shred (覆盖文件以隐藏其内容，并有选择地删除它)

After destroying the FILE data, shred will also delete the FILE(s) if --remove (-u) is specified. The default is not to remove the files because it is common to operate on entire 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: Take note that shred relies on an important assumption: that the file system overwrites data "in-place." This assumption is the traditional way to do things, but many modern file systems do not do things exactly this way. 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 file 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 manual. Also, 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.