Hi

I just solved a udev problem by adding ACTION=="add" to the rule. Before that the udev rule -- for a partition on a USB HDD -- was triggered when the USB HDD's partition was fscked.

What are the possible ACTION values and their significance?

The udev man page is coy:
Searching the /lib/udev/rules.d/* files showed ACTION values of "add", "change" and "remove" (and one "add|change").

Which changes are covered by "change"? In general they seem to be changes in a device's attributes; detail can be found by running udevadm monitor --property.

Doing so before an fsck showed two sets of changes but none of them were obviously related to fsck. Perhaps while running fsck, the kernel learns more about the partition so the "change" is "here are some more attributes" ... ?

I see by the timestamp on your post that you posted about 14 hours ago. You could have had your answer in a few minutes using a web browser.

You could have found this, from and article at Oracle.com:
It seems that ACTION is a reporting tool to match an action to a device name.

You could also have found this short article which gives one example of how to use information provided by ACTION.

Looks to me like a pretty bad example. The ACTION=="remove" rule will indeed be triggered when the device is unplugged, but by that time it's too late to run a umount script.

Thanks rknichols

Maybe I should state the questions better rather than reporting my research ...

• What are the possible actions (is add, change and remove the complete list)?
• Which events or class of events result in (the kernel communicating) a change action (to udevd)?

It turned out that adding ACTION=="add" to the rule was an incomplete fix. It fixed the problem of the RUN+= command being run when the partition on the USB HDD was fscked but it also resulted in the symlink created by SYMLINK+= being deleted.

The solution (tested but not yet by extensive usage) was to create a second rule, identical to the first except for ACTION=="change" and having no RUN+=.

The solution in the last reply has now been extensively tested and found effective.