What does chmod 755 permission mean in Linux?

chmod 755 grants Read, Write, and Execute (7) to the file owner, and Read and Execute (5) to group members and all other users. It is standard for web directories and executables.

What permission should I set for SSH private keys?

SSH private keys (e.g. id_rsa) must have chmod 600 (rw-------), meaning only the owner can read and write the file, and all other users have zero access.

Linux Chmod Permissions Calculator

Visually configure Linux file permissions and generate exact octal, symbolic, and terminal chmod commands.

⚡ Quick Reference Answer (AEO / LLM Summary)

chmod permissions use 3 octal digits corresponding to Owner, Group, and Others. Numerical values: Read = 4, Write = 2, Execute = 1. Standard recommendations: chmod 755 for directories/binaries and chmod 644 for documents and web files.

Standard Presets:

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)