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How often is /tmp deleted? I thought it was cleaned out boot time and every three days if you don't reboot, but I can't find any authoritative source for this.

I'm running the latest 10.6. (I suppose I would be interested in changes in this behavior in previous OS versions.)

  • 1
    How about the per-user temporary folders in /var/folders/ ? – adib Sep 10 '18 at 23:12
108

Short answer: by default, files that aren't accessed in three days are deleted from /tmp

Long answer:

  1. launchd sets up /usr/sbin/periodic daily to run every day at 3:15 am (definition in /System/Library/LaunchDaemons/com.apple.periodic-daily.plist).
  2. /usr/sbin/periodic daily runs the scripts in /etc/periodic/daily, including 110.clean-tmps.
  3. 110.clean-tmps uses find to delete files not accessed (using the -atime and -mtime parameters to find) in $daily_clean_tmps_days days which aren't listed in $daily_clean_tmps_ignore.
  4. Those two variables (and other related variables) are defined in /etc/periodic.conf. (Since OS 10.7 there is a file /etc/defaults/periodic.conf which defines the defaults, but for overwriting these defaults you should still create /etc/periodic.conf – see the periodic.conf(5) manual page.) If you haven't modified this file, $daily_clean_tmps_days is set to 3.
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    Note in 10.7 periodic.conf has moved to /etc/defaults . – Dan Nov 4 '11 at 0:47
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    Does the same apply to $TMPDIR? – ccnokes Jul 28 '16 at 21:38
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    No, I don't believe that it does. There's no reference to $TMPDIR in any of the config files mentioned. – Doug Harris Jul 29 '16 at 17:12
  • I have some indications that files are also cleared from /tmp on restart of the machine (I had a few gig of Blender renderings in /tmp that went poof and I think that they left this world when I restarted the machine) – Reb.Cabin Aug 21 '17 at 22:50
  • n.b. This answer is 7.5 years old at this point, macOS is now at 10.13 and I'm using 10.11. While the short answer is still correct (3 days), some of the details have definitely changed. For example, in 10.11, I don't see the line that schedules this for 3:15 a.m. in /System/Library/LaunchDaemons/com.apple.periodic-daily.plist. I've not had the time to learn more about the boot process to determine how /tmp is cleared at boot time (per the comment by @Reb.Cabin above) – Doug Harris Feb 16 '18 at 14:59

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