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LFCS · Question #519
LFCS Question #519: Real Exam Question with Answer & Explanation
The correct answer is C: They are reserved for system accounts.. Linux UIDs (User IDs) that are lower than 100 are conventionally reserved for system accounts.
Submitted by mateo_ar· Apr 18, 2026User and Group Management
Question
Which of the following is the conventional purpose of Linux UIDs that are lower than 100?
Options
- AThey are reserved for super user accounts.
- BThey are reserved for the system admin accounts.
- CThey are reserved for system accounts.
- DThey are unused, aside from 0, because they are targets of exploits.
- EThey are used to match with GIDs in grouping users.
Explanation
Linux UIDs (User IDs) that are lower than 100 are conventionally reserved for system accounts.
Common mistakes.
- A. Only UID 0 is reserved for the superuser (root); other low UIDs are for various system services, not for superusers.
- B. System admin accounts typically refer to human administrators and are usually assigned UIDs above the system account range (e.g., 1000+).
- D. The low UID range is primarily for system account assignment, not specifically left unused due to exploits, although system accounts can be targets of exploits.
- E. UIDs identify users, and while users belong to groups, the low UID range's primary purpose is not for matching with GIDs in grouping users.
Concept tested. Linux UID conventions
Reference. https://refspecs.linuxfoundation.org/FHS_3.0/fhs/ch04s04.html
Topics
#User IDs (UIDs)#System accounts#Linux conventions
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