Re: forking and avoiding zombies!

Discussion in 'Python' started by peter, Dec 11, 2012.

  1. peter

    peter Guest

    On 12/11/2012 08:47 AM, andrea crotti wrote:
    > Yes I wanted to avoid to do something too complex, anyway I'll just
    > comment it well and add a link to the original code..
    >
    > But this is now failing to me:
    >
    > def daemonize(stdin='/dev/null', stdout='/dev/null', stderr='/dev/null'):
    > # Perform first fork.
    > try:
    > pid = os.fork()
    > if pid > 0:
    > sys.exit(0) # Exit first parent.
    > except OSError as e:
    > sys.stderr.write("fork #1 failed: (%d) %s\n" % (e.errno, e.strerror))
    > sys.exit(1)
    >
    > # Decouple from parent environment.
    > os.chdir("/")
    > os.umask(0)
    > os.setsid()
    >
    > # Perform second fork.
    > try:
    > pid = os.fork()
    > if pid > 0:
    > sys.exit(0) # Exit second parent.
    > except OSError, e:
    > sys.stderr.write("fork #2 failed: (%d) %s\n" % (e.errno, e.strerror))
    > sys.exit(1)
    >
    > # The process is now daemonized, redirect standard file descriptors.
    > sys.stdout.flush()
    > sys.stderr.flush()
    >
    > si = file(stdin, 'r')
    > so = file(stdout, 'a+')
    > se = file(stderr, 'a+', 0)
    > os.dup2(si.fileno(), sys.stdin.fileno())
    > os.dup2(so.fileno(), sys.stdout.fileno())
    > os.dup2(se.fileno(), sys.stderr.fileno())
    >
    >
    > if __name__ == '__main__':
    > daemonize(stdout='sample_file', stderr='sample')
    > print("hello world, now should be the child!")
    >
    >
    > [andrea@andreacrotti experiments]$ python2 daemon.py
    > Traceback (most recent call last):
    > File "daemon.py", line 49, in <module>
    > daemonize(stdout='sample_file', stderr='sample')
    > File "daemon.py", line 41, in daemonize
    > so = file(stdout, 'a+')
    > IOError: [Errno 13] Permission denied: 'sample_file'
    >
    > The parent process can write to that file easily, but the child can't,
    > why is it working for you and not for me though?
    > (Running this on Linux with a non-root user)

    In the time when you fork the proccess you can't use relative path, is
    dangerous. You need to use absolute path's like this.

    import os, sys

    def daemonize(stdin='/dev/null', stdout='/dev/null', stderr='/dev/null'):
    # Perform first fork.
    try:
    pid = os.fork()
    if pid > 0:
    sys.exit(0) # Exit first parent.
    except OSError as e:
    sys.stderr.write("fork #1 failed: (%d) %s\n" % (e.errno,
    e.strerror))
    sys.exit(1)

    # Decouple from parent environment.
    os.chdir("/")
    os.umask(0)
    os.setsid()

    # Perform second fork.
    try:
    pid = os.fork()
    if pid > 0:
    sys.exit(0) # Exit second parent.
    except OSError, e:
    sys.stderr.write("fork #2 failed: (%d) %s\n" % (e.errno,
    e.strerror))
    sys.exit(1)

    # The process is now daemonized, redirect standard file descriptors.
    sys.stdout.flush()
    sys.stderr.flush()

    si = file(stdin, 'r')
    so = file(stdout, 'a+')
    se = file(stderr, 'a+', 0)
    os.dup2(si.fileno(), sys.stdin.fileno())
    os.dup2(so.fileno(), sys.stdout.fileno())
    os.dup2(se.fileno(), sys.stderr.fileno())


    if __name__ == '__main__':
    daemonize(stdout='/tmp/sample_file.log', stderr='/tmp/sample.log')
    print("hello world, now should be the child!")
    peter, Dec 11, 2012
    #1
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