How to read a chmod number (755, 644, 777)

The bits

So 7 = rwx (4+2+1), 6 = rw- (4+2), 5 = r-x (4+1), 4 = r--.

• r = 4 — read a file, or list a directory
• w = 2 — write a file, or create/delete names in a directory
• x = 1 — run a file, or enter a directory

Common modes

• 755 — owner full; group and others read and execute. Typical for directories and executable scripts you share read-only.
• 644 — owner read/write; everyone else read. Typical for ordinary files.
• 600 — only owner read/write. Private keys and .env files.
• 777 — everyone everything. Almost never what you want on a shared host.

Symbolic form

rwxr-xr-x is the same as 755. Leading bits for setuid/setgid/sticky make a four-digit mode (4755), which the chmod calculator also covers.