Udev

Usually when I plug in a usb drive, it will be allocated a slot at /dev/sda* (* denotes number 1, 2, 3 and so on). However if there were 2 usb drives or more, the drives will be allocated slots (nodes or slots? I don't know the correct terminology.) at /dev/sd* where * denotes the alphabet a, b, c and so on. This is troublesome as I mount my devices manually using the rules at /etc/fstab and it is a bother changing the rules everything to suite the alphabet sd*. Therefore now I use udev to customise the naming of device nodes. This was done by following instructions at the Gentoo Wiki.

1. My udev rules are kept in the file /etc/udev/rules.d/10-local.rules

2. Examples of rules in the file are: 

BUS=="usb", SYSFS{serial}=="00000000000000000182", KERNEL=="sd?1", NAME="%k", SYMLINK="pdrive"
BUS=="usb", SYSFS{serial}=="000000899406", KERNEL=="sd?2", NAME="%k", SYMLINK="ipod" 

3. The serial number in SYSFS{serial} is obtain as follows:

a. udevadm -a -p /sys/path/to/hardware/info - which for my pendrive and ipod is actually /dev/sda. Therefore:

i. $ udevadm -q path -n /dev/sda
That will result in /block/sda
ii. $ udevadm -a -p /sys/block/sda

b. (i) and (ii) can be combined : udevadm -a -p 'udevinfo -q path -n /dev/sda' 

4. My rules used to read 

BUS="usb", SYSFS{serial}="00000000000000000182", KERNEL="sd?1", NAME="%k", SYMLINK="pdrive" 

Note the single equal sign. That used to work until udev was upgraded to udev-103. After that the double equal signs have to be used or else the udev rules will not load with errors of 'invalid rules' and 'subsystem' not found (something like that).