I have a script running on the background of my linux server and I would like to catch signals like reboot or anything that would kill this script and instead save any importante information before actually exiting.
I think most of what I need to catch is, SIGINT, SIGTERM, SIGHUP, SIGKILL.
How do catch any of these signals and have it execute an exit function otherwise keep executing whatever it was doing ?
pseudo perl code:
#!/usr/bin/perl
use stricts;
use warnings;
while (true)
{
#my happy code is running
#my happy code will sleep for a few until its breath is back to keep running.
}
#ops I have detected an evil force trying to kill me
#let's call the safe exit.
sub safe_exit()
{
# save stuff
exit(1);
}
pseudo php code:
<?php
while (1)
{
#my happy code is running
#my happy code will sleep for a few until its breath is back to keep running.
}
#ops I have detected an evil force trying to kill me
#let's call the safe exit.
function safe_exit()
{
# save stuff
exit(1);
}
?>
The SIGTERM signal is sent to a process to request its termination. Unlike the SIGKILL signal, it can be caught and interpreted or ignored by the process.
There are two signals which cannot be intercepted and handled: SIGKILL and SIGSTOP.
The HUP signal is sent to a process when its controlling terminal is closed. It was originally designed to notify a serial line drop (HUP stands for "Hang Up"). In modern systems, this signal usually indicates the controlling pseudo or virtual terminal is closed.
a kill -HUP sends the signal "2" to the process. This tells the process to re-read its configuration but do not exit.
PHP uses pcntl_signal
to register a signal handler, so something like this:
declare(ticks = 1);
function sig_handler($sig) {
switch($sig) {
case SIGINT:
# one branch for signal...
}
}
pcntl_signal(SIGINT, "sig_handler");
pcntl_signal(SIGTERM, "sig_handler");
pcntl_signal(SIGHUP, "sig_handler");
# Nothing for SIGKILL as it won't work and trying to will give you a warning.
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