z3c.recipe.usercrontab 0.4

The problem

When deploying applications, it can be useful to have maintenance tasks be started periodically. On Unix platforms this is usually done using cron which starts cronjobs. Adding cronjobs to the system-wide cron directory (for example by placing a file in /etc/cron.d) can be handled using the zc.recipe.deployment package, but it does not support adding cronjobs by normal users. (as /etc/cron.d usually is world-writable).

The solution

z3c.recipe.usercrontab interfaces with cron using crontab(1), and allows normal users to install their own cronjobs. This is done by having buildout add and remove cronjobs when installing and uninstalling packages.

How to use it

To use z3c.recipe.usercrontab you need to add the following to your buildout.cfg:

[mycronjob]
recipe = z3c.recipe.usercrontab
times = 0 12 * * *
command = echo nothing happens at noon

and finally add mycronjob to the parts line(s) of your buildout.cfg

Detailed documentation

# Copyright (c) 2009 Zope Foundation and contributors. # All Rights Reserved. # # This software is subject to the provisions of the Zope Public License, # Version 2.1 (ZPL). A copy of the ZPL should accompany this distribution. # THIS SOFTWARE IS PROVIDED “AS IS” AND ANY AND ALL EXPRESS OR IMPLIED # WARRANTIES ARE DISCLAIMED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED # WARRANTIES OF TITLE, MERCHANTABILITY, AGAINST INFRINGEMENT, AND FITNESS # FOR A PARTICULAR PURPOSE.

The recipe z3c.recipe.usercrontab is a small recipe to facilitate the installing of cronjobs into user crontabs.

>>> from z3c.recipe.usercrontab.usercrontab import UserCrontabManager
>>> c = UserCrontabManager()

For these tests, we fake a crontab by filling the list of cron entries for this object:

>>> c.crontab = [ 'MAILTO=""', '@reboot echo "No-one will see this"']
>>> print c
MAILTO=""
@reboot echo "No-one will see this"

Now, we’re adding a method to it using the official way:

>>> c.add_entry('@reboot echo "example.com gets spammed!"',
...             MAILTO="example@example.com")

The object also has a convenient __repr__, so we can test its output:

>>> print c
MAILTO=""
@reboot echo "No-one will see this"
MAILTO=example@example.com
@reboot echo "example.com gets spammed!"

Adding another entry with yet another MAILTO line is placed at the end:

>>> c.add_entry('@reboot echo "example.com gets spammed twice!"',
...              MAILTO="twice@example.com")
>>> print c
MAILTO=""
@reboot echo "No-one will see this"
MAILTO=example@example.com
@reboot echo "example.com gets spammed!"
MAILTO=twice@example.com
@reboot echo "example.com gets spammed twice!"

When another entry is made with the same MAILTO, the MAILTO clause is not repeated again:

>>> c.add_entry('@reboot echo "twice@example.com gets spammed twice!"',
...             MAILTO="twice@example.com")
>>> print c
MAILTO=""
@reboot echo "No-one will see this"
MAILTO=example@example.com
@reboot echo "example.com gets spammed!"
MAILTO=twice@example.com
@reboot echo "twice@example.com gets spammed twice!"
@reboot echo "example.com gets spammed twice!"

Removing entries also works, and removes superfluous environment variables:

>>> c.del_entry('@reboot echo "example.com gets spammed!"') == 1
True
>>> print c
MAILTO=""
@reboot echo "No-one will see this"
MAILTO=twice@example.com
@reboot echo "twice@example.com gets spammed twice!"
@reboot echo "example.com gets spammed twice!"

Removing entries does not remove too much:

>>> c.del_entry('@reboot echo "twice@example.com gets spammed twice!"') == 1
True
>>> print c
MAILTO=""
@reboot echo "No-one will see this"
MAILTO=twice@example.com
@reboot echo "example.com gets spammed twice!"

Removing the last entry also removes the dangling MAILTO line:

>>> c.del_entry('@reboot echo "example.com gets spammed twice!"') == 1
True
>>> print c
MAILTO=""
@reboot echo "No-one will see this"

Removing the final entry removes the remaining MAILTO line, leaving us with an empty list:

>>> c.del_entry('@reboot echo "No-one will see this"') == 1
True
>>> len(c.crontab)
0

Adding an entry without a MAILTO environment line also doesn’t put in an empty one:

>>> c.add_entry('@reboot echo "Someone will see this"')
>>> print c
@reboot echo "Someone will see this"

Adding an entry with an empty MAILTO line adds it at the end, so the first entry is not disturbed:

>>> c.add_entry('@reboot echo "No-one will see this"', MAILTO="")
>>> print c
@reboot echo "Someone will see this"
MAILTO=""
@reboot echo "No-one will see this"

Next, test the read_crontab and write_crontab methods; we’ll use cat and a temporary file to not modifiy the crontab of the user running these tests:

>>> import tempfile
>>> t = tempfile.NamedTemporaryFile('w')
>>> crontestfile = t.name
>>> t.write("#dummy\n")

>>> c = UserCrontabManager(readcrontab="cat %s" % crontestfile,
...                        writecrontab="cat >%s" % crontestfile)
>>> c.read_crontab()
>>> a = repr(c)
>>> c.add_entry('# improbable entry')
>>> c.write_crontab()
>>> c.read_crontab()
>>> b =repr(c)
>>> a == b
False

Now, delete this entry again and make sure the old crontab is restored:

>>> c.del_entry('# improbable entry') == 1
True
>>> c.write_crontab()
>>> c.read_crontab()
>>> b = repr(c)
>>> a == b
True

Do the buildout shuffle:

>>> write('buildout.cfg',
... '''
... [buildout]
... parts = foo
...
... [foo]
... recipe = z3c.recipe.usercrontab
... times = # @reboot
... command = echo nothing happens
... readcrontab = cat %(crontest)s
... writecrontab = cat >%(crontest)s
...
... [bar]
... recipe = z3c.recipe.usercrontab
... times = # @reboot
... command = echo nothing happens
... readcrontab = cat %(crontest)s
... writecrontab = cat >%(crontest)s
... ''' % ( { 'crontest': crontestfile } ))


>>> import os
>>> print system(os.path.join('bin', 'buildout'))
Installing foo.
<BLANKLINE>

Check that it really was added to the crontab:

>>> c.read_crontab()
>>> b = repr(c)
>>> a == b
False

>>> '# @reboot\techo nothing happens' in c.crontab
True

>>> 'WARNING=The entries below were generated by buildout, do not modify' in c.crontab
True

Uninstall the recipe:

>>> print system(os.path.join('bin', 'buildout')+' buildout:parts=')
Uninstalling foo.
Running uninstall recipe.
<BLANKLINE>

And check that its entry was removed (i.e., the contents of the crontab are the same as when this test was started; in any case, the teardown from the testrunner makes sure the old situation is restored):

>>> c.read_crontab()
>>> b = repr(c)
>>> a == b
True

Now, break it by adding the same crontab entry twice:

>>> print system(os.path.join('bin', 'buildout')+' "buildout:parts=foo bar"')
Installing foo.
Installing bar.
<BLANKLINE>

>>> print system(os.path.join('bin', 'buildout')+' buildout:parts=') # doctest: +ELLIPSIS +NORMALIZE_WHITESPACE
Uninstalling bar.
Running uninstall recipe.
bar: FATAL ERROR: Found more than one matching crontab-entry during uninstall; please resolve manually.
Matched lines: # @reboot echo nothing happens
While:
  Installing.
  Uninstalling bar.
<BLANKLINE>
An internal error occured due to a bug in either zc.buildout or in a
recipe being used:
Traceback (most recent call last):
...
RuntimeError: Found more than one matching crontab-entry during uninstall
<BLANKLINE>

Manually fix it by removing the offending lines::

>>> c.read_crontab()
>>> c.del_entry("# @reboot\techo nothing happens")
2
>>> c.write_crontab()

And now we can uninstall again (albeit with some warnings)::

>>> print system(os.path.join('bin', 'buildout')+' buildout:parts=') # doctest:
Uninstalling bar.
Running uninstall recipe.
bar: WARNING: Did not find a crontab-entry during uninstall; please check manually if everything was removed correctly
Uninstalling foo.
Running uninstall recipe.
foo: WARNING: Did not find a crontab-entry during uninstall; please check manually if everything was removed correctly
<BLANKLINE>