The root drive on an Ubuntu 15.10 machine is nearly out of space, but I can't find the source. The drive that's running out of space is sdb2, 313M of 51G available. The filesystem is ext4.

Here is the sudo du -h / --max-depth=1 output:

Filesystem      Size  Used Avail Use% Mounted on
udev            3.9G     0  3.9G   0% /dev
tmpfs           789M  9.4M  780M   2% /run
/dev/sdb2        51G   48G  313M 100% /
tmpfs           3.9G   12K  3.9G   1% /dev/shm
tmpfs           5.0M  4.0K  5.0M   1% /run/lock
tmpfs           3.9G     0  3.9G   0% /sys/fs/cgroup
/dev/sdb1       511M  3.4M  508M   1% /boot/efi
tmpfs           789M  8.0K  789M   1% /run/user/1000
/dev/sda1       239G  122M  239G   1% /media/DATA

But I can't find any large files. Total usage at / seems to be only 3.4 G. Here is the output from sudo du -h / --max-depth=1:

4.0K    /mnt
188K    /tmp
406M    /home
339M    /var
8.1M    /etc
361M    /lib
du: cannot access ‘/proc/7626/task/7626/fd/4’: No such file or directory
du: cannot access ‘/proc/7626/task/7626/fdinfo/4’: No such file or directory
du: cannot access ‘/proc/7626/fd/3’: No such file or directory
du: cannot access ‘/proc/7626/fdinfo/3’: No such file or directory
0    /proc
13M    /bin
du: cannot access ‘/run/user/1000/gvfs’: Permission denied
9.4M    /run
1.6M    /root
4.0K    /lib64
16K    /lost+found
0    /sys
1.1M    /media
12K    /dev
222M    /opt
2.0G    /usr
62M    /boot
9.5M    /sbin
4.0K    /cdrom
8.0K    /srv
3.4G    /

I found a similar question here: Out of disk space, what's the source?

In that case, it looks like the problem was caused by a deleted log that somehow was not closed by a running process, and the way to find it was to run sudo lsof | grep deleted. In my case, the output is

lsof: WARNING: can't stat() fuse.gvfsd-fuse file system /run/user/1000/gvfs
      Output information may be incomplete.

Also, the problem persists after rebooting the system, so it's unlikely that that is the cause.

Another suggested solution is to unmount /var/lib/ureadahead/debugfs, but I'm hesitant to do that.

What else could be wrong?

  • do a reboot. there are some deleted but locked files. Jan 11, 2017 at 3:59
  • I tried that, but nothing changed. Jan 11, 2017 at 4:01
  • 1
    Check the filesystem for errors, and update to a supported Ubuntu release. Jan 11, 2017 at 5:15
  • 6
    just run "du -sh *" when you are in the root folder. Do not use --max-depth flag
    – Orphans
    Jan 11, 2017 at 7:00
  • 1
    @Orphans looks like I didn't see the * nestled up against ypu "
    – user9517
    Jan 11, 2017 at 7:55

4 Answers 4


Well, it's only a guess but it may works: I think that user once forget to mount /dev/sda1 as /media/DATA and all data was written on /dev/sdb2 instead of /dev/sda1.

To check this, please, unmount /media/DATA and check files and folders under this path.

  • Thanks, that's what it was! Except I think it might have been a bad drive connection rather than anyone forgetting to mount anything. That whole setup is unreliable and I'm not sure how that drive is mounted to /media/DATA -- it's not in /etc/fstab. Jan 11, 2017 at 7:28
  • If you don't want to unmount the filesystem (for example, if you don't want to shut down the processes that are using it), you can use a bind mount to see (and delete) the files hidden by the mount.
    – Johnny
    Jan 11, 2017 at 21:34

I regularly use 'ncdu' for that, it's small enough to still get it installed.

sudo apt-get install ncdu

Just make sure you run it as root or via sudo:

sudo ncdu /
  • 1
    Wouldn't have helped in this case though. Jan 11, 2017 at 9:22

When you want to know where space is being used in a particular filesystem, you can use this command to find the 20 largest directories, which can help you locate where the most space is used,

du -m / |sort -n |tail -20

But the root filesystem is more difficult, because all filesystems are mounted to root. But the -x (--one-file-system) argument will report only the desired filesystem,

du -m -x / |sort -n |tail -20
df -h *.* 

Might help.

Traverses directories and sums up bytes used.

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