Whenever we take a compute instance from cloud services like AWS, they often provide a .pem file for logging into the instance.

Problem

When we try to login via ssh using these .pem files using the command

ssh -i filename.pem username@ipaddress

We get the following error if the permissions of the .pem file is not correct

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@         WARNING: UNPROTECTED PRIVATE KEY FILE!          @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
Permissions 0644 for 'filename.pem' are too open.
It is required that your private key files are NOT accessible by others.
This private key will be ignored.
Load key "filename.pem": bad permissions
username@ipaddress: Permission denied (publickey).

Solution

Open a terminal where the .pem file is located and do the following

chmod 400 filename.pem

You will now be able to login to the remote server using the .pem file

Explanation

The permission of the file decides which users/usergroups can access or execute it. A secret file like .pem needs more restricted permission to improve security.