Podman warns about cgroups-v1 being deprecated, but don't provide more info on how to migrate to cgroup v2

[fishy]

Issue Description

When I run any podman command, it will warn about cgroups-v1 being deprecated in favor of cgroups-v2, but it does not provide any more info on how do I switch to cgroups-v2 (it does provide info about how to silent that warning):

$ podman version
WARN[0000] Using cgroups-v1 which is deprecated in favor of cgroups-v2 with Podman v5 and will be removed in a future version. Set environment variable `PODMAN_IGNORE_CGROUPSV1_WARNING` to hide this warning. 
Client:       Podman Engine
Version:      5.0.3
API Version:  5.0.3
Go Version:   go1.22.5
Built:        Wed Dec 31 16:00:00 1969
OS/Arch:      linux/amd64

I checked my ~/.config/containers/containers.conf file, and every reference of cgroup I can find there are in comments, which seems to suggest that everything related to cgroups are being configured to use the default config to me? I also don't have ~/.config/containers/storage.conf so that's default as well.

And it seems to me that my system supports both v1 and v2 of cgroups:

$ grep cgroup /proc/filesystems
nodev   cgroup
nodev   cgroup2

So if my system supports cgroups v2 and I did not explicitly configure podman to use cgroups v1 and cgroups v1 is deprecated in podman, it should auto pick v2 instead of warn me about that?

Steps to reproduce the issue

Steps to reproduce the issue
1.
2.
3.

Describe the results you received

Describe the results you received

Describe the results you expected

Describe the results you expected

podman info output

$ podman info
WARN[0000] Using cgroups-v1 which is deprecated in favor of cgroups-v2 with Podman v5 and will be removed in a future version. Set environment variable `PODMAN_IGNORE_CGROUPSV1_WARNING` to hide this warning. 
host:
  arch: amd64
  buildahVersion: 1.35.3
  cgroupControllers: []
  cgroupManager: cgroupfs
  cgroupVersion: v1
  conmon:
    package: conmon_2.1.10+ds1-1+b1_amd64
    path: /usr/bin/conmon
    version: 'conmon version 2.1.10, commit: unknown'
  cpuUtilization:
    idlePercent: 98.51
    systemPercent: 0.28
    userPercent: 1.21
  cpus: 8
  databaseBackend: boltdb
  distribution:
    codename: trixie
    distribution: debian
    version: unknown
  eventLogger: journald
  freeLocks: 2047
  hostname: penguin
  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: 6.6.30-02726-gb84bbdf6955e
  linkmode: dynamic
  logDriver: journald
  memFree: 10522427392
  memTotal: 15184396288
  networkBackend: netavark
  networkBackendInfo:
    backend: netavark
    dns:
      package: aardvark-dns_1.4.0-6_amd64
      path: /usr/lib/podman/aardvark-dns
      version: aardvark-dns 1.4.0
    package: netavark_1.4.0-4.1_amd64
    path: /usr/lib/podman/netavark
    version: netavark 1.4.0
  ociRuntime:
    name: /home/fishy/bin/runsc-podman.sh
    package: Unknown
    path: /home/fishy/bin/runsc-podman.sh
    version: |-
      runsc version release-20240729.0
      spec: 1.1.0-rc.1
  os: linux
  pasta:
    executable: /usr/bin/pasta
    package: passt_0.0~git20240726.57a21d2-1_amd64
    version: |
      pasta 0.0~git20240726.57a21d2-1
      Copyright Red Hat
      GNU General Public License, version 2 or later
        <https://www.gnu.org/licenses/old-licenses/gpl-2.0.html>
      This is free software: you are free to change and redistribute it.
      There is NO WARRANTY, to the extent permitted by law.
  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: false
  serviceIsRemote: false
  slirp4netns:
    executable: /usr/bin/slirp4netns
    package: slirp4netns_1.2.1-1+b1_amd64
    version: |-
      slirp4netns version 1.2.1
      commit: 09e31e92fa3d2a1d3ca261adaeb012c8d75a8194
      libslirp: 4.8.0
      SLIRP_CONFIG_VERSION_MAX: 4
      libseccomp: 2.5.5
  swapFree: 0
  swapTotal: 0
  uptime: 155h 40m 3.00s (Approximately 6.46 days)
  variant: ""
plugins:
  authorization: null
  log:
  - k8s-file
  - none
  - passthrough
  - journald
  network:
  - bridge
  - macvlan
  - ipvlan
  volume:
  - local
registries: {}
store:
  configFile: /home/fishy/.config/containers/storage.conf
  containerStore:
    number: 1
    paused: 0
    running: 1
    stopped: 0
  graphDriverName: vfs
  graphOptions: {}
  graphRoot: /home/fishy/.local/share/containers/storage
  graphRootAllocated: 136902082560
  graphRootUsed: 112356233216
  graphStatus: {}
  imageCopyTmpDir: /var/tmp
  imageStore:
    number: 5
  runRoot: /run/user/1000/containers
  transientStore: false
  volumePath: /home/fishy/.local/share/containers/storage/volumes
version:
  APIVersion: 5.0.3
  Built: 0
  BuiltTime: Wed Dec 31 16:00:00 1969
  GitCommit: ""
  GoVersion: go1.22.5
  Os: linux
  OsArch: linux/amd64
  Version: 5.0.3

### Podman in a container

Yes

### Privileged Or Rootless

Rootless

### Upstream Latest Release

No

### Additional environment details

I'm using podman distributed by Debian testing (trixie), so it's not the latest release.

### Additional information

Additional information like issue happens only occasionally or issue happens with a particular architecture or on a particular setting

[ScrambledBrain]

I agree, that the pre-requisites / requirements are not documented as they could / should be.

For example such links should contain more information about cgroups:
https://github.com/containers/podman/blob/main/docs/tutorials/podman_tutorial.md
https://github.com/containers/podman/blob/main/docs/tutorials/rootless_tutorial.md

Or maybe another "tutorial" link about OS configuration would help, which should contain the pre-requisites / requirements for rootless / rootful operating modes of podman with all the dis-/advantages [cgroups v1 vs. v2, sysctl settings, ...] in a nice table as a good overview.

I also only stumpled over the cgroups topic by the small sentence somewhere in the long text of Systemd Units via Quadlet :

Quadlet requires the use of cgroup v2, use podman info --format {{.Host.CgroupsVersion}} to check on the system.

[afbjorklund]

Strange that you didn't get systemd (with cgroups v2) and weird that it uses VFS (not overlayfs)

  cgroupControllers: []
  cgroupManager: cgroupfs
  cgroupVersion: v1

  graphDriverName: vfs
  graphStatus: {}

The default settings for my Podman 5.2.0 on Debian 12 (built from source code) ended up as:

  cgroupControllers:
  - cpu
  - pids
  cgroupManager: systemd
  cgroupVersion: v2

  graphDriverName: overlay
  graphStatus:
    Backing Filesystem: extfs
    Native Overlay Diff: "true"
    Supports d_type: "true"
    Supports shifting: "false"
    Supports volatile: "true"
    Using metacopy: "false"

[jaknz]

Strange that you didn't get systemd (with cgroups v2) and weird that it uses VFS (not overlayfs)

  cgroupControllers: []
  cgroupManager: cgroupfs
  cgroupVersion: v1

  graphDriverName: vfs
  graphStatus: {}

I'm running podman on WSL2 in Windows 11, and I'm getting this as well. Definitely do have cgroups v2 on my up-to-date Debian, but I'm wondering if we're getting pulled back to v1 because of the way the WSL2 kernel mounts the VFS?

[afbjorklund]

Debian changed to cgroups v2 by default, in Debian 11 "bullseye":

https://www.debian.org/releases/bullseye/amd64/release-notes/ch-whats-new.en.html#cgroupv2

For the older versions, it had to be enabled on the kernel cmdline:

systemd.unified_cgroup_hierarchy=true

[jaknz]

Found the solution, at least for WSL2!
https://github.com/spurin/wsl-cgroupsv2

[pavelanni]

I got this warning after upgrading from RHEL 9.4 to 9.5 in which Podman was upgraded from 4.9 to 5.2. I checked with podman info and indeed, it used groups v1. Probably because I kept updating this server for several years already and inherited this setting from pervious versions.

After searching for a while, I found this command and it solved the issue!

sudo grubby --update-kernel=ALL --args="systemd.unified_cgroup_hierarchy=1"

For reference, it was on Oracle's doc site: https://docs.oracle.com/en/learn/ol-cgroup-v2/#enable-control-group-version-2