cksum Command in Linux

The cksum command in Linux is used to verify file integrity by calculating a CRC (Cyclic Redundancy Check) value along with the file size. It is mainly used to detect accidental corruption during file transfer or storage.

• Displays CRC checksum, file size (in bytes), and file name
• Helps verify whether a file changed unintentionally
• Commonly used after copying or transferring files
• Suitable for error detection, not for security or authentication

Example 1: Check CRC of a Single File

This example shows how to calculate the checksum of a file.

cksum file.txt

Output :

Explanation:

• 2029622798: CRC value
• 39: File size in bytes
• file.txt: File name

Example 2: Check CRC of Multiple Files

You can calculate CRC values for multiple files in one command.

cksum file1.txt file2.txt file3.txt

Note: Each file is processed separately, and the output is displayed line by line for each file.

Example 3: Calculate CRC Using Standard Input

If no file name is provided, cksum reads data from standard input.

echo "Hello Linux" | cksum

Note: Useful for verifying the integrity of piped data or command output.

Example 4: Save Checksum Output to a File

You can redirect the output of cksum to a file for later comparison.

cksum file.txt > file_checksum.txt

Note: Stores the CRC value and file size, which can be reused to check file consistency later.

Example 5: Compare Current CRC with Stored CRC

This example compares the current checksum with a previously saved one.

cksum file.txt | diff - file_checksum.txt

Note: If no output is produced, the file has not changed. If output is shown, the file content has changed.

Syntax of `cksum` command in Linux

cksum [OPTION]... [FILE]...

• FILE: Name of the file to calculate CRC
• OPTION: Optional flags to modify command behavior

Options Available in `cksum` command in Linux

The cksum command provides very limited options compared to other checksum utilities.

Option 1. --help

Displays help information and usage details.

cksum --help

Note: Helpful when you want a quick reference for command usage.

Option 2. --version

Displays the version information of the cksum utility.

cksum --version

Note: Useful for debugging or checking compatibility across systems.

Real-World Use Cases of cksum

1. Verify File Transfer Integrity

After transferring large files over a network, compare CRC values to ensure no accidental corruption occurred.

cksum backup.tar

Note: Run this command before and after transferring the file, If both CRC values match, the file was transferred successfully.

2. Backup Validation

Helps confirm that backup files remain unchanged after creation.

cksum backup_2024.tar

Note: This command can be stored in logs or scripts and rechecked later to validate backups.

3. Data Consistency Checks

Used to monitor important files and detect unintended changes over time.

cksum config.cfg

Note: If the CRC value changes unexpectedly, it indicates accidental modification.