Use apenas shred da seguinte forma:
$ shred -fuvz /folder
Os switches acima são:
-f, --force
-u, --remove
-v, --verbose
-z, --zero write to hide the shred
Por padrão, shred sobrescreve três iterações com dados aleatórios. Isso acontece antes que o -z grave zeros para ocultar o fragmento. Você pode especificar um número diferente de iterações com a opção -n seguida de um dígito. Ou em formato longo com --iterations=N .
Uma palavra de cautela dos manpages do shred :
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.