Question 1

What does chmod mean?

Accepted Answer

chmod stands for "change mode" — the Unix command used to change the access permissions of a file or directory. Permissions control who can read, write to, or execute a file.

Question 2

What do the three digits in chmod mean?

Accepted Answer

Each digit represents a different user class: the first digit is the owner, the second is the group, and the third is everyone else (other/world). Each digit is a sum of read (4), write (2), and execute (1).

Question 3

What does chmod 755 mean?

Accepted Answer

chmod 755 gives the owner full permissions (7 = read + write + execute), and group and other read + execute (5 = read + execute). It is the standard permission for web server files and executable scripts.

Question 4

What is the difference between numeric and symbolic notation?

Accepted Answer

Numeric (octal) notation like 755 is concise and widely used in commands. Symbolic notation like rwxr-xr-x is more readable — it explicitly shows each permission for each user class.

Question 5

Should I use chmod 777?

Accepted Answer

Avoid it. chmod 777 gives every user on the system full read, write, and execute access — a serious security risk on shared or public servers. Use the most restrictive permissions your use case allows.