Triggering an action when a specific volume is connected

I have a USB key that contains my keepass2 password database and I’d like to perform some actions when it is plugged into my computer, namely:

  • Auto-mount it to some specific location
  • When the mounting is done properly, launching keepass2 on the password database file

Simple tasks I guess, but I can’t find how to do that.

I’m using Ubuntu 12.10, and it auto-mounts the device as a “media usb-key” and tries to open the images on it (even though there are none).

What is the best way to do that and to disable the ubuntu auto-mounting (so it doesn’t conflict) ?

Asked By: ereOn

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The best way of doing this would be writing your own udev rule(s) for this device. Unfortunately I can’t give any tips on how to do this as I’ve never done so. So unless someone else has a more detailed answer, google for ‘udev rules’ and look in /lib/udev for examples. Your custom udev rules should go in /etc/udev/rules.d

Answered By: Dennis Kaarsemaker

When a new device appears, udev is notified. It normally creates a device file under /dev based on built-in rules┬╣. You can override these rules to change the device file location or run an arbitrary program. Here is a sample such udev rule:

KERNEL=="sd*", ATTRS{vendor}=="Yoyodine", ATTRS{serial}=="123456789", NAME="keepass/s%n", RUN+="/usr/local/sbin/keepass-drive-inserted /dev/%k%n"

The NAME= directive changes the location of the device file, I included it for illustration purposes but it is probably not useful for your use case. The ATTRS rules identify the device; run udevinfo -a -n /dev/sdz when the drive is available as /dev/sdz to see what attributes it has. Beware that you can only use ATTRS rules from a single section of the udevinfo input (in addition, you can use ATTR rules from the initial section). See Understand output of `udevadm info -a -n /dev/sdb` for more background. This rule goes into a file called something like /etc/udev/rules.d/local-storage-keypass.rules.

Put the commands you want to run in the script given in the RUN directive. Something like:

#!/bin/sh
set -e
if [ -d /media/keypass-drive ]; then
  [ "$(df -P /media/keypass-drive | awk 'NR==2 {print $1}')" = "$(df -P /media | awk 'NR==2 {print $1}')" ]
else
  mkdir /media/keypass-drive
fi
mount "$1" /media/keypass-drive
su ereon -c 'keypass2' &

If you’re having trouble running a GUI program from a script triggered from udev, see Can I launch a graphical program on another user's desktop as root?

┬╣ Not on modern systems where /dev is on udevtmpfs.

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