What is chmod 755 in Linux?

chmod 755 assigns read, write, and execute permissions (7) to the owner, and read and execute permissions (5) to group members and all other users. It is represented symbolically as -rwxr-xr-x and is the standard permission for executable scripts and web directories.

What is chmod 644 in Linux?

chmod 644 assigns read and write permissions (6) to the file owner, and read-only permissions (4) to the group and others. Symbolically represented as -rw-r--r--, it is the most secure and common permission for web pages, static assets, and configuration files.

Linux Chmod Permissions Calculator & Generator

User (Owner)

Read (4) Write (2) Execute (1)

Group

Read (4) Write (2) Execute (1)

Others (Public)

Read (4) Write (2) Execute (1)

Octal Notation

Symbolic Notation

-rwxr-xr-x

Linux Terminal Command

chmod 755 filename.sh

Owner can Read, Write, Execute. Group can Read, Execute. Others / Public can Read, Execute.

Linux File Permissions Architecture & Octal Math

Every file and folder in Unix, Linux, and BSD operating systems contains an access control matrix assigning permissions across three user classes:

User (u): The account owner of the file.
Group (g): Members of the file's assigned user group.
Others (o): All other global users on the system.

Numerical Octal Calculation Table

Octal Value	Binary	Symbolic	Permission Meaning
`0`	`000`	`---`	No permissions granted
`1`	`001`	`--x`	Execute only
`2`	`010`	`-w-`	Write only
`3`	`011`	`-wx`	Write and Execute (2 + 1)
`4`	`100`	`r--`	Read only
`5`	`101`	`r-x`	Read and Execute (4 + 1)
`6`	`110`	`rw-`	Read and Write (4 + 2)
`7`	`111`	`rwx`	Read, Write, and Execute (4 + 2 + 1)