Question 1

What does chmod 755 mean?

Accepted Answer

755 means: Owner can read, write, execute (7). Group can read and execute (5). Others can read and execute (5). In symbolic: rwxr-xr-x. Common for directories and scripts.

Question 2

What is the difference between 644 and 755?

Accepted Answer

644 (rw-r--r--) is for files — owner can read/write, others can only read. 755 (rwxr-xr-x) is for directories and executables — adds execute permission.

Question 3

What does chmod 777 do?

Accepted Answer

777 gives full read, write, and execute permissions to everyone (owner, group, others). This is generally insecure and should be avoided on production servers.

Question 4

How do I fix "Permission denied" errors?

Accepted Answer

Use chmod to add the needed permission. For scripts: chmod +x script.sh. For files: chmod 644 file. For directories: chmod 755 dir. Use this calculator to find the right number.

Chmod Calculator

Common Permissions

About Chmod Calculator

	Read	Write	Execute
Owner
Group
Others