Using adb with a OnePlus X on Linux…

… is not really that hard. Just annoying. Since OnePlus’ USB ID is not in the default adb list, you need to add it yourself:
echo "0x2a70" >> ~/.android/adb_usb.ini
where 0x2a70 is the identifier for OnePlus. (you can find this with lsusb)

To add automatic permissions to the device node when it’s created, add this udev rule to /etc/udev/rules.d/51-android.rules (all on one line):

SUBSYSTEM=="usb", ATTR{idVendor}=="2a70", MODE="0666", GROUP="plugdev" ATTR{idVendor}=="2a70", ATTR{idProduct}=="9011|f003", SYMLINK+="libmtp-%k", MODE="660", GROUP="audio", ENV{ID_MTP_DEVICE}="1", ENV{ID_MEDIA_PLAYER}="1"