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Does an account has to be logged on to trigger the Time Machine backup, or does Time Machine run without any session active?

  • An interesting question that I hadn't thought of before. Now you have mme wondering too.... – Megan Walker May 21 '13 at 8:57
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    I have no answer, but it wouldn't be strange not to backup when no user changes its files. – mouviciel Jun 4 '13 at 7:34
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    @mouviciel But Time Machine runs hourly, so I think this scenario is possible: user is logged in; at 1000, Time Machine runs; at 1010 user makes some edits, then logs out. At 1100, no-one is logged in: will Time Machine start and back up those recent edits? (NB I've simplified: the times won't be on the hour, but I do believe it runs the backups every 60 minutes.) – Ashley Jun 6 '13 at 12:42
  • @Ashley - I didn't think of that scenario. Good point. – mouviciel Jun 6 '13 at 15:20
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Time Machine is a system-level daemon, not a user-level process. Time Machine will work even if you are not logged into your Mac.

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    Please provide verifiable evidence. – smokris May 23 '13 at 19:15
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    @smokris Time machine's process is called backupd.It is started by root and is a son of launchd. So it is a daemon. I also think the "d" stands for daemon. – Rnhmjoj May 25 '13 at 22:49
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    I really don't see it happening. I've several users on my mac, not all with admin rights. I don't know if it's important. – Pierre Watelet May 27 '13 at 9:09
  • @smokris - Launch Time Machine after a period with no user logged on, then check the dates of the last backups. This will give a definitive answer, be it yes or no. – mouviciel Jun 4 '13 at 7:33
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    If you need to mount an external drive to back up, then you need to be logged in – Vihung Dec 29 '13 at 20:26
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No. Mac OS X doesn't mount external drives so even if backupd was told to back up from an ssh session using tmutil startbackup the external drive that Time Machine normally uses would be absent and the backup would fail.

  • Do you mean that the OS doesn't mount external drives when nobody is logged in? – D A Vincent Mar 23 '17 at 9:23
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    @DAVincent Yes - or more precisely, both the backup process and the mounting of local drives happens when the first console user logs in and end when the last console user logs out. The net effect is you won't have backups in single user situations of you boot and no one is logged in or your single user logs out and leaves the computer running. – bmike Mar 23 '17 at 12:58
  • There is a very old claim here that it can be done, but I have not located the details that explain how to do it. – Mars Nov 2 at 21:58
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It is possible for the disk to be mounted while all users are logged out, but MacOS and other backup programs do not incorporate this feature. The only one that can mount drive with no one logged in is CarbonCopyCloner. Of course, it's not as simple as time machine.

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