Connect your serial adapter ([usbcom1a](https://pcengines.ch/usbcom1a.htm) works well if you don’t have one already) to the apu2c4 and start a program to use it, e.g. `screen /dev/ttyUSB0 115200`. Then, power on the apu2c4 and configure it to do PXE boot:
* Press `F10` to enter the boot menu
* Press `3` to enter setup
* Press `n` to enable network boot
* Press `c` to move mSATA to the top of the boot order
* Press `e` to move iPXE to the top of the boot order
* Press `s` to save configuration and exit
Connect a network cable on `net0`, the port closest to the serial console port:
Run `rtr7-recover -boot=/tmp/recovery/boot.img -mbr=/tmp/recovery/mbr.img -root=/tmp/recovery/root.img` to:
* trigger a reset [if a Teensy with the rebootor firmware is attached](#rebootor)
* serve a DHCP lease to all clients which request PXE boot (i.e., your apu2c4)
* serve via TFTP:
* the PXELINUX bootloader
* the router7 kernel
* an initrd archive containing the rtr7-recovery-init program and mke2fs
* serve via HTTP the boot and root images
* optionally serve via HTTP a backup.tar.gz image containing files for `/perm` (e.g. for moving to new hardware, rolling back corrupted state, or recovering from a disk failure)
* exit once the router successfully wrote the images to disk
## Updates
Run e.g. `rtr7-safe-update -updates_dir=$HOME/router7/updates` to:
* verify the router currently has connectivity, abort the update otherwise
* download a backup archive of `/perm`
* build a new image
* update the router
* wait until the router restored connectivity, roll back the update using `rtr7-recover` otherwise
The update step uses kexec to reduce the downtime to approximately 15 seconds.
## Manual Recovery
Given `rtr7-safe-update`’s safeguards, manual recovery should rarely be required.
To manually roll back to an older image, invoke `rtr7-safe-update` via the
`recover.bash` script in the image directory underneath `-updates_dir`, e.g.:
```shell
% cd ~/router7/updates/2018-07-03T17:33:52+02:00
% ./recover.bash
```
## Teensy rebootor {#rebootor}
The cheap and widely-available [Teensy++ USB development board](https://www.pjrc.com/store/teensypp.html) comes with a firmware called rebootor, which is used by the [`teensy_loader_cli`](https://www.pjrc.com/teensy/loader_cli.html) program to perform hard resets.
This setup can be used to programmatically reset the apu2c4 (from `rtr7-recover`) by connecting the Teensy++ to the [apu2c4’s reset pins](http://pcengines.ch/pdf/apu2.pdf):
* connect the Teensy++’s `GND` pin to the apu2c4 J2’s pin 4 (`GND`)
* connect the Teensy++’s `B7` pin to the apu2c4 J2’s pin 5 (`3.3V`, resets when pulled to `GND`)
You can find a working rebootor firmware .hex file at https://github.com/PaulStoffregen/teensy_loader_cli/issues/38
## Prometheus
See https://github.com/rtr7/router7/tree/master/contrib/prometheus for example
configuration files, and install the [router7 Grafana
