Oneshot daemon freezes install on start snap "foo" (unset) services


I’ve defined a daemon command specified for a snap. This command is designed to run only at certain instances and exit. I defined the command in the snapcraft.yaml as:

    command: bin/
     command: bin/
     daemon: oneshot
       - removable-media

Here there is a command that is defined not as a service, plus our daemon service. When I go to install the snap. It hangs on install

Start snap "foo" (unset) services

If I remove the oneshot daemon from the snapcraft.yaml it installs fine.
is there a proper way to define a oneshot daemon?


Thanks for reporting this. I was able to reproduce the problem although under some very specific conditions. Namely I had to make the ‘oneshot’ service loop or otherwise not terminate within a reasonable time.

The way snapd works is that we start all the services when a snap is getting installed. Meaning that the oneshot service gets started too by running systemctl snap.<snap-name>.<app-name>.service. For oneshot services, systemctl waits until the exec command finishes, thus blocking snapd from advancing the installation further.

Can you tell us more about the bin/ app? What does it do? How do you want it to be started? I understand it is possible for it to block if some conditions are not met.


Hi I’ll check through it. The tries 3 times to mount the usb. This oneshot daemon in normal usage is designed for running on a udev daemon when a usb is inserted for mounting the usb and then doing some stuff (like copying files). I haven’t set these up for the snap environment (I’m porting from a classic environment.) its likely that there is a loop somewhere that is hanging.

My questions around the way to run script on usb insertion is here


Ended up being path errors with the daemon script. If the script runs without errors, then install will proceed nicely.