$ sudo chmod 700 ~/.ssh/id_rsa

We trust you have received the usual lecture from the local System
Administrator. It usually boils down to these three things:

    #1) Respect the privacy of others.
    #2) Think before you type.
    #3) With great power comes great responsibility.

[sudo] password for ponsuke:
ponsuke is not in the sudoers file.  This incident will be reported.

$ cat /etc/group | grep wheel
wheel:x:10:centos

#Add user to wheel group
$ sudo usermod -aG wheel ponsuke

#added
$ cat /etc/group | grep wheel
wheel:x:10:centos,ponsuke

#Switch users
$ sudo su - ponsuke
Last login: Mon May  4 02:57:57 UTC 2020 on pts/0

#Sudo again
$ sudo chmod 700 ~/.ssh/id_rsa
[sudo] password for ponsuke:

#did it!
$ ls -la ~/.ssh/ | grep id_rsa
-rwx------. 1 centos     centos     1675 May  4 02:38 id_rsa

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