rsync - Apr 2025 - rsync --chmod affects the source permissions as well as destination permissions

Hi all,

Another thing I've found is that my backups have lost their permissions.

I misunderstood the --chmod option, thinking that it specified the permissions
at the destination. What actually happens is that it overrides the source
permissions, and has a side effect of the destination permissions being the same
as the source. It looks like it works, when metadata is lost.

I now need to fix this.

What option will set the permissions on the destination side, while not
affecting the permissions being fed into --fake-super on the source side?

The end goal is a simple backup of a source filesystem preserving all users, all
groups, all permissions, and all attributes, while the destination is a
filesystem of a normal non-root user account.

Regards,
Graham
--

On 08 Apr 2025, at 12:54, Graham Leggett via rsync <rsync at
lists.samba.org> wrote:
> Another thing I've found is that my backups have lost their
permissions.
> 
> I misunderstood the --chmod option, thinking that it specified the
permissions at the destination. What actually happens is that it overrides the
source permissions, and has a side effect of the destination permissions being
the same as the source. It looks like it works, when metadata is lost.
> 
> I now need to fix this.
> 
> What option will set the permissions on the destination side, while not
affecting the permissions being fed into --fake-super on the source side?
> 
> The end goal is a simple backup of a source filesystem preserving all
users, all groups, all permissions, and all attributes, while the destination is
a filesystem of a normal non-root user account.
I have proposed a --chmod-dest option to achieve this.

The --chmod-dest option allows the destination permissions to be specified
independently of the permissions backed up by --fake-super attributes.

This means the source permissions are maintained, while on the backup machine
permissions can be granted to allow specific users/groups to have read access to
the backups.

https://github.com/RsyncProject/rsync/pull/751

Regards,
Graham
--

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On Tue, Apr 08, 2025 at 12:54:24PM +0100, Graham Leggett via rsync
wrote:
> I misunderstood the --chmod option, thinking that it specified the
> permissions at the destination. What actually happens is that it
> overrides the source permissions, and has a side effect of the
> destination permissions being the same as the source. It looks like
> it works, when metadata is lost.
[...]
> 
> What option will set the permissions on the destination side, while
> not affecting the permissions being fed into --fake-super on the
> source side?
If I understand correctly, I believe using --chmod without using
--perms (or with --no-p) will do what you want.  Typical command lines
often use -a which equates to -rlptgoD (i.e. it includes -p/--perms).
So you either need to not use -a and instead use the remaining
combination of options explicitly, or use --no-p.

See the man page, specifically the sections for --perms and -a.

-- 
Derek Martin
Principal System Software Engineer
Akamai Technologies
demartin at akamai.com