--Environment - CentOS Linux release 7.8.2003 (Core)
Even if I entered the password I set, it didn't work ...
$ 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.
In the / etc / sudoers file, groups that can use the sudo command are prepared in advance. For Debian, the sudo group. Wheel group for CentOS. How to add a sudo user --Introduction to Linux --Webkaru
I wasn't in the wheel group
$ cat /etc/group | grep wheel wheel:x:10:centos
wheelgroup with ʻusermod`
#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