Python守护进程不会在Ubuntu的后台运行

在终端中使用以下命令，我的Python守护程序在Ubuntu系统的前台运行良好：

python /opt/my-daemon.py foreground

但是，当我尝试使用的“start”命令调用守护进程时失败了，为什么

python /opt/my-daemon.py start

这是我在

/etc/rc.local

文件中调用命令的方式：

python /opt/my-daemon.py start &

随函附上守则：

1.daemon.py

#!/usr/bin/env python
import sys, os, time, atexit
from signal import SIGTERM
class Daemon:
"""
A generic daemon class.

Usage: subclass the Daemon class and override the run() method
"""
def __init__(self, pidfile,
    stdin='/dev/null',stdout='/dev/null',stderr='/dev/null'):
    self.stdin = stdin
    self.stdout = stdout
    self.stderr = stderr
    self.pidfile = pidfile

def daemonize(self):
    """
    Do the UNIX double-fork magic. See Richard Stevens' "Advanced
    Programming in the UNIX Environment" for details (ISBN 0201563177)
    http://www.erlenstar.demon.co.uk/unix/faq_2.html#SEC16
    """
    try:
        pid = os.fork()
        if pid > 0:
            # exit first parent
            sys.exit(0)
    except OSError, e:
        sys.stderr.write("fork #1 failed: %d (%s)\n" % (e.errno,
                    e.strerror))
        sys.exit(1)
    # Decouple from parent environment
    os.chdir("/")
    os.setsid()
    os.umask(0)

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

    # Redirect standard file descriptors
    sys.stdout.flush()
    sys.stderr.flush()
    si = file(self.stdin, 'r')
    so = file(self.stdout, 'a+')
    se = file(self.stderr, 'a+', 0)
    os.dup2(si.fileno(), sys.stdin.fileno())
    os.dup2(so.fileno(), sys.stdout.fileno())
    os.dup2(se.fileno(), sys.stderr.fileno())

    # Write pidfile
    atexit.register(self.delpid)
    pid = str(os.getpid())
    file(self.pidfile,'w+').write("%s\n" % pid)

def delpid(self):
    os.remove(self.pidfile)

def start(self):
    """
    Start the daemon
    """
    # Check for a pidfile to see if the daemon already runs
    try:
        pf = file(self.pidfile,'r')
        pid = int(pf.read().strip())
        pf.close()
    except IOError:
        pid = None

    if pid:
        message = "pidfile %s already exist. Daemon already running?\n"
        sys.stderr.write(message % self.pidfile)
        sys.exit(1)

    # Start the daemon
    self.daemonize()
    self.run()

def stop(self):
    """
    Stop the daemon
    """
    # Get the pid from the pidfile
    try:
        pf = file(self.pidfile,'r')
        pid = int(pf.read().strip())
        pf.close()
    except IOError:
        pid = None

    if not pid:
        message = "pidfile %s does not exist. Daemon not running?\n"
        sys.stderr.write(message % self.pidfile)
        return # not an error in a restart

    # Try killing the daemon process
    try:
        while 1:
            os.kill(pid, SIGTERM)
            time.sleep(0.1)
    except OSError, err:
        err = str(err)
        if err.find("No such process") > 0:
            if os.path.exists(self.pidfile):
                os.remove(self.pidfile)
        else:
            print str(err)
            sys.exit(1)

def restart(self):
    """
    Restart the daemon
    """
    self.stop()
    self.start()

def run(self):
    """
    You should override this method when you subclass Daemon. It will be called after the process has been
    daemonized by start() or restart().
    """

import sys, time
from daemon import Daemon
import MySQLdb #MySQL libraries
#Database parameters
config = {"host":"localhost",...}
try:
    conn = MySQLdb.connect(config['host'],...
class MyDaemon(Daemon):
def run(self):
    while True:
        time.sleep(2)
                    #{Do processes, connect to the database, etc....}
                    ...
if __name__ == "__main__":
daemon = MyDaemon('/tmp/daemon-example.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()
    elif 'foreground' == sys.argv[1]: #This runs the daemon in the foreground
        daemon.run()
    else:
        print "Unknown command"
        sys.exit(2)
    sys.exit(0)
else:
    print "usage: %s start|foreground|stop|restart" % sys.argv[0]
    sys.exit(2)

2.my daemon.py

#!/usr/bin/env python
import sys, os, time, atexit
from signal import SIGTERM
class Daemon:
"""
A generic daemon class.

Usage: subclass the Daemon class and override the run() method
"""
def __init__(self, pidfile,
    stdin='/dev/null',stdout='/dev/null',stderr='/dev/null'):
    self.stdin = stdin
    self.stdout = stdout
    self.stderr = stderr
    self.pidfile = pidfile

def daemonize(self):
    """
    Do the UNIX double-fork magic. See Richard Stevens' "Advanced
    Programming in the UNIX Environment" for details (ISBN 0201563177)
    http://www.erlenstar.demon.co.uk/unix/faq_2.html#SEC16
    """
    try:
        pid = os.fork()
        if pid > 0:
            # exit first parent
            sys.exit(0)
    except OSError, e:
        sys.stderr.write("fork #1 failed: %d (%s)\n" % (e.errno,
                    e.strerror))
        sys.exit(1)
    # Decouple from parent environment
    os.chdir("/")
    os.setsid()
    os.umask(0)

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

    # Redirect standard file descriptors
    sys.stdout.flush()
    sys.stderr.flush()
    si = file(self.stdin, 'r')
    so = file(self.stdout, 'a+')
    se = file(self.stderr, 'a+', 0)
    os.dup2(si.fileno(), sys.stdin.fileno())
    os.dup2(so.fileno(), sys.stdout.fileno())
    os.dup2(se.fileno(), sys.stderr.fileno())

    # Write pidfile
    atexit.register(self.delpid)
    pid = str(os.getpid())
    file(self.pidfile,'w+').write("%s\n" % pid)

def delpid(self):
    os.remove(self.pidfile)

def start(self):
    """
    Start the daemon
    """
    # Check for a pidfile to see if the daemon already runs
    try:
        pf = file(self.pidfile,'r')
        pid = int(pf.read().strip())
        pf.close()
    except IOError:
        pid = None

    if pid:
        message = "pidfile %s already exist. Daemon already running?\n"
        sys.stderr.write(message % self.pidfile)
        sys.exit(1)

    # Start the daemon
    self.daemonize()
    self.run()

def stop(self):
    """
    Stop the daemon
    """
    # Get the pid from the pidfile
    try:
        pf = file(self.pidfile,'r')
        pid = int(pf.read().strip())
        pf.close()
    except IOError:
        pid = None

    if not pid:
        message = "pidfile %s does not exist. Daemon not running?\n"
        sys.stderr.write(message % self.pidfile)
        return # not an error in a restart

    # Try killing the daemon process
    try:
        while 1:
            os.kill(pid, SIGTERM)
            time.sleep(0.1)
    except OSError, err:
        err = str(err)
        if err.find("No such process") > 0:
            if os.path.exists(self.pidfile):
                os.remove(self.pidfile)
        else:
            print str(err)
            sys.exit(1)

def restart(self):
    """
    Restart the daemon
    """
    self.stop()
    self.start()

def run(self):
    """
    You should override this method when you subclass Daemon. It will be called after the process has been
    daemonized by start() or restart().
    """

import sys, time
from daemon import Daemon
import MySQLdb #MySQL libraries
#Database parameters
config = {"host":"localhost",...}
try:
    conn = MySQLdb.connect(config['host'],...
class MyDaemon(Daemon):
def run(self):
    while True:
        time.sleep(2)
                    #{Do processes, connect to the database, etc....}
                    ...
if __name__ == "__main__":
daemon = MyDaemon('/tmp/daemon-example.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()
    elif 'foreground' == sys.argv[1]: #This runs the daemon in the foreground
        daemon.run()
    else:
        print "Unknown command"
        sys.exit(2)
    sys.exit(0)
else:
    print "usage: %s start|foreground|stop|restart" % sys.argv[0]
    sys.exit(2)

---

<>而不是使用DaimO.Py，您可能需要考虑利用Ubuntu提供一个简单的方法来设置一个重生守护进程。从同一链接，它具有以下功能：

* Services may be respawned if they die unexpectedly
* Supervision and respawning of daemons which separate from their parent process

如果您使用的是Ubuntu9.10或更高版本，请以/etc/init/cron.conf为例。对于Ubuntu的早期版本，我相信upstart脚本位于/etc/event.d/

---

有关Upstart关键字的解释，请参阅。

已解决。我的印象是，

前台

和

开始

参数是两个不同的东西。结果我只需要做以下几件事

def run(self):
    while True:
        time.sleep(2)

到

然后我删除了

前台

参数，因为我可以使用

start

命令从终端运行脚本，以查看前台的输出

python /opt/my-daemon.py start

另外，在

rc.local

中，我按如下方式启动脚本：

python /opt/my-daemon.py start &

---

这会隐藏守护进程并在启动时执行脚本，而不管登录的用户是谁：）

您可以尝试此操作

如果使用

start

命令，会发生什么情况？您所说的“it fails”是什么意思？失败，因为in根本不运行。它使用前台命令运行。当我在终端中用&键入“start”命令时，在末尾我看到了PID，但它会立即终止守护进程；这就是发射过程。它应该在设置守护进程后退出。调用start时不需要附加符号。您好，谢谢您的回答，但我相信我发现了问题，但我将检查upstart系统。谢谢我很高兴您找到了一种让程序运行的方法，但我想您应该知道，通过覆盖上面描述的

start

，您正在删除启动守护进程的daemon.py中的代码。重写

start

可以避免脚本提前退出，这表明原始问题可能在于

daemon.start

。可能该文件已经存在？或者是

守护进程.daemonize

中的某些内容导致提前退出？您可以使用打印语句进行调查，或者改用Upstart进行调查。@Unutbu谢谢您的回答，我将进一步调查。