The answer is to set the setgid bit and configure ACL default permissions on /data. This works because the setgid bit forces any new file or directory created within /data to inherit the 'engineers' group ownership, while ACL default entries (setfacl -d -m g:engineers:rw-) ensure that group read/write permissions are applied regardless of the user's umask. On the CompTIA Linux+ XK0-005 exam, this question tests your understanding of how setgid and ACLs combine to enforce group ownership inheritance and permission policies in shared directories—a common real-world scenario. A frequent trap is thinking that setting the sticky bit or using ACLs alone is sufficient; remember, the sticky bit only prevents deletion, and ACLs without setgid won't change the file's group. For a quick memory tip: think "setgid for group, ACL for permissions"—the setgid bit locks the group, and default ACLs lock the permissions.
XK0-005 Security Practice Question
This XK0-005 practice question tests your understanding of security. 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.
A company is implementing a security policy that requires all files created in a shared directory /data to be owned by the group 'engineers' and have group read/write permissions, regardless of the user's umask. Which approach should be used?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Set the setgid bit and configure ACL default permissions on /data
Option D is correct because setting the setgid bit ensures new files inherit the group, and configuring ACL default entries sets the default permissions for new files. A is for deletion prevention, B alone doesn't set files' group, C alone doesn't set group inheritance.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Set the setgid bit only on /data
Why it's wrong here
Setgid makes new files inherit the group, but does not set default permissions.
✗
Set the sticky bit on /data
Why it's wrong here
The sticky bit prevents users from deleting files belonging to others, but does not affect ownership or permissions.
✗
Configure ACL default permissions only on /data
Why it's wrong here
ACL defaults set permissions but do not force group ownership; files still inherit the creator's primary group.
✓
Set the setgid bit and configure ACL default permissions on /data
Why this is correct
Setgid forces group inheritance, and ACL defaults set the desired permissions on new files.
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
A security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this XK0-005 question in full detail.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related XK0-005 subnetting questions on CIDR, address ranges, and subnet selection.
Security — This question tests Security — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Set the setgid bit and configure ACL default permissions on /data — Option D is correct because setting the setgid bit ensures new files inherit the group, and configuring ACL default entries sets the default permissions for new files. A is for deletion prevention, B alone doesn't set files' group, C alone doesn't set group inheritance.
What should I do if I get this XK0-005 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related XK0-005 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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