Each user and group is assigned an identification number (UID or GID). This ID number is stamped on all files, directories, and processes on local and NFS-mounted filesystems. When you create a new user or group, a new UID or GID number is automatically generated, but you can specify another by entering it in the text field.
Change the ID number for an existing user with the
command. You can include -U option to change the users
files to the new UID, as in this example:
usermod -u 712 -U jstone
This command also changes any crontab files. The -U option changes the ownership of files found in directories specified in /etc/default/usermod; it does not locate all files owned by the user.
The groupmod(1M) performs similar functions for groups.
To alter the range of GIDs from which you select for new groups, select Options Group Defaults.