Unix File Permission Calculator

What Is the Unix File Permission Calculator?

Unix/Linux file permissions can be written two ways: symbolic (rwxr-xr--) or numeric (754), the format chmod commonly uses. This tool converts between them in either direction, since translating one to the other by hand is a common source of small mistakes.

How to Use This Tool

Choose a conversion direction and enter permissions in the matching format. The converted value appears instantly.

How Unix Permissions Work

Worked Example

Practical Uses

• Quickly translating a chmod command's numeric argument into its symbolic meaning
• Double-checking a permission setting before running chmod on a production server
• Learning how Unix's rwx permission model maps to the common numeric shorthand

For a general number base conversion (not specifically permissions), see the Number Base Converter.

Input Rules the Tool Enforces

In symbolic-to-numeric mode, enter either nine characters such as rw-r--r--, or ten characters where the first is the file-type marker as in ls output, for example -rw-r--r--. The leading marker is dropped before converting. In numeric-to-symbolic mode, enter exactly three digits, each from 0 to 7. Four-digit values such as 0755 or 4755 are rejected, as are digits 8 and 9, and the tool shows an error message rather than guessing.

More Worked Examples

• rw------- converts to 600: owner has read and write (4+2=6), group and others have nothing. This is a common setting for private key files.
• rwxr-x--- converts to 750: the owner has full access, the group can read and execute, and others are locked out.
• Going the other way, 640 becomes rw-r-----: the owner reads and writes, the group only reads, and others get nothing.
• 777 becomes rwxrwxrwx, which lets every user read, modify, and execute the file.

A Note on Directories

The digits mean slightly different things for directories than for files. Read lets you list the names inside, write lets you create or delete entries, and execute lets you enter the directory or reach items inside it by path. A directory with 644 is usually a mistake because the missing execute bit stops people from accessing its contents even though they can see its name. The calculator itself only converts notation; it does not know whether the target is a file or a directory, so apply this reasoning yourself.

Common Mistakes

• Reversing the order. The three groups are always owner, group, others, in that order.
• Using 777 as a quick fix for a "permission denied" error. It is broad access for everyone on the system and can be a real security risk on shared or public-facing servers. Work out which user or group actually needs access instead.
• Typing uppercase letters. The parser looks for lowercase r, w, and x in their expected positions, so rWx will not count the W as write.
• Forgetting the umask. New files are not created with the mode you expect, because the system subtracts its umask, so check the mode with a directory listing after creation.

Special Characters and Limits

If a symbolic string contains s or t in the execute position, the calculator treats that position as execute set and outputs only the ordinary three digits. It does not produce the fourth leading digit for setuid, setgid, or sticky bits, so a value like rwsr-xr-x will come out as 755 without any indication of the special bit. Access control lists and file attributes are also outside its scope. For any change on a production server, confirm the meaning with your system administrator or documentation, and test on a copy first.

Frequently Asked Questions