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I cannot ping or mount using hostname of server on domain network.

Server is almost fresh install, just using apache, mysql, php for webhosting.

If I ping server with its hostname it result with this error:

Temporary failure in name resolution

Pinging ip address works.

If I try to mount server with hostname:

mount error: could not resolve address for server_name: Unknown error

If I tried to ping FQDN of server, it also resulted with same error

ping server_name.domain_name.local
Temporary failure in name resolution

After I changed symlink from

resolv.conf -> ../run/systemd/resolve/stub-resolv.conf

to

resolv.conf -> /run/systemd/resolve/resolv.conf

using

sudo ln -sf /run/systemd/resolve/resolv.conf /etc/resolv.conf

with help from answer here Ubuntu 18.04 .local domain dns lookup not working

The real issue is that Ubuntu 18.04 has its resolv.conf sym-linked to a stub file that points to the localhost for name resolution. Localhost DNS name resolution means that the system refuses to check the supplied DNS server for .local names, believing (incorrectly) that such names are invalid.

I can now ping FQDN, but pinging hostname still doesn't work.

I can see now that system is using correct DNS server (not that default localhost ip):

resolvectl status
Global
       Protocols: -LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
resolv.conf mode: uplink

Link 2 (eth0)
    Current Scopes: DNS
         Protocols: +DefaultRoute +LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
Current DNS Server: ip_of_my_dns_server_on_lan
       DNS Servers: ip_of_my_dns_server_on_lan

What to do to be able ping hostname? (and mount using hostname etc.)

SheldonCopper
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    What is your search domain set to? If it is not se to domain_name.local then simply trying to go by hostname won't work, the search domain component is what says what additional domain name roots to try appending to your hostname to search for in DNS. – Thomas Ward Mar 06 '24 at 15:31
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    I put my domain_name.local into /etc/netplan file under network/ethernets/eth0/nameserver like this search: [domain_name.local] and after sudo netplan apply it works, I can ping just by hostname. Thank you very much. – SheldonCopper Mar 07 '24 at 08:22
  • @ThomasWard I also changed symlink back sudo ln -sf ../run/systemd/resolve/stub-resolv.conf /etc/resolv.conf and it stil works – SheldonCopper Mar 07 '24 at 08:57

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