Allow execution without cron/crontab present

[m4rcu5]

Describe the problem, feature or ask a question:

Hiya,

Let me start of by acknowledging that I have done my research trough other issues, and I totally respect your position that cron is the scheduler and there is no support for systemd-timers, as you also stated in #1741.

I did notice that a lot of internal functions with regards to cron and crontab do fail graceful informing the user that you should install/start cron if they want scheduling to work (for example in #1761).
Except that you cannot run BIT when there is no contab or fcrontab command installed due to the following section:

backintime/common/schedule.py

Lines 27 to 51 in 5083d24

	def _determine_crontab_command() -> str:
	"""Return the name of one of the supported crontab commands if available.
	Returns:
	(str): The command name. Usually "crontab" or "fcrontab".
	Raises:
	RuntimeError: If none of the supported commands available.
	"""
	to_check_commands = ['crontab', 'fcrontab']
	for cmd in to_check_commands:
	proc = subprocess.run(
	['which', cmd],
	stdout=subprocess.PIPE,
	check=False
	)
	if proc.returncode == 0:
	return cmd
	# syslog is not yet initialized
	logger.openlog()
	msg = 'Command ' + ' and '.join(to_check_commands) + ' not found.'
	logger.critical(msg)
	raise RuntimeError(msg)

Patching it out, and setting CRONTAB_COMMAND to /bin/false seems to make BIT run as expected (sans the scheduling features) and I have backed up my machine without issues.

My request would be if it would be possible to let BIT execute without a dependency on crontab. Or ideally grey-out/lock-out the scheduling gui parts when there is not crontab available.

Just to clarify, I don't "run arch, btw", but OpenSUSE Tumbleweed, which also by default does not come with cron or crontab, nor does it come with any compatibility layer. They now seem to rely completely on timers.

[buhtz]

Hello Marcus,

Thank you for taking the time to report the issue and providing the
details. I appreciate your feedback and work on a solution to the best of my ability.

It is a reasonable request I am open to implement that in the upcoming release.

Some questions:

• How do you install BIT on OpenSUSE Tumbleweed? Is there an official distro package?
• So you do the scheduling by yourself writing systemd-timers stuff?

If you have any more details to share, feel free to reach out.

Not sure when we'll find the time to work on it. Please see the projects background information to get an idea about our workflow and priorities:

• Maintenance status
• The team
• Strategy outline / Roadmap

Best regards,
Christian