Yrurtj

I was wondering:

1. Is it possible to create a checksum of a directory (using something like md5sum)


2. Is it possible to recursively create checksum for each file inside the dir (and then print it out)?


3. Or both?

I'm using bash

md5sum won't take directory as input, however

 tar cf - FOO | md5sum

will checksum it, if a file is change any place within FOO, checksum will change, but you won't have any hint of which file. The checksum will also change if any file metadata changes (permissions, timestamps, …).

You might consider using :

 find FOO -type f -exec md5sum {} ;  > FOO.md5

which will md5 every file individually, and save the result in FOO.md5. This makes it easier to check which file has changed. This variant only depends on file content, not on metadata.

ZFS creates such a checksum but this is for internal use only.

In order to calculate a checksum from an object, you need to read this object and for directories, this is not granted to be possible.

Many filesystems return the EISDIR error when trying to read(2) a directory and ZFS in addition sets the "size" of the directory to the number of entries in that directory instead of the number of bytes (what you may expect when you like to read(2) a directory).

The fact that some filesystems still allow you to read(2) directories is a bug - a left over artefact from the 1970s when there was no readdir() call.

BTW: on my WOFS, all directories have size 0 as they don't have any file type content because the files instead say in their meta data "hey, I am in this directory". If you wonder what WOFS is: all other basic concepts from WOFS have been incorporated into ZFS.

1.Why do you need md5sum on directory? If you want to be sure of file consistency and/or integrity you can tar it and make hash of tar/tar.gz file.

2.If you have sub directories it will be a little harder. If you have files only, try this as example:

#!/bin/bash



for i in /home/{username}/Books/rhel/; do

  md5sum "$i"

done

Output example:

dd7a684cc8668d208ca5dcf00bc58e8d  Red_Hat_Enterprise_Linux-6-Deployment...

775602071a1ec5a1ac1a99cee9d065fa  Red_Hat_Enterprise_Linux-7-High_Av..

On https://blake2.net/ they claim:

" BLAKE2 is a cryptographic hash function faster than MD5, SHA-1, SHA-2, and SHA-3, yet is at least as secure as the latest standard SHA-3. BLAKE2 has been adopted by many projects due to its high speed, security, and simplicity. "

Therefore, some tools are using it, e.g. rmlint https://github.com/sahib/rmlint .

Anyway, following https://unix.stackexchange.com/a/228758/9689 , you can also do :

find "${dirname}"/ -type f -exec b2sum -b -l 256 {} ;  > "${dirname}".blake2sum_l256

And later check with:

b2sum -c "${dirname}".blake2sum_l256

Or this to see only failing ones:

b2sum --quiet -c "${dirname}".blake2sum_l256