Cannot ssh or ping hostname, but dig and nslookup work on Ubuntu 18.04

domain-name-systemnetplanresolv.confubuntu-18.04

I updated my kernel this weekend, and now I'm using 5.3.1.

christopher@HAL4:~$ uname -r
5.3.1-050301-generic

I need to login to servers, but I cannot do so by hostname any longer. For example, I have a server, "web4," and it's local IP is 192.168.64.140. If I run dig: 

christopher@HAL4:~$ dig web4

; <<>> DiG 9.11.3-1ubuntu1.9-Ubuntu <<>> web4
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 1580
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1280
;; QUESTION SECTION:
;web4.              IN  A

;; ANSWER SECTION:
web4.           0   IN  A   192.168.64.140

;; Query time: 0 msec
;; SERVER: 192.168.3.222#53(192.168.3.222) <---- Correct! 
;; WHEN: Mon Sep 30 09:50:31 CDT 2019
;; MSG SIZE  rcvd: 49

Same thing for nslookup: 

christopher@HAL4:~$ nslookup web4
Server:     192.168.3.222
Address:    192.168.3.222#53

Name:   web4
Address: 192.168.64.140

However, neither ping or ssh work ('login' is a bash script that uses my key):

christopher@HAL4:~$ ping web4
ping: web4: Name or service not known
christopher@HAL4:~$ login web4
ssh: Could not resolve hostname web4: Name or service not known

My /etc/resolv.conf is: 

# This file is managed by man:systemd-resolved(8). Do not edit.
#
# This is a dynamic resolv.conf file for connecting local clients directly to
# all known uplink DNS servers. This file lists all configured search domains.
#
# Third party programs must not access this file directly, but only through the
# symlink at /etc/resolv.conf. To manage man:resolv.conf(5) in a different way,
# replace this symlink by a static file or a different symlink.
#


# See man:systemd-resolved.service(8) for details about the supported modes of
# operation for /etc/resolv.conf.

nameserver 192.168.3.222
nameserver 192.168.70.80

It is a symlink to /run/systemd/resolve/resolv.conf.

Here is my /etc/netplan/01-network-manager-all.yaml file: 

christopher@HAL4:~$ cat /etc/netplan/01-network-manager-all.yaml 
# Let NetworkManager manage all devices on this system
network:
  version: 2
  renderer: NetworkManager
  ethernets:
          enp4s0:
                  dhcp4: no
                  addresses: [192.168.2.47/19]
                  gateway4: 192.168.1.1
                  nameservers:
                          addresses: [192.168.3.222,192.168.70.80]

What happened to my DNS?!

Best Answer

Check /etc/nsswitch.conf

look for the line that starts hosts and make sure it has dns on it.

hosts: files dns

Update - as you say in the comments, your nsswitch.conf has:

hosts: files mdns4_minimal [NOTFOUND=return] resolve [!UNAVAIL=return] dns myhostname

This means that hosts resolution will first look in /etc/hosts, and then use mdns4_minimal, which implied that youre using the avahi daemon service, perhaps this isnt running? If it fails to resolve using mdns, host resolution will fail - this is usually by design, to ensure that resolution is sure to use avahi, the fact that youve got resolve [!UNAVAIL=return] after this, means that the systemd resolver may be configured too... [!UNAVAILBLE=return] means that systemd-resolved will always be used if its up, but continue to nss-dns if not. So, determine how you want to resolve names to addresses, if you arent using mdns you can remove mdns4_minimal [NOTFOUND=return] so this may be better for you:

hosts: files resolve [!UNAVAIL=return] dns myhostname

or even:

hosts: files dns myhostname
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