Linux File Permissions Explained

1 min readPublished 22 Jul 2026

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Linux security starts with file permissions — a simple, powerful model you'll use constantly.

Interactive explainer

Linux File Permissions

rwx, user/group/other, chmod and chown — the Linux security model.

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1. Read, Write, Execute

The three permissions.

Every file has read (r), write (w) and execute (x) permissions. On a directory, x means you can enter it. These three are the whole model.

Check your understanding

1. What does chmod 755 grant?

2. Best practice for administrative tasks is to…

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Linux Permissions The Linux Shell CompTIA Security+ CompTIA A+

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The model

Three permissions — read (r), write (w), execute (x) — for three sets: user (owner), group and other, shown as rwxr-xr-- in ls -l. On a directory, x means you can enter it.

chmod sets permissions: chmod u+x script.sh or numerically chmod 755 script.sh (7=rwx, 5=r-x).
chown changes ownership; sudo runs a single command as root.

Best practice: never work as root full-time — use sudo and least privilege, exactly as in Windows administration and Security+.

Interview Intelligence

How this topic actually shows up in interviews — and how to demonstrate you understand it.

Why employers ask about this

Permissions are the core Linux security control and a guaranteed interview topic.

Technical questions

Explain Linux permissions and chmod.+

rwx for user/group/other; chmod sets them symbolically or numerically (e.g. 755); use least privilege.

Behavioural questions

Describe applying least privilege on a system.+

Show scoping permissions to need and using sudo rather than root.

Real-world scenarios

“A script won't run.”+

Expected answer: Check execute permission (chmod +x) and ownership before assuming a code problem.

Practise in AI Interview™Rehearse these questions, scored.Plan with Career Coach™A personalised path to your goal.Evidence it in Career Passport™Prove this skill to employers.

Employability Intelligence

Where this knowledge takes you — the jobs, skills and certifications it feeds into.

Relevant roles

Linux AdministratorSecurity EngineerSOC Analyst

Skills you're proving

PermissionsLeast privilegesudo

Recommended certifications

CompTIA Security+

Career progression

Linux Fundamentals → Security/DevOps roles.

What employers expect

That you can navigate, administer and troubleshoot Linux from the command line.

Frequently asked questions

What does chmod 755 mean?

rwx for the owner, r-x for group and other — a common default for scripts and directories.

What is sudo?

A way to run a single command with elevated (root) privileges, instead of logging in as root.

Why avoid chmod 777?

It grants everyone full access — a security risk. Grant only what's needed.

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Missiora is an AI Employability Intelligence platform. Our resources are researched and reviewed by the Missiora team to help you measure, improve and prove your career readiness.