Quick Start

Provided a starting point for using QEMU's microvm machine type.

QEMU
microvm is minimalist machine type without PCI nor ACPI support.
- Inspired by Firecracker
- Designed for short-lived guests.

Quick Start

Build initial root file system: podman run --rm -v .:/work --workdir /work public.ecr.aws/docker/library/alpine:3.22.4 create-bb-initframfs.sh
Build kernel - TODO
Run qemu-system-x86_64 -m 512m -append 'console=hvc0 reboot=triple' -kernel .\linux6.18-virtio-donno-net.bzImage -M microvm,rtc=off,acpi=off,pic=on,pit=on -device virtio-serial-device -chardev stdio,id=virtiocon0,mux=on -device virtconsole,chardev=virtiocon0 -mon chardev=virtiocon0 -device virtio-net-device,netdev=net-uDC8gBXd0 -netdev user,id=net-uDC8gBXd0 -display none -initrd .\bbmicrovm-initramfs -accel whpx
- Tweak accel from whpx to kvm if on Linux instead of Windows.

Components

Linux Kernel
Initial RAM file system (initramfs)
- Busybox - Shell, shell tools and init system.
- Dropbear - SSH Server
QEMU

Linux Kernel

Rough notes which I plan to clean-up.

I used Alpine 3.22.

apk add alpine-sdk flex bison gawk bc ncurses-dev elfutils-dev git
- The other packages are needed for building.
- git was used to clone the repository. A tar could have been used instead.
- ncurses-dev is needed for the configuration menu.
- elfutils-dev was needed for gelf.h

difftool may be useful needed to avoid diff: unrecognized option: Icaused by BusyBox's diff applet.

git clone --depth 1 --branch "v6.18" https://github.com/torvalds/linux
make tinyconfig
make menuconfig
make -j4
cp arch/x86/boot/bzImage /mnt/d/vms/qemu/linux6.18-virtio-donno-net.bzImage
cp System.map /mnt/d/vms/qemu/linux6.18-virtio-donno-net.System.map
cp .config /mnt/d/vms/qemu/linux6.18-virtio-donno-net.config

Kernel Configuration

Assume all the options below should be enabled when listed unless otherwise told to disable.

Linux Kernel Configuration
- 64-bit Kernel
- Process type and features
  - Symmetric multi-processing support
  - Linux Guest support

TODO:

Consider Device Drivers -> Generic Driver Options -> Maintain a devtmpfs filesystem to mount at /dev (CONFIG_DEVTMPFS=y)

Initial RAM file system

This was built in a Linux container (Alpine 3.23.4) where a directory on the host was volume mounted to /host within the container.

The file system is in the archive of the cpio format which is then gzipped. The Linux kernel will extract it into the root file system once it boots up. It will then execute the "init" to bring up the system. Typically, it will use this to mount the block device that has the real root device, in our case we simply run from the initial file system for now.

(cd bin && ./busybox --list | xargs -n1 -P8 ln -s busybox)
find . | cpio -o -H newc --owner=root:root > /host/bbmicrovm-initramfs

Additional files will end up as:

/etc/passw - Define users (the password file)
/etc/hostname - Define the host name - this is read during init and set as the hostname of the machine.
/etc/group - Define groups
/etc/shadow - Define the passwords
/etc/fstab - Define describesfile systems that can be mounted (mount -a)
/etc/resolv.conf - Define namespaces for resolving domain names.
/etc/inittab - configuration file for the init daemon (BusyBox's init).
/etc/init.d/rcS
/etc/init.d/S99setup-network

Additional symlinks

/var/run to /run

BusyBox + SSH

The initial RAM file system came to 2,422,800 bytes uncompressed and 1,244,123 bytes compressed or 4733 blocks. Coupled with the Linux kernel was 2,892,800 bytes.

On Windows host, /init started at 0.336004 seconds and ssh at 4 seconds.

File listing (excluding directories)

/bin/dropbear
/bin/busybox (+ symlinks)
/home/donno/.ssh/authorized_keys
/etc/fstab
/etc/hostname
/etc/network
/etc/inittab
/etc/shadow
/etc/passwd
/etc/init.d
/etc/init.d/rcS
/etc/init.d/S90setup-network
/etc/init.d/S91setup-sshd
/etc/resolv.conf
/etc/group
/mystart.sh - This could have been removed.

# Linux
ssh -o "UserKnownHostsFile /dev/null" -p 2222 root@localhost

# Windows
ssh -o "UserKnownHostsFile NUL" -p 2222 root@localhost

Build

podman run --rm -v .:/work --workdir /work public.ecr.aws/docker/library/alpine:3.22.4 create-bb-initframfs.sh

Interactive Build

podman run -it --rm -v .:/work --workdir /work public.ecr.aws/docker/library/alpine:3.22.4
# Within container:
./create-bb-initframfs.sh
vi /busybox-root/mystart.sh
./create-bb-initframfs.sh

TODO: Consider making this automated -> shell script for adding a build and edit-build (edit a file with vi then rebuild on close).

QEMU

The following command is for Microsoft Windows with the Hypervisor Platform (whpx), but you should likely be able to change that for kvm for a Linux host.

qemu-system-x86_64 -smp 2 -m 512m -append 'printk.time=1 console=hvc0' -kernel .\linux6.18-virtio-donno-net.bzImage -M microvm,rtc=off,acpi=off,pic=on,pit=on,accel=whpx -device virtio-serial-device -chardev stdio,id=virtiocon0,mux=on -device virtconsole,chardev=virtiocon0 -mon chardev=virtiocon0 -device virtio-net-device,netdev=net-uDC8gBXd0 -netdev user,id=net-uDC8gBXd0,ipv6=off -display none -initrd bbmicrovm-initramfs

For using the normal machine type, which is how some of it was tested

-kernel .\linux6.18-virtio-donno-net.bzImage -initrd bbmicrovm-initramfs --append "console=ttyS0" -serial stdio  -device virtio-net-pci,netdev=net-uDC8gBXd0 -netdev user,id=net-uDC8gBXd0,ipv6=off

When using the custom kernel, -nic user -net user can't be used as that expects a normal emulated network card rather than the virtio-net based card.

Command Breakdown

-smp 2 specific the use of 2 cores
-m 512m specifics allocation of 512 megabytes of memory for the VM.
-kernel specifies the compressed kernel image to use.
-M specifics the machine type
- microvm - The machine type that controls what devices are provided.
- accel=whpx - Use acceleration via the Windows Hypervisor Platform.
- rtc=off - Turn off MC146818 RTC - Real-Time Clock
- acpi=off
- pic=on - Turn on i8259 PIC - Programmable interrupt controller
- pit=on - Turn on i8254 PIT - Programmable interval timers
initrd specifies the initial RAM disk to use.
Kernel command line (provided via -apend)
- printk.time=1 - Adds the unmodified local hardware clock timestamp to printk messages. Essentially provides easy way to see the boot time.
- earlyprintk=hvc0 console=hvc0 - Use the virtual console for output.
- reboot=triple - Informs the kernel to perform a triple fault which is how QEMU's recommended way to trigger a guest-initiated shut down.
Set-up virtual console using the virtio-serial-device and output it to stdio.
- The mux=on allows it to also be connected to QEMU monitor via the -mon argument.
- By extension configure QEMU monitor to output to standard output.
Set-up virtio network device
Disable the display as there is no VGA device (-display none)

Journey

This is the longer form version of the journey to where I ended up getting to.

First initial RAM file system

The first iteration with a handwritten script to serve as init.

mkdir busybox-root && cd busybox-root
mkdir -p bin dev etc lib mnt proc sys tmp var home
wget -O bin/busybox https://busybox.net/downloads/binaries/1.35.0-x86_64-linux-musl/busybox
cat > init << EOF
#!/bin/busybox sh
/bin/busybox --install /bin
mount -t proc proc /proc
mount -t sysfs sysfs /sys
mount -t devtmpfs devtmpfs /dev
mount -t tmpfs tmpfs /tmp
sh
EOF
cat > etc/passwd << EOF
root:x:0:0:root:/root:/bin/sh
nobody:x:65534:65534:nobody:/:/sbin/nologin
EOF
cat > etc/group << EOF
root:x:0:root
nobody:x:65534:
EOF
find . | cpio -ov --format=newc | gzip --best > /host/bb-initramfz && find . | cpio -ov --format=newc > /host/bb-initramfs && echo "Built images"

The passwd and group were set-up as I was trying out mdev and that dealt with different users.
The command at the end rebuilds the images.
I suspect that this init failed when using the kernel built ourselves because the CONFIG_BINFMT_SCRIPT option was not provided.. The documentation even says

Most systems will not boot if you say M or N here. If unsure, say Y.

Using BusyBox's init

The piece of this puzzle I was missing and didn't understand was /etc/inittab in the final image.

Essentially instead of commands in the init shell script, the commands to run can be put in the inittab under sysinit which as the name suggests occurs when you do the init.

::sysinit:/bin/mount -a
::sysinit:/bin/hostname -F /etc/hostname
::sysinit:/bin/mkdir -p /dev/pts
::sysinit:/bin/ln -sf pts/ptmx /dev/ptmx
::sysinit:/bin/mount -t devpts -o gid=5,mode=620,ptmxmode=666 devpts /dev/pts
::sysinit:/bin/mkdir -p /dev/shm
::sysinit:/bin/mount -t tmpfs -o mode=1777,nosuid,nodev tmpfs /dev/shm
::sysinit:/bin/ip link set lo up
::ctrlaltdel:/bin/reboot
::shutdown:/bin/echo SHUTTING DOWN
::shutdown:/bin/umount -a -r
tty1::respawn:/bin/getty 38400 tty1
tty2::askfirst:/bin/getty 38400 tty2
tty3::askfirst:/bin/getty 38400 tty3
tty4::askfirst:/bin/getty 38400 tty4

What about mounting /dev and /proc?
- That is handled by /etc/fstab
```
devtmpfs /dev devtmpfs defaults 0 0
proc /proc proc defaults 0 0
```
- The question to follow-up is, why isn't /dev/shm setup through fstab?
Since this reads /etc/hostname that file needs to be created. echo bbmicrovm > etc/hostname
- It would be good to be able to set this via a kernel parameter so its provided on the command line of the kernel.
Downside is due to the use of getty it now wants to login rather than auto-login.
- This requires setting up /etc/shadows with a password.
To save me having to add an entry every time I wanted to try something else out on initalisation, I added ::sysinit:/bin/sh /mystart such that it will call the script mystart.

Various Issues

mount: mounting devpts on /dev/pts failed: No such device

The first error was due kernel and /etc/inittab configuration
- The problematic line of the inittab was ::sysinit:/bin/mount -t devpts -o gid=5,mode=620,ptmxmode=666 devpts /dev/pts
- This is simply because those the pseudo teletype terminal wasn't configured. I didn't write down which kernel configuration this was related to.
- The other /dev/pts parts are also removed.

Inital error
mount: mounting tmpfs on /dev/shm failed: Invalid argument

Call through strace.
mount("tmpfs", "/dev/shm", "tmpfs", MS_NOSUID|MS_NODEV|MS_SILENT, NULL) = -1 EINVAL (Invalid argument)

CONFIG_TMPFS is false but grep -i tmpfs /proc/filesystems included tempfs.

Filesystems -> Pseudo filesystems -> Tmpfs virtual memory file system support (former shm fs),
"Tmpfs POSIX Access Control Lists " was turned on as wel.

That worked they now mounted.

~ # mount
rootfs on / type rootfs (rw,size=246996k,nr_inodes=61749)
devtmpfs on /dev type devtmpfs (rw,relatime,size=246996k,nr_inodes=61749,mode=755)
proc on /proc type proc (rw,relatime)
tmpfs on /run type tmpfs (rw,nosuid,nodev,relatime,size=50336k,mode=755)
tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev,relatime)
devpts on /dev/pts type devpts (rw,relatime,mode=600,ptmxmode=666)

Building Kernel

Since my host operating system is Microsoft Windows, I used the Alpine 3.22 distribution I had in WSL2.

The main source for setting-up the kernel was bluedragon1221's minimal Linux project. This also served as a great example of what I was missing from being able to use BusyBox's init instead of my own shell script.

apk add alpine-sdk flex bison gawk bc ncurses-dev elfutils-dev git
- The other packages are needed for building.
- git was used to clone the repository. A tar could have been used instead.
- ncurses-dev is needed for the configuration menu.
- elfutils-dev was needed for gelf.h

git clone --depth 1 --branch "v6.18" https://github.com/torvalds/linux
make tinyconfig
make menuconfig
make -j4
cp arch/x86/boot/bzImage /mnt/d/vms/qemu/linux6.18-virtio-donno-net.bzImage
cp System.map /mnt/d/vms/qemu/linux6.18-virtio-donno-net.System.map
cp .config /mnt/d/vms/qemu/linux6.18-virtio-donno-net.config

With v3.19 (7d0a66e4b) and ended up with a 800kb kernel (bzImage).
It didn't do the logging on boot.
CONFIG_VIRTIO_MMIO - Required due to microvm machine type lacking a PCI bus.

Timings

The initial output didn't include the timing information.

NET: Registered PF_INET6 protocol family
Unpacking initramfs...
printk: legacy console [hvc0] enabled
Segment Routing with IPv6
In-situ OAM (IOAM) with IPv6

Eventually I stumped across CONFIG_PRINTK_TIME which was turned off when this kernel was built. however, thee behavior can be controlled by the kernel command line parameter printk.time=1, so that is what I used instead, as seen below:

[    0.056001] NET: Registered PF_INET6 protocol family
[    0.056001] Unpacking initramfs...
[    0.080003] printk: legacy console [hvc0] enabled
[    0.096004] Segment Routing with IPv6
[    0.096004] In-situ OAM (IOAM) with IPv6

Networking

Turned on the networking stack as seen by

NET: Registered PF_NETLINK/PF_ROUTE protocol family
NET: Registered PF_VSOCK protocol family
NET: Registered PF_INET protocol family

The latter option corresponds with CONFIG_INET

However, still had no eth0.
The cause "Network Device Support" was not enabled
- This setting was found under the Device Drivers option.
- The config name for this setting is CONFIG_NETDEVICES
Need "Virtio network driver"
- This is Device Drivers -> Network device support
- The config name for this setting is CONFIG_VIRTIO_NET
I also enabled "Wireguard secure network tunnel" just in case.

The next part was setting up DHCP so in the /mystart script added the following:

ip link show > /dev/hvc0
udhcpc --interface eth0 --foreground --script /usr/share/udhcpc/default.script > /dev/hvc0
ip link show > /dev/hvc0

The result (omitting the ip link as that isn't relevant yet) was didn't work:

udhcpc: started, v1.35.0
udhcpc: socket(AF_PACKET,2,8): Address family not supported by protocol

Need "Packet socket"
- Found Kernel Configuration -> Networking Support -> Networking options
- The CONFIG_PACKET configuration corresponds to a module called af_packet.

Rerunning it:

udhcpc: started, v1.35.0
udhcpc: broadcasting discover
udhcpc: sendto: Network is down
udhcpc: read error: Network is down, reopening socket

Fix: ip link set eth0 up first.

It still wasn't working, but at least once I ended up with:

udhcpc: started, v1.35.0
udhcpc: broadcasting discover
udhcpc: broadcasting select for 10.0.2.15, server 10.0.2.2

Take step back and try static IP with ip addr add 192.168.1.100/24 dev eth0 which resulted in error, which was hard to find, needed to copy a static version of strace into the image.

socket(AF_UNIX, SOCK_DGRAM|SOCK_CLOEXEC, 0) = -1 EAFNOSUPPORT (Address family not supported by protocol)

That problem can be fixed by enabling Unix Domain Sockets.
- In the config it is under Networking support -> Networking options -> Unix domain sockets

There is the following message output from dmesg:

could not register sysctl

Need "Sysctl support"
- This enables /proc/sys
- The sysctl interface provides a means of dynamically changing certain kernel parameters and variables on the fly without requiring
- Found Kernel Configuration -> File systems -> Pseudo filesystems > Sysctl support (/proc/sys)
- This is the CONFIG_PROC_SYSCTL configuration option.
- The warning associated with this is it will add 8KB to the kernel.

Still doesn't work it gets stuck (no IP is selected) and when an IP is selected it never returns.

Progress: discovered /etc/network/interfaces is used by ifup and the build of BusyBox that is being used doesn't include that applet so its configuration is pointless. Switching to a purely manual approach, does improve it but hits an error:

ip addr add 10.0.2.15/24 dev eth0
ip route add default via 10.0.2.2
ip link set eth0 up

The error is:

ip: RTNETLINK answers: Network unreachable

The fix is to set-up the link first.

ip link set eth0 up
ip addr add 10.0.2.15/24 dev eth0
ip route add default via 10.0.2.2

Now there is no errors and:

ip addr show eth0 2>&1 > /dev/hvc0

Outputs:

4: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether 52:54:00:12:34:56 brd ff:ff:ff:ff:ff:ff
    inet 10.0.2.15/24 scope global eth0
       valid_lft forever preferred_lft forever
    inet6 fe80::5054:ff:fe12:3456/64 scope link tentative
       valid_lft forever preferred_lft forever

Next problem is the networking is hanging, wget and nslookup.

This is due to the Windows Hypervisor Platform (WHPX) having issues delivering interrupts due to pic=on on Microsoft Windows 10 as per the QEMU documentation. The fix is to turn on CONFIG_KVM_GUEST as the documentation from 6.18.13 states:

It includes a paravirtualized clock, so that instead of relying on a PIT (or probably other) emulation by the underlying device model, the host provides the guest with timing infrastructure such as time of day, and system time

This setting was under Processor type and features -> Linux guest support >

KVM Guest support (including kvmclock). This in turn meant turning on CONFIG_HYPERVISOR_GUEST which enables basic hypervisor detection and platform setup.

The expectation if this works is cp /proc/interrupts /dev/hvc0 should show show IO-APIC next to the interrupt for the VirtIO network device. However, in my case it still stays XT-PIC, however after playing around it ended up saying IO-APIC. That said, when I turn off pic and pit on QEMU, there is no output from QEMU after it says the accelerator is operational

The following should be in the output of dmesg:

IOAPIC0: apic_id 2, version 32, address 0xfec00000, GSI 0-23

Before

  0:         29   XT-PIC      timer
  2:          0   XT-PIC      cascade
 11:          2   XT-PIC      virtio1
 12:         15   XT-PIC      virtio0

After Removing noapic nolapic acpi=off from the kernel command line, the last option was doing nothing as it is being ignored anyway.

  0:         66  IO-APIC   2-edge      timer
  2:          0   XT-PIC      cascade
 11:          2  IO-APIC  11-edge      virtio1
 12:         18  IO-APIC  12-edge      virtio0

Now check the network is working by adding the following to the mystart.sh

wget http://ifconfig.me/all -O -

Set-up SSH Server

For this, the plan is to use dropbear which can be statically compiled.

wget -O bin/dropbear https://static-binaries.gitlab.io/dropbear/dropbear-2019.78.x86_64-linux-android
chmod +x bin/dropbear

Trying to run it in the foreground to ensure we have everything working:

Added command /bin/dropbear -F -R 2>&1 > /dev/hvc0 to /mystart.sh
setsockopt(4, SOL_IPV6, IPV6_TCLASS, 16, 4) = -1 ENOPROTOOPT (Protocol not available)
openat(AT_FDCWD, "/var/run/dropbear.pid", O_WRONLY|O_CREAT|O_TRUNC, 0666) = -1 ENOENT (No such file or directory)
- /var/run is for run-time variable data and has since been moved to /run but Dropbear seems to be following the old ways.
  - It is valid to implement /var/run as a symlink to /run.
- Due to the folder not existing it means it is unable to write the pid file so it won't be able to detect if it is already running.
The server keys are not created until the first user tries to connect.
- This requires /etc/dropbear/ to exist.
Can't SSH as root with a password as that is disallowed by default, so the set-up a normal user account for that.

This is resulting in

Login attempt for nonexistent user

The user can be logged in interactive.*
Log message comes here: https://github.com/mkj/dropbear/blob/672f5963a525c167dc6c103b86d2aa1aceb1a3ec/src/svr-auth.c#L262

Confirming permissions:

drwxr-xr-x    3 root     root           0 May 12  2026 .
drwxr-xr-x   14 root     root           0 Jan  1 00:00 ..
drwxr-xr-x    3 donno    users          0 May 12  2026 donno
total 0
drwxr-xr-x    3 donno    users          0 May 12  2026 .
drwxr-xr-x    3 root     root           0 May 12  2026 ..
drwx------    2 donno    users          0 May 12  2026 .ssh
total 4K
drwx------    2 donno    users          0 May 12  2026 .
drwxr-xr-x    3 donno    users          0 May 12  2026 ..
-rw-------    1 donno    users        462 May 12  2026 authorized_keys

Tried adding /etc/shell.

I took a break here and did the Valey part. The problem seemed to be with the version of dropbear I was using. Updating to version 2026.91, gave progress.

[53] Jan 01 00:00:00 Not backgrounding
[54] Jan 01 00:00:08 Child connection from 10.0.2.2:50289
[54] Jan 01 00:00:08 Generated hostkey /etc/dropbear/dropbear_ecdsa_host_key, fingerprint is SHA256:hyX6N9so323/GHx7zhbdRUJYcdRoPimsNAChDQk8acI
[54] Jan 01 00:00:09 Pubkey auth succeeded for 'donno' with ssh-rsa key SHA256:sfHZhHKkXNMnspPTa2eZSkZ2/XPdYEGUeuoUfvtjFlA from 10.0.2.2:50289
[54] Jan 01 00:00:09 pty_allocate: openpty: No such file or directory
[54] Jan 01 00:00:09 No pty was allocated, couldn't execute
[54] Jan 01 00:00:09 Exit (donno) from <10.0.2.2:50289>: Error reading: Connection reset by peer

The INSTALL.md for dropbear happens to metion about openpty.

If openpty() is being used (HAVE_OPENPTY defined in config.h) and it fails, you can try compiling with --disable-openpty.
I suspect this may need CONFIG_UNIX98_PTYS from Device Drivers -> Character devices -> Unix98 PTY support, however that option seemed to have disappeared after I disabled the expert mode and the setting is enabled on the config.
The problem was there is no /dev/pts, needed to add mount -t devpts devpts /dev/pts -o gid=5,mode=620.

Connecting and disconnecting:

[58] Jan 01 00:00:06 lastlog_perform_login: Couldn't stat /var/log/lastlog: No such file or directory
[58] Jan 01 00:00:06 lastlog_openseek: /var/log/lastlog is not a file or directory!
[58] Jan 01 00:00:06 wtmp_write: problem writing /dev/null/wtmp: Not a directory
[57] Jan 01 00:00:32 wtmp_write: problem writing /dev/null/wtmp: Not a directory
[57] Jan 01 00:00:32 Exit (donno) from <10.0.2.2:51233>: Disconnect received

When building Dropbear there is an option to disable lastlog (--disable-lastlog) which could be the simpler option. The idea of this VM was short lived / not persistent so the log wouldn't be all taht useful anyway.
When building Dropbear there is an option to disable wtemp (--disable-wtmp) which is meant to also store uuser logins, logouts, system boots, and shutdowns. To view them you can type last in a shell.

The final result was the initial RAM filesystem came to 2,422,800 bytes uncompressed containing and the Linux kernel was 2,892,800 bytes:

Busybox
Dropbear
Several small text files

For Linux there were some kernel models that are unused:

Wireguard
i8042: No controller found

Valkey

Instead of hosting SSH considered what if the plan was to run an appliance.

In this case, an existing container image will be used

wget https://github.com/opencontainers/umoci/releases/download/v0.6.0/umoci.linux.amd64
wget https://github.com/lework/skopeo-binary/releases/download/v1.20.0/skopeo-linux-amd64
chmod +x umoci.linux.amd64 skopeo-linux-amd64
./skopeo-linux-amd64 --insecure-policy copy docker://docker.io/valkey/valkey:9.0.0 oci:valkey:9.0.0
./umoci.linux.amd64 unpack --image valkey:9.0.0 /busybox-root/opt/valkey

To the /mystart.sh script added:

echo Running valkey > /dev/hvc0
chroot /opt/valkey/rootfs ./usr/local/bin/valkey-server 2>&1 > /dev/hvc0
reboot

Re-built the image and ran it.

[    0.980043]     TERM=linux
Hello from mystart.sh
Running valkey
The futex facility returned an unexpected error code.
Aborted

The much larger initial RAM file system has made it take quite a bit longer to boot.
The program fails as when compiling the kernel, the futex feature wasn't enabled.
- Found under Linux Kernel Configuration -> General setup -> Configure standard kernel features (expert users) -> Enable futex support
- CONFIG_FUTEX.
- This was hard to find, I then discovered you can search in menuconfig by typing / and a search box appears.
If this did work, then would added hostfwd=tcp::2229-:6379 to map 6379 within the VM to port 2229 on the host.

next one:

46:M 01 Jan 1970 00:00:01.180 * oO0OoO0OoO0Oo Valkey is starting oO0OoO0OoO0Oo
46:M 01 Jan 1970 00:00:01.184 * Valkey version=9.0.0, bits=64, commit=00000000, modified=0, pid=46, just started
46:M 01 Jan 1970 00:00:01.184 # Warning: no config file specified, using the default config. In order to specify a config file use ./usr/local/bin/valkey-server /path/to/valkey.conf
46:M 01 Jan 1970 00:00:01.184 * Increased maximum number of open files to 10032 (it was originally set to 1024).
46:M 01 Jan 1970 00:00:01.184 * monotonic clock: POSIX clock_gettime
46:M 01 Jan 1970 00:00:01.184 # Failed creating the event loop. Error message: 'Function not implemented'

Where the fucntion not implemetned is:

epoll_create(1024)                      = -1 ENOSYS (Function not implemented)

Aftert sorting out futex wasn't enabled and now this onem I realised it was because an expert user section was enabled, rather than try to find the config that enables it, I simply went back and turned off the expert user setting which keeps Futex support enabled (as turning the expert setting on essentially turns of Futex).

Hello from mystart.sh
Running valkey
53:M 01 Jan 1970 00:00:01.040 * oO0OoO0OoO0Oo Valkey is starting oO0OoO0OoO0Oo
53:M 01 Jan 1970 00:00:01.040 * Valkey version=9.0.0, bits=64, commit=00000000, modified=0, pid=53, just started
53:M 01 Jan 1970 00:00:01.040 # Warning: no config file specified, using the default config. In order to specify a config file use ./usr/local/bin/valkey-server /path/to/valkey.conf
53:M 01 Jan 1970 00:00:01.040 * Increased maximum number of open files to 10032 (it was originally set to 1024).
53:M 01 Jan 1970 00:00:01.040 * monotonic clock: POSIX clock_gettime
                .+^+.
            .+#########+.
        .+########+########+.           Valkey 9.0.0 (00000000/0) 64 bit
    .+########+'     '+########+.
 .########+'     .+.     '+########.    Running in standalone mode
 |####+'     .+#######+.     '+####|    Port: 6379
 |###|   .+###############+.   |###|    PID: 53
 |###|   |#####*'' ''*#####|   |###|
 |###|   |####'  .-.  '####|   |###|
 |###|   |###(  (@@@)  )###|   |###|          https://valkey.io
 |###|   |####.  '-'  .####|   |###|
 |###|   |#####*.   .*#####|   |###|
 |###|   '+#####|   |#####+'   |###|
 |####+.     +##|   |#+'     .+####|
 '#######+   |##|        .+########'
    '+###|   |##|    .+########+'
        '|   |####+########+'
             +#########+'
                '+v+'

53:M 01 Jan 1970 00:00:01.044 * Server initialized
53:M 01 Jan 1970 00:00:01.044 * Ready to accept connections tcp

I was then able to connect on valkey-cli.exe -p 2229.

The last time from printk was 0.988045 seconds and given Valkey is outputting the same time with each message it seems to suggest the actual kernel start time to was 1.04 seconds.

Future

Where to go next from this:

Build a ext3 filesystem image of the contents of the container so it can be provided to system separated and mounted to /app_root.
Going too far into containers, i.e. enable cgroups and namespaces to allow container to work such that runc does as per my previous experiment. However, at this point then this is trying to reinvent boot2container.
- It might be nice to explore setting up a Linux kernel targetting microvm for use by boot2container. There is already a minimised for QEMU kernel produced but haven't checked if it works with microvm.

TODO:

Compare configuration settings to https://github.com/bsbernd/tiny-qemu-virtio-kernel-config
Consider building own busybox - that could have saved a lot of effort with the lack of ifup. It may be needed for the hardshutdown applet to cause the VM to stop - this wasn't needed in the end enabling the APIC allowed reboot to do the triple fault.
- Alternative is try to use sysctl kernel.reboot=1" since I turned on the sysctl config. See https://docs.kernel.org/admin-guide/sysctl/kernel.html
Set-up GitHub Actions for building the file system and kernel.
Build BusyBox and Dropbear from source so there is no question about GPL conformance.
Consider addressing the following seen when running dropbear (SSH server).

setsockopt(4, SOL_IPV6, IPV6_TCLASS, 16, 4) = -1 ENOPROTOOPT (Protocol not available)

Future Kernel Options

Additional features that I would consider enabling in the future are:

File system support
- Provide a place for persistent storage
Container support (or container kernel variant)
- Namespace
- Control groups
Symmetric multi-processing support
Linux guest support
Link Time Optimization (LTO)

Initial file system

Outside of busybox which populates /bin

The folder/file list looks like so

./bin/busybox
./bin/... (symlinks to busybox here)
./dev
./root
./sbin
./sbin/init
./etc
./etc/fstab
./etc/hostname
./etc/inittab
./etc/shadow
./etc/environment
./etc/passwd
./etc/group
./init.old
./init
./mystart
./proc
./usr
./usr/sbin

Optionally a /etc/motd could be provided which will be shown when a user logins.

Reminder

Redistributing the kernel and the RAM disk is subject to the licences of the software that makes it up. For both the Linux kernel and BusyBox that is GNU General Public License, version 2

Name		Name	Last commit message	Last commit date
Latest commit History 17 Commits
.github/workflows		.github/workflows
LICENSE		LICENSE
README.md		README.md
create-bb-initframfs.sh		create-bb-initframfs.sh
linux6.18-microvm-net.config		linux6.18-microvm-net.config
make-dropbear.sh		make-dropbear.sh
make-kernel.sh		make-kernel.sh
microvm.config		microvm.config

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