What is the normal reason for changing user ID?

Solution 1:

Some examples of reasons where someone would need to edit the User ID:

• User IDs (UID) can have special meanings on a system. And not every Linux system uses the same groups of UIDs.

  • Some Linux distributions begin UIDs for non-privileged users at 100. Others, such as Red Hat, begin them at 500, and still others, such Debian, start them at 1000. Because of the differences among distributions, manual intervention can be necessary if multiple distributions are used in a network in an organization.

  So a transition from Redhat to Ubuntu where there are UIDs 500 through 999 on the Redhat system need to be changed to 1000+ if they are to act the same as they did on Redhat. Could be done manually from this GUI.

• A UID is unique when created normally but it does not have to be. You can change the UID here to match another users UID. Use-case: https://askubuntu.com/a/427257/15811

• It is also possible to recycle UIDs (where you edit the UID to match a sequence).

• The UID can be used to group users. Just like Ubuntu uses UIDs 1000+ as a group someone could create there own rules and create a group 2000-2999, 3000-3999 and put special meaning to those groups. Yes user a group ID would be smarter/quicker.

• Another reason for changing user or group ID is to match them up with another server.