[ubuntu-us-in] Free up disk space on ext2/3 partitions

[Jeremy Nelson]

Hi all - I've run into a problem several times lately where despite my
SNMP checker warning me about machines with < 5% free disk space, I
still ran out of disk space.  I had never had time to track it down
until it happened again this morning.  I was really confounded by the
fact that df -h shows the following:

Filesystem            Size  Used Avail Use% Mounted on
/dev/sda1              99G   93G  868M 100% /

Turns out that ext2/3 reserves 5% of the filesystem space for the root
user to allow for recovery from a disk full condition, so you actually
run out of space at 95% usage.

It turns out that this is really only necessary on root partitions,
and 5% on large disks is probably really overkill (and since mine are
VMs, anyway, I can mount the filesystem and fix the problem or simply
grow the device & filesystem without logging in easily enough).

Here's a more in depth article on it - hope this helps somebody else
avoid this frustration!

http://boncey.org/2006_11_18_reclaiming_ext3_disk_space

Jeremy Nelson