rsync - May 2015 - rsync - Management of UIDs and GIDs when reserved on a Remote system

Kevin Korb <kmk <at> sanitarium.net> writes:
> 
> 3) --numeric-ids copies both as the number.  This is what you normally
> want for backups.  This way you have the exact UID and GID stored on
> the backups regardless of what those numbers mean to the backup
> system.  Just remember to use --numeric-ids when you restore.  This is
> especially important if you have to restore from a live environment
> that has completely different UIDs and GIDs than your normal system.
> That environment would have no idea how to translate names from option
> #2 during a restore.
Hi Kevin,

Regarding the option --numeric-ids, how would rsync manage the situation
where the UID and GID(s), of a file being copied to a Remote system, have
been reserved on the Remote system. Does rsync search for and allocate the
next available IDs?

Thanks, Michael.

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No, rsync would store the files with the numeric UID and GID as is on
the source without regard to the existence or non-existence of a
matching account.  This could mean that ls would show numbers in those
columns, or incorrect names in those columns, or (perhaps by
coincidence) show the correct names in those columns.  The important
thing is that if you backup and restore with --numeric-ids you will
get back what you started with regardless of what the backup system
thinks about the data.

On 05/18/2015 09:16 PM, Michael wrote:
> Kevin Korb <kmk <at> sanitarium.net> writes:
>> 
>> 3) --numeric-ids copies both as the number.  This is what you
>> normally want for backups.  This way you have the exact UID and
>> GID stored on the backups regardless of what those numbers mean
>> to the backup system.  Just remember to use --numeric-ids when
>> you restore.  This is especially important if you have to restore
>> from a live environment that has completely different UIDs and
>> GIDs than your normal system. That environment would have no idea
>> how to translate names from option #2 during a restore.
> 
> Hi Kevin,
> 
> Regarding the option --numeric-ids, how would rsync manage the
> situation where the UID and GID(s), of a file being copied to a
> Remote system, have been reserved on the Remote system. Does rsync
> search for and allocate the next available IDs?
> 
> Thanks, Michael.
> 
> 
> 
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	Kevin Korb			Phone:    (407) 252-6853
	Systems Administrator		Internet:
	FutureQuest, Inc.		Kevin at FutureQuest.net  (work)
	Orlando, Florida		kmk at sanitarium.net (personal)
	Web page:			http://www.sanitarium.net/
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Kevin Korb <kmk at sanitarium.net> wrote:
> No, rsync would store the files with the numeric UID and GID as is on
> the source without regard to the existence or non-existence of a
> matching account.  This could mean that ls would show numbers in those
> columns, or incorrect names in those columns, or (perhaps by
> coincidence) show the correct names in those columns.  The important
> thing is that if you backup and restore with --numeric-ids you will
> get back what you started with regardless of what the backup system
> thinks about the data.
Yes, that's what I do for my backups. Since the backup system doesn't
have the same software (and hence S/W specific users) as the various systems I
back up, it means a lot of files with numeric owner/group - and of course, some
with seemingly strange ownership where the backup system has a different
user/group for the same ID !
If you have to restore, then the system you restore to needs to have the same
passwd and group files - which is not a problem when you are restoring files to
the same machine, or restoring the entire machine (in which case the passwd and
group files come back with the rest of the files during the restore.

The problem is if you need to restore to a different machine - in that case you
will have problems. There isn't an easy way round that.

So you either use numeric IDs in which case the backup is the same as your
source; or you don't, in which case you need to do some careful user-id and
group-id management to avoid problems (ie ensure that the destination has a user
and group name to match ever name used on every source) and rsync will match
names.

Thanks for the clarification Kevin!!