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How is the /tmp directory cleaned up? Is it automatic? If so, how frequently is it cleaned up?

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Note! This answer is outdated since at least ubuntu 14.04. See other answers for current situation and if they prove correct then upvote them furiously. Also post comment so I can put link here to current correct answer.

For 14.04 see https://askubuntu.com/a/759048/1366

For 16.10 see https://askubuntu.com/a/857154/453746

Old answer from 2011:

The cleaning of /tmp is done by the upstart script /etc/init/mounted-tmp.conf. The script is run by upstart everytime /tmp is mounted. Practically that means at every boot.

The script does roughly the following: if a file in /tmp is older than $TMPTIME days it will be deleted.

The default value of $TMPTIME is 0, which means every file and directory in /tmp gets deleted. $TMPTIME is an environment variable defined in /etc/default/rcS.

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  • 1
    That's not true for 14.04 anymore (the script does not exist anymore).
    – Martin Schröder
    Apr 19, 2016 at 12:02
  • @Martin Schröder - the script exists on my system & it is a clean install of 14.04 and tmpreaper doesn't exist!
    – Lance Holland
    Jun 17, 2016 at 13:18
  • I am using arch linux now so I cannot verify. Sorry. Please someone verify this and comment or edit my answer.
    – Lesmana
    Jun 18, 2016 at 12:31
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    in ubuntu 16.04 tmpreaper is abandoned as un-secure please see: fossies.org/linux/tmpreaper/debian/README.security
    – tamerlaha
    Oct 27, 2016 at 15:14
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    No. In Ubuntu 16.04 it is simply superseded by a systemd mechanism. Read that document, and what you will actually find is an explanation of why the security analysis claiming insecurity is flawed.
    – JdeBP
    Sep 16, 2018 at 9:40
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The directory is cleared by default at every boot, because TMPTIME is 0 by default.

Here you can change the time in the following file:

/etc/default/rcS

TMPTIME says how frequent the tmp dir sould be cleared in days

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  • 13
    Clearing at every boot is not ideal for a machine that is never rebooted, like a server. I've got over 500,000 files taking 5Gb space in my /tmp because my server has 378 days uptime. I'm reluctant to reboot it, simply because clearing those files on reboot make take hours.
    – rjmunro
    Jan 25, 2012 at 11:47
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    In your case you should give tmpreaper a chance.
    – qbi
    Feb 24, 2013 at 23:01
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    A CRON job could easily solve that.
    – Ken Sharp
    Mar 8, 2014 at 14:27
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    It looks like Ubuntu/systemd already provides a solution. I'd say more but.... systemd.
    – Ken Sharp
    May 13, 2017 at 7:50
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    cat: /etc/default/rcS: No such file or directory
    – user677955
    Oct 10, 2019 at 22:16
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While the /tmp folder is not a place to store files long-term, occasionally you want to keep things a little longer than the next time you reboot, which is the default on Ubuntu systems. I know a time or two I’ve downloaded something to /tmp during testing, rebooted after making changes and then lost the original data again. This can be changed if you’d like to keep your /tmp files a little bit longer.

Changing the /tmp Cleanup Frequency

The default setting that tells your system to clear /tmp at reboot is held in the /etc/default/rcS file. The value we’ll look at is TMPTIME.

The current value of TMPTIME=0 says delete files at reboot despite the age of the file. Changing this value to a different (positive) number will change the number of days a file can survive in /tmp.

TMPTIME=7

This setting would allow files to stay in /tmp until they are a week old, and then delete them on the next reboot. A negative number (TMPTIME=-1) tells the system to never delete anything in /tmp. This is probably not something you want, but is available.

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  • 1
    good explanation. But in which script is the cleanup command? I have seen /etc/init/mounted-temp.conf, but it has the line start on mounted MOUNTPOINT=/tmp that make me think it is non applicable.
    – enzotib
    Jan 9, 2011 at 19:56
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    If you don't want a file to be removed automatically, put it in /var/tmp instead of /tmp.
    – Gilles 'SO- stop being evil'
    Jan 10, 2011 at 21:29
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    It's also handy to keep files you don't want to lose (rendered video frames) when your machine crashes, possibly due to OOM. A better solution would be to fix the problem, of course. :-)
    – Ken Sharp
    Mar 8, 2014 at 14:28
  • Can this be done inside Cygwin?
    – CMCDragonkai
    May 14, 2014 at 8:19
  • I think it would be better to keep such longer-term temp files in /var/tmp (as Gilles said). Then you can mount /tmp as tmpfs (as Arch Linux does).
    – Guildenstern
    Feb 26, 2021 at 10:19
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I'm checking this on Ubuntu 16.10. I can certify that editing /etc/default/rcS has no effect at all anymore and the files in tmp are wiped out by reboot no matter what you put in that file. As others mention, tmpreaper is no longer used.

I think the right answer is that Ubuntu 16.10 has a new setup. There is a folder /etc/tmpfiles.d, documented in the man page "tmpfiles.d". In that folder, one should place a configuration file to control whether the /tmp is to be erased. This is what I am doing to stop reboots from erasing files in /tmp unless they are 20 days old:

#/etc/tmpfiles.d/tmp.conf

d /tmp 1777 root root 20d

Replace "20d" by "-" if you never want files deleted. This is my best effort, that man page is nearly impenetrable with detail.

The advantage of the new setup is that a file cleaner can still run even if the system is not rebooted (as in the case of an always on server). That's a big plus, I think.

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  • 11
    man tmpfiles.d
    – Martin Schröder
    Apr 15, 2017 at 1:52
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    I found that you can preserve the original file permissions and owner by using hyphens: d /tmp/ - - - 20d
    – Dave Yarwood
    May 22, 2018 at 15:38
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    Also worth noting: you can test your configuration by running the cleaning job manually: systemctl start systemd-tmpfiles-clean
    – Dave Yarwood
    May 22, 2018 at 15:38
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    @kapad: I just verified that this works on Ubuntu 18.04, too.
    – Gene Vincent
    Dec 6, 2018 at 8:52
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    Creating /etc/tmpfiles.d/tmp.conf overrides /usr/lib/tmpfiles.d/tmp.conf causing the configuration for the other directories there to be lost if not copied (e.g., /var/tmp/systemd-private-%b-*). See the source.
    – Mihai Capotă
    Aug 23, 2019 at 19:14
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In Ubuntu 14.04 this is done by tmpreaper, which is called daily by cron (from /etc/cron.daily). The program can be configured via /etc/default/rcS and /etc/tmpreaper.conf.

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  • on my system, tmpreaper wasn't in /etc/cron.daily -- but I was able to install it with apt-get
    – Joe Germuska
    Nov 3, 2017 at 19:46
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    Note: you should NOT install tmpreaper on 16 and 18, b/c it has a built-in system
    – jitbit
    Mar 22, 2020 at 9:34
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In a systemd Ubuntu (15.10 and newer), this is done by systemd, using the systemd-tmpfiles-clean service and timer:

$ systemctl cat systemd-tmpfiles-clean.service 
# /lib/systemd/system/systemd-tmpfiles-clean.service
#  This file is part of systemd.
#
#  systemd is free software; you can redistribute it and/or modify it
#  under the terms of the GNU Lesser General Public License as published by
#  the Free Software Foundation; either version 2.1 of the License, or
#  (at your option) any later version.

[Unit]
Description=Cleanup of Temporary Directories
Documentation=man:tmpfiles.d(5) man:systemd-tmpfiles(8)
DefaultDependencies=no
Conflicts=shutdown.target
After=local-fs.target time-sync.target
Before=shutdown.target

[Service]
Type=oneshot
ExecStart=/bin/systemd-tmpfiles --clean
IOSchedulingClass=idle

And

$ systemctl cat systemd-tmpfiles-clean.timer  
# /lib/systemd/system/systemd-tmpfiles-clean.timer
#  This file is part of systemd.
#
#  systemd is free software; you can redistribute it and/or modify it
#  under the terms of the GNU Lesser General Public License as published by
#  the Free Software Foundation; either version 2.1 of the License, or
#  (at your option) any later version.

[Unit]
Description=Daily Cleanup of Temporary Directories
Documentation=man:tmpfiles.d(5) man:systemd-tmpfiles(8)

[Timer]
OnBootSec=15min
OnUnitActiveSec=1d

You can change the timer behaviour itself using systemctl edit systemd-tmpfiles-clean.timer, and using various systemd Timer configuration options (see man 5 systemd.timer).

So systemd-tmpfiles-clean runs on shutdown, and once per day otherwise. The files it cleans can be extended using /etc/tmpfiles.d (mentioned in another answer).

It's interesting to note that as default /etc/tmpfiles.d is empty. The file where the /tmp policy is defined is here:

/usr/lib/tmpfiles.d/tmp.conf

Actual content:

#  This file is part of systemd.
#
#  systemd is free software; you can redistribute it and/or modify it
#  under the terms of the GNU Lesser General Public License as published by
#  the Free Software Foundation; either version 2.1 of the License, or
#  (at your option) any later version.

# See tmpfiles.d(5) for details

# Clear tmp directories separately, to make them easier to override
D /tmp 1777 root root -
#q /var/tmp 1777 root root 30d

So, as already noted, to override it, you can see the other answer about tmpfiles.d.

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  • I've changed the timer to 20min, and i see that status command shows that it is actually using 20min configuration. but my problem is that /tmp still not cleaned up. and i need it to be cleaned up. even manual start sudo systemctl start systemd-tmpfiles-clean doesn't do the trick. Any ideas why?
    – user2932688
    Jun 27, 2019 at 13:34
  • @ValerioBozz see the answer I linked to: askubuntu.com/a/857154/158442
    – muru
    Dec 28, 2021 at 11:33
  • I'm deleting my comments since now are integrated
    – Valerio Bozz
    Dec 30, 2021 at 11:47
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Before 14.04:

It is cleaned up every time you reboot.

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  • Appears with 14.04+ it only uses tmpreaper, not the "per boot" script FWIW
    – rogerdpack
    Sep 8, 2016 at 16:03
  • My 14.04 systems all clean up on reboot. Never even heard of tmpreaper.
    – Ken Sharp
    May 13, 2017 at 7:51
  • what if the you never reboot the system?
    – phuclv
    Dec 5, 2017 at 11:37
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On one of our servers running Ubuntu, we have a script to remove files in /tmp and it runs nightly.

The script is:

#!/bin/sh
# Clean file and dirs more than 3 days old in /tmp nightly

/usr/bin/find /tmp -type f -atime +2 -mtime +2  |xargs  /bin/rm -f &&

/usr/bin/find /tmp -type d -mtime +2 -exec /bin/rm -rf '{}' \; &&

/usr/bin/find /tmp -type l -ctime +2 |xargs /bin/rm -f &&

/usr/bin/find -L /tmp -mtime +2 -print -exec rm -f {} \;

Just save the contents above to a file chmod 775 the file and create a cron entry to run it. Since this is a web server we don't want to reboot it for obvious reasons.

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  • 7
    You might be better off using tmpwatch.
    – poolie
    Sep 28, 2011 at 4:59
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    The last line is extremely dangerous. Normally, everyone is able to run ln -s /usr /tmp/kaboom or even ln -s /* /tmp/ ...
    – Daniel Alder
    Feb 28, 2016 at 22:25

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