udev provides powerul rules that can be used to perform custom tasks whenever there is activity on usb ports. here's what i created in /etc/udev/rules.d/99-sync_music_files_on_android_devices.rules:

    
ACTION=="add|change", ATTR{size}=="31114240", ATTRS{vendor}=="SAMSUNG", ATTRS{model}=="GT-I9003", NAME="galaxy_s_external_sd", RUN+= "mkdir /media/galaxy_s_external_sd", RUN+="mount /dev/galaxy_s_external_sd /media/galaxy_s_external_sd", RUN+="/home/vinu/bin/sync_music_files_on_android_device.sh"
ACTION=="remove", RUN+="/bin/umount -l /media/galaxy_s_external_sd", RUN+="/bin/rmdir /media/galaxy_s_external_sd"   LABEL="sync_music_files_on_android_devices_end"

the first line registers an action to add/change event of a usb device that has attributes as size: 31114240 and parent device having attributes of vendor: "samsung" and so on. you can find the attributes related to your device by using udevadm as:

   $ udevadm info -q all -n /dev/{device_label}       

udevadm is pretty interesting and can provide a lot of information about devices, shows all applicable rules for a device, and also allows testing your rules using triggers. see the udevadm man page for details.

i've also asked the device label to be custom (NAME) as: galaxy_s_external_sd so that i can refer to it that way in RUN which creates a mount point and mounts the device at the desired location. then i RUN the shell script that actually syncs the media files and logs the activity:

#!/bin/bash
rsync -r -t -v --progress --delete-before /home/vinu/Music/sync /media/galaxy_s_external_sd/Music >> /home/vinu/log/rsync.log

interesting isn't it? let me know if you try this out, or if you've done more interesting stuff related to udev or, in general with linux, through comments.

references:

http://reactivated.net/writing_udev_rules.html

http://wiki.archlinux.org/index.php/Udev -- lots of examples