you cant able to ins
hostnamectl set-hostname mail.saraswatishrestha.com.np exec bash hostname -f
vi /etc/hosts 172.31.1.43 mail.saraswatishrestha.com.np mail
For RHEL/CentOS/Rocky Linux systems: sudo fips-mode-setup –disable sudo reboot cat /proc/sys/crypto/fips_enabled # 0
For Ubuntu systems: sudo ua disable fips / apparmor
service firewalld stop service iptables stop service ip6tables stop systemctl disable firewalld systemctl disable iptables systemctl disable ip6tables