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Daemon process control library and tools for Unix-bases systems

Project Description
``zdaemon`` process controller for Unix-based systems

.. contents::

'zdaemon' is a Python package which provides APIs for managing applications
run as daemons. Its principal use to date has been to manage the application
server and storage server daemons for Zope / ZEO, although it is not limited
to running Python-based applications (for instance, it has been used to
manage the 'spread' daemon).

zdaemon Changelog

zdaemon 2.0.3 (2009/04/11)

- Added support to bootstrap on Jython.

- If the run directory does not exist it will be created. This allow to use
`/var/run/mydaemon` as run directory when /var/run is a tmpfs (LP #318118).

Bugs Fixed

- No longer uses a hardcoded filename (/tmp/demo.zdsock) in unit tests.
This lets you run the tests on Python 2.4 and 2.5 simultaneously without
spurious errors.

- make -h work again for both runner and control scripts.
Help is now taken from the __doc__ of the options class users by
the zdaemon script being run.

zdaemon 2.0.2 (2008/04/05)

Bugs Fixed

Fixed backwards incompatible change in handling of environment option.

zdaemon 2.0.1 (2007/10/31)

Bugs Fixed

Fixed test renormalizer that did not work in certain cases where the
environment was complex.

zdaemon 2.0.0 (2007/07/19)

Final release for 2.0.0.

zdaemon 2.0a6 (2007/01/11)

Bugs Fixed

- When the user option was used, it only affected running the daemon.

zdaemon 2.0a3, 2.0a4, 2.0a5 (2007/01/10)

Bugs Fixed

- The new (2.0) mechanism used by zdaemon to start the daemon manager
broke some applications that extended zdaemon.

- Added extra checks to deal with programs that extend zdaemon
and copy the schema and thus don't see updates to the ZConfig schema.

zdaemon 2.0a2 (2007/01/10)

New Features

- Added support for setting environment variables in the configuration
file. This is useful when zdaemon is used to run programs that need
environment variables set (e.g. LD_LIBRARY_PATH).

- Added a command to rotate the transcript log.

zdaemon 2.0a1 (2006/12/21)

Bugs Fixed

- In non-daemon mode, start hung, producing annoying dots
when the program exited.

- The start command hung producing annoying dots if the deamon failed
to start.

- foreground and start had different semantics because one used
os.system and another used os.spawn

New Features

- Documentation

- Command-line arguments can now be supplied to the start and
foreground (fg) commands

- zdctl now invokes itself to run zdrun. This means that it's
no-longer necessary to generate a separate zdrun script. This
especially when the magic techniques to find and run zdrun using
directory sniffing fail to set the path corrrectly.

- The daemon mode is now enabled by default. To get non-deamon mode,
you have to use a configuration file and set deamon to off
there. The old -d option is kept for backward compatibility, but is
a no-op.

zdaemon 1.4a1 (2005/11/21)

Fixed a bug in the distribution setup file.

zdaemon 1.4a1 (2005/11/05)

First semi-formal release.

After some unknown release(???)

- Made 'zdaemon.zdoptions' not fail for --help when __main__.__doc__
is None.

After zdaemon 1.1

- Updated test 'testRunIgnoresParentSignals':

o Use 'mkdtemp' to create a temporary directory to hold the test socket
rather than creating the test socket in the test directory.
Hopefully this will be more robust. Sometimes the test directory
has a path so long that the test socket can't be created.

o Changed management of ''. This script is now created by
the test in the temporarary directory with the necessary
permissions. This is to avoids possible mangling of permissions
leading to spurious test failures. It also avoids management of a
file in the source tree, which is a bonus.

- Rearranged source tree to conform to more usual zpkg-based layout:

o Python package lives under 'src'.

o Dependencies added to 'src' as 'svn:externals'.

o Unit tests can now be run from a checkout.

- Made umask-based test failures due to running as root emit a more
forceful warning.

zdaemon 1.1 (2005/06/09)

- SVN tag: svn://

- Tagged to make better 'svn:externals' linkage possible.


More docs:

- Document/demonstrate some important features, such as:

- working directory


- help command

Detailed Documentation

Using zdaemon

zdaemon provides a script, zdaemon, that can be used to running other
programs as POSIX (Unix) daemons. (Of course, it is only usable on
POSIX-complient systems.

Using zdaemon requires specifying a number of options, which can be
given in a configuration file, or as command-line options. It also
accepts commands teling it what do do. The commands are:

Start a process as a daemon

Stop a running daemon process

Stop and then restart a program

Find out if the program is running

foreground or fg
Run a program

kill signal
Send a signal to the daemon process

Reopen the transcript log. See the discussion of the transcript
log below.

help command
Get help on a command

Commands can be given on a command line, or can be given using an
interactive interpreter.

Let's start with a simple example. We'll use command-line options to
run the echo command:

>>> system("./zdaemon -p 'echo hello world' fg")
echo hello world
hello world

Here we used the -p option to specify a program to run. We can
specify a program name and command-line options in the program
command. Note, however, that the command-line parsing is pretty
primitive. Quotes and spaces aren't handled correctly. Let's look at
a slightly more complex example. We'll run the sleep command as a
daemon :)

>>> system("./zdaemon -p 'sleep 100' start")
. .
daemon process started, pid=819

This ran the sleep deamon. We can check whether it ran with the
status command:

>>> system("./zdaemon -p 'sleep 100' status")
program running; pid=819

We can stop it with the stop command:

>>> system("./zdaemon -p 'sleep 100' stop")
. .
daemon process stopped

>>> system("./zdaemon -p 'sleep 100' status")
daemon manager not running

Normally, we control zdaemon using a configuration file. Let's create
a typical configuration file:

>>> open('conf', 'w').write(
... '''
... <runner>
... program sleep 100
... </runner>
... ''')

Now, we can run with the -C option to read the configuration file:

>>> system("./zdaemon -Cconf start")
. .
daemon process started, pid=1136

If we list the directory:

>>> system("ls")

We'll see that a file, zdsock, was created. This is a unix-domain
socket used internally by ZDaemon. We'll normally want to control
where this goes.

>>> system("./zdaemon -Cconf stop")
. .
daemon process stopped

>>> open('conf', 'w').write(
... '''
... <runner>
... program sleep 100
... socket-name /tmp/demo.zdsock
... </runner>
... '''.replace('/tmp', tmpdir))

>>> system("./zdaemon -Cconf start")
. .
daemon process started, pid=1139

>>> system("ls")

>>> import os
>>> os.path.exists("/tmp/demo.zdsock".replace('/tmp', tmpdir))

>>> system("./zdaemon -Cconf stop")
. .
daemon process stopped

In the example, we included a command-line argument in the program
option. We can also provide options on the command line:

>>> open('conf', 'w').write(
... '''
... <runner>
... program sleep
... socket-name /tmp/demo.zdsock
... </runner>
... '''.replace('/tmp', tmpdir))

>>> system("./zdaemon -Cconf start 100")
. .
daemon process started, pid=1149

>>> system("./zdaemon -Cconf status")
program running; pid=1149

>>> system("./zdaemon -Cconf stop")
. .
daemon process stopped

Environment Variables

Sometimes, it is necessary to set environment variables before running
a program. Perhaps the most common case for this is setting
LD_LIBRARY_PATH so that dynamically loaded libraries can be found.

>>> open('conf', 'w').write(
... '''
... <runner>
... program env
... socket-name /tmp/demo.zdsock
... </runner>
... <environment>
... LD_LIBRARY_PATH /home/foo/lib
... HOME /home/foo
... </environment>
... '''.replace('/tmp', tmpdir))

>>> system("./zdaemon -Cconf fg")

Transcript log

When zdaemon run a program in daemon mode, it disconnects the
program's standard input, standard output, and standard error from the
controlling terminal. It can optionally redirect the output to
standard error and standard output to a file. This is done with the
transcript option. This is, of course, useful for logging output from
long-running applications.

Let's look at an example. We'll have a long-running process that
simple tails a data file:

>>> f = open('data', 'w', 0)
>>> import os
>>> f.write('rec 1\n'); os.fsync(f.fileno())

>>> open('conf', 'w').write(
... '''
... <runner>
... program tail -f data
... transcript log
... </runner>
... ''')

>>> system("./zdaemon -Cconf start")
. .
daemon process started, pid=7963

.. Wait a little bit to make sure tail has a chance to work

>>> import time
>>> time.sleep(0.1)

Now, if we look at the log file, it contains the tail output:

>>> open('log').read()
'rec 1\n'

We can rotate the transcript log by renaming it and telling zdaemon to
reopen it:

>>> import os
>>> os.rename('log', 'log.1')

If we generate more output:

>>> f.write('rec 2\n'); os.fsync(f.fileno())

.. Wait a little bit to make sure tail has a chance to work

>>> time.sleep(1)

The output will appear in the old file, because zdaemon still has it

>>> open('log.1').read()
'rec 1\nrec 2\n'

Now, if we tell zdaemon to reopen the file:

>>> system("./zdaemon -Cconf reopen_transcript")

and generate some output:

>>> f.write('rec 3\n'); os.fsync(f.fileno())

.. Wait a little bit to make sure tail has a chance to work

>>> time.sleep(1)

the output will show up in the new file, not the old:

>>> open('log').read()
'rec 3\n'

>>> open('log.1').read()
'rec 1\nrec 2\n'

Reference Documentation

The following options are available for use in the runner section of
configuration files and as command-line options.

Command-line option: -p or --program

This option gives the command used to start the subprocess
managed by zdaemon. This is currently a simple list of
whitespace-delimited words. The first word is the program
file, subsequent words are its command line arguments. If the
program file contains no slashes, it is searched using $PATH.
(Note that there is no way to to include whitespace in the program
file or an argument, and under certain circumstances other
shell metacharacters are also a problem.)

Command-line option: -s or --socket-name.

The pathname of the Unix domain socket used for communication
between the zdaemon command-line tool and a deamon-management
process. The default is relative to the current directory in
which zdaemon is started. You want to specify
an absolute pathname here.

This defaults to "zdsock", which is created in the directory
in which zdrun is started.

Command-line option: -d or --daemon.

If this option is true, zdaemon runs in the background as a
true daemon. It forks a child process which becomes the
subprocess manager, while the parent exits (making the shell
that started it believe it is done). The child process also
does the following:

- if the directory option is set, change into that directory

- redirect stdin, stdout and stderr to /dev/null

- call setsid() so it becomes a session leader

- call umask() with specified value

The default for this option is on by default. The
command-line option therefore has no effect. To disable
daemon mode, you must use a configuration file::

program sleep 1
daemon off

Command-line option: -z or --directory.

If the daemon option is true (default), this option can
specify a directory into which changes as part of the
"daemonizing". If the daemon option is false, this option is

Command-line option: -b or --backoff-limit.

When the subprocess crashes, zdaemon inserts a one-second
delay before it restarts it. When the subprocess crashes
again right away, the delay is incremented by one second, and
so on. What happens when the delay has reached the value of
backoff-limit (in seconds), depends on the value of the
forever option. If forever is false, zdaemon gives up at
this point, and exits. An always-crashing subprocess will
have been restarted exactly backoff-limit times in this case.
If forever is true, zdaemon continues to attempt to restart
the process, keeping the delay at backoff-limit seconds.

If the subprocess stays up for more than backoff-limit
seconds, the delay is reset to 1 second.

This defaults to 10.

Command-line option: -f or --forever.

If this option is true, zdaemon will keep restarting a
crashing subprocess forever. If it is false, it will give up
after backoff-limit crashes in a row. See the description of
backoff-limit for details.

This is disabled by default.

Command-line option: -x or --exit-codes.

This defaults to 0,2.

If the subprocess exits with an exit status that is equal to
one of the integers in this list, zdaemon will not restart
it. The default list requires some explanation. Exit status
0 is considered a willful successful exit; the ZEO and Zope
server processes use this exit status when they want to stop
without being restarted. (Including in response to a
SIGTERM.) Exit status 2 is typically issued for command line
syntax errors; in this case, restarting the program will not

NOTE: this mechanism overrides the backoff-limit and forever
options; i.e. even if forever is true, a subprocess exit
status code in this list makes zdaemon give up. To disable
this, change the value to an empty list.

Command-line option: -u or --user.

When zdaemon is started by root, this option specifies the
user as who the the zdaemon process (and hence the daemon
subprocess) will run. This can be a user name or a numeric
user id. Both the user and the group are set from the
corresponding password entry, using setuid() and setgid().
This is done before zdaemon does anything else besides
parsing its command line arguments.

NOTE: when zdaemon is not started by root, specifying this
option is an error. (XXX This may be a mistake.)

XXX The zdaemon event log file may be opened *before*
setuid() is called. Is this good or bad?

Command-line option: -m or --umask.

When daemon mode is used, this option specifies the octal umask
of the subprocess.

If this option is true, zdaemon enters interactive mode
when it is invoked without a positional command argument. If
it is false, you must use the -i or --interactive command line
option to zdaemon to enter interactive mode.

This is enabled by default.

This option specifies a log file that is the default target of
the "logtail" zdaemon command.

NOTE: This is NOT the log file to which zdaemon writes its
logging messages! That log file is specified by the
<eventlog> section described below.

The name of a file in which a transcript of all output from
the command being run will be written to when daemonized.

If not specified, output from the command will be discarded.

This only takes effect when the "daemon" option is enabled.

The prompt shown by the controller program. The default must
be provided by the application.

(Note that a few other options are available to support old
configuration files, but aren't needed any more and can generally be

In addition to the runner section, you can use an eventlog section
that specified one or more logfile subsections::

path /var/log/foo/foo.log


In this example, log output is sent to a file and to standard out.
Log output from zdaemon usually isn't very interesting but can be
handy for debugging.

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