Create New OS User, Enable SSH and Generate Key Pair in OCI Compute Instance

=> Here I am creating a user called xxtomcat under new group xxtomcat

Note: Below commands to be run as root user. Login as opc and switch to root

[opc@oci-compute-host-001 ~]# sudo su - root

[root@oci-compute-host-001 ~]# groupadd xxtomcat

[root@oci-compute-host-001 ~]# useradd -g xxtomcat -d /home/xxtomcat xxtomcat

[root@oci-compute-host-001 ~]# id xxtomcat

uid=54324(xxtomcat) gid=54332(xxtomcat) groups=54332(xxtomcat)

[root@oci-compute-host-001 ~]#

=> Create .ssh directory under $HOME directory and give 0700 permissions. 

Note 1 : Below commands should be run as xxtomcat user

Note 2 : These permissions are required for Public and Private Key authentication to work.

[xxtomcat@oci-compute-host-001 ~]$ mkdir .ssh

[xxtomcat@oci-compute-host-001 ~]$ chmod 0700 .ssh

[xxtomcat@oci-compute-host-001 ~]$ cd .ssh

=> Create authorized_keys under .ssh directory and give 0600 permissions

Note 1 : Below commands should be run as xxtomcat user

Note 2 : These permissions are required for Public and Private Key authentication to work.

[xxtomcat@oci-compute-host-001 .ssh]$ touch authorized_keys

[xxtomcat@oci-compute-host-001 .ssh]$ chmod 0600 authorized_keys

[xxtomcat@oci-compute-host-001 .ssh]$ ls -ltr

total 4

-rw------- 1 xxtomcat xxtomcat 398 Apr 12 12:28 authorized_keys

[xxtomcat@oci-compute-host-001 .ssh]$

=> Disable Password Expiry for xxtomcat user

[root@oci-compute-host-001 ~]# chage -m 0 -M 99999 -I -1 -E -1 xxtomcat

[root@oci-compute-host-001 ~]# chage -l xxtomcat

Last password change                                    : Apr 28, 2022

Password expires                                        : never

Password inactive                                       : never

Account expires                                         : never

Minimum number of days between password change          : 0

Maximum number of days between password change          : 99999

Number of days of warning before password expires       : 7

[root@oci-compute-host-001 ~]#

=> Enable SSH for the user

Note: Below commands to be run as root user. Login as opc and switch to root

Add the entry AllowUsers xxtomcat at the end of /etc/ssh/sshd_config file

[root@oci-compute-host-001 ~]# grep -i AllowUsers /etc/ssh/sshd_config

AllowUsers xxtomcat

[root@oci-compute-host-001 ~]#

=> Restart sshd service

[root@oci-compute-host-001 ~]# /sbin/service sshd restart

=> To login the server from Putty directly as xxtomcat user, you have to generate Public and Private Key Pair using Putty Key Gen Tool

Make sure below 3 default values are selected in PuttyGen Tool

=> Click on Generate

Generate some randomness by hovering mouse on the blank area

 

=> Copy the public key content and paste it in the authorized_keys file in the server as xxtomcat user $HOME/.ssh/authorized_keys

Note: Do not click on save public key, as this will save in putty supported format

=> Click on Save private key to save the private key in Putty supported format .ppk

=> Login to the server through putty as xxtomcat user by providing private key file 

=> Enter the server IP address

=> Select the Private Key : SSH => Auth => Private Key

=> Login as xxtomcat user