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rotcheck

A simple shell script to recursively generate, update and verify checksums for files you care about. It's useful for detecting bit rot.

It's written in POSIX shell, but requires GNU coreutils, BusyBox or some other collection that includes similar checksum tools.

Advantages compared with other tools

Simple and should work forever (because it's POSIX shell). It's also trivial to edit the code for your own needs.

Disadvantages compared with other tools

Verifying checksums is just as fast as any other tool, but generating or updating checksums is slower (because it's POSIX shell).

Maybe use a faster tool if you have millions of files and regularly update your checksums.

Installation

Download this script to somewhere in your $PATH. For example:

curl -O https://raw.githubusercontent.com/jamielinux/rotcheck/master/rotcheck
sudo cp rotcheck /usr/local/bin/rotcheck
sudo chmod +x /usr/local/bin/rotcheck
rotcheck -h

Usage

Create first checksum file (located at ./.rotcheck):

$ cd /backups
$ rotcheck -a

You've added some new files and need to append some checksums:

$ cd /backups
$ rotcheck -av
ADDED: ./backups/foo/one.tar.gz
ADDED: ./backups/foo/two.tar.gz

You've edited some files and need to update the checksums:

$ cd /backups
$ rotcheck -uv
CHANGED: ./backups/bar/three.tar.gz

Verify checksums:

$ cd /backups
$ rotcheck -c
./backups/baz/bitrot.tar.gz: FAILED
sha512sum: WARNING: 1 of 49231 computed checksums did NOT match

Full help text

Usage: rotcheck MODE [OPTIONS]
   or: rotcheck MODE [OPTIONS] -- [DIRECTORY]... [ARBITRARY FIND OPTION]...
Recursively generate, update and verify checksums.

MODES:
 -a           APPEND mode: Record checksums for any files without a checksum
              already. Never modify existing checksums.
 -c           CHECK mode: Check that files checksums are the same.
 -d           DELETE mode: Remove checksums for files that don't exist.
 -u           APPEND-AND-UPDATE mode: Like append-only mode, but also update
              checksums for files with a modification date newer than the
              the checksum file. (NB: Also see `-M`.)

OPTIONS:
 -b COMMAND   Checksum command to use. Default: sha512sum
 -f FILE      File to store checksums. For relative paths, prefix with "./"
              or the checksum file will be checksummed. Default: ./.rotcheck
 -h           Display this help.
 -n           Don't follow symlinks. The default is to follow symlinks.
 -v           Be more verbose when adding, deleting, changing or verifying
              checksums.
 -w           Warn about improperly formatted checksum lines.
 -x           Exclude all hidden files and directories when generating
              checksums. The default is to include them.
 -M           Use with `-u` to update checksums regardless of modification
              time. This is very slow so avoid if possible; try `touch`
              instead to bump the modification time of specific files.
              WARNING: The checksums might have changed due to bit rot so
              use this option with care!

 (specific to GNU coreutils >= 8.25)
 -i           Ignore missing files when verifying checksums.


Supported commands:
  GNU coreutils:
    md5sum, sha1sum, sha224sum, sha256sum, sha384sum, sha512sum, b2sum

  BusyBox (applets must be symlinked):
    md5sum, sha1sum, sha256sum, sha512sum, sha3sum

  BSD & macOS (install GNU coreutils):
    gmd5sum, gsha1sum, gsha224sum, gsha256sum, gsha384sum, gsha512sum, gb2sum


Examples:
  # Create checksum file (located at "./.rotcheck"):
  rotcheck -a

  # You've added some new files and need to append some checksums:
  rotcheck -va

  # You've edited some files and need to update the checksums (for files with
  # a modification time newer than the checksum file):
  rotcheck -vu

  # Verify checksums:
  rotcheck -c

  # Search other directories instead of the current directory.
  # WARNING: checksums might get duplicated if mixing relative and absolute
  # paths, or if you change the way you specify directory paths!
  rotcheck -a -- /mnt/archive-2018/ /mnt/archive-2019/

  # Exclude .git folders (these arguments are passed directly to find):
  rotcheck -a -- ! -path '*/\.git/*'