rsync 3.2.3 possible bug on md5sum

[Alessandro Baggi]

Hi,

I'm using rsync in a script to perform backups (using hardlink). It 
works very well. In my case I use an alternative output format to 
retrieve md5hash for every synced file so that I can save the hash and 
run an integrity check when needed. I use this because I noticed that 
the md5sum printed from rsync is like file md5sum and this avoid me to 
calculate md5 checksum for every downloaded file and I can save time 
(specially in the first backup on large dataset). Currently I use this 
command:

rsyc -avElHA --out-format"%i||%n||%C" source dest

(well, I have reduced the original command to this to see if the problem 
was generated by an option. The original command include ssh option and 
timeout and other option)

The problem:

I noticed that using rsync 3.2.3 (protocol version 31) the md5 hash does 
not correspond to the md5 file hash so if I run a check I got corrupted 
file alerts.

My current backup machine runs Debian 11.1 with rsync 3.2.3 (installed 
from debian repository) and it works in pull. The following rsync 
version is related to remote host.

What I tested (I tested only trasferring one file of ~30MB with the 
previous command):

Sync from Debian 11.1 | problem found | rsync 3.2.3
Sync from RockyLinux 8.4 | problem not found | rsync 3.1.3
Sync from Debian 10.11 | problem not found | rsync 3.1.3
Sync from Slackware15 (current) | problem found | rsync 3.2.3
Sync file locally | problem found | rsync 3.2.3

So this happens only when the remote host has rsync 3.2.3 while with 
rsync 3.1.3 no problem.

I don't know if this is a bug or a new behaviour of the protocol.

Any help will be appreciated.

Thank you in advance.

Alessandro.