When you modify the host name, you can directly use the tools provided by the system.  

[root@localhost centos]# hostnamectl
   Static hostname: localhost.localdomain
         Icon name: computer-vm
           Chassis: vm
        Machine ID: 89bf177f78dc49f6b4954e1e9511e267
           Boot ID: 8f46edc8b7b648f58d5d4c1f3c15cbee
    Virtualization: vmware
  Operating System: CentOS Linux 8
       CPE OS Name: cpe:/o:centos:centos:8
            Kernel: Linux 4.18.0-240.10.1.el8_3.x86_64
      Architecture: x86-64
[root@localhost centos]# sudo hostnamectl set-hostname k8s-slave
[root@localhost centos]# hostnamectl
   Static hostname: k8s-slave
         Icon name: computer-vm
           Chassis: vm
        Machine ID: 89bf177f78dc49f6b4954e1e9511e267
           Boot ID: 8f46edc8b7b648f58d5d4c1f3c15cbee
    Virtualization: vmware
  Operating System: CentOS Linux 8
       CPE OS Name: cpe:/o:centos:centos:8
            Kernel: Linux 4.18.0-240.10.1.el8_3.x86_64
      Architecture: x86-64
[root@localhost centos]# cat /etc/hostname 
k8s-slave
[root@localhost centos]# cat /etc/hosts
127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4
::1         localhost localhost.localdomain localhost6 localhost6.localdomain6
[root@localhost centos]# vi /etc/hosts
[root@localhost centos]# cat /etc/hosts
127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4
::1         localhost localhost.localdomain localhost6 localhost6.localdomain6

192.168.187.151  k8s-slave
[root@localhost centos]#