Out of disk space, what's the source?-Collection of common programming errors

It seems like /var/lib/ureadahead/debugfs may be a red-herring. Here’s why…

While /var/lib/ureadahead/debugfs does exist in /etc/mtab, it is not found in /proc/mounts:

$ mount | grep debug
none on /sys/kernel/debug type debugfs (rw)
none on /var/lib/ureadahead/debugfs type debugfs (rw,relatime)

$ cat /proc/mounts | grep debug
none /sys/kernel/debug debugfs rw,relatime 0 0

The df command seems to be reporting exactly the same thing for /var/lib/ureadahead/debugfs and /

$ df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/sda1             10321208   1681128   8115792  18% /
none                    830388       120    830268   1% /dev
none                    880752         0    880752   0% /dev/shm
none                    880752        60    880692   1% /var/run
none                    880752         0    880752   0% /var/lock
none                    880752         0    880752   0% /lib/init/rw
none                  10321208   1681128   8115792  18% /var/lib/ureadahead/debugfs
/dev/sdb             153899044    192068 145889352   1% /mnt

Creating a 1GB file in /tmp:

$ dd if=/dev/zero of=/tmp/carypjunk.out bs=1M count=1024
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB) copied, 52.7234 s, 20.4 MB/s

Shows the size reported in both places:

$ df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/sda1             10321208   2730216   7066704  28% /
none                    830388       120    830268   1% /dev
none                    880752         0    880752   0% /dev/shm
none                    880752        60    880692   1% /var/run
none                    880752         0    880752   0% /var/lock
none                    880752         0    880752   0% /lib/init/rw
none                  10321208   2730216   7066704  28% /var/lib/ureadahead/debugfs
/dev/sdb             153899044    192068 145889352   1% /mnt

So, it seems like /var/lib/ureadahead/debugfs device is a red-herring as it is just mirroring the stats from /. If you are running out of space, it is due to something filling up your root filesystem. I would check your /var/log first.