[systemd-devel] Which udev action is run on boot for my device?

[Andrei Borzenkov]

25.10.2020 20:36, Marcin Kocur пишет:
> Hello,
> 
> as the topic states, I want to know which action(s) from "add",
> "remove", "change", "move", "online", "offline", "bind", and "unbind"
> were triggered on my device. Is there any way to check that?
> 
> At the beginning of  /usr/lib/udev/rules.d/49-sane.rules there is:
> 
> ACTION!="add", GOTO="libsane_rules_end"
> 
> Udevadm info doesn't show libsane_matched property for my scanner.
> 
> If I trigger the device manually with action "change", the variable is
> still not there, as per the rule.
> 
> But if I trigger it with "add", the variable is there and also uaccess
> rule gets executed.
> 
> So the ultimate quesiton is: what kind of trigger was executed on my
> device on boot time?
> 

When device is detected by kernel it emits ADD event. This may happen in
initrd where not all rules are available. Later traditionally equivalent
of "udevadm trigger" was executed; in current upstream systemd sources
this invokes

ExecStart=udevadm trigger --type=subsystems --action=add
ExecStart=udevadm trigger --type=devices --action=add


Your distribution is free to not perform udevadm trigger or to modify
service to call it with different parameters. So it is something that
cannot be answered upstream.