Limiting UID range for new local user accounts

Solution 1:

Check out UID_MIN & UID_MAX in /etc/login.defs to control what the range is for local users.

Solution 2:

Be on the lookout for /etc/adduser.conf This conf file is, at least, present on Ubuntu 14.04 LTS and overrides login.defs

# FIRST_[GU]ID to LAST_[GU]ID inclusive is the range of UIDs of dynamically
# allocated user accounts/groups.
FIRST_UID=1000
LAST_UID=29999