Chmod Calculator

How octal permissions work

Each of the three digit groups (owner, group, others) is a sum: read = 4, write = 2, execute = 1. So 6 = read+write, 5 = read+execute, 7 = everything. The classic 755 means the owner can do anything while everyone else can read and run — the standard for directories and scripts; 644 lets the owner edit while others only read — the standard for static files; 600 keeps secrets readable by the owner alone — what you want for SSH keys.

The symbolic form (like u=rwx,go=rx) is what you'd pass to chmod in its letter mode; both forms shown here produce identical results. Changing permissions with chmod 755 file applies the exact bits — recursive -R applies them to every file and subdirectory, which is usually not what you want for mixed trees.