Error when I purge snapd package in late-commands

[Francois Lafont]

Hi,

I use this iso https://releases.ubuntu.com/20.04/ubuntu-20.04.3-live-server-amd64.iso (sha1 a6077cb573271ec3c85f9d8abb60c60471dcb73b) to make a full automatic install of Ubuntu Focal. In "late-commands", I want to purge snapd to have a minimal install. Here is my user-data file:

```yaml
#cloud-config
autoinstall:
  version: 1
  locale: en_US.UTF-8
  keyboard:
    layout: fr
    variant: ""
  proxy: http://aptproxy.virt.priv:3142
  apt:
    preserve_sources_list: false
    primary:
      - arches: [amd64]
        uri: "http://archive.ubuntu.com/ubuntu"
    geoip: false
  network:
    network:
      version: 2
      ethernets:
        enp0s3:
          dhcp4: true
  storage:
    layout:
      name: direct
  identity:
    hostname: focal-vbox
    realname: packer
    username: packer
    password: $6$e70e7d9a7b031659$ID9RRN/tqPeis32k3GEsXluR1FNIR5RuyhVdJfZXUZ/H2de6p3D4sIChX8YCdOOfRIpCVWkDQBadBNjr7Y3Yn1
  ssh:
    install-server: yes
  user-data:
    timezone: "Europe/Paris"
  late-commands:
    - curtin in-target --target=/target -- sh -c 'printf "root:root\n" | chpasswd'
    - sed -i -r 's/^#?PermitRootLogin .*$/PermitRootLogin yes/' /target/etc/ssh/sshd_config
    - curtin in-target --target=/target -- apt-get -y -q purge snapd
    - sleep 10000 # Just to have time to ssh on the installer and retrieve all logs.
```

In the installer, I can see this error (via journalctl):

```
Oct 10 23:36:30 ubuntu-server subiquity_log.2004[36987]: Removing snap snapd and revision 12704
Oct 10 23:36:30 ubuntu-server subiquity_log.2004[36987]: Removing snap-snapd-12704.mount
Oct 10 23:36:30 ubuntu-server subiquity_log.2004[36987]: Discarding preserved snap namespaces
Oct 10 23:36:30 ubuntu-server subiquity_log.2004[37372]: umount: /run/snapd/ns/lxd.mnt: not mounted.
Oct 10 23:36:30 ubuntu-server subiquity_log.2004[37373]: rm: cannot remove '/run/snapd/ns/lxd.mnt': Device or resource busy
Oct 10 23:36:30 ubuntu-server subiquity_log.2004[36986]: dpkg: error processing package snapd (--purge):
Oct 10 23:36:30 ubuntu-server subiquity_log.2004[36986]: installed snapd package post-removal script subprocess returned error exit status 1
Oct 10 23:36:30 ubuntu-server subiquity_log.2004[36986]: Errors were encountered while processing:
Oct 10 23:36:30 ubuntu-server subiquity_log.2004[36986]: snapd
Oct 10 23:36:32 ubuntu-server subiquity_log.2004[36772]: E: Sub-process /usr/bin/dpkg returned an error code (1)
```

Maybe there is a way to avoid this error when snapd is purged but, to be honest, I would much prefer an option in the `user-data` file to have a **minimal** install, so without snapd installed, something with just `apt-get` basically.

Feel to handle this "bug" (is it really a bug?) as you want.

As an attachment, a .gz file with:
- the file /autoinstall.yml from the installer server.
- the output of `journalctl` from the installer server.
- the /var/log/ directory from the installer server (ignore the ssh errors, it's just paker which tries to ssh on the VM during the installation).

Regards.

[Michael Hudson-Doyle (mwhudson)]

> - curtin in-target --target=/target -- sh -c 'printf "root:root\n" |
> chpasswd'
> - sed -i -r 's/^#?PermitRootLogin .*$/PermitRootLogin yes/'
> /target/etc/ssh/sshd_config
> - curtin in-target --target=/target -- apt-get -y -q purge snapd
> - sleep 10000 # Just to have time to ssh on the installer and retrieve
> all logs.
> ```
>
> In the installer, I can see this error (via journalctl):
>
> ```
> Oct 10 23:36:30 ubuntu-server subiquity_log.2004[36987]: Removing snap
> snapd and revision 12704
> Oct 10 23:36:30 ubuntu-server subiquity_log.2004[36987]: Removing
> snap-snapd-12704.mount
> Oct 10 23:36:30 ubuntu-server subiquity_log.2004[36987]: Discarding
> preserved snap namespaces
> Oct 10 23:36:30 ubuntu-server subiquity_log.2004[37372]: umount:
> /run/snapd/ns/lxd.mnt: not mounted.
> Oct 10 23:36:30 ubuntu-server subiquity_log.2004[37373]: rm: cannot remove
> '/run/snapd/ns/lxd.mnt': Device or resource busy
> Oct 10 23:36:30 ubuntu-server subiquity_log.2004[36986]: dpkg: error
> processing package snapd (--purge):
> Oct 10 23:36:30 ubuntu-server subiquity_log.2004[36986]: installed snapd
> package post-removal script subprocess returned error exit status 1
> Oct 10 23:36:30 ubuntu-server subiquity_log.2004[36986]: Errors were
> encountered while processing:
> Oct 10 23:36:30 ubuntu-server subiquity_log.2004[36986]: snapd
> Oct 10 23:36:32 ubuntu-server subiquity_log.2004[36772]: E: Sub-process
> /usr/bin/dpkg returned an error code (1)
> ```
>

Hmmm. You might have better luck with chroot /target apt-get purge snapd.
Or at least it would be worth a try :)

> Maybe there is a way to avoid this error when snapd is purged but, to be
> honest, I would much prefer an option in the `user-data` file to have a
> **minimal** install, so without snapd installed, something with just
> `apt-get` basically.
>

Well, luckily for you this feature has been implemented in the soon to be
released Ubuntu 21.10!

[Francois Lafont (francois-lafont)]

Hi,

> Hmmm. You might have better luck with chroot /target apt-get purge snapd.
> Or at least it would be worth a try :)

Thx Michael, it works via "chroot /target apt-get -y -q purge snapd". I admit that I don't understand well why it works with chroot and not with curtin.

> Well, luckily for you this feature has been implemented in the soon to be
> released Ubuntu 21.10!

Good news. :)

I think we can consider that this bug is solved, no?

Thx.

[Francois Lafont (francois-lafont)]

Hi,

@mwhudson said:

> Well, luckily for you this feature has been implemented in the soon to
> be released Ubuntu 21.10!

@mwhudson, sorry for this message. I know this bug is closed and it's ok. But, now I would like to install Ubuntu 22.04 via Subiquity and the user-data file (ie a full automatic install). I have searched the way to make a minimal install but I have not found in documentation. Can you tell me which option I have to put the in user-data file to have a minimal install?

Thx.