What Does CHMOD 600 Mean?
CHMOD 600 restricts file access exclusively to the file owner, granting read and write capabilities while denying all access to group members and other users.
6
Owner
Read + Write (4+2+0)The owner has complete read and modify access to the file.
0
Group
No Access (0+0+0)Group members cannot view, edit, or execute the file.
0
Others
No Access (0+0+0)All other system users are blocked from reading or altering the file.
Why SSH Requires 600 for Private Keys
OpenSSH enforces strict permission validation on private key files (such as ~/.ssh/id_rsa or ~/.ssh/id_ed25519).
If your private key file is readable by group or public users, OpenSSH will abort the connection with an error message:
# SSH Error when key permissions are too open:
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ WARNING: UNPROTECTED PRIVATE KEY FILE! @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@Permissions 0644 for '/home/user/.ssh/id_rsa' are too open.It is required that your private key files are NOT accessible by others.Running chmod 600 ~/.ssh/id_rsa resolves this protection check by locking the file to your user account only.
Common Use Cases for CHMOD 600
- SSH Private Keys:
~/.ssh/id_rsa,~/.ssh/id_ed25519 - Environment Credentials:
.envfiles containing database passwords, API tokens, and secret keys - Database Configs:
wp-config.phpor application secrets - Personal Notes / Log Files: Files containing confidential logs or user data
How to Apply CHMOD 600
# Lock down SSH private key
chmod 600 ~/.ssh/id_rsa# Lock down application secret filechmod 600 /var/www/html/.env