Add example of running centos distribution

[afbjorklund]

Requires all the other patches, before it actually works.

But otherwise very similar to fedora (it's based on fc28)

CentOS Linux

This is supported until the end of the year.
https://cloud.centos.org/centos/8/
(downstream of RHEL)

https://www.centos.org/centos-linux/

CentOS Stream

And then it can be substituted for "Stream".
https://cloud.centos.org/centos/8-stream/
(upstream of RHEL)

https://www.centos.org/centos-stream/

---

See https://blog.centos.org/2020/12/future-is-centos-stream/

And https://www.centos.org/centos-stream/ for Stream 9 status

[jandubois]

@AkihiroSuda Should this config also be added to .cirrus.yml?

PR will need to be rebased for the test to pass though.

[AkihiroSuda]

@AkihiroSuda Should this config also be added to .cirrus.yml?

Either is fine to me.

[AkihiroSuda]

$ sudo systemctl is-system-running
degraded

/var/log/cloud-init-output.log :

...
[INFO] Starting systemd unit "stargz-snapshotter.service"
+ systemctl --user start stargz-snapshotter.service
+ sleep 3
+ systemctl --user --no-pager --full status stargz-snapshotter.service
● stargz-snapshotter.service - stargz snapshotter (Rootless)
   Loaded: loaded (/home/suda.linux/.config/systemd/user/stargz-snapshotter.service; disabled; vendor preset: enabled)
   Active: activating (auto-restart) (Result: exit-code) since Tue 2021-10-19 07:21:38 UTC; 691ms ago
  Process: 14414 ExecStart=/usr/local/bin/containerd-rootless-setuptool.sh nsenter -- containerd-stargz-grpc -address /run/user/501/containerd-stargz-grpc/containerd-stargz-grpc.sock -root /home/suda.linux/.local/share/containerd-stargz-grpc -config /home/suda.linux/.config/containerd-stargz-grpc/config.toml (code=exited, status=1/FAILURE)
 Main PID: 14414 (code=exited, status=1/FAILURE)
+ set +x
[ERROR] Failed to start stargz-snapshotter.service. Run `journalctl -n 20 --no-pager --user --unit stargz-snapshotter.service` to show the error log.
[ERROR] Before retrying installation, you might need to uninstall the current setup: `/usr/local/bin/containerd-rootless-setuptool.sh uninstall -f ; /usr/local/bin/rootlesskit rm -rf /home/suda.linux/.local/share/containerd`
+ echo 'WARNING: rootless stargz does not seem supported on this host (kernel older than 5.11?)'
WARNING: rootless stargz does not seem supported on this host (kernel older than 5.11?)
+ '[' -n 1 ']'
+ echo 'Restoring SELinux'
Restoring SELinux
+ setenforce 1
LIMA| Exiting with code 1

[AkihiroSuda]

We have to skip containerd-rootles-setuptool.sh install-stargz for CentOS 8, as its kernel is older than 5.11

[AkihiroSuda]

Also could you add CentOS 8 to examples/README.md?

[AkihiroSuda]

Added commit 40-install-containerd.sh: skip install-stargz on EL8, but 20-rootless-base.sh still fails

/var/log/cloud-init-output.log:

+ loginctl enable-linger suda
Could not enable linger: Connection timed out
LIMA| WARNING: Failed to execute /mnt/lima-cidata/boot/20-rootless-base.sh

[AkihiroSuda]

Added several follow-up commits.

LGTM if green.