How to set up a Raspberry Pi without a keyboard, mouse, or monitor

There are plenty of guides out there about how to set up headless Raspberry Pis, but they get out of date quickly, and I do this often enough that I'm constantly searching for up to date ones.  So for my own benefit here's my documentation of the process.

Download Raspbian Lite.  This is the version without the GUI components.

Put your SD card in your computer and use lsblk to identify which drive your SD card is. Be careful, if you use the wrong drive below you will overwrite your main hard drive.

Use dd to copy the data over.  They constantly recommend you use the program Etcher, but I've never had it work successfully.  The command is sudo dd bs=4M if=2018-10-09-raspbian-stretch-lite.img of=/dev/sde conv=fsync status=progress

Once done, your card should have 2 partitions, open the boot partition and add an empty file called ssh to enable ssh, and create a file called wpa_supplicant.conf to configure wifi.  The contents of the file are this:

country=US
ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
update_config=1

network={
    ssid="YourSSID"
    psk=abcdef1234567890
    key_mgmt=WPA-PSK
}

You can either put your actual password in there as the psk, or use the tool wpa_passphrase to convert your password into a hash that will also work.

Put the card in the Pi, boot it up, and it should connect to your network and you should be able to ssh in with username pi and password raspberry.  Note that you need to boot once for it to expand the filesystem.

You should put your public key in ~/.ssh/authorized_keys and turn off password ssh access in /etc/ssh/sshd_config.  You should also run sudo raspi-config once you ssh in, and update with sudo apt update && sudo apt upgrade