chmod Calculator

Convert between octal and symbolic Unix file permissions.

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What does this tool solve?

Unix permissions are three triplets — owner, group, other — each combining read (4), write (2), and execute (1). chmod 755 means owner can do everything, everyone else can read and execute. Toggle the boxes or type octal or symbolic notation; all three stay in sync.

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What examples should you start with?

Web server directory

rwxr-xr-x — owner full, others read+execute

Private key

rw------- — owner read+write only

Shared config

rw-r--r-- — owner writes, everyone reads

How does it work?

Each octal digit is the sum of its triplet's bits: read=4, write=2, execute=1. 7 means rwx, 5 means r-x, 0 means ---.

The symbolic form is the same information written out: three triplets of rwx characters, with - where a bit is unset.

What are the edge cases and limits?

777 is almost never right — it lets anyone modify the file or directory.
Directories need the execute bit to be entered; 644 on a directory makes it unusable.
Special bits (setuid, setgid, sticky) are a fourth, leading octal digit (e.g. 1755) and are not covered by this calculator.
Permissions compose with ownership; chmod alone cannot fix a file owned by the wrong user.

Technical reference

POSIX chmod specification

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	Read	Write	Execute
owner
group
other