Question 1

What does chmod mean?

Accepted Answer

chmod stands for change mode. It is the Unix command used to change the read, write, and execute permissions of files and directories for three classes of users: the owner, the group, and all others.

Question 2

How is the numeric permission calculated?

Accepted Answer

Each permission class (owner, group, others) is represented as a sum of three values: read = 4, write = 2, execute = 1. A value of 7 means all permissions (4+2+1). A value of 5 means read and execute (4+1). The three digits together form the octal mode.

Question 3

What does 755 mean?

Accepted Answer

755 means the owner has full read, write, and execute permissions (7), while group and others have read and execute permissions only (5). This is the standard permission for web server directories and executable scripts.

Question 4

What does 644 mean?

Accepted Answer

644 means the owner can read and write the file (6), while group and others can only read it (4). This is the standard permission for regular files like HTML pages and configuration files.

Question 5

What is the symbolic notation?

Accepted Answer

The symbolic notation uses r for read, w for write, and x for execute. A hyphen means the permission is not set. The nine characters represent the three permission classes in order: owner, group, others. For example, rwxr-xr-x is equivalent to 755.

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