Hi, Ian--

On Mar 26, 2009, at 12:40 PM, Ian Rose wrote:
I'm new to this list so if this question is better directed elsewhere please point me in the right direction.

Welcome; this list is a good place.

My research group has a server running 7.2-PRERELEASE and an odd problem has cropped up: most signals are not being delivered to processes. For example, if I run 'sleep 10' from the shell, ctrl-c won't interrupt it. kill -KILL <pid> still works, but this sort of makes sense since it involves only the OS and doesn't require delivery to the process itself.

Both your shells and /bin/kill should be using kill(2) system call; see /usr/src/bin/kill/kill.c, /usr/src/contrib/tcsh/sh.proc.c, etc for the details. For a signal to work, the OS does deliver it to the process, which must be in a runnable state or else delivery will block until the process has returned from a system call or whatever is blocking it.

I have performed a fairly extensive series of tests:

using bash:

   * ctrl-c does nothing
   * ctrl-z does nothing
   * kill -XXX <pid> works for SIGKILL and SIGSTOP only
   * kill -XXX <pid> does nothing for all other signals
* a C program does not receive a SIGHUP, SIGINT, SIGABRT or SIGTERM that it has sent to itself via 'kill(getpid(), SIGxxx)' * a C program will react appropriately when it sends itself a SIGKILL or SIGSTOP
   * a C program will react appropriately when you call abort(3)
* a C program will die with the error "Floating point exception: 8 (core dumped)" if it divides by zero, but not if it sends itself a SIGFPE.

That's significantly odd. What does "stty -a" say about your control character settings? You should see something like:

% stty -a
speed 9600 baud; 58 rows; 90 columns;
[ ... ]
cchars: discard = ^O; dsusp = ^Y; eof = ^D; eol = <undef>;
        eol2 = <undef>; erase = ^?; erase2 = ^H; intr = ^C; kill = ^U;
        lnext = ^V; min = 1; quit = ^\; reprint = ^R; start = ^Q;
        status = ^T; stop = ^S; susp = ^Z; time = 0; werase = ^W;

...which has the mappings for ^C => SIGINT, ^Z => SIGTSTP, etc.


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