Question 1

What does chmod 755 mean?

Accepted Answer

755 means the owner can read, write and execute (7 = rwx), while group and others can read and execute but not write (5 = r-x). It is a common setting for directories and executable scripts.

Question 2

What is the difference between octal and symbolic notation?

Accepted Answer

Octal notation uses digits like 644, where each digit is the sum of read (4), write (2) and execute (1) for owner, group and others. Symbolic notation spells out the same permissions as letters, such as rw-r--r--.

Question 3

What are setuid, setgid and the sticky bit?

Accepted Answer

They are special permission bits stored in a leading fourth octal digit. setuid (4) runs an executable as its owner, setgid (2) runs it as its group or makes new files in a directory inherit the group, and the sticky bit (1) on a directory lets only the owner of a file delete it.

Question 4

How do I read rwxr-xr-x?

Accepted Answer

Read it in three groups of three: rwx for the owner, r-x for the group, and r-x for others. A letter means the permission is granted and a dash means it is denied.

Question 5

Is my input sent to a server?

Accepted Answer

No. The chmod calculator runs entirely in your browser using JavaScript. Nothing you type is uploaded or stored.

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