Kraftfile cmd not added as kernel argument

[LucaSeri]

Describe the bug

When providing a cmd in the kraftfile, for an application running through the elfloader, the following error is generated:
[ 0.117956] ERR: [appelfloader] Program name missing (no argv[1]).

This is caused because the cmd is no longer passed as a kernel argument.

Steps to reproduce

spec: v0.6

runtime: base:latest

rootfs: ./Dockerfile

cmd: ["/server"]

$ kraft run

Expected behavior

The cmd should be added.

Which architectures were you using or does this bug affect?

No response

Which operating system were you using or does this bug affect?

No response

Relevant log output

qemu-system-x86_64 -append vfs.fstab=[ "initrd0:/:extract:::" ] env.vars=[ "PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin" ] --  -cpu host,+x2apic,-pmu -daemonize -device virtio-net-pci,mac=02:b0:b0:21:8f:01,netdev=hostnet0 -device pvpanic -device sga -display none -enable-kvm -initrd .unikraft/build/initramfs-x86_64.cpio -kernel /tmp/kraft-run-4262159733/unikraft/bin/kernel -machine pc,accel=kvm -m size=64M -monitor unix:/home/kero/.local/share/kraftkit/runtime/c3aa2335-0a11-4bd1-ad81-17aecfdb20a0/qemu_mon.sock,server,nowait -name c3aa2335-0a11-4bd1-ad81-17aecfdb20a0 -netdev user,id=hostnet0,hostfwd=tcp::8080-:8080 -nographic -no-reboot -S -parallel none -pidfile /home/kero/.local/share/kraftkit/runtime/c3aa2335-0a11-4bd1-ad81-17aecfdb20a0/machine.pid -qmp unix:/home/kero/.local/share/kraftkit/runtime/c3aa2335-0a11-4bd1-ad81-17aecfdb20a0/qemu_control.sock,server,nowait -qmp unix:/home/kero/.local/share/kraftkit/runtime/c3aa2335-0a11-4bd1-ad81-17aecfdb20a0/qemu_events.sock,server,nowait -rtc base=utc -serial file:/home/kero/.local/share/kraftkit/runtime/c3aa2335-0a11-4bd1-ad81-17aecfdb20a0/machine.log -smp cpus=1,threads=1,sockets=1 -vga none

[LucaSeri]

On further inspection, this seems to be overwritten when building the rootfs, here: https://github.com/unikraft/kraftkit/blob/staging/internal/cli/kraft/run/utils.go#L410
I am not sure what the interaction should be between:

• Dockerfile's CMD
• Kraftfile's cmd

In my case, I have a Dockerfile with no CMD:

FROM golang:1.21.3-bookworm AS build

WORKDIR /src

COPY ./server.go /src/server.go

RUN set -xe; \
    CGO_ENABLED=1 \
    go build \
      -buildmode=pie \
      -ldflags "-linkmode external -extldflags '-static-pie'" \
      -tags netgo \
      -o /server server.go \
    ;

FROM scratch

COPY --from=build /server /server
COPY --from=build /lib/x86_64-linux-gnu/libc.so.6 /lib/x86_64-linux-gnu/
COPY --from=build /lib64/ld-linux-x86-64.so.2 /lib64/

[nderjung]

Hi @LucaSeri, this is a recent addition, towards having better compatibility with Dockerfiles. The priority of arguments should be:

CLI > Kraftfile > Dockerfile

1. If the user has supplied -a|--args flag, this takes the highest priority and everything else is ignored.
2. If the user has not supplied the -a|--args flag, and the Kraftfile has a cmd entry, use this.
3. If neither the -a|--args flag is supplied nor the Kraftfile has a cmd element, try to use the Dockerfile's CMD.

[LucaSeri]

Thanks @nderjung. That all makes sense. Maybe this should be revisited since it seems the -a flag cannot directly replace the cmd field. The parser gives the following error:
expected param to be in the format 'libname.param=value' but got: '/server'

[Krechals]

I've also looked a bit into this, because I had the same issues when running many applications from the catalog with kraft, including helloworld-c.

Looking at the codebase, it seems that the -a|--args flag is used for setting kernel arguments, while the cmd element in both Kraftfile and Dockerfile is used for application arguments.

I got a fix in #1622, but I'm not aware how to provide application arguments directly from the CLI (using kraft run).