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I noticed when checking the size of the tmp folder (df -h /tmp) that it's quite large ~70 GB and fluctuates a few GB every minute. I don't have anything in my application saving to the /tmp folder and am wondering what is going on? What is the "mask" file that appears under /tmp? Also, I was under the impression that a /tmp folder clears all contents when a dyno is restarted, it's ephemeral, so why is so much storage taken.

Below is the output from Heroku Bash, I ran df -h /tmp seconds apart.

~ $ df -h /tmp Filesystem Size Used Avail Use% Mounted on /dev/mapper/evg0-evol0 376G 75G 282G 21% /tmp ~ $ df -h /tmp Filesystem Size Used Avail Use% Mounted on /dev/mapper/evg0-evol0 376G 77G 280G 22% /tmp ~ $ cd /tmp /tmp $ dir mask

David Hurley
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    The `/tmp` filesystem is used by a *lot* of different things. I would tend to worry only if the direction of "space used" is always upward :-) – paxdiablo Nov 25 '19 at 01:50
  • @paxdiablo any idea what would be using ~20% of it immediately after deploying the app? Just curios as this seems like a decent chunk of the disk space. Thanks for the thoughts! – David Hurley Nov 25 '19 at 02:14
  • Sorry, David, I know very little about Heroku. But you can no doubt run `du -sh`-type commands to identify the culprits (biggest files or large number of small files) and then try to figure out what's writing to them (by checking content or the `procfs` file system to see if anything's got them open). Based on your output, this is probably just the single `mask` file so the first thing to try would be `ls -al /tmp` to get the size. But, as stated, if it simpy fluctuates between (for example) 20% and 25%, I wouldn't be too concerned. – paxdiablo Nov 25 '19 at 02:17

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