fail2ban/utils/process.py

# This file is part of Fail2Ban.
#
# Fail2Ban is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# Fail2Ban is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with Fail2Ban; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

# Author: Cyril Jaquier
# 
# $Revision$

__author__ = "Cyril Jaquier"
__version__ = "$Revision$"
__date__ = "$Date$"
__copyright__ = "Copyright (c) 2004 Cyril Jaquier"
__license__ = "GPL"

import os, logging, signal

# Gets the instance of the logger.
logSys = logging.getLogger("fail2ban")

def createDaemon():
	""" Detach a process from the controlling terminal and run it in the
		background as a daemon.
	
		http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/278731
	"""

	try:
		# Fork a child process so the parent can exit.  This will return control
		# to the command line or shell.  This is required so that the new process
		# is guaranteed not to be a process group leader.  We have this guarantee
		# because the process GID of the parent is inherited by the child, but
		# the child gets a new PID, making it impossible for its PID to equal its
		# PGID.
		pid = os.fork()
	except OSError, e:
		return((e.errno, e.strerror))	 # ERROR (return a tuple)

	if (pid == 0):	   # The first child.

		# Next we call os.setsid() to become the session leader of this new
		# session.  The process also becomes the process group leader of the
		# new process group.  Since a controlling terminal is associated with a
		# session, and this new session has not yet acquired a controlling
		# terminal our process now has no controlling terminal.  This shouldn't
		# fail, since we're guaranteed that the child is not a process group
		# leader.
		os.setsid()
	
		# When the first child terminates, all processes in the second child
		# are sent a SIGHUP, so it's ignored.
		signal.signal(signal.SIGHUP, signal.SIG_IGN)
	
		try:
			# Fork a second child to prevent zombies.  Since the first child is
			# a session leader without a controlling terminal, it's possible for
			# it to acquire one by opening a terminal in the future.  This second
			# fork guarantees that the child is no longer a session leader, thus
			# preventing the daemon from ever acquiring a controlling terminal.
			pid = os.fork()		# Fork a second child.
		except OSError, e:
			return((e.errno, e.strerror))  # ERROR (return a tuple)
	
		if (pid == 0):	  # The second child.
			# Ensure that the daemon doesn't keep any directory in use.  Failure
			# to do this could make a filesystem unmountable.
			os.chdir("/")
		else:
			os._exit(0)	  # Exit parent (the first child) of the second child.
	else:
		os._exit(0)		 # Exit parent of the first child.

	# Close all open files.  Try the system configuration variable, SC_OPEN_MAX,
	# for the maximum number of open files to close.  If it doesn't exist, use
	# the default value (configurable).
	try:
		maxfd = os.sysconf("SC_OPEN_MAX")
	except (AttributeError, ValueError):
		maxfd = 256	   # default maximum

	for fd in range(0, maxfd):
		try:
			os.close(fd)
		except OSError:   # ERROR (ignore)
			pass

	# Redirect the standard file descriptors to /dev/null.
   	os.open("/dev/null", os.O_RDONLY)	# standard input (0)
	os.open("/dev/null", os.O_RDWR)		# standard output (1)
	os.open("/dev/null", os.O_RDWR)		# standard error (2)

	return True

def killPID(pid):
	""" Kills the process with the given PID using the
		INT signal (same effect as <ctrl>+<c>).
	"""
	try:
		return os.kill(pid, 2)
	except OSError:
		logSys.error("Can not kill process " + `pid` + ". Please check that " +
					"Fail2Ban is not running and remove the file " +
					"'/tmp/fail2ban.pid'")
		return False

def executeCmd(cmd, debug):
	""" Executes an OS command.
	"""
	if cmd == "":
		logSys.debug("Nothing to do")
		return None
	
	logSys.debug(cmd)
	if not debug:
		retval = os.system(cmd)
		if not retval == 0:
			logSys.error("'" + cmd + "' returned " + `retval`)
		return retval
	else:
		return None