[Bug 1956447] [NEW] "No DNS servers known" in /run/systemd/resolve/resolv.conf

[Pavel Derendyaev]

Public bug reported:

1) The release of Ubuntu you are using, via 'lsb_release -rd' or System -> About Ubuntu
Description:	Ubuntu 20.04.3 LTS
Release:	20.04

2) The version of the package you are using, via 'apt-cache policy pkgname' or by checking in Software Center
systemd:
  Installed: 245.4-4ubuntu3.13
  Candidate: 245.4-4ubuntu3.13

3) What you expected to happen

/etc/network/interfaces:

auto lo
iface lo inet loopback
    dns-nameservers 1.1.1.1 8.8.8.8

auto eth0
iface eth0 inet static
    address ip/24
    mtu 1500
    post-up route add default gw gw_ip || true
    pre-down route del default gw gw_ip || true


When system rebooted I expected in

/run/resolvconf/resolv.conf:
nameserver 1.1.1.1
nameserver 8.8.8.8
nameserver 127.0.0.53

and in /run/systemd/resolve/resolv.conf:
nameserver 1.1.1.1
nameserver 8.8.8.8

This is stated in "man 8 systemd-resolved":
systemd-resolved maintains the /run/systemd/resolve/resolv.conf file for compatibility with traditional Linux programs

4) What happened instead

/run/systemd/resolve/resolv.conf:
# No DNS servers known.

But after restarting systemd-resolved it update this file correctly.


5) Also

The system behaves correctly when DHCP is used. So when in /etc/network/interfaces:
auto lo
iface lo inet loopback
auto eth0
iface eth0 inet dhcp

Then /run/systemd/resolve/resolv.conf updated correctly straight without
restart.

** Affects: systemd (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1956447

Title:
  "No DNS servers known" in /run/systemd/resolve/resolv.conf

Status in systemd package in Ubuntu:
  New

Bug description:
  1) The release of Ubuntu you are using, via 'lsb_release -rd' or System -> About Ubuntu
  Description:	Ubuntu 20.04.3 LTS
  Release:	20.04

  2) The version of the package you are using, via 'apt-cache policy pkgname' or by checking in Software Center
  systemd:
    Installed: 245.4-4ubuntu3.13
    Candidate: 245.4-4ubuntu3.13

  3) What you expected to happen

  /etc/network/interfaces:

  auto lo
  iface lo inet loopback
      dns-nameservers 1.1.1.1 8.8.8.8

  auto eth0
  iface eth0 inet static
      address ip/24
      mtu 1500
      post-up route add default gw gw_ip || true
      pre-down route del default gw gw_ip || true

  
  When system rebooted I expected in

  /run/resolvconf/resolv.conf:
  nameserver 1.1.1.1
  nameserver 8.8.8.8
  nameserver 127.0.0.53

  and in /run/systemd/resolve/resolv.conf:
  nameserver 1.1.1.1
  nameserver 8.8.8.8

  This is stated in "man 8 systemd-resolved":
  systemd-resolved maintains the /run/systemd/resolve/resolv.conf file for compatibility with traditional Linux programs

  4) What happened instead

  /run/systemd/resolve/resolv.conf:
  # No DNS servers known.

  But after restarting systemd-resolved it update this file correctly.

  
  5) Also

  The system behaves correctly when DHCP is used. So when in /etc/network/interfaces:
  auto lo
  iface lo inet loopback
  auto eth0
  iface eth0 inet dhcp

  Then /run/systemd/resolve/resolv.conf updated correctly straight
  without restart.

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