File permissions control who can read, write, or execute files on a server. They matter because a website needs enough access to run, but not so much access that any compromise becomes worse.
Files and Directories Differ
Files usually need to be readable by the web server. Directories also need execute permission so the server can enter them. Upload directories may need write access, but most application code should not be writable by everyone.
Be Wary of 777
Some old guides tell you to set files or directories to 777. That gives very broad write access. If an installer temporarily needs it, tighten permissions again once installation completes.
Ownership Matters
The right permission depends on who owns the file and which user PHP runs as. On many modern hosting platforms, safer permissions work because the site user owns the files.
Common Symptoms
- Upload failures.
- Plugin updates failing.
- 403 errors.
- Cache files not being created.
- Installers complaining about unwritable folders.
Change permissions carefully and avoid broad changes across the whole site unless you understand the impact.
Permissions Work with Ownership
Read, write and execute bits apply to the owner, group and others, but the correct value depends on which user runs PHP and owns the files. A numerically restrictive mode can still be wrong when ownership is wrong. Check both before changing a whole directory tree.
Files and Directories Need Different Treatment
Directories need execute permission to be traversed; ordinary PHP, CSS and image files generally do not. Common baselines are often 755 for directories and 644 for files, but follow the hosting platform's guidance. Sensitive configuration may need tighter access.
Do Not Use 777 as a Fix
World-writable permissions let unrelated processes alter content and hide the real ownership or application problem. Record the original state, change the smallest affected path and test the required operation. If permissions unexpectedly change again, investigate deployment tools, plugins or compromise.
