The Daemon Extension enables applications Built on Cement (tm) to easily perform standard daemonization functions.
- Python 2.6+, Python 3+
- Available on Unix/Linux only
- Configurable runtime user and group
- Adds the
--daemoncommand line option
app.daemonize()function to trigger daemon functionality where necessary (either in a cement
pre_runhook or an application controller sub-command, etc)
- Manages a pid file including cleanup on
The daemon extension is configurable with the following settings under the [daemon] section.
- user - The user name to run the process as. Default: os.getlogin()
- group - The group name to run the process as. Default: The primary group of the ‘user’.
- dir - The directory to run the process in. Default: /
- pid_file - The filesystem path to store the PID (Process ID) file. Default: None
- umask - The umask value to pass to os.umask(). Default: 0
Configurations can be passed as defaults to a CementApp:
from cement.core.foundation import CementApp from cement.utils.misc import init_defaults defaults = init_defaults('myapp', 'daemon') defaults['daemon']['user'] = 'myuser' defaults['daemon']['group'] = 'mygroup' defaults['daemon']['dir'] = '/var/lib/myapp/' defaults['daemon']['pid_file'] = '/var/run/myapp/myapp.pid' defaults['daemon']['umask'] = 0 app = CementApp('myapp', config_defaults=defaults)
Application defaults are then overridden by configurations parsed via a
[demon] config section in any of the applications configuration paths.
An example configuration block would look like:
[daemon] user = myuser group = mygroup dir = /var/lib/myapp/ pid_file = /var/run/myapp/myapp.pid umask = 0
The following example shows how to add the daemon extension, as well as
trigger daemon functionality before
app.run() is called.
from time import sleep from cement.core.foundation import CementApp class MyApp(CementApp): class Meta: label = 'myapp' extensions = ['daemon'] with MyApp() as app: app.daemonize() app.run() count = 0 while True: count = count + 1 print('Iteration: %s' % count) sleep(10)
An alternative to the above is to put the
daemonize() call within a
def make_daemon(app): app.daemonize() def load(app): app.hook.register('pre_run', make_daemon)
Finally, some applications may prefer to only daemonize certain sub-commands rather than the entire parent application. For example:
from cement.core.foundation import CementApp from cement.core.controller import CementBaseController, expose class MyBaseController(CementBaseController): class Meta: label = 'base' @expose(help="run the daemon command.") def run_forever(self): from time import sleep self.app.daemonize() count = 0 while True: count = count + 1 print(count) sleep(10) class MyApp(CementApp): class Meta: label = 'myapp' base_controller = MyBaseController extensions = ['daemon'] with MyApp() as app: app.run()
By default, even after
app.daemonize() is called… the application will
continue to run in the foreground, but will still manage the pid and
user/group switching. To detach a process and send it to the background you
simply pass the
--daemon option at command line.
$ python example.py --daemon $ ps -x | grep example 37421 ?? 0:00.01 python example2.py --daemon 37452 ttys000 0:00.00 grep example
This class provides a mechanism for altering the running processes environment.
- stdin – A file to read STDIN from. Default:
- stdout – A file to write STDOUT to. Default:
- stderr – A file to write STDERR to. Default:
- dir – The directory to run the process in.
- pid_file – The filesystem path to where the PID (Process ID) should be written to. Default: None
- user – The user name to run the process as.
- group – The group name to run the process as.
Default: The primary group of
- umask – The umask to pass to os.umask(). Default:
Fork the current process into a daemon.
- UNIX Programming FAQ:
- 1.7 How do I get my program to act like a daemon? http://www.unixguide.net/unix/programming/1.7.shtml http://www.faqs.org/faqs/unix-faq/programmer/faq/
- Advanced Programming in the Unix Environment
- Richard Stevens, 1992, Addison-Wesley, ISBN 0-201-56317-7.
Switch the current process’s user/group to
self.group. Change directory to
self.dir, and write the current pid out to
- stdin – A file to read STDIN from. Default:
After application run time, this hook just attempts to clean up the pid_file if one was set, and exists.
This function switches the running user/group to that configured in
config['daemon']['group']. The default user is
os.getlogin()and the default group is that user’s primary group. A pid_file and directory to run in is also passed to the environment.
It is important to note that with the daemon extension enabled, the environment will switch user/group/set pid/etc regardless of whether the
--daemonoption was passed at command line or not. However, the process will only ‘daemonize’ if the option is passed to do so. This allows the program to run exactly the same in forground or background.
--daemonargument to the argument object, and sets the default
[daemon]config section options.