One of my linux boxes ran out of disk space, which surprised me, because it definitely didn’t have that much stuff on it. When I check with df it says I have used 212GB on my / path:

$ df -h /
Filesystem      Size  Used Avail Use% Mounted on
/dev/sda1       227G  212G  5.2G  98% /

So, I tried to use du to see if maybe a runaway log file was the cause, but this says I have only used 101GB on my / path (this is also more in-line with how much space I expected to be used):

$ du -h | sort -h
...
101G    /

Using those commands with sudo outputs the same sizes.

My filesystem is Btrfs, I’ve tried the suggestion to use btrfs balance start ... but this actually INCREASED my disk usage to 99% lol

So my question is… what on earth is using the remaining 111GB?? Why can I not see it in du?

  • Kruulos@sopuli.xyz
    10·
    16 hours ago

    I had the exact same problem on one of my virtual boxes. The problem baffled me for two years and I just added more space to the box a few times to fight it as I couldn’t solve the issue. It wasn’t the inodes, deleted but open files or anything common like that.

    The problem was my mounts. I had occasionally failing mounts combined with crontabs that accessed and wrote data to those mounts. Do you know what happens when you accidentally wrote let’s say 200gb data to /mnt/a and then later mount a drive over that mount point? It magically ‘disappears’ as you’d exclude that mount from the calculations.

    Might be you don’t have anything mounted and none of the above is useful to you. But this solved my issue and it’s quite curious and silly. Just set up mount points to not be writeable and problem went away.

    • Jozzo@lemmy.worldOP
      2·
      13 hours ago

      Interesting, this could be it? I haven’t configured any mounts on this device yet, but when I tried one of the other suggestions from this thread and use btdu, I get this error:

      $ ./btdu -x /
Fatal error: The mount point you specified, "/", is not the top-level btrfs subvolume ("subvolid=5,subvol=/").
It is the btrfs subvolume "subvolid=256,subvol=/@rootfs".
Please specify the path to a mountpoint mounted with subvol=/ or subvolid=5.
E.g.: mkdir /mnt/sda1 && mount -o subvol=/ /dev/sda1 /mnt/sda1 && ./btdu /mnt/sda1

Note that the top-level btrfs subvolume ("subvolid=5,subvol=/") is not the same as the root of the filesystem ("/").

      I’m fairly new to the workings of Btrfs so this is jibberish to me right now, but I’ll look into it more

      EDIT: Nevermind! I was just using the tool wrong. I needed to mount my btrfs “sub-volume” then do the scan against that:

      sudo mkdir -p /mnt/btdu

      sudo mount -o subvolid=5 /dev/sda1 /mnt/btdu

      sudo ./btdu /mnt/btdu