Chmod Calculator
With the chmod calculator you set file permissions by ticking boxes or type a number such as 755, and instantly see the rwxr-xr-x notation, the chmod command and what it means.
Source: The Open Group – POSIX chmod (Klassen u g o a, Operatoren, Rechte r w x X s t). Updated: .
How it is calculated
chmod 755 means rwxr-xr-x: the owner may read, write and execute, group and others may read and execute. Each of the three digits is the sum of read (4), write (2) and execute (1).
How it works
The first digit applies to the owner (u, user), the second to the group (g), the third to everyone else (o, others). 7 = 4 + 2 + 1 (all), 6 = 4 + 2 (read and write), 5 = 4 + 1 (read and execute), 4 = read only. A fourth digit in front stands for the special bits: 4 = setuid, 2 = setgid, 1 = sticky bit. Besides numbers, the calculator understands the nine characters from ls -l and expressions such as u=rwx,g=rx,o=rx or a+x.
Good to know
- For directories, “execute” means you may enter the directory and reach files in it. Without x a directory is practically locked.
- 777 gives everyone full access and is almost never the right fix. Correcting owner or group with chown is better.
- Relative changes such as
g+walter only single permissions; give the current permissions under “Starting permissions” for them. - With
-Rthe change applies recursively to a whole directory and its contents.
Frequently asked questions
What does chmod 755 mean?
Owner: read, write, execute (7). Group and others: read and execute (5). In ls -l notation that is rwxr-xr-x, typical for directories and scripts.
What does chmod 644 mean?
The owner may read and write (6), group and others may only read (4), so rw-r--r--. This is the usual setting for ordinary files such as web pages.
How do you calculate the chmod number?
Per user class add read = 4, write = 2, execute = 1. Example: read and write gives 6. The three digits stand for owner, group and others.
What is the difference between chmod 755 and 777?
With 777 group and others may also write and change files, which is a security risk. 755 lets them only read and execute.
Sources and legal basis
- The Open Group – POSIX chmod (Klassen u g o a, Operatoren, Rechte r w x X s t)
- GNU Coreutils – chmod invocation (symbolic and numeric modes, setuid, setgid, sticky bit)
- Wikipedia – chmod
As of: · Editorial policy
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