| Linux / Unix Command: shred |
NAME
shred - delete a file securely, first overwriting it to hide its contentsSYNOPSIS
shred [OPTIONS] FILE [...]DESCRIPTION
Overwrite the specified FILE(s) repeatedly, in order to make it harder for even very expensive hardware probing to recover the data.
Mandatory arguments to long options are mandatory for short options too.
- -f, --force
- change permissions to allow writing if necessary
- -n, --iterations=N
- Overwrite N times instead of the default (25)
- -s, --size=N
- shred this many bytes (suffixes like K, M, G accepted)
- -u, --remove
- truncate and remove file after overwriting
- -v, --verbose
- show progress
- -x, --exact
- do not round file sizes up to the next full block
- -z, --zero
- add a final overwrite with zeros to hide shredding
- -
- shred standard output
- --help
- display this help and exit
- --version
- output version information and exit
Delete FILE(s) if --remove (-u) is specified. The default is not to remove the files because it is common to operate on device files like /dev/hda, and those files usually should not be removed. When operating on regular files, most people use the --remove option.
CAUTION: Note that shred relies on a very important assumption: that the filesystem overwrites data in place. This is the traditional way to do things, but many modern filesystem designs do not satisfy this assumption. The following are examples of filesystems on which shred is not effective:
* log-structured or journaled filesystems, such as those supplied with
- AIX and Solaris (and JFS, ReiserFS, XFS, Ext3, etc.)
* filesystems that write redundant data and carry on even if some writes
- fail, such as RAID-based filesystems
* filesystems that make snapshots, such as Network Appliance's NFS server
* filesystems that cache in temporary locations, such as NFS
- version 3 clients
* compressed filesystems
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.
SEE ALSO
The full documentation for shred is maintained as a Texinfo manual. If the info and shred programs are properly installed at your site, the command- info shred
should give you access to the complete manual.
Important: Use the man command (% man) to see how a command is used on your particular computer.
