On my Debian Linux laptop a couple of days ago I got my 23GB root EXT4 partition full (probably I installed more software than I expected).

Since I have plenty of space in my BTRFS home partition, 466GB of which 400GB available, I moved the contents of /usr/share/doc into /home/share/doc, and I created a link /usr/share/doc -> /home/share/doc. The size of this doc directory was around 2.4GB.

After this change, the system has been working correctly for the past 24 hours.

All at once I got the KDE menu bar and the desktop environment disappear, with only the applications' windows still open. I switched to the command line, and with df -h I found out that all the 466GB of my home partition are used.

With tree --du -h . from /home, I get "4.8G used", a realistic figure.

So, who is right? df or tree? Where do the remaining 460GB come from?

Since the doc directory I copied is still 2.4GB, I suspect that moving it and creating the link is not the reason of my problem.

How can I fix this and get a stable system back?


sudo btrfs filesystem usage -h -T /home

    Device size:         465.66GiB
    Device allocated:    465.66GiB
    Device unallocated:      0.00B
    Device missing:          0.00B
    Used:                464.28GiB
    Free (estimated):     64.00KiB  (min: 64.00KiB)
    Data ratio:               1.00
    Metadata ratio:           1.00
    Global reserve:      490.34MiB  (used: 0.00B)

                   Data        Metadata    System
Id Path            single      single      single      Unallocated
-- --------------- ---------- ----------- ----------- ------------
 1 /dev/nvme0n1p9  463.65GiB   2.01GiB      4.00MiB          0.00B
-- --------------- ---------- ----------- ----------- ------------
Total              463.65GiB   2.01GiB      4.00MiB          0.00B
Used               463.65GiB 644.72MiB     80.00KiB          0.00B

Debian 9.5
Dell Precision 7720
home directory: BTRFS
/ directory: EXT4

  • 3
    Three thoughts: (1) If a filesystem is full and files within sum up to a lot smaller size, it may be because some file(s) is still open (and maybe growing) after being unlinked. Assuming this is the case, some process probably has gone awry. (2) A Btrfs subvolume mounted elsewhere (or not at all) cannot be seen by tree /home, yet df prints what the filesystem as a whole reports to it. (3) What df prints for Btrfs mountpoints might be strange sometimes because calculating free space on Btrfs is tricky. You may get clearer… no, different picture with btrfs filesystem df /mountpoint. – Kamil Maciorowski Oct 11 '18 at 18:11
  • @KamilMaciorowski - I updated my question. – Pietro Oct 12 '18 at 9:25

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