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Chapter 4 Setting Up User Accounts 67
Modifying User IDs
A user ID is a number that uniquely identifies a user. Mac OS X computers use the
user ID to track a user’s folder and file ownership.
When a user creates a folder or file, the user ID is stored as the ID of the user who
created the folder or file. This user ID has read and write permissions to the folder or file
by default.
The user ID should be a unique string of digits from 500 through 2,147,483,647. It is risky
to assign the same user ID to different users, because two users with the same user ID
have identical directory and file permissions.
User IDs between 0 and 100 are reserved for system use and should not be deleted or
modified except to change the password of the root user. Accounts with user IDs
below 100 aren’t listed in the login window.
In general, after user IDs are assigned and users start creating files and folders, you
shouldn’t change user IDs. However, one possible scenario where you might need to
change a user ID is when merging users that were created on different servers onto a
new server or cluster of servers. The same user ID might still be associated with a
different user on the previous server.
When you create a user account in a shared directory domain, Workgroup Manager
assigns a user ID. The value assigned is an unused user ID (1025 or greater) in the
server’s search policy. (Users created using the Accounts pane of System Preferences
are assigned user IDs starting at 501.)
You can use Workgroup Manager to edit the user ID of an account stored in an Open
Directory domain or in the local directory domain. You can also use Workgroup
Manager to review the user ID in any directory domain accessible from the server
you’re using.
To change a user ID in Workgroup Manager:
1 In Workgroup Manager, click Accounts.
2 Select the user account you want to work with.
To select an account, click the globe icon above the accounts list, choose the directory
domain where the user’s account resides, and then select the user.
3 To authenticate, click the lock and enter the name and password of a directory domain
administrator.
4 In the Basic pane, specify a value in the User ID field.