Linux kernel and /sbin/init only system

This is a minimal example, how can you run a system with only a Linux kernel and single ELF binary.

Why?

• This uses minimal resources. It can run with less than 45 MB RAM.
• The /sbin/init acts as full user space software written in Rust --> fast, efficient and secure.
• The architecture is more secure because of this single /sbin/init system: one can't execute a reverse shell, etc., because it does't contain any binaries for that, and the system is read-only.
• The Linux distributions are very complex with weekly security upgrades. A machine running this minimal system will inherently have a smaller attack surface, thus, updates are less critical (though still important).
• The start time is very fast, from the start of booting the Linux kernel to "Hello, world from Rust!" it takes only 1.083 seconds on my laptop with i7-1165G7 CPU in Qemu and an initrd environment.

Here is a block diagram of the secure architecture:

What is sysdiag?

It serves some status information over a TCP port.

$ echo -e "mounts\n loadavg\n proc\n meminfo" | nc IPv4_or_IPv6_addr 7878

To shut this VM down:

$ echo "pwroff" | nc IPv4_or_IPv6_addr 7878

If you don't have a SLAAC router and DHCPv4 support

In one of my tests I use the docker0 bridge interface for qemu. You can connect via the link local interface, but you have to give the name of interface.

$ echo -e "meminfo\n quit" | nc fe80::5054:ff:fe12:3456%docker0 7878

For IPv4 DHCP, the udhcpd is the simplest way on the host Linux.

$ sudo apt install udhcpd
# edit /etc/udhcpd/conf (interface docker0) and the /etc/default/udhcp (no -> yes)
$ sudo systemctl restart udhcpd