Commands:
Viewing the hostname with 'hostname' - hostname {-f|-s}
# hostname
localhost.localdomain
Viewing the hostname with 'hostnamectl'
# hostnamectl
Static hostname: localhost.localdomain
Icon name: computer-vm
Chassis: vm
Machine ID: b31bb9e7fc544e65beae56247bdd423f
Boot ID: 876d1a6703d0469384df37a4855fa1f0
Virtualization: oracle
Operating System: Red Hat Enterprise Linux 8.3 (Ootpa)
CPE OS Name: cpe:/o:redhat:enterprise_linux:8.3:GA
Kernel: Linux 4.18.0-240.1.1.el8_3.x86_64
Architecture: x86-64
When used with an argument, the command 'hostname' temporarily sets the hostname until the next reboot
# hostname rhel8-lab
# hostname
rhel8-lab
You can edit '/etc/hostname' to change the hostname permanently.
Sets the hostname permanently.
# hostname rhel8-lab
# hostname
rhel8-lab
📌 EXAM TIP: For the test, make sure that 'bind-utils' is installed so you have the 'host' resolution utility.
Update it with 'nmcli'
# nmcli con mod [connection name] ipv4.dns [DNS IP]
Restart the connection or the network
# nmcli connection down [conn name] && nmcli connection up [conn name]
Or
# systemctl restart NetworkManager
Optionally, if you need to add a secondary DNS server, add a '+' before 'ipv4.dns
# nmcli con mod [connection name] +ipv4.dns [secondary DNS IP]
📝 Notes
The '/etc/hosts' file is a simple text file that associates IP addresses with hostnames, one line per IP address. You can use '/etc/hosts' to overwrite DNS resolution (for programs that use the GNY C library).
# cat /etc/hosts
127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4
::1 localhost localhost.localdomain localhost6 localhost6.localdomain6
127.0.0.1 myhost myhost.com
Reference:
Commands:
The Name Service Switch (NSS) configuration file /etc/nsswitch.conf is used by the GNU C Library and certain other applications to determine the sources from which to obtain name-service information in a range of categories, and in what order.
By default, '/etc/hosts' (files) is given priority over DNS queries:
# grep hosts /etc/nsswitch.conf
# hosts: files dns
# hosts: files dns # from user file
# Valid databases are: aliases, ethers, group, gshadow, hosts,
hosts: files dns myhostname
Both 'nslookup' and 'host' commands do not use C library, thus are not affected by nsswitch.conf (or /etc/hosts).
You can use 'nslookup' for name resolution
# nslookup google.ca
Server: 10.13.15.1
Address: 10.13.15.1#53
Non-authoritative answer:
Name: google.ca
Address: 172.217.165.3
Name: google.ca
Address: 2607:f8b0:400b:802::2003
You can also use 'host' for name resolution
# host google.ca
google.ca has address 172.217.165.3
google.ca has IPv6 address 2607:f8b0:400b:802::2003
google.ca mail is handled by 40 alt3.aspmx.l.google.com.
google.ca mail is handled by 10 aspmx.l.google.com.
google.ca mail is handled by 30 alt2.aspmx.l.google.com.
google.ca mail is handled by 50 alt4.aspmx.l.google.com.
google.ca mail is handled by 20 alt1.aspmx.l.google.com.
dig is an advanced DNS tool and is here mainly for reference
# dig google.ca +noall +answer
google.ca. 210 IN A 172.217.165.3