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In this article, I will change hostname in RAC (both the nodes in my RAC environment). But you can follow these steps and apply the same in the standalone database to change hostname in Linux. Currently, hostname for the both nodes is localhost.

Please find the below details that I will set to change hostname in rac for both nodes. If you are doing this in the standalone database then ignore the below table.

	NODE1	NODE2
Public IP	192.168.56.11	192.168.56.12
Private IP	192.168.10.1	192.168.10.2
VIP	192.168.56.21	192.168.56.22
SCAN	192.168.56.50	192.168.56.50

Now we have to update below four files below in both nodes with the VI editor to change hostname in Linux system:

 1)/etc/hosts              
 2)/etc/sysconfig/network  
 3)/etc/sysctl.conf        
 4)/etc/hostname          

1.Update the below details in the /etc/hosts file of both nodes. This file is used to resolve domain names locally before querying DNS.

NODE1 AND NODE2:
cat /etc/hosts

#PUBLIC IP
192.168.56.11   node1
192.168.56.12   node2

#PRIVATE IP
192.168.10.1       nodep1
192.168.10.2       nodep2

#VIRTUAL IP
192.168.56.21   nodevip1
192.168.56.22   nodevip2

#SCAN
192.168.56.55   cluster12-scan

2. Update the /etc/sysconfig/network file with the hostname. This file is used for proper system identification and network functionality.

NODE1:
[root@localhost ~]# cat /etc/sysconfig/network
# Created by anaconda
# oracle-database-preinstall-19c : Add NOZEROCONF=yes
NOZEROCONF=yes
hostname=node1

NODE2:
[root@localhost ~]# cat /etc/sysconfig/network
# Created by anaconda
# oracle-database-preinstall-19c : Add NOZEROCONF=yes
NOZEROCONF=yes
hostname=node2

3. Update the file /etc/sysctl.conf with kernel hostname. This file is used to set the hostname of the system at the kernel level.

NODE1:
[root@localhost ~]# cat /etc/sysctl.conf
# sysctl settings are defined through files in
# /usr/lib/sysctl.d/, /run/sysctl.d/, and /etc/sysctl.d/.

# Vendors settings live in /usr/lib/sysctl.d/.
# To override a whole file, create a new file with the same in
# /etc/sysctl.d/ and put new settings there. To override
# only specific settings, add a file with a lexically later
# name in /etc/sysctl.d/ and put new settings there.

# For more information, see sysctl.conf(5) and sysctl.d(5).
kernel.hostname=node1	

NODE2:
[root@localhost ~]# cat /etc/sysctl.conf
# sysctl settings are defined through files in
# /usr/lib/sysctl.d/, /run/sysctl.d/, and /etc/sysctl.d/.

# Vendors settings live in /usr/lib/sysctl.d/.
# To override a whole file, create a new file with the same in
# /etc/sysctl.d/ and put new settings there. To override
# only specific settings, add a file with a lexically later
# name in /etc/sysctl.d/ and put new settings there.

# For more information, see sysctl.conf(5) and sysctl.d(5).
kernel.hostname=node2   

4. Update /etc/hostname file. This file is used to persistently set the hostname across reboots.

NODE1:
[root@localhost ~]# cat /etc/hostname
node1

NODE2:
[root@localhost ~]# cat /etc/hostname
node2

5. Open a new terminal window to reflect the changes and login to node1 and node2. Once logged in ping the public and private IP addresses to check if it is reachable.

NODE1:

[root@node1 ~]# ping -c 3 node2
PING node2 (192.168.56.12) 56(84) bytes of data.
64 bytes from node2 (192.168.56.12): icmp_seq=1 ttl=64 time=0.778 ms
64 bytes from node2 (192.168.56.12): icmp_seq=2 ttl=64 time=0.698 ms
64 bytes from node2 (192.168.56.12): icmp_seq=3 ttl=64 time=0.932 ms

--- node2 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2003ms
rtt min/avg/max/mdev = 0.698/0.802/0.932/0.102 ms

[root@node1 ~]# ping -c 3 nodep2
PING nodep2 (192.168.10.2) 56(84) bytes of data.
64 bytes from nodep2 (192.168.10.2): icmp_seq=1 ttl=64 time=1.61 ms
64 bytes from nodep2 (192.168.10.2): icmp_seq=2 ttl=64 time=0.875 ms
64 bytes from nodep2 (192.168.10.2): icmp_seq=3 ttl=64 time=0.838 ms

--- nodep2 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2002ms
rtt min/avg/max/mdev = 0.838/1.109/1.616/0.360 ms

NODE2:

[root@node2 ~]# ping -c 3 node1
PING node1 (192.168.56.11) 56(84) bytes of data.
64 bytes from node1 (192.168.56.11): icmp_seq=1 ttl=64 time=1.11 ms
64 bytes from node1 (192.168.56.11): icmp_seq=2 ttl=64 time=1.09 ms
64 bytes from node1 (192.168.56.11): icmp_seq=3 ttl=64 time=0.675 ms

--- node1 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2004ms
rtt min/avg/max/mdev = 0.675/0.961/1.112/0.204 ms

[root@node2 ~]# ping -c 3 nodep1
PING nodep1 (192.168.10.1) 56(84) bytes of data.
64 bytes from nodep1 (192.168.10.1): icmp_seq=1 ttl=64 time=1.43 ms
64 bytes from nodep1 (192.168.10.1): icmp_seq=2 ttl=64 time=0.737 ms
64 bytes from nodep1 (192.168.10.1): icmp_seq=3 ttl=64 time=1.10 ms

--- nodep1 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2005ms
rtt min/avg/max/mdev = 0.737/1.090/1.433/0.284 ms

Hope this article helped you to change hostname in RAC as well as change hostname in linux system. If you want to know the network configuration for Oracle RAC in VirtualBox then you can follow my other article RAC node1 network configuration and RAC node2 network configuration.