Rebooter is a small HTTP server written in Go whose purpose is to install a new kernel image on the current machine and reboot on that image using GRUB. The second next reboot will select the default image again, so that rebooter can be reused without needing to SSH on the machine.

On the server:

sudo ./rebooter <disk-device> <menu-entry>
# e.g.: sudo ./rebooter /dev/sdb myOS

And from a client:

curl http://<server-url>:8080/ --data-binary @<path-to-kernel-image>

• A GNU/Linux distribution, e.g. Ubuntu, with GRUB.
• A free disk or partition to use for the image.
• A GRUB menu entry corresponding to the target disk device must be created.

Adding a new menu entry:

Menu entries can be added by editing one of the files under /etc/grub.d (e.g. 40_custom in ubuntu), and then running update-grub to regenerate /boot/grub/grub.cfg.

For instance, this will add a "myOS" menu entry booting on the second hard drive (GRUB starts from hd0), i.e. /dev/hdb in Linux parlance.

menuentry "myOS" {
    set root="(hd1)"
    chainloader +1
}

With systemd:

Create a file /etc/systemd/system/rebooter.service and add the following content:

[Unit]
Description=Start the rebooter HTTP server

[Service]
Type=oneshot
ExecStart=/bin/sh -c "/path/to/rebooter <disk-device> <menu-entry>"

[Install]
WantedBy=multi-user.target

Then enable the service

sudo systemctl enable --now rebooter.service

See stack-overflow question.

Be very careful about which disk to target, this disk content will get overwritten!