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On Fri, Oct 1, 2021 at 3:37 PM antlists <antlists@××××××××××××.uk> wrote: |
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> I'm trying to get a systemd unit to fire on boot once a week. Reading up |
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> on timer units, I can't work out how to get it to work. |
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> |
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> This is tied up with my earlier systemd mount post - I've now got that |
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> sorted - I've got dm-integrity to fire before fstab. |
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> |
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> I now want to run lvm snapshot on the first boot of the weekend. Writing |
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> a unit to do the snapshot seems pretty easy, but obviously I don't want |
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> it firing every boot, if I stick the date in the volume name I don't |
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> want it colliding with an earlier run the same day, etc etc. |
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> |
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> The question really is - if I have a weekly timer fire and activate the |
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> unit, is the activation going to survive the reboot to run on the next |
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> boot? |
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> |
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> The problem I'm having is that all the stuff I've seen about timers says |
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> you have two lines - activate on Saturdays, and activate on boot. Snag |
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> is, they seem to be independent such that EITHER condition will activate |
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> the service. As I say, I want BOTH. I don't want the service running |
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> while the system is up and running. |
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> |
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I'm not sure timer units have enough flexibility to do what you want. |
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I think it would be much simpler to have a Type=oneshot service at boot, |
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and the Exec= line to call a script. You can store the timestamp of the |
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last time it was called someplace in the filesystem (say, |
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/var/lib/my-script or something), and if the timestamp doesn't exists or is |
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older than one week, the scripts executes lvm snapshot and updates the |
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timestamp; otherwise it ends without doing anything. |
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The timer units are very similar to cron, and I believe what you want |
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cannot be done with cron either; you need special logic and state ("I'm |
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booting AND haven't run this in at least a week"), so a script is necessary |
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(I think). Luckly, systemd allows you to smartly manage your scripts and |
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impose dependencies on them (you need /var in my example, and you can set |
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it to run before starting X). |
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Regards. |
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-- |
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Dr. Canek Peláez Valdés |
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Profesor de Carrera Asociado C |
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Departamento de Matemáticas |
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Facultad de Ciencias |
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Universidad Nacional Autónoma de México |
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