chmod 600 Explained — Owner-Only Read-Write

What Does chmod 600 Mean?

Permission 600 is the most restrictive commonly used permission that still allows the owner to work with the file:

Role	Octal	Symbolic	Permissions
Owner	6	rw-	Read + Write
Group	0	---	No access
Others	0	---	No access

Why 600 Matters

This permission is critical for files containing sensitive data. Without it, other users on the system could potentially read confidential information.

SSH Key Requirements

SSH is particularly strict about permissions. If your private key file has permissions broader than 600, SSH will refuse to use it:

# Set correct permissions for SSH private key
chmod 600 ~/.ssh/id_rsa
chmod 600 ~/.ssh/id_ed25519

# SSH error when permissions are too open:
# @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
# @         WARNING: UNPROTECTED PRIVATE KEY FILE!          @
# @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
# Permissions 0644 for '/home/user/.ssh/id_rsa' are too open.

Other Files That Need 600

# Database credentials
chmod 600 /etc/mysql/my.cnf

# Application secrets
chmod 600 .env
chmod 600 wp-config.php

# SSH authorized_keys
chmod 600 ~/.ssh/authorized_keys

# PGP/GPG private keys
chmod 600 ~/.gnupg/private-keys-v1.d/*

600 vs 400

Permission 400 (read-only for owner) provides even more protection by preventing accidental modification. Use 400 for files that should never be edited after creation, like deployed SSL certificates.