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List:       rsync
Subject:    How to backup/restore NFS data and preserve ACL's on Linux?
From:       Chandler via rsync <rsync () lists ! samba ! org>
Date:       2023-02-02 22:23:06
Message-ID: 7b804c6c-5941-b8f7-9ec6-270ffac06ed2 () genome ! arizona ! edu
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On the backup system, I have mounted the directories to backup over NFS (v4.2), then \
rsync is run on the backup system (by root) to copy the data from NFS to its local \
filesystem (ZFS with xattr and posixacl properties).

I can verify the backup system can see the source ACL's with nfs4_getfacl.  I can \
also create and verify ACL's on the backup file system with set/getfacl.  I guess the \
problem arises due to differences in NFS and posix ACL formats and mapping between \
them?  I read a bunch this morning and tried various commands.  The best I could come \
up with was something like this:

rsync -aAX --filter='-x system.posix_acl' --fake-super

I guess I literally have to remove/filter out the original ACL metadata, because \
without the filter, rsync saves `user.rsync.%stat` in the xattrs but when I checked \
the data with `getfattr -d`, it doesn't have any of the ACL data.

and `--fake-super` appears to be needed, otherwise rsync tries to write nfs4 ACL's, \
which aren't compatible with linux:

rsync: [receiver] rsync_xal_set: lsetxattr("testacldata","system.nfs4_acl") failed: \
Operation not supported (95)

With both flags, I am getting an additional `user.rsync.system.nfs4_acl` saved in the \
xattrs as a base64 encoded string I guess (begins with 0s).  I tried giving the data \
after "0s" to `base64 -d` and it spits out somewhat readable data and I can at least \
see the second gid in there, from the original ACL.

So is this the best I can do?

Then if I ever need to restore this data:

Mount the backup data over NFS on the restore system.  I can see the \
`user.rsync.%stat` and `user.rsync.system.nfs4_acl` in the backup data.  All the \
backup data is now saved with root.root as the owner.group so it's essential to \
somehow map the rsync xattrs back to the restored data... how to do that?  or any \
other ideas to do this right?

Thanks

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