Question 1

What is the difference between 755 and 644?

Accepted Answer

755 gives the owner full control and allows everyone else to read and execute. 644 gives the owner read/write and everyone else read-only. Use 755 for directories and executable scripts, 644 for regular files like HTML, CSS, and images.

Question 2

Why should I never use chmod 777?

Accepted Answer

777 means every user on the system can read, write, and execute the file. On a web server, this means any compromised process could modify your files. Use the most restrictive permissions that still allow your application to function (usually 755 for directories and 644 for files).

Question 3

What does the execute permission do for directories?

Accepted Answer

For directories, execute means 'traverse' -- the ability to cd into the directory and access files inside it. A directory with read but not execute lets you list filenames but not open any files. Most directories need the execute bit set.

Question 4

How do I set permissions recursively?

Accepted Answer

Use chmod -R to apply permissions to a directory and everything inside it. For example, chmod -R 755 foldername/. Be careful with recursive chmod because files and directories often need different permissions. A common pattern is: find . -type d -exec chmod 755 {} + for directories and find . -type f -exec chmod 644 {} + for files.

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