[SOLVED] Where is the documentation for the lxc launch command that uses "images:"?

bgoodr · 12-09-2017, 01:25 PM

Hi,

My ultimate goal is to create a LXD container that replicates, as close possible, one of my real RHEL 6.7 machines contains in terms of both kernel images and packages. If I have to use a CentOS 6.7 initially before talking to Red Hat Sales, that is fine too. The goal is to be able to ultimately execute some processes within that container but under varying conditions such as memory and CPU resources, which, from all I've read, indicate that is possible.

Working through the tutorials, I ran into a documentation issue:

From https://linuxcontainers.org/lxd/getting-started-cli/ I see:

Code:

To start a container from them, simply do:
...
lxc launch images:centos/6/amd64 my-centos

I've verified this works on my Ubuntu 17.10 desktop:

Code:

drunkard@thebar:~$ lxc launch images:centos/6/amd64 my-centos
Creating my-centos
Starting my-centos
drunkard@thebar:~$ lxc list
+---------------+---------+---------------------+-----------------------------------------------+------------+-----------+
|     NAME      |  STATE  |        IPV4         |                     IPV6                      |    TYPE    | SNAPSHOTS |
+---------------+---------+---------------------+-----------------------------------------------+------------+-----------+
| first-machine | RUNNING | 10.58.21.150 (eth0) | fd42:702a:7a67:d113:216:3eff:fee2:dfa6 (eth0) | PERSISTENT | 0         |
+---------------+---------+---------------------+-----------------------------------------------+------------+-----------+
| my-centos     | RUNNING | 10.58.21.69 (eth0)  | fd42:702a:7a67:d113:216:3eff:fe03:86b (eth0)  | PERSISTENT | 0         |
+---------------+---------+---------------------+-----------------------------------------------+------------+-----------+
drunkard@thebar:~$

(the first-machine was from an earlier experiment with an ubuntu container). I need to know what the proper syntax is for that "images:XXXX" part of the command. Where do they get the "amd64" in the "images:centos/6/amd64" part of the command?

I viewed the man page for lxc and it is not indicating the details of what is to the right of the ":" there.

I can "see" what is "out there" but I don't know what "where" is, from a command of:

Code:

drunkard@thebar:~$ lxc image list images: | grep -C1 -i centos
+---------------------------------+--------------+--------+------------------------------------------+---------+----------+-------------------------------+
| centos/6 (3 more)               | 64b9709c2368 | yes    | Centos 6 amd64 (20171209_02:16)          | x86_64  | 75.58MB  | Dec 9, 2017 at 12:00am (UTC)  |
+---------------------------------+--------------+--------+------------------------------------------+---------+----------+-------------------------------+
| centos/6/i386 (1 more)          | dcf545b99fec | yes    | Centos 6 i386 (20171209_02:16)           | i686    | 75.74MB  | Dec 9, 2017 at 12:00am (UTC)  |
+---------------------------------+--------------+--------+------------------------------------------+---------+----------+-------------------------------+
| centos/7 (3 more)               | 3230d10b1ab5 | yes    | Centos 7 amd64 (20171209_02:16)          | x86_64  | 82.22MB  | Dec 9, 2017 at 12:00am (UTC)  |
+---------------------------------+--------------+--------+------------------------------------------+---------+----------+-------------------------------+
--
+---------------------------------+--------------+--------+------------------------------------------+---------+----------+-------------------------------+
|                                 | 2e325f5f2bfe | yes    | Centos 6 amd64 (20171207_02:16)          | x86_64  | 75.58MB  | Dec 7, 2017 at 12:00am (UTC)  |
+---------------------------------+--------------+--------+------------------------------------------+---------+----------+-------------------------------+
|                                 | 411ad3f9de4a | yes    | Centos 6 amd64 (20171208_02:16)          | x86_64  | 75.58MB  | Dec 8, 2017 at 12:00am (UTC)  |
+---------------------------------+--------------+--------+------------------------------------------+---------+----------+-------------------------------+
|                                 | 7aeb93209940 | yes    | Centos 6 i386 (20171207_02:16)           | i686    | 75.74MB  | Dec 7, 2017 at 12:00am (UTC)  |
+---------------------------------+--------------+--------+------------------------------------------+---------+----------+-------------------------------+
|                                 | 9b0db8db5995 | yes    | Centos 6 i386 (20171208_02:16)           | i686    | 75.74MB  | Dec 8, 2017 at 12:00am (UTC)  |
+---------------------------------+--------------+--------+------------------------------------------+---------+----------+-------------------------------+
|                                 | b71f00b408da | yes    | Centos 7 amd64 (20171207_02:16)          | x86_64  | 82.21MB  | Dec 7, 2017 at 12:00am (UTC)  |
+---------------------------------+--------------+--------+------------------------------------------+---------+----------+-------------------------------+
|                                 | 468dd7e55654 | yes    | Centos 7 amd64 (20171208_02:16)          | x86_64  | 82.21MB  | Dec 8, 2017 at 12:00am (UTC)  |
+---------------------------------+--------------+--------+------------------------------------------+---------+----------+-------------------------------+
drunkard@thebar:~$

Am I supposed to know about "amd64" from the above somehow, and somehow know that a slash must precede it in the "images:" part of the lxc launch command?

Thanks,
bg

wpeckham · 12-10-2017, 07:47 AM

I stopped using LXC a couple of years ago, but as I recall the image is a template location on the image server. In creating a new container you are installing from an image, which is automatically downloaded from the image server if it is not found on the local host. This is all covered, although not clearly, in the lxc/lxd documentation.

The Ubuntu folks seem to document mostly for people who do not care HOW it works, but only "how to do the next step" without knowing WHY. The information IS out there, but you may have to dig a little.

simosx · 12-10-2017, 03:30 PM

First of all, it is interesting to have a way to convert a host into a container.
The maintainer of LXD has a presentation for the FOSDEM conference that talks about that.

Second, to get the raw documentation, look into https://github.com/lxc/lxd/tree/master/doc

For your question, there are two official amd64 images for Centos in the images: repository,

Code:

| centos/6 (3 more)               | 84e21ff4a00f | yes    | Centos 6 amd64 (20171210_02:16)          | x86_64  | 75.58MB  | Dec 10, 2017 at 12:00am (UTC) |
| centos/7 (3 more)               | 007272ac2dde | yes    | Centos 7 amd64 (20171210_02:16)          | x86_64  | 82.22MB  | Dec 10, 2017 at 12:00am (UTC) |

Their respective names are centos/6 and centos/7. Each have 3 more aliases (not shown yet), and also have a fingerprint (the 84e21ff4a00f) that you can use instead.
Let's figure out those aliases.

Code:

$ lxc image info images:centos/6
Fingerprint: 84e21ff4a00f04c1e9eb2ad126f9de980d6eb00ec5e5f993da5b65680dcacd7d
Size: 75.58MB
Architecture: x86_64
Public: yes
Timestamps:
    Created: 2017/12/10 00:00 UTC
    Uploaded: 2017/12/10 00:00 UTC
    Expires: never
    Last used: never
Properties:
    architecture: amd64
    serial: 20171210_02:16
    description: Centos 6 amd64 (20171210_02:16)
    os: Centos
    release: 6
Aliases:
    - centos/6/default
    - centos/6/default/amd64
    - centos/6
    - centos/6/amd64
Cached: no
Auto update: disabled

Therefore, the following are all equivalent,

Code:

lxc launch images:centos/6
lxc launch images:centos/6/default
lxc launch images:centos/6/default/amd64
lxc launch images:centos/6/amd64
lxc launch images:84e21ff4a00f
lxc launch images:84e21ff4a00f04c1e9eb2ad126f9de980d6eb00ec5e5f993da5b65680dcacd7d

You can see that amd64 is the default, and if you do not want the default, you need to specify i386.

You can see more about what to do with LXD images at https://stgraber.org/2016/03/30/lxd-...anagement-512/
You can use a container image as a base to make your own image and so on.

Full documentation for the images and how they were created, at https://us.images.linuxcontainers.org/

You may want to have a look at the LXD forum, at https://discuss.linuxcontainers.org/

bgoodr · 12-10-2017, 06:55 PM

The lxc image info command was what I missed. Thanks for both of you for your responses!