Offline snap installation

LXD
1

Hi,

I’m trying to install lxd with snap on ubuntu 16.04 server.
As the server has no internet acces, I’ve download the .assert and .snap using ‘snap download lxd’.
This gives me a .snap and .assert file:
lxd_8011.assert
lxd_8011.snap

After copying to the server, I would like to install it with:

$ sudo snap ack lxd_8011.assert
$ sudo snap install lxd_8011.snap

The install fails with:

$ sudo snap ack lxd_8011.assert
$ sudo snap install lxd_8011.snap
-- ensure prerequisites for "lxd" are available (get https://api.snapcraft.io/api/vs/snaps/details/core?channel=stable&fields=anon_dowload_url%2Carchitecture%2Cchannel%2Cdownload_sha4_384%2Csummary%2Cdescription%2Cdeltas%2Cbinary_fileize%2Cdownload_url%2Cepoch%2Cicon_url%2Clast_updated%2Cpackage_name%2Cprices%2Cpublisher%2Cratings_average%2Crevision%2Cscreenshot_urls%2Csnap_id%2Clicense%2Cbase%2Csupport_url%2Ccontact%2Ctitle%2Ccontent%2Cversion%2Corigin%2Cdeveloper_id%2Cprivate%2Cconfinement%2Cchannel_maps_list : dial tcp: lookup api.snapcraft.io on [::1]:53: read udp [::1]:53788 -> [::1]:53 read: connection refused)

Indicating to me that the snap tries to connect to the internet to find prerequisites. I’ve searched snap documentation, but I feel this is snap-specific.

tl;dr: Offline install isn’t working. Has this been tested for LXD?

2

It worked for me. Below, I create a container with nesting support, then snap download LXD. Finally, I perform the installation.

$ lxc launch ubuntu:18.04 offline --config security.nesting=true
Creating offline
Starting offline

$ lxc ubuntu offline
To run a command as administrator (user "root"), use "sudo <command>".
See "man sudo_root" for details.

ubuntu@offline:~$ sudo snap download lxd
Fetching snap "lxd"
Fetching assertions for "lxd"
Install the snap with:
   snap ack lxd_8011.assert
   snap install lxd_8011.snap
ubuntu@offline:~$ sudo snap ack lxd_8011.assert 
ubuntu@offline:~$ sudo snap install lxd_8011.snap
2018-08-01T12:46:12Z INFO Waiting for restart...
lxd 3.3 from 'canonical' installed
ubuntu@offline:~$
3

I see, thank you for your fast reply.
Does your container have internet acces?
Because manual installation succeeds if I have internet acces, but fails otherwise:

$ lxc launch ubuntu:16.04 offline
Creating offline
Starting offline

$lxc exec offline -- sudo --login --user ubuntu
ubuntu@offline:~$ sudo snap download lxd
Fetching snap "lxd"
Fetching assertions for "lxd"
Install the snap with:
    snap ack lxd_8011.assert
    snap install lxd_8011.snap
ubuntu@offline:~$ sudo ifdown eth0
ubuntu@offline:~$ sudo snap ack lxd_8011.assert
ubuntu@offline:~$ sudo snap install lxd_8011.snap
error: cannot perform the following tasks:
- Ensure prerequisites for "lxd" are available (Post https://api.snapcraft.io/v2/snaps/refresh: dial tcp: lookup api.snapcraft.io on [::1]:53: read udp [::1]:37859->[::1]:53: read: connection refused)
ubuntu@offline:~$ sudo ifup eth0
ubuntu@offline:~$ sudo snap install lxd_8011.snap
ubuntu@offline:~$ sudo snap download lxd
2018-08-01T14:07:42Z INFO Waiting for restart...
lxd 3.3 from 'canonical' installed

So with working network it’s fine, without it fails.

edit: I saved somewhere halfway through my post

4

Okay, I managed to reproduce what you get.

When you perform the snap install of the .snap package, it indeed tries to connect to api.snapcraft.io to perform a POST to https://api.snapcraft.io/v2/snaps/refresh.

This is a snap issue, and there are some discussions like https://forum.snapcraft.io/t/offline-snap-installers-and-possibility-to-update/275
I believe snap install performs a validity check on the downloaded .snap package.

It would be suitable to ask about this on https://forum.snapcraft.io/ and pick their brains.

5

Thank you, so it’s not my setup.

The snap install validity check should be fine because of the snap ack lxd*.assert. Other snaps do install offline, so I figured it might be the way the lxd snap is set up. I will check with the snapcraft forum, and if any answers come up I’ll post them here as well.

6

Does passing --dangerous and not using the assertion somehow work?

7

If there is no bug in snapd, I believe that snapd would try to figure out whether an offline snap package has been retracted, etc.

Otherwise, it could be a bug in snapd.

8

After removing the snap that was succesfully installed, it would reinstall offline. The ‘core’ snap was missing. (although i had manually installed the ubuntu-core snap, as suggested by snap documentation.)

Trying it now on a physical machine

edit: installing core first solves the problem:

$ sudo snap download core
$ sudo snap download lxd

and then on the offline device:

$ sudo snap ack /path/to/core\*assert
$ sudo snap install /path/to/core\*snap
$ sudo snap ack /path/to/lxd\*assert
$ sudo snap install /path/to/lxd\*snap

succesfully installs withouth network connection.

Note: the core snap is a prerequisite for every snap application.

Thanks for the help!

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