What does chmod 644 mean?

chmod 644 gives the owner read and write permissions (6), and gives the group and others read-only permission (4). This is the standard permission for regular files like HTML, CSS, and config files.

chmod 777 gives everyone (owner, group, and others) full read, write, and execute permissions. This is generally insecure on a server and should be avoided.

What is chmod?

Q: What does chmod 755 mean?

chmod 755 gives the owner read, write, and execute permissions (7), and gives the group and others read and execute permissions (5). This is the standard permission for public directories and executable files on web servers.

chmod (change mode) is a Unix command that sets file and directory permissions — who can read, write, or execute a file. The numeric codes like 755 or 644 encode these permissions.

Permission Bits

Each file has three sets of permissions: owner, group, and others. Each set has three bits: read (4), write (2), execute (1). Add them together for the numeric code:

7 = read + write + execute (4+2+1)
6 = read + write (4+2)
5 = read + execute (4+1)
4 = read only
0 = no permissions

Common Permission Codes

755 — owner: full; group+others: read & execute. Standard for directories and scripts.
644 — owner: read & write; group+others: read only. Standard for static files.
600 — owner: read & write; group+others: none. For private keys and config files.
777 — everyone: full permissions. Insecure on servers; avoid.
400 — owner: read only. For files that must not be modified (e.g. SSH private keys).

Syntax

chmod 755 myscript.sh — sets the file to 755.

chmod -R 755 /var/www/html — applies 755 recursively to all files and subdirectories.

Calculate chmod permissions and see exactly what each code means: Open chmod Calculator →

Frequently Asked Questions

What does chmod 755 mean?

Owner has read, write, and execute (7). Group and others have read and execute (5). Standard for directories and executables.

Why is chmod 777 bad?

It grants write and execute access to everyone on the system. On a web server, any user process could overwrite or execute the file — a major security risk.