Calculate Unix/Linux file permissions in octal and symbolic notation.
Permission Matrix
Read (4)
Write (2)
Execute (1)
owner
group
public
Output
-rw-r--r--
chmod 644 filename
About this calculator
Overview
Chmod (change mode) sets file permissions in Unix/Linux systems. Permissions control read (r), write (w), and execute (x) access for owner, group, and others. Understanding chmod is essential for server security and file management.
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Pro Tips
755 is common for web directories (rwxr-xr-x).
644 is standard for web files (rw-r--r--).
Never use 777 (full access) on production servers.
Use chmod +x to add execute permission.
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Fun Facts
"Read=4, Write=2, Execute=1 (sum for combined permissions)."
"Root user bypasses all permission restrictions."
"Setuid bit (4xxx) allows running as file owner."
"Incorrect permissions are a common security vulnerability."
