We have had to do this. At first it seemed impossible because the oldest users on the master system had UIDs which clashed with system users the backup system.

Do not embark on this sort of exercise without an Ignite backup and a full backup of your system and a decent amount of booked downtime.

To cut a long story short, and working on a non-Trusted system:

Used "vipw" on the master system to move any system accounts to be definitely before any user accounts in /etc/passwd. This is only needed if system software was installed after any user accounts. i.e. what normally happens.

Created a cross-reference table of before-and-after UIDs and changed every non-system UID to a new range well clear of the system accounts (I chose 1001+). The choice of 1001 for the base was because I did not have any UID higher than 1001 on the master system or the backup system. This is not trivial because after changing the passwd file with "vipw" it involves issuing the correct "find" and "chown" command for every file owned by every non-system user.

Once you have got all your user accounts in a section of /etc/passwd which definitely does not contain any system accounts you can copy files at will to your backup system and periodically replace the "user" section of the /etc/passwd file with the user section from your source system using "vipw" (which can be scripted).

I must stress again that this technique does not work at all on Trusted systems.


There was a hint earlier. Never delete a user account. Lock it, remove data files, whatever, but do not delete it from /etc/passwd. It will mess up you backup system big time the moment you allow two different users to have the same UID.

Imho. In a D.R. backup scenario, never let two different users have the same UID.