Where is vmlinux on my Ubuntu installation?

The easiest(and non-hacky) way to obtain vmlinux under Ubuntu is to add ddebs repository:

echo "deb http://ddebs.ubuntu.com $(lsb_release -cs)-updates main restricted universe multiverse
deb http://ddebs.ubuntu.com $(lsb_release -cs)-security main restricted universe multiverse
deb http://ddebs.ubuntu.com $(lsb_release -cs)-proposed main restricted universe multiverse" | \
sudo tee -a /etc/apt/sources.list.d/ddebs.list

sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 428D7C01

and install kernel debug symbols:

sudo apt-get update
sudo apt-get install linux-image-$(uname -r)-dbgsym

vmlinux then can be found here:

/usr/lib/debug/boot/vmlinux-$(uname -r)

Hm, just wanted to put this as a comment to the above answer by @paxdiablo, but cannot find the comment button? Anyways..

The thing is that the vmlinuz file is compressed - and for debugging purposes, you need an uncompressed vmlinux one (and preferably one built with debugging symbols - which the default vmlinuz-es coming with Ubuntu do not have, as they are stripped of symbols).

Now, it is possible to unpack a vmlinuz into a vmlinux file - however, that is not trivial; first you have to find a byte offset in vmlinuz where the compressed file starts, and then use dd and zcat to unpack only the necessary part. In detail, this is explained in: "[ubuntu] How to trace this bug? - Ubuntu Forums - post #4"; in brief, below is my example terminal command log, based on that post:

$ od -A d -t x1 /boot/vmlinuz-$(uname -r) | grep '1f 8b 08 00' --colour
0013920 f3 a5 fc 5e 8d 83 70 23 3d 00 ff e0 *1f 8b 08 00*

$ wcalc 13920+12
 = 13932

$ dd if=/boot/vmlinuz-$(uname -r) bs=1 skip=13932 | zcat > vmlinux-$(uname -r)
4022132+0 records in
4022132+0 records out
4022132 bytes (4,0 MB) copied, 42,1695 s, 95,4 kB/s

gzip: stdin: decompression OK, trailing garbage ignored


$ file vmlinux-2.6.32-25-generic 
vmlinux-2.6.32-25-generic: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), statically linked, stripped

Well, hope this helps,

Cheers!

you can download source and compile your own using the following command:

apt-get source linux-image-$(uname -r)
apt-get build-dep --no-install-recommends linux-image-$(uname -r)
cd linux-2.6.32/
fakeroot make -f debian/rules binary-generic skipdbg=false  

or you can download the ddeb package here and install it by sudo dpkg -i linux-image-3.2.0-60-virtual-dbgsym_3.2.0-60.91_amd64.ddeb