Re: rsync --delete with empty source folder for fast snapshot deletion: Permissions of hardlinked files are changed to 644. Workaround?

Here is the missing attachment ;-)



On Fri, 2023-09-22 at 21:01 +0200, rsync--- via rsync wrote:
> On Fri, 2023-09-22 at 07:37 -0400, Kevin Korb wrote:
> > So I decided to do a quick test using the Linux kernel source tree since 
> > it has lots of files.
> 
> Excellent idea using kernel sources! A lot of different files...
> I will use this to create indicative benchmarks for different scenarios...
> 
> >   I duplicated a tree, used 'find . -type f -exec 
> > chmod 444 {} +' to make read only files for rsync to want to chmod, then 
> > used cp -al to make several duplicate trees using hard linked files.
> > [...]
> > But also, I did not experience the problem you are describing.  My surviving 
> > hard links in the duplicate trees were still 444.
> 
> If attached a script that does the same (with one file instead of the kernel source tree)
> but in my case 444 became 644 again.
> 
> - Q: Which rsync version, distro and file system do you use?
> 
> - Q: Does my attached script reproduce the permission change?
> 
> - Q: Did my script attached to the initial post here reproduce the permission change?
> 
> 
> 
> PS: In my case the attached script shows (excerpt):
> 
> ./setup_cp_al.sh
> 
> Tested with
> - rsync  version 3.2.7  protocol version 31
> - ext4 file system
> - Ubuntu 22.04
> 
> File stats BEFORE rsync --delete:
> 
>   File: snapshot2/read_only.txt
>   Size: 0               Blocks: 0          IO Block: 4096   regular empty file
> Device: 10305h/66309d   Inode: 17571021    Links: 3
> Access: (0444/-r--r--r--)  Uid: ( 1000/ user1)   Gid: ( 1000/ user1)
> Access: 2023-09-22 20:51:16.690961150 +0200
> Modify: 2023-09-22 20:51:16.690961150 +0200
> Change: 2023-09-22 20:51:16.694961109 +0200
>  Birth: 2023-09-22 20:51:16.690961150 +0200
> 
> File stats AFTER rsync --delete
> 
>   File: snapshot2/read_only.txt
>   Size: 0               Blocks: 0          IO Block: 4096   regular empty file
> Device: 10305h/66309d   Inode: 17571021    Links: 2
> Access: (0644/-rw-r--r--)  Uid: ( 1000/ user1)   Gid: ( 1000/ user1)
> Access: 2023-09-22 20:51:16.690961150 +0200
> Modify: 2023-09-22 20:51:16.690961150 +0200
> Change: 2023-09-22 20:51:16.694961109 +0200
>  Birth: 2023-09-22 20:51:16.690961150 +0200
> 
> Results (after deleting snapshot1 via rsync --delete):
> 1. The 'Change' time of the hardlinked file was updated
> 2. The hardlinked file has now different access rights (644 instead of 444 so it is writable again!)
> This does NOT happen if 'rm -f snapshot1/' is used!
> 
>

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#!/bin/bash
clear

# Test if permissions changes from 444 to 644 with rsync --delete and snapshots taken with cp -al

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 "- Ubuntu 22.04"
echo
rm -rf MRE
mkdir MRE
cd MRE
mkdir source
touch source/read_only.txt
# chmod 444 source/read_only.txt
find source -type f -exec chmod 444 {} +

mkdir snapshot1
# rsync --perms --executability --group --owner source/* snapshot1/
cp -al source/* snapshot1/

mkdir snapshot2
# rsync --perms --executability --group --owner --link-dest=../snapshot1 source/* snapshot2/
cp -al source/* snapshot2/
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
echo "File stats AFTER rsync --delete"
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