podman run fails without /etc/hosts

[martinpitt]

/kind bug

Description

Starting a podman container (as root/system or as user, same issue) fails if the host does not have an /etc/hosts file. Having one is not really necessary -- nss-systemd auto-resolves things like "localhost", "localhost6" and the host's own hostname automatically, so in most cases /etc/hosts is just an obsolete boilerplate file these days.

Steps to reproduce the issue:

1. sudo mv /etc/hosts{,.disabled}

2. podman run -it --rm docker.io/busybox

Describe the results you received:

Error: error creating hosts file for container ab…: open /etc/hosts: no such file or directory

This is a bit pointless -- the container's /etc/hosts is generated by podman anyway.

Describe the results you expected:

Container starts up.

Fixing this can be done by sudo touch /etc/hosts, i. e. just having an empty file.

Output of podman version:

Version:      3.4.4
API Version:  3.4.4
Go Version:   go1.16.8
Built:        Wed Dec  8 22:45:07 2021
OS/Arch:      linux/amd64

Output of podman info --debug:

host:
  arch: amd64
  buildahVersion: 1.23.1
  cgroupControllers:
  - memory
  - pids
  cgroupManager: systemd
  cgroupVersion: v2
  conmon:
    package: conmon-2.0.30-2.fc35.x86_64
    path: /usr/bin/conmon
    version: 'conmon version 2.0.30, commit: '
  cpus: 8
  distribution:
    distribution: fedora
    version: "35"
  eventLogger: journald
  hostname: abakus
  idMappings:
    gidmap:
    - container_id: 0
      host_id: 1000
      size: 1
    - container_id: 1
      host_id: 100000
      size: 65536
    uidmap:
    - container_id: 0
      host_id: 1000
      size: 1
    - container_id: 1
      host_id: 100000
      size: 65536
  kernel: 5.15.8-200.fc35.x86_64
  linkmode: dynamic
  logDriver: journald
  memFree: 9495232512
  memTotal: 16529924096
  ociRuntime:
    name: crun
    package: crun-1.3-1.fc35.x86_64
    path: /usr/bin/crun
    version: |-
      crun version 1.3
      commit: 8e5757a4e68590326dafe8a8b1b4a584b10a1370
      spec: 1.0.0
      +SYSTEMD +SELINUX +APPARMOR +CAP +SECCOMP +EBPF +CRIU +YAJL
  os: linux
  remoteSocket:
    exists: true
    path: /run/user/1000/podman/podman.sock
  security:
    apparmorEnabled: false
    capabilities: CAP_CHOWN,CAP_DAC_OVERRIDE,CAP_FOWNER,CAP_FSETID,CAP_KILL,CAP_NET_BIND_SERVICE,CAP_SETFCAP,CAP_SETGID,CAP_SETPCAP,CAP_SETUID,CAP_SYS_CHROOT
    rootless: true
    seccompEnabled: true
    seccompProfilePath: /usr/share/containers/seccomp.json
    selinuxEnabled: true
  serviceIsRemote: false
  slirp4netns:
    executable: /usr/bin/slirp4netns
    package: slirp4netns-1.1.12-2.fc35.x86_64
    version: |-
      slirp4netns version 1.1.12
      commit: 7a104a101aa3278a2152351a082a6df71f57c9a3
      libslirp: 4.6.1
      SLIRP_CONFIG_VERSION_MAX: 3
      libseccomp: 2.5.3
  swapFree: 0
  swapTotal: 0
  uptime: 34m 10.71s
plugins:
  log:
  - k8s-file
  - none
  - journald
  network:
  - bridge
  - macvlan
  volume:
  - local
registries:
  search:
  - registry.fedoraproject.org
  - registry.access.redhat.com
  - docker.io
  - quay.io
store:
  configFile: /var/home/martin/.config/containers/storage.conf
  containerStore:
    number: 8
    paused: 0
    running: 1
    stopped: 7
  graphDriverName: overlay
  graphOptions:
    overlay.mount_program:
      Executable: /usr/bin/fuse-overlayfs
      Package: fuse-overlayfs-1.7.1-2.fc35.x86_64
      Version: |-
        fusermount3 version: 3.10.5
        fuse-overlayfs: version 1.7.1
        FUSE library version 3.10.5
        using FUSE kernel interface version 7.31
  graphRoot: /home/martin/.local/share/containers/storage
  graphStatus:
    Backing Filesystem: extfs
    Native Overlay Diff: "false"
    Supports d_type: "true"
    Using metacopy: "false"
  imageStore:
    number: 9
  runRoot: /run/user/1000/containers
  volumePath: /home/martin/.local/share/containers/storage/volumes
version:
  APIVersion: 3.4.4
  Built: 1638999907
  BuiltTime: Wed Dec  8 22:45:07 2021
  GitCommit: ""
  GoVersion: go1.16.8
  OsArch: linux/amd64
  Version: 3.4.4

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

podman-3.4.4-1.fc35.x86_64

Have you tested with the latest version of Podman and have you checked the Podman Troubleshooting Guide? (https://github.com/containers/podman/blob/master/troubleshooting.md)

No, but even Rawhide does not have a newer version -- there is no newer release.

[vrothberg]

Thanks for the report, @martinpitt! I'll take a stab.