How to use "command:"

snapcraft
1

Hello, I’m trying to create my first snap from the Hypnotix project just for playing with snapcraft, but I can’t understand how the “command:” parameter must be used.

eg.

parts: hypnotix-unofficial: # See ‘snapcraft plugins’ plugin: python source: https://github.com/linuxmint/hypnotix.git

apps: hypnotix-unofficial: command: bin/hypnotix-unofficial plugs: [home, network, network-bind, removable-media]

returns: Failed to generate snap metadata: The specified command ‘bin/hypnotix-unofficial’ defined in the app ‘hypnotix-unofficial’ does not exist. Ensure that ‘bin/hypnotix-unofficial’ is installed with the correct path.

I read the documentation that says

Each key under apps is the command name that should be made available on users’ systems.

I thought “command:” is an “output” binary that I may name as I want, not an “input” command that should already exist on the system.

Can someone please help me to understand?

2

It isn’t an “output” binary, it is what to run when the command name is run.

It needs to match the content of the snap. The snap content comes from the parts: section.

3

Thanks for your reply, but you mean that “command:” is what to run AFTER the Snap is installed or when the snap is created?

I can’t understand why it says that The specified command ‘bin/hypnotix-unofficial’ defined in the app ‘hypnotix-unofficial’ does not exist.

In the docs they make an example creating

apps:
  hello:
    command: bin/hello

so I guess that “hello” can be whatever I want, but creating the Snap it says that ‘hypnotix-unofficial’ doesn’t exists.

4

this is relative to the toplevel of your snap, so you are telling it that executing /snap/bin/hypnotix-unofficial (or simply hypnotix-unofficial when /snap/bin is in your path) will execute:

/snap/hypnotix-unofficial/current/bin/hypnotix-unofficial

after switching into the confined namespace. you need to make sure it exists in this place when you make your command: point to it …

5

Hello, thanks for the explanation.

After many tests I understood that the command: path is the executing path of the standard application (not the snapped one). Eg. if the non-snapped application would run from /usr/bin/hypnotix the command: path should be /usr/bin/hypnotix. Can you please confirm?

Moreover I found that using /usr/bin/hypnotix - which is the right path for hypnotix binary - returns a “non exiting path” error… Looking from an online example I tried adding this stage part and it seems to work

stage:
- usr
- usr/bin

is this part necessary to use the path? It’s not written in the documentation I’m looking at (maybe it’s something which affects only me) https://snapcraft.io/docs/python-apps

The snap still doesn’t run, but it’s a little step forward :slight_smile: Thanks

6

no, this is wrong, it is the path where your part: did put the executable inside the snap, this path is relative to the top level of your snap.

i.e. if your part: does something like:

part:
  foo:
    plugin: nil
      override-build: |
        cp mybinary $CRAFT_PART_INSTALL/my/shiny/bin/path/

your command: would then look like:

apps:
  mycommand:
    command: my/shiny/bin/path/mybinary

and you would then be able to execute it as “mycommand” from /snap/bin after installation …

indeed, if the non-snapped app runs from /usr/bin/hypnotix and your part actually installed it in this path your command would then be usr/bin/hypnotix … but often building from source installs things into /usr/local/bin or somewhere else …

what helps here is to completely omit the apps block, build the snap. take a look inside the built snap where things ended up and only then create the apps block with the correct command: … one thing to not forget is that you should always omit the first slash and that everything is relative to the snaps top level.

1 Like
7

Thanks, it’s clear now.