What does chmod 755 mean?

Owner has read+write+execute (7), group has read+execute (5), others have read+execute (5). This is the standard permission for web directories and executable scripts.

What is the difference between 644 and 755?

644 gives the owner read+write and everyone else read-only. 755 additionally gives execute permission to all users. Use 644 for files and 755 for directories and scripts.

Why is chmod 777 dangerous?

777 gives every user on the system full read, write, and execute access. On a web server, this means any process (including compromised scripts) can modify or delete the file.

How to Calculate Unix File Permissions (chmod)

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