TOOL
chmod Calculator
Toggle read, write and execute for owner, group and others to get the octal mode, symbolic notation and chmod command.
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How to use it
Toggle read, write and execute for the owner, group and others, and the octal mode, symbolic notation (rwxr-xr-x) and the chmod command update together. You can also type an octal value like 755 to set the checkboxes.
The permission model
Unix files have three permission classes, owner, group and others, each with read (4), write (2) and execute (1). Adding those within a class gives one octal digit, so three digits describe the whole file. Common values:
- 755: directories and scripts (owner full, others read and execute).
- 644: regular files (owner read/write, others read).
- 600: private files such as SSH keys (owner only); SSH refuses keys that are more permissive.
Windows uses a different, richer model of access control lists; see Windows file permissions. A web 403 is often a Unix permission problem on the server's files.
Frequently asked questions
What does chmod 755 mean?
Owner can read, write and execute (7 = 4+2+1); group and others can read and execute (5 = 4+1). It is the usual mode for directories and executable scripts. 644 (owner read/write, others read) is usual for regular files.
How do the numbers work?
Each digit is the sum of read (4), write (2) and execute (1) for owner, group and others in turn. So 6 = read+write, 5 = read+execute, 7 = all three. Toggle the checkboxes to see it build up.