Question (TL;DR):

For an SDcard with multiple partitions, how to get at least "change" event for the mounted nodes from udev, when an uSD or SDcard is removed from USB-SD reader, without disconnecting USB cable from your PC?

Bonus: Get "add/remove" event for "partition" nodes ( e.g "/dev/sdh2" )

What does not work:

When a partition is mounted, udev does not output any event for the partition node, when the card is removed !!!

Steps to reproduce:

• You need a USB-SD reader ( I highly recommend: https://www.kingston.com/en/flash/readers/FCR-HS4 ). But I tested on many other USB-SD readers (Such as GenesysLogic based ones), situation is the same.


• You need an uSD or SDcard , with at least 1 or 2 partition.

Step1:

Create a new udev rule, named as: /etc/udev/rules.d/98-test.rules
Content:

KERNEL!="sd*" , SUBSYSTEM!="block", GOTO="END"

LABEL="WORK"

ACTION=="add", RUN+="/usr/bin/logger *****Received add event for %k*****"

ACTION=="remove", RUN+="/usr/bin/logger *****Received remove event for %k*****"

ACTION=="change", RUN+="/usr/bin/logger *****Received change event for %k*****"



LABEL="END"

Step2:

Install ccze ( sudo apt install ccze ). This will give you beautiful colored logging for events.

Open a terminal, run following command:

journalctl -f | ccze -A

Result:

Mar 09 23:01:32 Ev-Turbo kernel: sd 6:0:0:3: [sdh] 30408704 512-byte logical blocks: (15.6 GB/14.5 GiB) 

Mar 09 23:01:32 Ev-Turbo kernel:  sdh: sdh1 sdh2 

Mar 09 23:01:33 Ev-Turbo root[19519]: *****Received change event for sdh***** 

Mar 09 23:01:33 Ev-Turbo root[19523]: *****Received change event for sdh***** 

Mar 09 23:01:33 Ev-Turbo root[19545]: *****Received add event for sdh2***** 

Mar 09 23:01:33 Ev-Turbo root[19552]: *****Received add event for sdh1*****

Step3:

Now remove the uSD card from the slot, but don't disconnect USB cable from your PC. Watch the log:

Mar 09 23:06:56 Ev-Turbo root[21220]: *****Received change event for sdh***** 

Mar 09 23:06:56 Ev-Turbo root[21223]: *****Received remove event for sdh2***** 

Mar 09 23:06:56 Ev-Turbo root[21222]: *****Received remove event for sdh1***** 

Step4:

Now, insert your uSD card again, you will see:

Mar 09 23:11:21 Ev-Turbo kernel: sd 6:0:0:3: [sdh] 30408704 512-byte logical blocks: (15.6 GB/14.5 GiB) 

Mar 09 23:11:21 Ev-Turbo kernel:  sdh: sdh1 sdh2 

Mar 09 23:11:21 Ev-Turbo root[22652]: *****Received change event for sdh***** 

Mar 09 23:11:21 Ev-Turbo root[22653]: *****Received change event for sdh***** 

Mar 09 23:11:21 Ev-Turbo root[22679]: *****Received add event for sdh2***** 

Mar 09 23:11:21 Ev-Turbo root[22682]: *****Received add event for sdh1*****

And now, try mount one of the partitions to somewhere in your system:

sudo mount /dev/sdh2 /media/uSD2

You can double check if it is really mounted ( run commands: lsblk, mount...etc)

Step5:

Now, while the partition is mounted, remove your uSD card from the slot. Watch the log:

Mar 09 23:12:32 Ev-Turbo root[23049]: *****Received change event for sdh*****

Nothing more... Why there is no "remove" event anymore???

BONUS NOTES (Irrelevant to above question):

1) Most of the info on the web regarding udev/systemd/systemd-udevd and mount scripts are obsolete. Especially, for systemd v239, many of the "solved/working" answers are not usable ( Working on the issue for 2 weeks, read most of the solutions on the web, Tested on Debian 9.7, Linux Mint 18.3, Ubuntu 18.04 )

2) For systemd versions > 212, you need service files to mount your removable devices. Example:
https://serverfault.com/questions/766506/automount-usb-drives-with-systemd

3) Especially for systemd v239, you need to disable PrivateMounts to achieve automatic mounting via systemd units. For details: https://unix.stackexchange.com/questions/464959/udev-rule-to-automount-media-devices-stopped-working-after-systemd-was-updated-t

4) Mount unit files does not fit for every case, for example, when you want to mount to some specific directories based on USB host, port,lun numbers... But for some cases, this approach is very easy: https://dev.to/adarshkkumar/mount-a-volume-using-systemd-1h2f