signal processing INT or TERM



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signal processing INT or TERM

Postby rsarpi » Fri, 31 Oct 2008 05:50:54 GMT

perl 5.8.2
OS: AIX fully POSIX compliant

my script moves files from one dir to another.
When I want my script to stop, should I pass it along the signal INT
or TERM?

INT just interrupts the script.  It finishes whatever it's processing
and then it's done.

TERM on the other hand, just sends a TERMination signal, waits a few
seconds, then KILLs the program.  TERM is more common I guess when
starting/stopping unix shell scripts in the init dir.

My fear is that if I pass the TERM signal, maybe the system will chop
off the files that are being moved on the fly.  The "few seconds" are
unpredictable in value at least on my system. So the system might say
'it's been too long, let's kill it."

Any thoughts? Is there a "perlish" way to do it?

Re:signal processing INT or TERM

Postby pangj » Fri, 31 Oct 2008 23:20:37 GMT

 > Message du 30/10/08 10:45

SIGTERM and SIGINT are almost the same usage. See 'man 8 kill' and look for signals.
You may want to redefine the POSIX signal handlers.
See also L. Stein's "Network programming with Perl", that will give the full details.


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Re: signal processing INT or TERM

Postby carnildo » Sun, 02 Nov 2008 05:22:20 GMT

I'd send a custom signal (say, USR1).  When the script receives that
signal, it sets a flag indicating it should perform a clean exit.
Totally untested:

my $done = 0;

sub sigusr {
    $done = 1;

$SIG{USR1} = \&sigusr;

    # Do something
# Clean up and exit

It won't work if "do something" is perpetually blocked on a read or
somesuch, but if you wake up periodically to go through the loop,
you'll be fine.

Mark Wagner

Similar Threads:

1.Signal Handling/Term::ReadLine problem in Perl

2.KILL INT can not wake up $SIG{INT}

Hi list,

Anyone has such experience? KILL INT pid cannot wake up $SIG{INT}  sub{}.

my code is like;

$SIG{INT} = sub {#load pm}

$SIG{ALRM} = sub {print "Driver $pm is going to sleep... bye.\n"; exit;};

the pm actually has a system call to execute something
sub xxx {


my $tmp = kill "INT", $pid; ## it returns number of processes, eg: 1
cannot wake up the $SIG{INT}  at all after $SIG{ALRM} has been executed.

does system call cause the problem?


3.(fwd) Toplevel doesn't update (signals not processed in MainLoop)

> I suspect this is part of Perl's safe signal handling - the *operating
> system* signal isn't being delivered because perl isn't doing anything.
> Once you wave the cursor over a window an *X11 signal* is raised and
> the Tk event loop restarts.
> So, one way to have an alien process alert an idle Tk program is to
> never have it idle - i.e. keep the event loop active.
> So, alien process does "kill USR2, ptk-process", and ptk-process does:
>      $SIG{USR2} = sub { &synchronize };
>      $mw->repeat( 10_000 => sub { $mw->idletasks } );

Yes, I read about the safe signal handling in Perl. But I  think this 
behaviour of Tk isn't OK, it should be considered as a bug or unwanted 
feature. IMO there is no reason for not handling signals imediately, while 
being idle in the MainLoop.
Keeping the MainLoop active isn't an option for my program.
I read the "Tk + perl-5.8.0 eat and delays signals"-thread on the same 
newsgroup, where someone suggests using the old signal-handler-stuff via 
the POSIX module and sigaction...

1) Maybe someone can check if the MainLoop / Signal problem can be improved?

2) I should find a better design for my process communication
        (and will start a new thread for that ;-)


4.process signals

I have an application system command that is like tail -f in UNIX and I 
want to say

while x < 10
        'command'  append to log
        print "\n" append to log
        issue HANGUP or KILL SIGNAL

How do I issue a hangup signal to this process using perl?

Derek B. Smith
OhioHealth IT
UNIX Support

5.Call For Manuscripts: International Journal of Signal Processing (IJSP)

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7. Call For Manuscripts: International Journal of Signal Processing (IJSP)

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