[Galaxy S 5 Q&A, Help & Troubleshooting] sparr0:
I'm trying to solve a battery usage problem that requires me to root my phone to get more info. I'm trying to follow various instructions for rooting my T-Mobile S5 with current baseband version ...FOG6. I'm stuck at the step of getting the TWRP (or any other) recovery installed so that I can flash unofficial images.

I've gotten adb working, so I can get into bootloader mode by either powering up the phone while holding voldown+home OR I can do `adb reboot bootloader` from my computer while the phone is in usb debugging mode. However, once it's booted into bootloader/fastboot mode and I'm looking at the "Downloading... Do not turn off target!!" screen on the phone, I can't get the fastboot tool to talk to the phone, it just gets stuck at "< waiting for device >".

Here's some potentially relevant info:

syslog entries when performing `adb reboot bootloader` (device 7 was the phone in normal usb debugging mode):

Nov 16 12:05:24 daphne-xubuntu kernel: [ 379.270044] usb 1-1.2: USB disconnect, device number 7
Nov 16 12:05:24 daphne-xubuntu kernel: [ 379.272847] cdc_acm 1-1.2:1.1: failed to set dtr/rts
Nov 16 12:05:24 daphne-xubuntu ModemManager[723]: <info> (tty/ttyACM2): released by modem /sys/devices/pci0000:00/0000:00:1d.0/usb1/1-1/1-1.2
Nov 16 12:05:24 daphne-xubuntu NetworkManager[738]: <info> (ttyACM2): device state change: disconnected -> unmanaged (reason 'removed') [30 10 36]
Nov 16 12:05:27 daphne-xubuntu kernel: [ 382.540941] usb 1-1.2: new high-speed USB device number 8 using ehci-pci
Nov 16 12:05:27 daphne-xubuntu kernel: [ 382.634182] usb 1-1.2: New USB device found, idVendor=04e8, idProduct=685d
Nov 16 12:05:27 daphne-xubuntu kernel: [ 382.634190] usb 1-1.2: New USB device strings: Mfr=1, Product=2, SerialNumber=0
Nov 16 12:05:27 daphne-xubuntu kernel: [ 382.634195] usb 1-1.2: Product: MSM8960
Nov 16 12:05:27 daphne-xubuntu kernel: [ 382.634199] usb 1-1.2: Manufacturer: Sasmsung
Nov 16 12:05:27 daphne-xubuntu kernel: [ 382.635509] cdc_acm 1-1.2:1.0: ttyACM3: USB ACM device
Nov 16 12:05:27 daphne-xubuntu mtp-probe: checking bus 1, device 8: "/sys/devices/pci0000:00/0000:00:1d.0/usb1/1-1/1-1.2"
Nov 16 12:05:27 daphne-xubuntu mtp-probe: bus: 1, device: 8 was not an MTP device
Nov 16 12:05:47 daphne-xubuntu ModemManager[723]: <info> Creating modem with plugin 'Generic' and '1' ports
Nov 16 12:05:47 daphne-xubuntu ModemManager[723]: <warn> Could not grab port (tty/ttyACM3): 'Cannot add port 'tty/ttyACM3', unhandled serial type'
Nov 16 12:05:47 daphne-xubuntu ModemManager[723]: <warn> Couldn't create modem for device at '/sys/devices/pci0000:00/0000:00:1d.0/usb1/1-1/1-1.2': Failed to find primary AT port

various command outputs after doing so:

$ lsusb | grep Samsung
Bus 001 Device 008: ID 04e8:685d Samsung Electronics Co., Ltd GT-I9100 Phone [Galaxy S II] (Download mode)
$ ls -la /dev/bus/usb/001/008
crw-rw-rw- 1 root root 189, 7 Nov 16 12:05 /dev/bus/usb/001/008
$ hexdump -C /dev/bus/usb/001/008
00000000 12 01 00 02 02 02 00 40 e8 04 5d 68 00 01 01 02 |.......@..]h....|
00000010 00 01 09 02 43 00 02 01 00 c0 19 09 04 00 00 01 |....C...........|
00000020 02 02 01 03 05 24 00 10 01 05 24 01 00 01 04 24 |.....$....$....$|
00000030 02 0f 05 24 06 00 01 07 05 82 03 10 00 09 09 04 |...$............|
00000040 01 00 02 0a 00 00 00 07 05 81 02 00 02 00 07 05 |................|
00000050 01 02 00 02 00 |.....|
00000055

What else can I try?