Posts Tagged clear

How to fill unused drive space with zeros in Linux

Filling unused drive space with zeros is useful for cleaning a drive and for preparing a drive image for compression.  A drive whose unused space is filled with zeros will compress to a much smaller size than one that is not.  There are two methods typically used to fill a Linux drive with zeros:

A simple shell script

The following shell script simply creates a file and fills it with zeros until all drive space in exhausted, then it deletes the file.  This isn’t a perfect solution, but it’s better than nothing.

#!/bin/bash
cat /dev/zero > /zero.fill
sync
sleep 5
sync
rm -f /zero.fill

The ‘zerofree’ utility.

The zerofree utility, written by Ron Yorston, only works on devices containing an ext2 or ext3 file system. It seems to work fairly well, however I have crashed one system with it so be careful. You should probably clone the drive you plan to zerofree before doing so.

References

http://intgat.tigress.co.uk/rmy/uml/sparsify.html
http://packages.ubuntu.com/search?keywords=zerofree

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