Developer Utilities
Chmod Calculator
Convert Unix permissions between octal, symbolic, and checkbox forms.
How the chmod calculator works
Unix permission modes group read, write, and execute bits for the owner, group, and others. Adding the bit values produces each octal digit: read is 4, write is 2, and execute is 1. The calculator keeps the octal, rwx, and checkbox representations synchronized.
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Security boundary
- Avoid broad write permissions such as 777 unless the exact threat model and environment require them.
- A mode does not show file ownership, ACLs, capabilities, SELinux or AppArmor rules, mount flags, container mappings, or inherited policy.
- Uppercase S or T means the special bit is set while the corresponding execute bit is not set.
- Review the target path and ownership before running any copied chmod command, especially recursively.
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How to Use Chmod Calculator
- Enter a three- or four-digit octal mode such as 755 or 4755.
- Alternatively, toggle read, write, execute, and special bits.
- Review the synchronized octal and symbolic representations.
- Copy the command only after checking the target path and ownership.
Frequently Asked Questions
What do 755 and 644 mean?
- Each octal digit combines read (4), write (2), and execute (1). Mode 755 is rwxr-xr-x, while 644 is rw-r--r--.
What are setuid, setgid, and sticky bits?
- They are special mode bits represented by a leading octal digit. Their exact security effect depends on the object type, operating system, filesystem, mount options, and execution context.
Does this tool change a file?
- No. It only calculates and copies permission notation; it cannot access or modify your filesystem.
Sources & references
Primary references: POSIX chmod utility specification.
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