Hi

I start all my processes via crontab using init scripts. One day I was investigating process monitoring and had epiphany - why bother adding another set of monitoring rules when the crontab describes perfectly when a process should and shouldn't be running?

I came up with the below which almost seems too simple for such great benefit 

#!/usr/bin/perl -w

use strict;

use File::Basename;
use POSIX 'strftime';
use Sys::Syslog;

sub logit($);

logit('starting up');

my $cron_cmd = 'crontab -l';

while ( 1 ) {
  my $now   = strftime('%H%M', localtime);
  my $today = strftime('%w', localtime);

  for ( qx/$cron_cmd/ ) {
    if ( /^([\d*]+)\s+([\d*]+)\s+([\d*]+)\s+([\d*]+)\s+([\d\-*]+)\s+(.
+*)/ ) {
      my ( $min, $hour, $day, $mon, $dow, $cmd ) = ( $1, $2, $3, $4, $
+5, $6 );
      my $pattern;

      if ( $dow =~ m/\-/ ) {
        $pattern = "[$dow]";
      } elsif ( $dow =~ m/,/ ) {
        $dow =~ s/,//;
        $pattern = "[$dow]";
      } elsif ( $dow =~ m/^\d$/ ) {
        $pattern = "^$dow";
      } else {
        $pattern = ".*";
      }

      next unless $today =~ qr/$pattern/;

      if ( $cmd =~ m#(/etc/init.d/[^\s]+)\s+(start|stop)# ) {
        my ( $init, $mode ) = ( $1, $2 );
        if ( $mode eq 'start' ) {
          $schedule{$init}{start} = "$hour$min";
        } else {
          $schedule{$init}{stop}  = "$hour$min";
        }
      }
    }
  }
  for ( keys %schedule ) {
    if ( $now > $schedule{$_}{start} && $now < $schedule{$_}{stop} ) {
      if ( system("$_ status >/dev/null") ) {
        if ( $schedule{$_}{status} ne 'FAIL' || !$schedule{$_}{status}
+ ) {
          logit("$_ isnt running");
          $schedule{$_}{status} = 'FAIL';
        }
      } else {
          if ( defined $schedule{$_}{status} && $schedule{$_}{status} 
+eq 'FAIL' ) {
            logit("$_ is back to normal");
          }
          $schedule{$_}{status} = 'OK';
      }
    }
  }
  sleep 5;
}
logit('shutting down');

sub logit($) {
  my $msg = shift;
  openlog(basename($0), '', 'LOG_DAEMON');
  syslog('info', $msg);
  closelog();
}

[download]
This seems to work exactly how I expect but there seems to be an issue with it falsely identifying processes which shouldn't be running anyway. For instance processes which should only be running on Sunday are falsely being flagged as not running today (Monday) when they shouldn't be anyway?

The below is triggering alerts today even though date +%w == 1 

00 05 * * 0 /etc/init.d/foo start
00 22 * * 0 /etc/init.d/foo stop

[download]

the below crontab have so far caused no alerts today 

00 05 * * 1-5 /etc/init.d/foo2 start
00 22 * * 1-5 /etc/init.d/foo2 stop

[download]

I can't spot the issue myself and appeal for help. Other improvements are very much appreciated also

Thank you

In reply to Process Monitoring Madness by woland

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