config.txt : Hostname [duplicate]

Question

As you might have guessed from the title, I would like to know if it is possible to change a RasPis hostname from the config.txt file on the SD card.

I'm making a lot of SDs from a custom image, and obviously the hostnames collide when booting (they are used from other apps in the network).

Answer 1

It is not possible to set the device hostname through config.txt. A full list of commands can be found on the Raspberry Pi Foundation's website.

An Alternative:

You mention that you're creating a custom image. In this case, I believe the best practice would be to write the assigned hostname to /etc/hostname during the card creation process. It does require a reboot (assuming the RPi is currently running), but so does changing anything in config.txt.

If you really want to get around the restart thing, it's possible, but can cause some issues. The hostname can be temporarily changed by the command sudo hostname {super_cool_name_here}. Once that's set, restart the network service with sudo service network restart.

Now, if you run hostname you should see your new hostname as active. This change is not permanent. When you restart the device it will go back to whatever is stored in /etc/hostname.

Answer 2

Okay, from your comments on the other answer, it looks like you want to change the hostname of Raspberry Pi image without actually booting it. This should be trivial. We want to modify the /etc/hostname in the second partition, so we will find its location in the image using fdisk.

fdisk -l image.img

Where image.img is your image file. Look under the start column for the second (Linux ext4) partition to find the block it starts on. Substitute that into the command below. Note that this won't change after this process, so you can change the hostname, send off the image, and then change it again, without needing to run fdisk and use a new value.

sudo mount -o loop,offset=$((TYPE_START_BLOCK_HERE*512)) image.img /mnt
nano /mnt/etc/hostname

Get rid of the default and type in the hostname you want, and then hit Ctrl-x, then y, and then enter. We can now unmount the image like this.

sudo umount /mnt

Done! Using dd to load the image onto the SD card and booting the card in a Pi will set the Pi's hostname to the one you specified above.

To automate this process and change the hostname of an image quickly between dd's, one could write a bash script:

#!/bin/bash

mkdir tst;
echo ${1:?"Set argument one to filename"} > /dev/null;
echo ${2:?"Set argument two to desired hostname"} > /dev/null;
mount -o loop,offset=$(($(fdisk -l $1 |awk '$7=="Linux"{print $2}')*512)) $1 
tst;
echo $2 > tst/etc/hostname;
umount tst;
rmdir tst;

Answer 3

Why not create a service?

[Unit]
Description=Change hostname from sd
ConditionPathExists=/boot/hostname
Before=dhcpcd.service

[Service]
Type=oneshot
ExecStartPre=/bin/bash -c 'CURRENT_HOSTNAME=$(/bin/cat /etc/hostname | /usr/bin/tr -d "\t\n\r");NEW_HOSTNAME=$(/bin/cat /boot/hostname | /usr/bin/tr -d "\t\n\r");/bin/sed -i "s/127.0.1.1.*$CURRENT_HOSTNAME/127.0.1.1\t$NEW_HOSTNAME/g" /etc/hosts'
ExecStart=/bin/mv /boot/hostname /etc/hostname
ExecStartPost=/sbin/reboot

[Install]
WantedBy=multi-user.target

Answer 4

In the 'modern' Raspberry Pi Imager using the cog wheel in the first screen allows you to set some presets including the hostname but also wifi configuration, default user name, whether SSH is enabled or not, very useful!

If you select a new hostname, this will create a file on the 'bootfs' partition of your SD card after writing. So if you do not want to use the Raspberry Pi Imager, you can also do this manually. Create a file called firstrun.sh and add this, for changing the hostname to jackfruit.local:

#!/bin/bash

set +e

CURRENT_HOSTNAME=`cat /etc/hostname | tr -d " \t\n\r"`
if [ -f /usr/lib/raspberrypi-sys-mods/imager_custom ]; then
   /usr/lib/raspberrypi-sys-mods/imager_custom set_hostname jackfruit
else
   echo jackfruit >/etc/hostname
   sed -i "s/127.0.1.1.*$CURRENT_HOSTNAME/127.0.1.1\tjackfruit/g" /etc/hosts
fi
rm -f /boot/firstrun.sh
sed -i 's| systemd.run.*||g' /boot/cmdline.txt
exit 0

and modify cmdline.txt to add systemd.run=/boot/firstrun.sh, for my 'headless raspbian' it currently looks like the below:

console=serial0,115200 console=tty1 root=PARTUUID=544c6228-02 rootfstype=ext4 fsck.repair=yes rootwait quiet init=/usr/lib/raspberrypi-sys-mods/firstboot systemd.run=/boot/firstrun.sh systemd.run_success_action=reboot systemd.unit=kernel-command-line.target%