This LPIC-1 practice question tests your understanding of gnu and unix commands. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
-rwxr-xr-x 1 root root 12345 Jan 1 12:00 /usr/bin/myapp -rwsr-xr-x 1 root root 23456 Jan 1 12:00 /usr/bin/su -rw-rw-rw- 1 user1 user1 0 Jan 1 12:00 /tmp/shared
Refer to the exhibit. Which file has a special permission that allows a user to execute the file with the privileges of the file owner?
-rwxr-xr-x 1 root root 12345 Jan 1 12:00 /usr/bin/myapp -rwsr-xr-x 1 root root 23456 Jan 1 12:00 /usr/bin/su -rw-rw-rw- 1 user1 user1 0 Jan 1 12:00 /tmp/shared
/usr/bin/myapp
Why wrong: No setuid bit; permissions are rwxr-xr-x.
/tmp/shared
Why wrong: No setuid bit; permissions are rw-rw-rw-.
/usr/bin/su
Has setuid bit (rws).
None of the above
Why wrong: /usr/bin/su has setuid.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
/usr/bin/su
The /usr/bin/su command has the SUID (Set User ID) special permission set (typically mode 4755). This allows any user who executes the file to run it with the effective user ID of the file owner (root), enabling privilege escalation to perform administrative tasks. The SUID bit is represented by an 's' in the owner's execute position when viewed with ls -l.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
/usr/bin/myapp
Why it's wrong here
No setuid bit; permissions are rwxr-xr-x.
/tmp/shared
Why it's wrong here
No setuid bit; permissions are rw-rw-rw-.
/usr/bin/su
Why this is correct
Has setuid bit (rws).
Related concept
Read the scenario before looking for a memorised answer.
None of the above
Why it's wrong here
/usr/bin/su has setuid.
Common exam traps
The trap here is that candidates often confuse the SUID permission with the SGID or sticky bit, or assume that any executable file in /usr/bin has special permissions, when in fact only specific system binaries like su, sudo, and passwd are configured with SUID for security reasons.
Detailed technical explanation
The SUID bit works by setting the process's effective UID to the file owner's UID during execution, as defined in the POSIX standard. This is implemented in the kernel's execve() syscall, which checks the file's mode bits and, if SUID is set, changes the effective UID before the program starts. A real-world scenario is the /usr/bin/passwd command, which also has SUID set to allow non-root users to modify the /etc/shadow file, demonstrating how SUID enables controlled privilege escalation for specific tasks.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A junior network technician can log in to a core router but cannot reach the enable prompt or configuration mode. The AAA server is authenticating the login — but the authorisation policy only grants privilege level 1, not 15. Authentication (who you are) is working; authorisation (what you can do) is not.
What to study next
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FAQ
GNU and Unix Commands — This question tests GNU and Unix Commands — Read the scenario before looking for a memorised answer..
The correct answer is: /usr/bin/su — The /usr/bin/su command has the SUID (Set User ID) special permission set (typically mode 4755). This allows any user who executes the file to run it with the effective user ID of the file owner (root), enabling privilege escalation to perform administrative tasks. The SUID bit is represented by an 's' in the owner's execute position when viewed with ls -l.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 25, 2026
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