Chmod Calculator
A chmod calculator converts between the boxes you tick, read, write and execute for owner, group and others, and the three-digit octal number Linux uses. It shows the octal, the symbolic rwx string and the exact chmod command, and explains what each bit means on files versus directories.
Last reviewed by the Radiatus Cloud team
Chmod Calculator
Calculate Linux file permissions in numeric and symbolic formats.
| Permission | Owner (u) | Group (g) | Public (o) |
|---|---|---|---|
| Read (4) | |||
| Write (2) | |||
| Execute (1) |
Numeric Value
Symbolic Value
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How octal permissions work
Each of the three groups, owner, group and others, gets a digit from 0 to 7, the sum of read (4), write (2) and execute (1). So 6 is read plus write, 7 is all three, 5 is read plus execute. The common 644 means the owner can read and write, everyone else can only read; 755 adds execute for all, which is what a directory or a script needs; 600 keeps a file private to its owner.
| Octal | Symbolic | Typical use |
|---|---|---|
| 644 | rw-r--r-- | A normal file |
| 755 | rwxr-xr-x | A directory or an executable script |
| 600 | rw------- | A private file, such as an SSH key |
| 700 | rwx------ | A private directory |
| 664 | rw-rw-r-- | A group-writable file |
Execute means different things
On a file, execute lets it run as a program. On a directory, execute means you can enter it and access files inside; without it, read on the directory only lets you list names. This is why 644 on a directory is broken and 755 is correct: a directory needs execute to be usable.
Why 777 is almost always wrong
777 grants everyone read, write and execute. On a web server it lets any user or compromised process modify your files, and many PHP and SSH tools refuse to use files or keys that are world-writable or world-readable. If a tutorial tells you to chmod 777 to fix a permission error, the real fix is almost always correct ownership (chown) plus 755 or 644.
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Frequently Asked Questions
What does 755 mean?
Owner has read, write and execute (7); group and others have read and execute (5 each). It is the standard for directories and executable scripts, because execute on a directory is what allows entering it.
Why is execute needed on a directory?
On a directory, the execute bit controls whether you can enter it and access the files inside. Read alone only lets you list names. So directories generally need execute (the x in 755) while plain files do not.
Is chmod 777 ever correct?
Almost never. It makes a file writable by everyone, including any compromised process. Permission errors are usually solved by fixing ownership with chown and using 755 or 644, not by opening a file to the world.
What permissions should an SSH private key have?
600 (rw-------), readable and writable only by the owner. SSH refuses to use a private key that is readable by group or others, so 644 will cause it to reject the key.
What is the difference between symbolic and octal?
They express the same permissions two ways. Octal is the three-digit number (755); symbolic is the rwx string (rwxr-xr-x). chmod accepts both, plus relative symbolic changes like chmod +x to add execute.
Privacy & Security
Calculated locally.
About This Tool
This tool runs entirely in your browser. No data is sent to any server, ensuring complete privacy. Simply use the interface above to get started — no registration or login required.
Disclaimer: This tool is provided "as is" without warranty of any kind. Results are for educational and utility purposes.
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