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Prior to Ubuntu 12.04 the udev database was available and updated at /dev/.udev/db but in 12.04 and greater, the directory /dev/.udev/ exists but the database doesn't. Does anyone know where it went?

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After running an strace on the udevadm info command, I saw that it now looks in /run/udev/data. However, instead of the devices being listed by kernel name (e.g. /dev/sda or /dev/sdb), they are listed by their major and minor number and device type.

So I ran strace -f -e open udevadm info -q all -n /dev/sda and I saw:

open("/run/udev/data/b8:0", O_RDONLY|O_CLOEXEC) = 3

It opens b8:0 because /dev/sda is a block special file with a major number of 8 and a minor number of 0. You will also see other data files like c10:1 and input:input1. I don't know what the input is for, but I know that the c is for character special files and the 10:1 is for a major number of 10 and a minor number of 1.

I found the information about block special files and character special files by looking at man mknod.

As a note: I am running Ubuntu 13.04 and udevadm version 175.

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