We sometimes need to connect to computer in other network. It is necessary the key like pem(Private Enhanced Mail) When we connect. I will just write the flow about it.

flow

1. Generate .pem key (I am using AWS).
2. Change mode of .pem file to 400 to read it.
3. Identify file and connect to ssh (AWS linux for me).
4. DONE

Change permission of file

I will change mode of key file and connect to ssh with it.

~ $ ls -alh

drwxr-xr-x 6 roomy staff 192B Apr 3 10:09 .
drwxr-xr-x+ 41 roomy staff 1.3K Apr 3 10:10 ..
-rw-r--r--@ 1 roomy staff 1.7K Apr 3 10:54 test.pem
-r--------@ 1 roomy staff 1.7K Feb 13 18:02 dev.pem

test.pem file has -rw-r–r– permission. It can be separated like -, rw-, r–, r–. The first - means a file. and d is for directory. Then second 3 bits are for owner, third is for group, and the last is for other. So all users can read test.pem file, as r means read, w means write and x means execute.

~ $ chmod 400 test.pem
~ $ ls -alh

drwxr-xr-x 6 roomy staff 192B Apr 3 10:09 .
drwxr-xr-x+ 41 roomy staff 1.3K Apr 3 10:10 ..
-r--------@ 1 roomy staff 1.7K Apr 3 10:54 test.pem
-r--------@ 1 roomy staff 1.7K Feb 13 18:02 dev.pem

Now the only owner can read that private key file.

Connect to ssh

I simply connect to server with ssh command. -i option means identify file using key.

~ \$ ssh -i ~/.ssh/test.pem ec2-user@example.com

       __|  __|_  )
       _|  (     /   Amazon Linux 2 AMI
      ___|\___|___|

https://aws.amazon.com/amazon-linux-2/
\$