This post is mostly a reminder for myself, because I will probably forget this (again) soon.
Sometimes you want to use a RaspberryPi as a headless machine, so first you download the newest Rasbian image, ‘dd’ it to the SD card, insert the SD card into your RaspberryPi, connect the ethernet and power cables, check the IP in your DHCP server logs, run ‘ssh <ip>‘ and..
..connection refused!
I have no idea why, but the ssh server is disabled by default (probably a security feature, since the default password is easy to guess, but still..). Then you start googling, and first couple of links all say that you need to connect the keyboard, display, log in localy, etc. etc. But you’re lazy, and want to do it directly on the PC when you write the image to the SD card. So the easiest way is, after you’re done with ‘dd’-ing, you mount the first partition (a smaller, FAT partition containing the boot files), and just create an empty ‘ssh’ file (with eg: touch ssh) in that folder.
If you also wish to enable wifi (which is enabled by default, but no configurations are stored), you also need to mount the second (ext4) partition, containing the full system – there you can edit ‘./etc/wpa_supplicant/wpa_supplicant.conf‘ file, and add your wireless configuration
After that, sync, umount, insert the card, connect all the cables, and it works!