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Recently I found out that on one of my servers (Ubuntu 16.04) I get significant drops on free disk space, at nights:

enter image description here

zooming to the last 1h (from right now):

enter image description here

one can see this happens abruptly. Just minutes ago when I ran watch df I could see that Available and Use% for the partition mounted at / change very fast, but Used is only different by 28B. Eg. just when diskspace started to drop:

Filesystem     1K-blocks    Used Available Use% Mounted on
/dev/simfs      52428800 7700776   4374316  64% /
devtmpfs         2097152       0   2097152   0% /dev
tmpfs            2097152       4   2097148   1% /dev/shm
tmpfs            2097152  209300   1887852  10% /run
tmpfs               5120       0      5120   0% /run/lock
tmpfs            2097152       0   2097152   0% /sys/fs/cgroup
none             2097152       0   2097152   0% /run/shm

and a few minutes later:

Filesystem     1K-blocks    Used Available Use% Mounted on
/dev/simfs      52428800 7700804   2354044  77% /
devtmpfs         2097152       0   2097152   0% /dev
tmpfs            2097152       4   2097148   1% /dev/shm
tmpfs            2097152  209300   1887852  10% /run
tmpfs               5120       0      5120   0% /run/lock
tmpfs            2097152       0   2097152   0% /sys/fs/cgroup
none             2097152       0   2097152   0% /run/shm

Therefore my question is what happens there, that Used disk space stays almost constant but available space not?

I run 2 web apps on the server but they don't allow any uploading and nginx says no one accesses them at night. I actually expect no disk changes on this system, excluding logs. I tried to use ncdu \ -e some_file during the day and at night and then diff them, but the output is terrible to read and compare, so I cannot really tell where the growing/new files are at.

(regarding security - no one is logged in except for me and I couldn't spot any unusual processes being run, but will dive into logs later)

  • 1
    maybe related serverfault.com/questions/714219/… – frostschutz Mar 1 '18 at 0:10
  • oh god, @frostschutz, you're right, I was totally not looking this direction. I've just triple checked and it really is OpenVZ and other VPSs eating space on host. thanks a lot, might I accept your answer? – adamczi Mar 1 '18 at 0:15

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