Domain name within the output of ping command.

Issue

• Identical configuration of two systems, produce different ping output when the ping is run locally.
• Why the output of ping command is inconsistent and where is it taken from?

[root@testmachine1 ~]$ cat /etc/hosts
127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4
::1         localhost localhost.localdomain localhost6 localhost6.localdomain6

[root@testmachine1 ~]# ping testmachine1
PING testmachine1.example.com (10.10.10.10) 56(84) bytes of data.
64 bytes from testmachine1 (10.10.10.10): icmp_seq=1 ttl=64 time=0.013 ms
64 bytes from testmachine1 (10.10.10.10): icmp_seq=2 ttl=64 time=0.028 ms

[root@testmachine2 ~]#$ cat /etc/hosts
127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4
::1         localhost localhost.localdomain localhost6 localhost6.localdomain6

[root@testmachine2 ~]# ping testmachine2
PING testmachine2.example.com (10.10.10.20) 56(84) bytes of data.
64 bytes from testmachine2.example.com (10.10.10.20): icmp_seq=1 ttl=64 time=0.018 ms
64 bytes from testmachine2.example.com (10.10.10.20): icmp_seq=2 ttl=64 time=0.028 ms