Comment by blibble

jorvi 5 days ago

> like "at least one real IP address is available" or "time has been synced"

"network-online.target is a target that actively waits until the network is “up”, where the definition of “up” is defined by the network management software. Usually it indicates a configured, routable IP address of some kind. Its primary purpose is to actively delay activation of services until the network has been set up."

For time sync checks, I assume one of the targets available will effectively mean a time sync has happened. Or you can do something with ExecStartPre. You could run a shell command that checks for the most recent time sync or forces one.

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blibble 5 days ago

it's the "usually" that's the problem
this service (untouched by me) had:
After=local-fs.target network-online.target remote-fs.target time-sync.target
but it was still started without an IP address, and then failed to bind
just like this sort of problem: https://github.com/systemd/systemd/issues/4880#issuecomment-...
the entire thing is unreliable and doesn't act like you'd expect
> Or you can do something with ExecStartPre. You could run a shell command that checks for the most recent time sync or forces one.
at that point I might as well go back to init=/etc/rc

Reply View | 13 replies
- jorvi 5 days ago
  
  Are you running this particular unit file as a user unit or a system unit? Some targets like network-online.target don't work from user unit files.
  You could also try targeting NetworkManager or networkd's "wait-online" services. Or if that doesn't work, something is telling systemd that you have an IP when you don't. NetworkManager has "ipv4.may-fail" and "ipv6.may-fail" that might be errenously true.
  > at that point I might as well go back to init=/etc/rc
  The difference is that systemd is much better at ensuring correctness. If you write the invoked shell command properly, it'll communicate failure or success correct and systemd will then communicate that state to the unit. It's still a lot more robust than before.
  
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  blibble 5 days ago
  
  it's a system service file
  the problem is systemd
  > The difference is that systemd is much better at ensuring correctness.
  yeah, whatever mate
  
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  direwolf20 5 days ago
  
  > Some targets like network-online.target don't work from user unit files.
  So basically it just doesn't work sometimes for no particular reason.
  > The difference is that systemd is much better at ensuring correctness
  Uh, well, you just said that it isn't, because some targets like network-online.target don't work from user unit files.
  
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- magicalhippo 5 days ago
  
  > https://github.com/systemd/systemd/issues/4880
  I'm not a systemd hater or anything, but I continue to read stuff from Poettering which to me is deeply disturbing given the programs he works on.
  Saying it's not a bug that service is launched despite a stated required prerequisite dependency failed... WTF?
  Sure, I agree with him that most computers should probably boot despite NTP being unable to sync. But proposing that the solution to that is breaking Requires is just wild to me.
  
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  jcgl 5 days ago
  
  I'm not sure I understand why you think the solution proposed there is so bad.
  The question in that issue is around the semantics of time-sync.target. Targets are synchronization points for the system and don't (afaik) generally make promises about the units that are ordered before them (in this case chrony-wait.service.
  Does that answer your specific objection of "proposing that the solution to that is breaking Requires is just wild to me"? Basically, what is proposed in that issue is not breaking Requires=. The proposition is that the user add their own, specific Requires= as a drop-in configuration since that's not a generally-applicable default.
  
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- [removed] 5 days ago
  
  [deleted]
  
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direwolf20 5 days ago

Is it possible for network-online to mean that, or does network-on actually mean that?
It is possible for a specification to be so abstract that it's useless.

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- jcgl 5 days ago
  
  That's entirely defined by whatever units order themselves before network-online.target (normally a network management daemon like NetworkManager or systemd-networkd). systemd itself doesn't define the details; that's left up to how that distro and sysadmin have configured the network manager/system.
  
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bandrami 5 days ago

Sysadmins really hate the word "usually", and that is at the root of just about every systemd headache I've had

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