pystemd

This library allows you to talk to systemd over dbus from python, without actually thinking that you are talking to systemd over dbus. This allows you to programmatically start/stop/restart/kill and verify services status from systemd point of view, avoiding executing subprocess.Popen(['systemctl', ... and then parsing the output to know the result.

Show don't tell

In software as in screenwriting, its better to show how things work instead of tell. So this is how you would use the library from a interactive shell.

In [1]: from pystemd.systemd1 import Unit
In [2]: unit = Unit(b'postfix.service')
In [3]: unit.load()

Note: you need to call unit.load() because by default Unit will not load the unit information as that would require do some IO. You can auto load the unit by Unit(b'postfix.service', _autoload=True)

Once the unit is loaded, you can interact with it, you can do by accessing its systemd's interfaces:

In [4]: unit.Unit.ActiveState
Out[4]: b'active'

In [5]: unit.Unit.StopWhenUnneeded
Out[5]: False

In [6]: unit.Unit.Stop(b'replace') # require privilege account
Out[6]: b'/org/freedesktop/systemd1/job/6601531'

In [7]: unit.Unit.ActiveState
Out[7]: b'inactive'

In [8]: unit.Unit.SubState
Out[8]: b'running'

In [9]: unit.Unit.Start(b'replace') # require privilege account
Out[9]: b'/org/freedesktop/systemd1/job/6601532'

In [10]: unit.Unit.ActiveState
Out[10]: b'active'

In [11]: unit.Service.GetProcesses() # require systemd v238 and above
Out[11]:
[(b'/system.slice/postfix.service',
    1754222,
    b'/usr/libexec/postfix/master -w'),
 (b'/system.slice/postfix.service', 1754224, b'pickup -l -t fifo -u'),
 (b'/system.slice/postfix.service', 1754225, b'qmgr -l -t fifo -u')]

In [12]: unit.Service.MainPID
Out[12]: 1754222

The systemd1.Unit class provides shortcuts for the interfaces in the systemd namespace, as you se above, we have Service (org.freedesktop.systemd1.Service) and Unit (org.freedesktop.systemd1.Unit). Others can be found in unit._interfaces as:

In [12]: unit._interfaces
Out[12]:
{'org.freedesktop.DBus.Introspectable': <org.freedesktop.DBus.Introspectable of /org/freedesktop/systemd1/unit/postfix_2eservice>,
 'org.freedesktop.DBus.Peer': <org.freedesktop.DBus.Peer of /org/freedesktop/systemd1/unit/postfix_2eservice>,
 'org.freedesktop.DBus.Properties': <org.freedesktop.DBus.Properties of /org/freedesktop/systemd1/unit/postfix_2eservice>,
 'org.freedesktop.systemd1.Service': <org.freedesktop.systemd1.Service of /org/freedesktop/systemd1/unit/postfix_2eservice>,
 'org.freedesktop.systemd1.Unit': <org.freedesktop.systemd1.Unit of /org/freedesktop/systemd1/unit/postfix_2eservice>}

 In [13]: unit.Service
 Out[13]: <org.freedesktop.systemd1.Service of /org/freedesktop/systemd1/unit/postfix_2eservice>

Each interface has methods and properties, that can access directly as unit.Service.MainPID, the list of properties and methods is in .properties and .methods of each interface.

The above code operates on root user units by default. To operate on userspace units, explicitly pass in a user mode DBus instance:

from pystemd.dbuslib import DBus
with DBus(user_mode=True) as bus:
    unit = Unit(b"postfix.service", bus=bus)
    unit.load()

Alongside the systemd1.Unit, we also have a systemd1.Manager, that allows you to interact with systemd manager.

In [14]: from pystemd.systemd1 import Manager

In [15]: manager = Manager()

In [16]: manager.load()

In [17]: manager.Manager.ListUnitFiles()
Out[17]:
...
(b'/usr/lib/systemd/system/rhel-domainname.service', b'disabled'),
 (b'/usr/lib/systemd/system/fstrim.timer', b'disabled'),
 (b'/usr/lib/systemd/system/getty.target', b'static'),
 (b'/usr/lib/systemd/system/systemd-user-sessions.service', b'static'),
...

In [18]: manager.Manager.Architecture
Out[18]: b'x86-64'

In [19]: manager.Manager.Virtualization
Out[19]: b'kvm'

Extras:

We also include pystemd.run, the spiritual port of systemd-run to python. example of usage:

# run this as root
>>> import pystemd.run, sys
>>> pystemd.run(
    [b'/usr/bin/psql', b'postgres'],
    machine=b'db1',
    user=b'postgres',
    wait=True,
    pty=True,
    stdin=sys.stdin, stdout=sys.stdout,
    env={b'PGTZ': b'UTC'}
)

will open a postgres interactive prompt in a local nspawn-machine.

You also get an interface to sd_notify in the form of pystemd.daemon.notify docs.

# run this as root
>>> import pystemd.daemon
>>> pystemd.daemon.notify(False, ready=1, status='Gimme! Gimme! Gimme!')

And access to listen file descriptors for socket activation scripts.

# run this as root
>>> import pystemd.daemon
>>> pystemd.daemon.LISTEN_FDS_START
3
>>> pystemd.daemon.listen_fds()
1 # you normally only open 1 socket

And access if watchdog is enabled and ping it.

import time
import pystemd.daemon

watchdog_usec = pystemd.daemon.watchdog_enabled()
watchdog_sec = watchdog_usec/10**6

if not watchdog_usec:
  print(f'watchdog was not enabled!')

for i in range(20):
    pystemd.daemon.notify(False, watchdog=1, status=f'count {i+1}')
    time.sleep(watchdog_sec*0.5)

print('sleeping for 30 seconds')
time.sleep(watchdog_sec*2)
print('you will never reach me in a watchdog env')

We also provide basic journal interaction with pystemd.journal docs

import logging
import pystemd.journal

pystemd.journal.sendv(
  f"PRIORITY={logging.INFO}",
  MESSAGE="everything is awesome",
  SYSLOG_IDENTIFIER="tegan"
)

will result in the message (shorten for sake of example).

{

  "SYSLOG_IDENTIFIER" : "tegan",
  "PRIORITY" : "20",
  "MESSAGE" : "everything is awesome",
  ...
}

Install

So you like what you see, the simplest way to install pystemd is by:

$ pip install pystemd

pystemd is packaged in a few distros like Fedora and Debian. As of Fedora 32 and in EPEL as of EPEL 8.

It can be installed with:

$ sudo dnf install python3-pystemd # fedora
$ sudo apt install python3-pystemd # debian

which will also take care of installing any required dependencies. Keep in mind that most distros manage their own repos and version, and you may be getting old versions.

Build from source

you'll need to have:

• Python headers: Just use your distro's package (e.g. python-dev).
• systemd headers: Chances are you already have this. Normally, it is called libsystemd-dev or systemd-devel. You need to have at least v237. Please note that CentOS 7 ships with version 219. To work around this, please read this.
• systemd library: check if pkg-config --cflags --libs libsystemd returns -lsystemd if not you can install systemd-libs or libsystemd depending on your distribution, version needs to be at least v237.
• gcc: or any compiler that setup.py will accept.
• pkg-config command. Depending on your distro, the package is called "pkg-config", "pkgconfig" or a compatible substitute like "pkgconf"

if you want to install from source then after you clone this repo you need to

$ pip install -r requirements.txt # get six
$ python3 setup.py install # only python3 supported

but in addition to previous requirements you'll need:

• setuptools: Just use your distro's package (e.g. python-setuptools).
• Cython: at least version 0.21a1, just pip install it or use the official installation guide from cython homepage to get latest http://cython.readthedocs.io/en/latest/src/quickstart/install.html.

Learning more

This project has been covered in a number of conference talks:

• Using systemd in high level languages at All Systems Go! 2018
• systemd: why you should care as a Python developer at PyCon 2018
• Better security for Python with systemd at Pyninsula #10

A Vagrant-based demo was also developed for PyCon 2018.

License

pystemd is licensed under LGPL 2.1 or later.