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On Wed, Feb 25, 2015 at 2:50 AM, Marc Joliet <marcec@×××.de> wrote: |
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> Am Tue, 24 Feb 2015 16:44:59 -0500 |
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> schrieb Rich Freeman <rich0@g.o>: |
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> |
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>> > === Timers === |
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>> > |
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>> > Can a systemd timer depend on a mount point such that it waits until the mount |
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>> > point exists before running? Or will it fail after a timeout? I want to |
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>> > research this myself, but haven't gotten around to it yet. |
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>> |
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>> So, timer units are units, and units can have dependencies, and mounts |
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>> can be dependencies since mounts are units. However, if you set the |
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>> dependency on the timer itself, then the timer won't start running |
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>> until the mount exists. You probably want the depencency to be on the |
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>> service started by the timer (so the timer is watching the clock, but |
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>> the service won't start without the mount). |
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> |
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> Wait, so the timer won't start watching the clock until its dependencies are |
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> met (i.e, the mount point appears)? Is that what you mean? Because that might |
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> be more in line with what I want (though I'm not sure yet). |
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|
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If you set the dependency on the timer, then the timer doesn't start |
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watching the clock until they're met. If you set the dependency on |
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the service started by the timer then it will watch the clock but not |
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launch the service if the dependency isn't met. You can set the |
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dependency in either or both places. The timer and the service are |
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both units. |
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|
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> |
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>> If you set a |
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>> Requires=foo.mount and After=foo.mount, then the service shouldn't run |
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>> unless foo.mount is available. I suspect systemd will attempt to |
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>> mount the filesystem when it runs the service, and you'll get units in |
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>> the failed state if that doesn't work. |
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>> |
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>> However, I haven't tested any of this. I suspect it wouldn't take |
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>> much to work this out. I have a mount dependency in one of my |
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>> services. Just look at the mount units in /run/systemd/generator for |
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>> the name of the mount unit systemd is creating from fstab. |
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> |
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> Right, so IIUC, I would have a oneshot service that does the backup, and the timer |
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> runs that, and of course the timer can depend on the mount point. And if the |
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> mount point doesn't exist, then the service started by the timer will fail. |
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> |
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> What I would prefer to have is a timer that only runs if *both* the time *and* |
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> mount conditions are met. Skimming the man page, this does not seem possible. |
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> I suppose it would be nice if timers learned "conditions" on which they should |
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> wait in addition to the time condition, but maybe that's outside the scope of |
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> systemd? |
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|
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I think if you just set the dependency on the service you'll get the |
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behavior you desire. Systemd will try to mount the backup filesystem, |
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and if that fails it won't run the backup. |
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|
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You can set conditions on units as well, like only running if they're |
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on AC power or on amd64 or to run one unit the first time you start a |
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service and a different unit every other time. Some of that was |
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designed to implement some of the stateless system features they're |
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adding to systemd. |
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|
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-- |
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Rich |
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