Occasionally an application may crash unexpectedly. Instead of reinventing the wheel I found a simple unix/linux daemon in Python for the daemon functionality and just added the run section logic. Using the bits below I can monitor or potentially restart the failed application. The run section forks a daemon which checks for the existence of a processes using pgrep every 5 seconds in a loop. It reads from a file named observe.list for any number of named processes. Each line in observe.list should contain a unique process name like puppetmasterd and on the next line httpd or whatever you’d like to watch. I tried using logger with SysLogHandler but I’m not sure it was available with python 2.4.3 which ships with RHEL 5 or CentOS 5.
#!/usr/bin/env python
import sys, time, subprocess, syslog
from daemon import Daemon
# file which contains the list of process to observe
process_file = open('observe.list', 'r')
process_list = []
for line in process_file:
process_list.append(line.rstrip('\n'))
def isRunning ( process_name ):
ps = subprocess.call("pgrep "+process_name, shell=True, stdout=subprocess.PIPE)
if ps is 1:
return False
else:
return True
class Observe(Daemon):
def run(self):
while True:
for process in process_list:
if isRunning(process) == False:
syslog.syslog(process + " not running!")
time.sleep(5)
else:
syslog.syslog(process + ' is running!')
time.sleep(5)
if __name__ == "__main__":
daemon = Observe('/tmp/observe.pid')
if len(sys.argv) == 2:
if 'start' == sys.argv[1]:
daemon.start()
elif 'stop' == sys.argv[1]:
daemon.stop()
elif 'restart' == sys.argv[1]:
daemon.restart()
else:
print "Unknown command"
sys.exit(2)
sys.exit(0)
else:
print "usage: %s start|stop|restart" % sys.argv[0]
sys.exit(2)
