cksum Command in Linux
cksum is a command used in Linux that helps you verify file integrity by calculating a Cyclic Redundancy Check (CRC) value and displaying the byte count of a file. The cksum command is useful for detecting corrupted downloads or file transfers. For example, when downloading a Linux ISO file, you can compare its checksum value with one generated using cksum.
The official checksum value of the ISO file can be found on the developers website, if the checksum value matches, the file is likely intact.
Table of Contents
Here is a comprehensive guide to the options available with the cksum command −
- How to Install cksum Command in Linux?
- Syntax of cksum Command
- cksum Command Options
- Example of cksum Command in Linux
How to Install cksum Command in Linux?
The cksum command is included in the coreutils package, which is preinstalled on all Linux distributions. If you encounter command not found error while running the cksum command, you can reinstall the coreutils package from your Linux package manager.
For Linux systems like Debian, Ubuntu, or Kali Linux, the coreutils package can be reinstalled from the below-given apt command −
sudo apt install --reinstall coreutils
For other distributions, such as RHEL, CentOS and Fedora, the coreutils package can be reinstall using the below-provided yum command −
sudo yum install --reinstall coreutils
Once, you install the coreutils package, you can confirm the cksum installation by running the below-given command −
cksum --version
Syntax of cksum Command
The basic syntax for cksum command in Linux is as follows −
cksum filename
Replace filename with the actual name of the file you want to check. The cksum command will compute the CRC value and display the byte count for that file.
cksum Command Options
There are different options or flags you can use with the cksum command, these are discussed in the table given below −
| Option | Description |
|---|---|
| -a, --algorithm=TYPE | This option allows you to choose the digest type (hash algorithm) to use. You can specify the desired algorithm, such as SHA-256 or SHA-512 |
| --base64 | When this flag is used, the command emits base64-encoded digests instead of the usual hexadecimal format. |
| -c, --check | With this option, you can read checksum from files and verify them against the provided checksum values. |
| -l, --length=BTS | Specify the desired digest length in bits. |
| --raw | When this flag is used, the command emits raw binary digests instead of hexadecimal representation. |
| --tag | The default behavior creates a BSD-style checksum. You can use this option to explicitly request that style. |
| --untagged | This option creates a reverse style checksum without including the digest type. |
| -z, --zero | This option will end lines with NULL characters and disable file name escaping. |
| -w, --warn | This option will warn about improperly formatted check sum lines. |
| --ignore-missing | Dont fail or report status for missing files. |
| --status | It doesnt produce any visible output. Instead, it relies on the exit status code to indicate whether the operation was successful. |
| --quiet | Suppress printing OK for each successfully verified file. |
| --strict | Exit with a non-zero status for improperly formatted checksum lines. |
| --debug | Indicate which implementation is used. |
| --version | Output version information and exist. |
| --help | Display help information and exist. |
Examples of cksum Command in Linux
Lets discuss a few examples of cksum command that you can use on your Linux system −
- Single File Check
- Multiple Files Check
- Recursive Check for All Files in a Directory
- Redirect Output to a File
- Calculate Algorithm Checksum for a File
Single File Check
One of the basic examples of cksum command on Linux is to check the CRC value of a single file. You can do this by providing the name of the file with the cksum command. For example, to check for a file named sample.ppm, run the below-given command −
cksum sample.ppm
The cksum command will print the CRC value and file size in bytes for your specified file.
Multiple Files Check
If you want to check the CRC value of multiple files all at once, you can use the cksum command followed by the name of the files with space between their names. For example, the following command will check the checksum values of two files named sample.ppm and sample.jpg −
cksum sample.ppm sample.jpg
Recursive Check for All Files in a Directory
To recursively check all files in a directory including subdirectories, you can use the following command −
find /path/to/directory -type f -exec cksum {} \;
Replace /path/to/directory with the actual path to the directory you want to check. This command will calculate the checksum for each file within that directory structure.
Redirect Output to a File
You can also modify the cksum command in such a way that the checksum values of the files will be redirected to another file as an output. This can be done by using the redirection operator. For example, the following command will redirect the checksum value of a file named sample.ppm into another file called checksum.txt −
cksum sample.ppm > checksums.txt
Calculate Algorithm Checksum for a File
You can calculate the algorithm checksum for a file by specifying the desired cryptographic hash function using the --algorithm option. For instance, to calculate the SHA-256 checksum for a file named sample.ppm, you can use the following command −
cksum --algorithm=sha256 sample.ppm
The output will display the SHA-256 hash value for the file.
Thats how you can use the cksum command to calculate the checksum value for a file.
Conclusion
cksum is a useful Linux command that helps you calculate checksums, verify file integrity, and detect any changes or corruption. Whether you need CRC values, base64-encoded digests, or customized output formats, cksum provides flexibility for various use cases.
This tutorial covered the syntax of cksum command along with different options to be used with the command. The examples provided later on are straightforward and can help you understand the commands basics.