Many Raspberry Pi systems are required to run without a display, keyboard or mouse, with programming and control of the Pi being achieved from a PC via a network connection. This article describes how, starting from scratch, to setup your Pi (Zero upwards) to operate like this (i.e. as a Headless Server).

Pre-requisites

A Raspberry Pi of any flavour.
For initial setup either a wired ethernet connection or a display and keyboard. To use a wired ethernet connection on a Pi Zero you will need a USB Ethernet adaptor.
A PSU.
An SD card with up to date with Raspbian Buster Lite installed, you can download Raspbian Lite from here and load it onto the card as described in the linked installation guide.
A PC on the network to connect to the Pi with an ssh client. This is available by default on most Linux operating systems. For Windows you may need to install PuTTY, though I see that Windows 10 may now have an ssh client built in.

First Steps, initial configuration using wired ethernet connection

If you want to do the initial configuration using a wired ethernet connection then after burning the SD card create a file called ssh on the boot partition in order to enable ssh. You should be able to do this using the file manager on your PC as the boot partition is FAT format and can be accessed from any operating system.
Connect the pi to your network using an ethernet cable.
If you will be using wifi and the pi does not have onboard wifi then also plug in a wifi adaptor.
Power up.
Give it a minute to get going.
From the ssh client on the pc run ssh [email protected] and when it asks for a password enter raspberry. The password will not be echoed.
If it asks for a password but won’t accept it then you have probably typed it incorrectly (check you have not got caps lock on).
If instead of asking for a password it says something like ssh: Could not resolve hostname raspberrypi.local: Name or service not known then first try unplugging the ethernet cable for ten seconds then plug it back in, wait a bit, and try again. If still no joy then login to your router and find the section on DHCP leases, hopefully there you will find the pi along with the IP address the router has given it. Then run ssh [email protected] where nn.nn.nn.nn is the IP address, obviously.
If instead of asking for a password it says cannot connect then make sure you haven’t got another pi with the same host name (ie computer name), which is raspberrypi, on the network. If you have you will either have to disconnect it or change its host name.
Once you have managed to login the run sudo raspi-config and carry on as described below.

First Steps, initial configuration using keyboard and display

Connect a keyboard and Display and power up.
You should see on the display the power up log scrolling past. Wait for that to complete. Eventually it should stop with a login prompt. Don’t panic if it seems to have stopped without the login prompt, on a low powered pi it may stop for tens of seconds at a couple of points during the startup.
Once the login prompt appears type pi and Enter.
A password prompt should appear, enter raspberry and Enter. The password is not echoed. You should now be logged on.
Run raspi-config and select Interfacing Options and enable SSH, then continue as described below.

Host and Network Configuration with raspi-config

Note that raspi-config is a text application, even if you have a mouse connected you will not be able to use it. Use the cursor up/down arrows to step between selections, Enter to make a selection and Tab to move to other fields.
First you should change the default password, select that option and follow the instructions.
Next setup the network. Change the computer name (Hostname) to something other than the default of raspberrypi.
It is probably a good idea to reboot at this point in order to make sure those changes have taken (click Finish in raspi-config and you will be given an option to reboot).
Having rebooted you should now be able to login with your new password, if connecting via ssh then use ssh pi@host_name.local where host_name is the name you gave it above.
run sudo rasp-config again.
Select Localisation Options and check that the correct locale appropriate for your region for your region has been automatically selected. There will be a * against the selected one (for me in the UK this is en_GB.UTF8). Then setup the timezone.
If you want to use wifi to connect then in Network Options select Wifi and follow the instructions. Take care to enter the SSID and key correctly. When complete exit raspi-config and run ifconfig. You should see the wifi interface wlan0: and on the line below that it should show inet nnn.nnn.nnn.nnn where that is the ip address the router has allocated it on the wifi. If the inet line does not appear then it has not connected to the wifi. Assuming that it has connected then if you have been using an ethernet connection shutdown (using sudo halt), remove the ethernet connection, and power up again. You should now be able to connect again via ssh but now it will use the wifi connection.
If you have been using a keyboard and display then you should now be able to connect from your PC via wifi using ssh as described above in First Steps using an ethernet connection. Assuming that works you can shutdown (sudo halt), disconnect the keyboard and display and put them away in the cupboard, you should not need them again.

Optional - Set a fixed IP address

You may wish to set the Pi up with a fixed IP address otherwise it may be given a different address each time it connects to the network. There are two ways of doing this.

Set a fixed address in the router. This is the preferred technique if you can do it, but many older routers either do not support this or it is flaky. If your router does support this you will need to look in the router documentation to find out how. You will need the MAC address of the network interface in the Pi, which is shown in the output from ifconfig in a line below the header line for relevant interface, so for wifi look below the line for wlan0: and you will see something like

ether 00:0f:61:0c:84:4e

Where the MAC address in this case is 00:0f:61:0c:84:4e
Set the fixed address in the Pi network configuration. If you cannot do it in the router then this is the way. First determine the IP address of the pi by running ifconfig That will show information on the network connections, and under the section for eth0 (if using a wired connection) or wlan0 (if using wifi) there should be a line something like

inet 192.168.1.105 netmask 255.255.255.0 broadcast 192.168.49.255

The first address here (192.168.1.105 in this case) is the current ip address of the Pi. Check in the router config to find which addresses it will allocate dynamically to connected devices using DHCP. Often this will be something like 192.168.1.100 upwards. Then choose an address that is outside that range (such as 192.168.1.99 in this case). If you choose one inside the range then you may end up with two devices with the same address which is disastrous. The setting has to be added to the file /etc/dhcpcd.conf. You can do this using your favourite command line editor. If you have not got a favourite then you can use nano which is installed by default with Raspbian. This needs to be done with root permissions, which you can do using the sudo command. Run

sudo nano /etc/dhcpcd.conf

then scroll down to near the end where you will find an example static address specification. Remove the # characters (which are comment characters causing the line to be ignored) so you have something like

interface wlan0
static ip_address=192.168.1.99/24
static routers=192.168.1.1
static domain_name_servers=192.168.1.1 8.8.8.8

Obviously if it were eth0 that you were using then replace wlan0 with eth0. The address against routers and domain_name_servers should generally be that of the router, the fallback of 8.8.8.8 will be used if the router cannot supply an address

Save using Ctrl+O then Enter, and exit with Ctrl+X

Whether you have used option 1 or 2 above, now reboot using

sudo reboot

Give it a short while to power up and then you should be able to connect using the new address.

ssh [email protected]

Using whatever address you have chosen. You should still be able to connect using host_name.local

Update the Raspbian software

At some point it is a good idea to update all the software to the latest. This will take some time (dependent on your internet speed and on which model the Pi is), possibly an hour or more, so you can do this now or leave it till later if you like. To update:

sudo apt update && sudo apt full-upgrade

The first command updates the database describing which version of each package is available, and the second downloads the packages and updates the software. There has been a problem with updating the bluetooth driver on some boards, if the yupgrade command finishes with an error then reboot and run the complete command again and it will likely be ok.

Change the username

You may well wish to change the username from pi to something else, for security reasons if nothing else. If not then skip this section. It is preferable to change the name of the default user, rather than just adding a new one, so that the default user retains the UUID and GID 1000. If you do wish to change it then first you need to add a temporary user as you cannot change the name of a user whilst logged on as that user. I have chosen to call the user temp, but you may use what name you like. To add the temp user and add him/her to the sudo group

sudo adduser temp
sudo adduser temp sudo

You will be prompted for information, most of which can be left empty. You will also be prompted for a password for that user. Next disconnect from the pi using logout or exit and then reconnect as the temp user

ssh temp@host_name

Check that there are no processes running as the pi user

ps -u pi

should just show a heading line and no processes. Assuming that is ok then change the username pi to, for example, fred

sudo usermod -l fred pi

and rename the home folder

sudo usermod -d /home/fred -m fred

Logout then reconnect as the new user

ssh fred@host_name.local

Finally it is necessary to change fred’s group name (which will still be pi) to fred using

sudo groupmod --new-name fred pi

It is possible to remove the temp user, but I do not generally bother. There are times when it is useful to have a second user and the space used is minimal.

That is it, all done.