Chmod Calculator

Use this free chmod calculator to work out Unix and Linux file permissions in seconds. Tick the read, write, and execute boxes for the owner, group, and public, and the tool instantly shows the octal value (like 644 or 755), the symbolic notation (like rw-r–r–), and the exact chmod command to run.

What is chmod?

chmod (short for “change mode”) is the Unix command that sets the permissions of a file or directory. Every file has three permission groups — the owner, the group, and everyone else (public) — and each group can be granted read (r), write (w), and execute (x) access.

How octal permissions work

Each permission has a number: read is 4, write is 2, and execute is 1. You add them up for each group to get a single digit. For example, read + write = 6, and read + write + execute = 7. Three digits together form the full permission, such as 644 or 755.

Common chmod values

• 644 (rw-r–r–) — the usual setting for regular files. The owner can edit; everyone else can only read.
• 755 (rwxr-xr-x) — the usual setting for directories and scripts. The owner has full control; others can read and execute.
• 600 (rw——-) — private files such as SSH keys. Only the owner can read or write.
• 777 (rwxrwxrwx) — full access for everyone. Convenient but rarely safe on a server.

Frequently asked questions

What does chmod 755 mean?

755 gives the owner read, write, and execute (7), and the group and public read and execute (5 and 5). It is the standard permission for folders and executable scripts.

Is chmod 777 safe to use?

Almost never on a public server. 777 lets anyone read, change, and run the file, which is a common cause of security problems. Prefer 644 for files and 755 for directories.

What is the difference between octal and symbolic permissions?

They describe the same permissions two ways. Octal is the numeric form (644), and symbolic is the letter form (rw-r–r–) you see in the output of ls -l.