crc32

crc32 [OPTION]... [FILE]...

[FILE]...
    Optional. One or more input files to calculate the CRC-32 checksum for. If no files are specified, crc32 reads from standard input.

-s
    Optional. Suppress the output of filenames, printing only the CRC-32 checksum.

--help
    Optional. Display a help message and exit.

--version
    Optional. Output version information and exit.

The crc32 command is a Linux utility designed to calculate the 32-bit Cyclic Redundancy Check (CRC-32) checksum of a given file or stream of data.

A CRC-32 checksum is a type of hash function used primarily for detecting accidental changes to raw data, such as those that might occur during data transmission or storage. It operates by performing a polynomial division on the input data, with the remainder being the checksum. The crc32 utility reads data from the specified files; if no files are provided, it reads from standard input. The computed checksum is then printed to standard output, typically in an 8-character hexadecimal format.

While not cryptographically secure like MD5 or SHA hashes (meaning it's easier to find two different inputs that produce the same CRC-32 checksum), crc32 is efficient and widely used for non-cryptographic data integrity checks, such as verifying downloaded files or ensuring consistency of backups. It's particularly useful when speed is more critical than strong collision resistance.

The crc32 command is designed for error detection, not cryptographic security. It is relatively easy to find collisions (different inputs producing the same checksum), making it unsuitable for verifying data integrity against malicious tampering. For cryptographic integrity, utilities like md5sum or sha256sum should be used instead.

Note that some rare or custom crc32 implementations might use different polynomial or initial values, potentially yielding different checksums for the same data, though the standard CRC-32 (IEEE 802.3) is almost universally adopted in common Linux utilities.

By default, crc32 prints the computed checksum as an 8-character hexadecimal string, followed by a space and the filename for each processed file. If reading from standard input, only the checksum is printed.

Examples:
To calculate the CRC-32 of a file:
crc32 mydata.txt
Output: 1a2b3c4d mydata.txt

To calculate the CRC-32 of a string from standard input:
echo "Hello World" | crc32
Output: cbefcb75

To calculate the CRC-32 of multiple files silently:
crc32 -s file1.txt file2.txt
Output:
abcdef12
34567890

The concept of Cyclic Redundancy Checks (CRCs) dates back to the early 1960s, with CRC-32 becoming standardized, notably by the IEEE 802.3 Ethernet standard and popularized by applications like PKZIP. The crc32 command-line utility itself emerged as a simple wrapper around the widely available CRC-32 algorithms, often leveraging libraries like zlib which provide highly optimized CRC computation functions. Its development reflects the pervasive need for quick and efficient data integrity verification in various computing contexts, from network transmissions to file storage and archiving, becoming a standard tool in Linux environments for non-cryptographic checksumming.

md5sum(1), sha1sum(1), sha256sum(1), cksum(1), sum(1)