Missing resolv.conf in WSL2

[c-goes]

Is this a BUG REPORT or FEATURE REQUEST? (leave only one on its own line)

/kind bug

Description

When installing Ubuntu 20.04 rootfs for WSL
and Podman 2.1.1 no container starts because of missing /run/systemd/resolve/resolv.conf.

Steps to reproduce the issue:

1. Install Ubuntu 20.04 via tar in WSL2

2. Install Podman

3. Run a container as root: podman run hello-world

Describe the results you received:

# podman run hello-world
Error: error creating resolv.conf for container 59dc1c8f45abe1b1d7c880a21e315948ee36a5951be6be31945334b4a87ec716: unable to read /run/systemd/resolve/resolv.conf: open /run/systemd/resolve/resolv.conf: no such file or directory

Describe the results you expected:

Container starts without errors.

Additional information you deem important (e.g. issue happens only occasionally):

It works if I run cp /etc/resolv.conf /run/systemd/resolve/resolv.conf beforehand. But I need to repeat this every time I restart WSL.

Output of podman version:

(paste your output here)

Output of podman info --debug:

host:
  arch: amd64
  buildahVersion: 1.16.1
  cgroupManager: cgroupfs
  cgroupVersion: v1
  conmon:
    package: 'conmon: /usr/libexec/podman/conmon'
    path: /usr/libexec/podman/conmon
    version: 'conmon version 2.0.20, commit: '
  cpus: 8
  distribution:
    distribution: ubuntu
    version: "20.04"
  eventLogger: file
  hostname: wslhost
  idMappings:
    gidmap: null
    uidmap: null
  kernel: 4.19.128-microsoft-standard
  linkmode: dynamic
  memFree: 6718386176
  memTotal: 8345993216
  ociRuntime:
    name: runc
    package: 'runc: /usr/sbin/runc'
    path: /usr/sbin/runc
    version: 'runc version spec: 1.0.1-dev'
  os: linux
  remoteSocket:
    path: /run/podman/podman.sock
  rootless: false
  slirp4netns:
    executable: ""
    package: ""
    version: ""
  swapFree: 0
  swapTotal: 0
  uptime: 25m 40.16s
registries:
  search:
  - docker.io
  - quay.io
store:
  configFile: /etc/containers/storage.conf
  containerStore:
    number: 6
    paused: 0
    running: 0
    stopped: 6
  graphDriverName: overlay
  graphOptions: {}
  graphRoot: /var/lib/containers/storage
  graphStatus:
    Backing Filesystem: extfs
    Native Overlay Diff: "true"
    Supports d_type: "true"
    Using metacopy: "false"
  imageStore:
    number: 14
  runRoot: /var/run/containers/storage
  volumePath: /var/lib/containers/storage/volumes
version:
  APIVersion: 2.0.0
  Built: 0
  BuiltTime: Thu Jan  1 01:00:00 1970
  GitCommit: ""
  GoVersion: go1.15.2
  OsArch: linux/amd64
  Version: 2.1.1

Package info (e.g. output of rpm -q podman or apt list podman):

podman/unknown,now 2.1.1~2 amd64 [installed]
podman/unknown 2.1.1~2 arm64
podman/unknown 2.1.1~2 armhf
podman/unknown 2.1.1~2 s390x

Have you tested with the latest version of Podman and have you checked the Podman Troubleshooting Guide?

Yes

Additional environment details (AWS, VirtualBox, physical, etc.):

WSL2

[Luap99]

Can you check if /etc/resolv.conf is a symlink to /run/systemd/resolve/resolv.conf?

[c-goes]

Can you check if /etc/resolv.conf is a symlink to /run/systemd/resolve/resolv.conf?

# ls -l /etc/resolv.conf
lrwxrwxrwx 1 root root 39 Oct 16 23:39 /etc/resolv.conf -> ../run/systemd/resolve/stub-resolv.conf

Interestingly, when installed via appx-file, WSL-Ubuntu has another link

lrwxrwxrwx  1 root root         29 Oct  5 11:31 resolv.conf -> ../run/resolvconf/resolv.conf

But I need to use the Ubuntu installed via rootfs with Podman.

[c-goes]

Probably related: #7616

[Luap99]

What the content in /run/systemd/resolve/stub-resolv.conf?

I guess it is only the nameserver 127.0.0.53 entry. We cannot use this file as source since this ip will not be reachable from within the container. The /run/systemd/resolve/stub-resolv.conf and /run/systemd/resolve/resolv.conf files are managed by systemd-resolved. Only /run/systemd/resolve/resolv.conf will contain the real nameserver entries. That's why we have to use this file as source even if stub-resolv.conf is symlinked.

This is to some degree a configuration problem with your ubuntu image since systemd cannot be run in wsl AFAIK and therefore systemd-resolved wont work. Does the dns resolution even work with your wsl image?

However, we use default entries if /etc/resolv.conf is empty, so I think it would make sense to also add default ones if the file does not exists.