How do I recursively shred an entire directory tree?
Use the find command to execute shred recursively:
find <dir> -type f -exec shred {} \;
Beware of shred!
From the shred-manpage:
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.
Also, SSDs might thwart your attempts of overwriting data.
Solution: Use an encrypted filesystem, and just delete your files.
Use secure delete instead.
sudo apt-get install secure-delete
srm -r pathname
Done. Secure delete is a lot more paranoid than shred, using 38 passes instead of 3. To do a fast single pass, use
srm -rfll pathname
fll gets you a less random data generator, and only a single pass.