PeterHarding at 06:03, 19 July 2009

2009-07-19T06:03:44Z

← Older revision		Revision as of 16:03, 19 July 2009
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	[[Category:Python]]		[[Category:Python]]
			[[Category:Examples]]

PeterHarding at 00:01, 29 May 2008

2008-05-29T00:01:18Z

← Older revision		Revision as of 10:01, 29 May 2008
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	# Redirect standard I/O streams to "/dev/null".		# Redirect standard I/O streams to "/dev/null".

	Failed fork() calls will return a tuple: (errno, strerror). Again, this behavior can be modified to meet your program's needs.		Failed fork() calls will return a tuple:

			(errno, strerror).

			Again, this behavior can be modified to meet your program's needs.

	==Resources:==		==Resources:==

PeterHarding at 00:00, 29 May 2008

2008-05-29T00:00:59Z

← Older revision		Revision as of 10:00, 29 May 2008
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	Default behaviors are as follows, but they can be modified:		Default behaviors are as follows, but they can be modified:

	1) Ignore SIGHUP signals.		# Ignore SIGHUP signals.
	2) Default current working directory to the "/" directory.		# Default current working directory to the "/" directory.
	3) Set the current file creation mode mask to 0.		# Set the current file creation mode mask to 0.
	4) Close all open files (0 to [SC_OPEN_MAX or 256]).		# Close all open files (0 to [SC_OPEN_MAX or 256]).
	5) Redirect standard I/O streams to "/dev/null".		# Redirect standard I/O streams to "/dev/null".

	Failed fork() calls will return a tuple: (errno, strerror). Again, this behavior can be modified to meet your program's needs.		Failed fork() calls will return a tuple: (errno, strerror). Again, this behavior can be modified to meet your program's needs.

PeterHarding at 03:58, 25 February 2008

2008-02-25T03:58:22Z

← Older revision		Revision as of 13:58, 25 February 2008
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	==Script==		==Script==

	</pre>		<pre>
	#!/usr/bin/env python		#!/usr/bin/env python

PeterHarding: New page: =A Reference Implementation of a Daemon = Default behaviors are as follows, but they can be modified: 1) Ignore SIGHUP signals. 2) Default current working directory to the "/" director...

2008-02-25T03:58:11Z

New page: =A Reference Implementation of a Daemon = Default behaviors are as follows, but they can be modified: 1) Ignore SIGHUP signals. 2) Default current working directory to the "/" director...

New page

=A Reference Implementation of a Daemon =

Default behaviors are as follows, but they can be modified:

1) Ignore SIGHUP signals.
2) Default current working directory to the "/" directory.
3) Set the current file creation mode mask to 0.
4) Close all open files (0 to [SC_OPEN_MAX or 256]).
5) Redirect standard I/O streams to "/dev/null".

Failed fork() calls will return a tuple: (errno, strerror). Again, this behavior can be modified to meet your program's needs.

==Resources:==

* Advanced Programming in the Unix Environment: W. Richard Stevens
* Unix Network Programming (Volume 1): W. Richard Stevens
* http://www.erlenstar.demon.co.uk/unix/faq_2.html#SEC16

==Script==

</pre>
#!/usr/bin/env python

"""Disk And Execution MONitor (Daemon)

Default daemon behaviors (they can be modified):
1.) Ignore SIGHUP signals.
2.) Default current working directory to the "/" directory.
3.) Set the current file creation mode mask to 0.
4.) Close all open files (0 to [SC_OPEN_MAX or 256]).
5.) Redirect standard I/O streams to "/dev/null".

Failed fork() calls will return a tuple: (errno, strerror). This behavior
can be modified to meet your program's needs.

Resources:
Advanced Programming in the Unix Environment: W. Richard Stevens
Unix Network Programming (Volume 1): W. Richard Stevens
http://www.erlenstar.demon.co.uk/unix/faq_2.html#SEC16
"""

__author__ = "Chad J. Schroeder"
__version__ = "$Id$"

import os # Miscellaneous OS interfaces.
import sys # System-specific parameters and functions.
import signal # Set handlers for asynchronous events.

def createDaemon():
"""Detach a process from the controlling terminal and run it in the
background as a daemon.
"""

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
# seesion, 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("/")
# Give the child complete control over permissions.
os.umask(0)
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).

if (os.sysconf_names.has_key("SC_OPEN_MAX")):
maxfd = os.sysconf("SC_OPEN_MAX")
else:
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(0)

if __name__ == "__main__":
# Self-test.

retCode = createDaemon()

# If executed with superuser privilages, there should be a new file in the
# "/" directory. It should contain the function's return code, the daemon's
# PID, PPID, and PGRP. Its PID should not equal its PGRP, and its PPID
# should equal 1. If it's executed without superuser privilages, the file
# won't be created and no errors will be reported.

open("createDaemon.log", "w").write("rc: %s; pid: %d; ppid: %d; pgrp: %d" %\
(retCode, os.getpid(), os.getppid(), os.getpgrp()))

sys.exit(0)
</pre>

[[Category:Python]]

Daemon.py - Revision history

PeterHarding at 06:03, 19 July 2009

PeterHarding at 00:01, 29 May 2008

PeterHarding at 00:00, 29 May 2008

PeterHarding at 03:58, 25 February 2008

PeterHarding: New page: =A Reference Implementation of a Daemon = Default behaviors are as follows, but they can be modified: 1) Ignore SIGHUP signals. 2) Default current working directory to the "/" director...