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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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  • 14
    My temporary files never get written to the disk. They get written to a RAM disk. I did put tmpfs /tmp tmpfs defaults,noatime,mode=1777 0 0 in /etc/fstab. – Anonymous Nov 16 '11 at 23:43
181

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 This answer is outdated since at least ubuntu 14.04.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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  • That's not true for 14.04 anymore (the script does not exist anymore). – Martin Schröder Apr 19 '16 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 '16 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 '16 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 '16 at 15:14
  • No. In Ubuntu 16.04 it is simply superseded by a systemd mechanism.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 '18 at 9:40
137

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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  • 9
    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 '12 at 11:47
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    In your case you should give tmpreaper a chance. – qbi Feb 24 '13 at 23:01
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    A CRON job could easily solve that. – Ken Sharp Mar 8 '14 at 14:27
  • Also tmpwatch should be an appropriate tool. – ArekBulski Oct 28 '15 at 12:29
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    It looks like Ubuntu/systemd already provides a solution. I'd say more but.... systemd. – Ken Sharp May 13 '17 at 7:50
60

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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    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 '11 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 Jan 10 '11 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 '14 at 14:28
  • Can this be done inside Cygwin? – CMCDragonkai May 14 '14 at 8:19
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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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  • 4
    man tmpfiles.d – Martin Schröder Apr 15 '17 at 1:52
  • I found that you can preserve the original file permissions and owner by using hyphens: d /tmp/ - - - 20d – Dave Yarwood May 22 '18 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 '18 at 15:38
  • @pauljohn32 is this also true for versions after 16.10? – kapad Nov 1 '18 at 20:18
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    @kapad: I just verified that this works on Ubuntu 18.04, too. – Gene Vincent Dec 6 '18 at 8:52
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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 '17 at 19:46
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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 '16 at 16:03
  • My 14.04 systems all clean up on reboot. Never even heard of tmpreaper. – Ken Sharp May 13 '17 at 7:51
  • what if the you never reboot the system? – phuclv Dec 5 '17 at 11:37
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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

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.

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).

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5

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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  • 6
    You might be better off using tmpwatch. – poolie Sep 28 '11 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 '16 at 22:25

protected by Community♦ Feb 11 '15 at 14:09

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