Context
-------
I am one of the active developers of the open source application "Back in Time"
which uses "rsync" as backend and I want to fix an open issue:
"Back in Time"-Bug:
https://github.com/bit-team/backintime/issues/994#issuecomment-1724211507
"Back in Time" uses "--link-dest" to reduce traffic and storage by hardlinking
unchanged files in the backups/snapshots and tries to keep the permissions
by using "--perms --group --owner" by default.
Older snapshots are then deleted according to a schedule.
Issue
-----
When deleting a complete snapshot folder with rsync using an empty source folder
(which is a best practice for faster deletion than "rm -f") the permissions of
hardlinked
files are changed from eg. 444/-r--r--r-- to 644/-rw-r--r-- for all deleted
files
with existing hardlinks:
mkdir empty
rsync -a --delete -s empty/ snapshot1/
This distorts the backup history.
There is a corrsponding 6-year-old issue in Bugzilla incl. a patch but the
issue is still unfixed:
https://bugzilla.samba.org/show_bug.cgi?id=12806
Questions
---------
1. Is there a reliable workaround ("--super" is proposed in the issue but may
probably not always work)?
2. If a rsync developer is reading this: Is there any chance to fix this?
Steps to reproduce
------------------
I have attached a bash script "setup.sh" as txt file which makes the issue
fully reproducible (on Ubuntu 22.04).
#!/bin/bash
clear
echo
echo "Minimal reproducible example (MRE)"
echo "----------------------------------"
echo
echo "Tested with"
echo "- rsync version 3.2.7 protocol version 31"
echo "- ext4 file system"
echo
rm -rf MRE
mkdir MRE
cd MRE
mkdir source
touch source/read_only.txt
chmod 444 source/read_only.txt
mkdir snapshot1
# rsync --recursive --times --devices --specials --hard-links --human-readable
-s --links --perms --executability --group --owner source/* snapshot1/
rsync --perms --executability --group --owner source/* snapshot1/
mkdir snapshot2
# rsync --recursive --times --devices --specials --hard-links --human-readable
-s --links --perms --executability --group --owner --link-dest=../snapshot1
source/* snapshot2/
rsync --perms --executability --group --owner --link-dest=../snapshot1 source/*
snapshot2/
# stat snapshot1/read_only.txt
echo "File stats BEFORE rsync --delete":
echo
stat snapshot2/read_only.txt
mkdir empty
# delete snapshot1 using an empty source directory (shall be the fastest way to
delete a subdir)
# --debug=ALL
rsync -a --delete -s empty/ snapshot1/
# rm -f snapshot1/ # works as expected (unlink does neither change 'Changed'
time nor file permissions)
# strace -c rm -rf snapshot1
echo
stat snapshot2/read_only.txt
echo
echo "Results (after deleting snapshot1 via rsync --delete):"
echo "1. The 'Change' time of the hardlinked file was updated"
echo "2. The hardlinked file has now different access rights (644 instead of
444 so it is writable again!)"
echo "This does NOT happen if 'rm -f snapshot1/' is used!"
echo
echo "Files in snapshot2:"
ls -l snapshot2
--
Please use reply-all for most replies to avoid omitting the mailing list.
To unsubscribe or change options: https://lists.samba.org/mailman/listinfo/rsync
Before posting, read: http://www.catb.org/~esr/faqs/smart-questions.html
