Chmod Calculator (Linux Permissions)

Build Linux file permissions without memorizing the numbers. Enter an octal value like 755 to see what it means — or work from the permission math directly. Owner, group and others, each with read/write/execute.

How to use this calculator

Enter an octal permission like 755, 644 or 600.
Read the breakdown for owner, group and others.
Copy the ready chmod 755 filename command.

Formula used

Each digit = read(4) + write(2) + execute(1), for owner, group, others

Each of the three digits sums the permissions granted: read is 4, write is 2, execute is 1. So 7 = 4+2+1 (all), 6 = 4+2 (read+write), 5 = 4+1 (read+execute), 4 = read only. Three digits cover owner, group and others in that order.

Example calculation

Worked example

755 = rwxr-xr-x: owner has 7 (read+write+execute), group and others have 5 (read+execute). Standard for scripts and directories.

644 = rw-r--r--: owner read+write, everyone else read-only — the normal setting for regular files.

Reading Linux permissions

Every Linux file carries permissions for three audiences — owner, group, others — each able to read, write and/or execute. The octal shorthand encodes each audience's permissions as one digit (0–7) by summing read=4, write=2, execute=1, which is why 755 and 644 appear everywhere in tutorials and deploy scripts.

The security discipline lives in restraint: 777 (everyone can do everything) is a frequent quick-fix that opens real vulnerabilities. Directories need execute (5 or 7) to be enterable, private keys want 600, and web files typically sit at 644 with 755 directories — least privilege that still works.

Why use this calculator?

Decode permission numbers without reciting the 4-2-1 table.
Get the exact chmod command to copy into your terminal.
Understand what 755, 644 and 777 actually grant before you run them.

Frequently asked questions

What does chmod 755 mean?

Owner gets read+write+execute (7), while group and others get read+execute (5 each) — written rwxr-xr-x. It's the standard for executable scripts and directories: the owner can modify, everyone can read and run.

What's the difference between 644 and 755?

644 (rw-r--r--) has no execute bit — right for regular files like text, images and documents. 755 adds execute — needed for scripts and for directories (which require execute to be entered). Using 644 on a directory makes it unusable.

Is chmod 777 safe?

Rarely — it lets any user read, modify and execute the file, a common source of security holes. It's often used as a lazy fix for permission errors; the correct approach is granting the minimum needed, like 755 for scripts or 664 for group-writable files.