[Nexus 4 Q&A, Help & Troubleshooting] digitalramble:
OK, I am trying to root my Nexus 4. What follows is a pretty comprehensive description of what I've done but the TL;DR version is that I managed to unlock my nexus4 using fastboot oem unlock -- but now fastboot and adb are very consistently (across different computers and different cables) not picking up my nexus4 anymore. I did check out MTP mounting, and that's successful. It could be that I'm misunderstanding something, but this is getting kind of frustrating. I have been using information from three or four different tutorials here on xda. So anyway, here's the grisly details:

I am running Ubuntu 12.04 (32 bit on my laptop, 64 bit on my desktop).

Now, on the LAPTOP:

Firstly I powered up my N4 (vol down + power) to get the LOCK STATE - locked information. I connected to the laptop via USB port with the cable supplied with the N4.

I went to the adt.../sdk/platform-tools (from unpacking the ADT bundle archive) directory on my laptop.

digitalramble@laptop $ sudo ./fastboot devices

this gave me a string of numbers followed by fastboot in response. [Note that this is the one and only and ever time I sucessfully listed the N4.] So far so good. Then

digitalramble@laptop $ sudo ./fastboot oem unlock
...

Again so far so good. After answering yes to the unlock question on the N4, the N4 now shows LOCKED STATE - unlocked.

Now here is where it got weird. I wanted to start up adb, so

adb devices
daemon not running, starting on 5037
list of devices attached

... and no devices. Repeated with sudo, no difference (except daemon already running. Huh.

The above is from my written notes. More detail below on the desktop as I've got all this in another window here.

That was yesterday. So then I checked with my desktop today. This is what's on my desktop:

digitalramble@desktop:~$ uname -a
Linux desktop 3.2.0-35-generic #55-Ubuntu SMP Wed Dec 5 17:42:16 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux

I downloaded the ADT Bundle. (I notice that despite checking the 32 bit on download, it seems to have given me the 64 bit version. Hm...)

digitalramble@desktop:~/SDK/adt-bundle-linux-x86_64/sdk/platform-tools$ ls
aapt aidl dexdump fastboot llvm-rs-cc renderscript
adb api dx	lib NOTICE.txt source.properties

digitalramble@desktop:~/SDK/adt-bundle-linux-x86_64/sdk/platform-tools$ sudo ./adb devices
* daemon not running. starting it now on port 5037 *
* daemon started successfully *
List of devices attached

digitalramble@desktop:~/SDK/adt-bundle-linux-x86_64/sdk/platform-tools$ sudo ./adb devices
List of devices attached

I changed the USB cable and repeated, same results. Is it the N4?

This computer wasn't set up with MTP, so I did that quickly:

digitalramble@desktop:~$ cd /etc/udev/rules.d/

digitalramble@desktop:/etc/udev/rules.d$ sudo vi 51-android.rules
[sudo] password for digitalramble:

digitalramble@desktop:/etc/udev/rules.d$ more 51-android.rules
# nexus 7
SUBSYSTEM==”usb”, ATTR{idVendor}==”18d1”, ATTR{idProduct}==”4e41”, MODE=”0666”,
OWNER=”digitalramble”
# nexus 4
SUBSYSTEM==”usb”, ATTR{idVendor}==”1004”, MODE=”0666”, OWNER=”digitalramble”

digitalramble@desktop:/etc/udev/rules.d$ sudo service udev restart
udev stop/waiting
udev start/running, process 6945

And then installed the mtp software

digitalramble@desktop:~/$ sudo apt-get install mtp-tools mtpfs

digitalramble@desktop:~/SDK/adt-bundle-linux-x86_64/sdk/platform-tools$ sudo mkdir /media/nexus4
digitalramble@desktop:~/SDK/adt-bundle-linux-x86_64/sdk/platform-tools$ sudo chmod 755 /media/nexus4
digitalramble@desktop:~/SDK/adt-bundle-linux-x86_64/sdk/platform-tools$ sudo mtpfs -o allow_other /media/nexus4
digitalramble@desktop:~/SDK/adt-bundle-linux-x86_64/sdk/platform-tools$ ls /media/nexus4
Alarms	DCIM	Movies Notifications Playlists Ringtones
Android Download Music Pictures	Podcasts
digitalramble@desktop:~/SDK/adt-bundle-linux-x86_64/sdk/platform-tools$

So I can't figure out why fastboot or adb won't list my N4? I've swapped out computers, cables, everything but the N4 itself. Yet, the N4 is working otherwise normally (it's doing what I expect on the screen, it can be listed via MTP tools. But if fastboot won't see it, how can I proceed with fastboot flash recovery recovery.img, or or fastboot boot boot.img or whatever? I was going to try to play with adb push/pull instead but neither of them are listing the N4 when I check...

Thanks for any ideas...I'm stumped. I've tried to include all the relevant bits of information.