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4.16. Removing Data Securely Using scrub

The scrub utility sets patterns on special files or disk devices to make retrieving data more difficult. Using scrub is faster than writing random data on a disk. This process provides high availability, reliability, and data protection.
To start using the scrub command, install the scrub package:
Copy to Clipboard Toggle word wrap 
~]# yum install scrub
The scrub utility operates in one of the following basic modes:
Character or Block Device
The special file corresponding to a whole disk is scrubbed and all data on it, is destroyed. This is the most effective method.
Copy to Clipboard Toggle word wrap 
scrub [OPTIONS] special file
File
A regular file is scrubbed and only the data in the file is destroyed.
Copy to Clipboard Toggle word wrap 
scrub [OPTIONS] file
Directory
With the -X option, a directory is created and filled with files until the file system is full. Then, the files are scrubbed as in file mode.
Copy to Clipboard Toggle word wrap 
scrub -X [OPTIONS] directory

Example 4.7. Scrubbing a Raw Device

To scrub a raw device /dev/sdf1 with default National Nuclear Security Administration (NNSA) patterns, enter the following command:
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~]# scrub /dev/sdf1
scrub: using NNSA NAP-14.1-C patterns
scrub: please verify that device size below is correct!
scrub: scrubbing /dev/sdf1 1995650048 bytes (~1GB)
scrub: random  |................................................|
scrub: random  |................................................|
scrub: 0x00    |................................................|
scrub: verify  |................................................|

Example 4.8. Scrubbing a File

  1. Create a 1MB file: Copy to Clipboard Toggle word wrap 
    ~]$ base64 /dev/urandom | head -c $[ 1024*1024 ] > file.txt
  2. Show the file size: Copy to Clipboard Toggle word wrap 
    ~]$ ls -lh
total 1.0M
-rw-rw-r--. 1 username username 1.0M Sep  8 15:23 file.txt
  3. Show the contents of the file: Copy to Clipboard Toggle word wrap 
    ~]$ head -1 file.txt
JnNpaTEveB/IYsbM9lhuJdw+0jKhwCIBUsxLXLAyB8uItotUlNHKKUeS/7bCRKDogEP+yJm8VQkL
  4. Scrub the file: Copy to Clipboard Toggle word wrap 
    ~]$ scrub file.txt
scrub: using NNSA NAP-14.1-C patterns
scrub: scrubbing file.txt 1048576 bytes (~1024KB)
scrub: random  |................................................|
scrub: random  |................................................|
scrub: 0x00    |................................................|
scrub: verify  |................................................|
  5. Verify that the file contents have been scrubbed: Copy to Clipboard Toggle word wrap 
    ~]$ cat file.txt
SCRUBBED!
  6. Verify that the file size remains the same: Copy to Clipboard Toggle word wrap 
    ~]$ ls -lh
total 1.0M
-rw-rw-r--. 1 username username 1.0M Sep  8 15:24 file.txt
For more information on scrub modes, options, methods, and caveats, see the scrub(1) man page.
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