Suppose you visit a bad location on earth with your laptop.
Thieves are about to break in and steal your laptop.
So you run :
rm -rf /folder
but what if thieves have very advanced tools to recover deleted files ? perhaps as advanced as FBI / CIA tools.
Perhaps they will be able to recover that deleted folder w/ files ?
What would be the a way to ensure they can not ?
Just use shred like this:
$ shred -fuvz /folder
The switches above are:
-f, --force
-u, --remove
-v, --verbose
-z, --zero write to hide the shred
By default shred will overwrite three iterations with random data. This happens before the -z writes zeros to hide the shred. You can specify a different number of iterations with the -n switch followed by a digit. Or in long form with --iterations=N.
A word of caution from the shred manpages:
CAUTION: Note that shred relies on a very important assumption: that the file system overwrites data in place. This is the traditional way to do things, but many modern file system designs do not satisfy this assumption. The following are examples of file systems on which shred is not effective, or is not guaranteed to be effective in all file system modes:
log-structured or journaled file systems, such as those supplied with AIX and Solaris (and JFS, ReiserFS, XFS, Ext3, etc.)
file systems that write redundant data and carry on even if some writes fail, such as RAID-based file systems
file systems that make snapshots, such as Network Appliance's NFS server
file systems that cache in temporary locations, such as NFS version 3 clients
compressed file systems
In the case of ext3 file systems, the above disclaimer applies (and shred is thus of limited effectiveness) only in data=journal mode, which journals file data in addition to just metadata. In both the data=ordered (default) and data=writeback modes, shred works as usual. Ext3 journaling modes can be changed by adding the data=something option to the mount options for a particular file system in the /etc/fstab file, as documented in the mount man page (man mount).
In addition, file system backups and remote mirrors may contain copies of the file that cannot be removed, and that will allow a shredded file to be recovered later.
