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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.)

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    How about the per-user temporary folders in /var/folders/ ?
    – adib
    Commented Sep 10, 2018 at 23:12

1 Answer 1

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

Long answer:

This was changed significantly in MacOS Sonoma 14

Prior to Sonoma, it works like this:

  1. launchd sets up /usr/sbin/periodic daily to run every 86400 seconds (1 day) (definition in /System/Library/LaunchDaemons/com.apple.periodic-daily.plist). Older versions of Mac OS scheduled it to run at 3:15 am each day.
  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.

periodic daily logs its output to /var/log/daily.out. Files deleted from /tmp are logged under the heading "Removing old temporary files:".

In MacOS Sonoma, this was migrated to be controlled more directly with launchd

  1. There is a new launch daemon configured specifically for cleaning /tmp in /System/Library/LaunchDaemons/com.apple.tmp_cleaner.plist
  2. Using StartCalendarInterval, it runs /usr/libexec/tmp_cleaner daily at hour 0 (i.e. midnight)
  3. tmp_cleaner is a shell script that is very similar to 110.clean-tmps used pre-Sonoma but it does not provide any easy way to override the 3 day setting. You'd have to manually edit this file (and do it again on OS update0
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    Note in 10.7 periodic.conf has moved to /etc/defaults .
    – Dan
    Commented Nov 4, 2011 at 0:47
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    Does the same apply to $TMPDIR?
    – ccnokes
    Commented Jul 28, 2016 at 21:38
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    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) Commented Feb 16, 2018 at 14:59
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    Using OSX 10.14.5, can confirm that /tmp seems to be wiped out on reboot.
    – karlos
    Commented Jul 23, 2019 at 21:53
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    Instructions appear to be current as of Aug-2019 / MacOS Mojave 10.14.6. Commented Aug 5, 2019 at 14:45

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