawar, Aug 01 '12 at 06:53

Dilawar · Accepted Answer · 2021-05-31T10:46:21.997

28

Command,

stty sane

did the job. If enter doesn't work, you may use ^J.

stty sane ^J

Sometimes CR/LF interpretation is broken so use the ^J explicitly.

edited May 31 '21 at 10:46

answered Aug 01 '12 at 07:06

Dilawar

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I still do not see the cursor. – AlwaysLearning Aug 02 '16 at 09:51
suggest writting the control J as below comment Thomas Dickey – serup Sep 28 '16 at 06:51
scroll now instead goes to a different command in history instead of scrolling up and down in terminal view – mekb May 30 '21 at 11:49
The comment about "older terminal" is incorrect. – Thomas Dickey May 31 '21 at 09:54

score 18 · Answer 2 · answered Apr 19 '16 at 12:33

ncurses (any curses implementation) sets the terminal modes to raw and noecho while running, and allows applications to simulate these using the raw and noraw, echo and noecho functions. It does this for performance, to avoid waiting when switching between these modes.

When an application calls endwin, ncurses restores the terminal modes. It can also do this for reset_shell_mode, though endwin is used far more often.

If your application crashes, or exits without restoring the terminal modes using endwin, the most obvious problem is that you cannot see what you are typing, and that pressing enter does not work.

ncurses provides a signal handler to catch the user-initiated signals SIGINT, SIGTERM, and will cleanup when those are caught. It does not try to catch SIGSEGV because at that point, your application is dead and trying to resurrect it to repair things is counter productive.

Some people might advise using stty sane to restore the terminal modes. That "works", but on Unix platforms is likely to leave your erase key set to an unexpected value. It happens to work as expected for Linux- and modern BSD-systems.

However, beyond that, ncurses normally resets

colors (default colors for the terminal)
line-drawing (disabled)
mouse protocol (to disable it)

If your application uses any of these features, then the reset command is the appropriate choice. It usually clears the screen as well (perhaps not what was wanted). And it uses fewer characters:

resetcontrolJ
stty sanecontrolJ

Further reading:

Signal handlers in curs_initscr(3x)
Portability in tput(1)
reset - reinitialization

score 7 · Answer 3 · answered Jul 03 '13 at 15:59

7

The command

reset

also worked for me on Ubuntu, probably overkill though. What worked best was setting an alias like:

alias 'clean'='stty sane;clear;'

in my .bash_aliases as I found myself needing to do this alot in debugging.

answered Jul 03 '13 at 15:59

JDong

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I still do not see the cursor. – AlwaysLearning Aug 02 '16 at 09:51
The reset command "should" do this, as a side-effect of the initialization strings it sends. The terminal description may not do that, but **`tput cnorm`** is more explicit and more likely to work. – Thomas Dickey May 31 '21 at 10:09

score 4 · Answer 4 · answered Aug 01 '12 at 07:10

4

Write a signal handler for SIGSEGV, etc. that calls endwin().

answered Aug 01 '12 at 07:10

Kevin Grant

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Here is how to do it (only be sure to handle SIGSEGV and not SIGTERM): http://www.linuxquestions.org/questions/programming-9/ncurses-dev-254581-print/ – AlwaysLearning Aug 02 '16 at 10:13
That won't work (will actually aggravate the situation). – Thomas Dickey May 31 '21 at 10:02

score 0 · Answer 5 · answered Aug 29 '19 at 19:40

I had this problem recently on a Mac OSX terminal. Following set of commands worked whereas stty sane did not.

stty discard '^O'
stty dsusp '^Y'
stty eof '^D'
stty eol '^@'
stty eol2 '^@'
stty erase '^?'
stty intr '^C'
stty kill '^U'
stty lnext '^V'
stty min 1
stty quit '^\'
stty reprint '^R'
stty start '^Q'
stty status '^T'
stty stop '^S'
stty susp '^Z'
stty time 0
stty werase '^W'

Clean up ncurses mess in terminal after a crash

5 Answers5

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