crc.1

NAME

crc - checksum files

crcdiff - compare two crc lists and report the difference

SYNOPSYS

crc [-dv] [-i initial_crc] file ...

crcdiff [-s] [-c critical_list] crclist crclist

DESCRIPTION

For each file, crc calculates and prints a 32-bit CRC in hexadecimal. With the -v optin it additionally prints file permissions, file owner, group and the file name. It is typically used to validate files transferred between different systems, and is useful in detecting subtle disk corruption. crc uses a checksum compatible with the DOS version of crc, the 32 bit CRC used by PKZIP version 0.9. as well as the "crc" command in ZCOMM and Professional-YAM (high reliability communications programs). With the -d option, the 32-bit CRC is printed in decimal. You can use -i option to initialize CRC with initial_crc instead of 0.

The 32-bit CRC used is the frame check sequence in ADCCP (ANSI X3.66, also known as FIPS PUB 71 and FED-STD-1003, the U.S. version of CCITT's X.25 link-level protocol).

crcdiff compares two crc lists and reports the differences. If -c option is used, directories/files listed in critical_list will be used to give L2 warnings for changes to such files.

  corrupt    - crc changed without date change 
  replaced   - crc + date changed
  permiss    - permissions changed
  own/grp    - owner or group changed
  deleted    - 
  added      - Print the info for the new file
  WARNING L1 - Changes to setuid, setgid files
  WARNING L2 - Changes to file in critical_list

If crclist files are sorted you can use the -s option which makes crcdiff(1) run faster.

To generate crclist you can use

 find / -print | sort | xargs crc -v > crc_file

to generate a crc list. Assume that no files have tabs or spaces in the name.

BUGS

Altough extremely unlikely, files with different data may still produce the same crc value.

SEE ALSO

sum(1) md5sum(1) sha1sum sha224sum sha256sum sha284sum sha512sum