Urunc makes use of the initrd to pass information to Linux based guests. In more details, if the rootfs is not initrd based, then the urunit configuration is passed as the initrd of the VM and urunit reads it. While the above works correctly for Qemu and Firecracker, it does not for cloud-hypervisor.
$ docker run --rm -it --runtime io.containerd.urunc.v2 harbor.nbfc.io/nubificus/urunc/busybox-cloud-hypervisor-linux-raw:latest
[2026-07-22T15:48:33Z INFO virtiofsd] Waiting for vhost-user socket connection...
[2026-07-22T15:48:33Z INFO virtiofsd] Client connected, servicing requests
[ 0.000000] Linux version 6.12.36 (@b702d6ef5e06) (gcc (Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.0, GNU ld (GNU Binutils for Ubuntu) 2.38) #1 SMP Sun Jul 20 19:15:21 UTC 2025
[ 0.000000] Command line: panic=-1 console=ttyS0 root=fs0 rw rootfstype=virtiofs ip=172.17.0.5::172.17.0.1:255.255.0.0:urunc:eth0:off retain_initrd URUNIT_CONFIG=/sys/firmware/initrd init=/urunit -- /bin/sh
[ 0.000000] BIOS-provided physical RAM map:
[ 0.000000] BIOS-e820: [mem 0x0000000000000000-0x000000000009ffff] usable
[ 0.000000] BIOS-e820: [mem 0x00000000000a0000-0x00000000000fffff] reserved
[ 0.000000] BIOS-e820: [mem 0x0000000000100000-0x0000000010bfffff] usable
[ 0.000000] BIOS-e820: [mem 0x00000000e8000000-0x00000000f7ffffff] reserved
[ 0.000000] NX (Execute Disable) protection: active
[ 0.000000] APIC: Static calls initialized
[ 0.000000] SMBIOS 3.2.0 present.
[ 0.000000] DMI: Cloud Hypervisor cloud-hypervisor, BIOS 0
[ 0.000000] DMI: Memory slots populated: 0/0
[ 0.000000] Hypervisor detected: KVM
[ 0.000000] kvm-clock: Using msrs 4b564d01 and 4b564d00
[ 0.000004] kvm-clock: using sched offset of 217263016 cycles
[ 0.000176] clocksource: kvm-clock: mask: 0xffffffffffffffff max_cycles: 0x1cd42e4dffb, max_idle_ns: 881590591483 ns
[ 0.000778] tsc: Detected 791.999 MHz processor
[ 0.007446] last_pfn = 0x10c00 max_arch_pfn = 0x400000000
[ 0.009259] MTRR map: 0 entries (0 fixed + 0 variable; max 16), built from 8 variable MTRRs
[ 0.009722] x86/PAT: Configuration [0-7]: WB WC UC- UC WB WP UC- WT
[ 0.012879] found SMP MP-table at [mem 0x000f0090-0x000f009f]
[ 0.013442] Using GB pages for direct mapping
[ 0.014727] ACPI: Early table checksum verification disabled
[ 0.015915] ACPI: RSDP 0x00000000000A0000 000024 (v02 CLOUDH)
[ 0.016100] ACPI: XSDT 0x00000000000A13F1 00003C (v01 CLOUDH CHXSDT 00000001 RVAT 01000000)
[ 0.016448] ACPI: FACP 0x00000000000A124F 000114 (v06 CLOUDH CHFACP 00000001 RVAT 01000000)
[ 0.016571] ACPI: DSDT 0x00000000000A0024 00122B (v06 CLOUDH CHDSDT 00000001 RVAT 01000000)
[ 0.016588] ACPI: APIC 0x00000000000A1363 000052 (v05 CLOUDH CHMADT 00000001 RVAT 01000000)
[ 0.016600] ACPI: MCFG 0x00000000000A13B5 00003C (v01 CLOUDH CHMCFG 00000001 RVAT 01000000)
[ 0.016610] ACPI: Reserving FACP table memory at [mem 0xa124f-0xa1362]
[ 0.016616] ACPI: Reserving DSDT table memory at [mem 0xa0024-0xa124e]
[ 0.016619] ACPI: Reserving APIC table memory at [mem 0xa1363-0xa13b4]
[ 0.016621] ACPI: Reserving MCFG table memory at [mem 0xa13b5-0xa13f0]
[ 0.020922] No NUMA configuration found
[ 0.020927] Faking a node at [mem 0x0000000000000000-0x0000000010bfffff]
[ 0.021021] NODE_DATA(0) allocated [mem 0x10bfb040-0x10bfffff]
[ 0.023534] Zone ranges:
[ 0.023702] DMA [mem 0x0000000000001000-0x0000000000ffffff]
[ 0.023711] DMA32 [mem 0x0000000001000000-0x0000000010bfffff]
[ 0.023717] Normal empty
[ 0.023804] Device empty
[ 0.023807] Movable zone start for each node
[ 0.023809] Early memory node ranges
[ 0.023895] node 0: [mem 0x0000000000001000-0x000000000009ffff]
[ 0.023985] node 0: [mem 0x0000000000100000-0x0000000010bfffff]
[ 0.024075] Initmem setup node 0 [mem 0x0000000000001000-0x0000000010bfffff]
[ 0.024942] On node 0, zone DMA: 1 pages in unavailable ranges
[ 0.034975] On node 0, zone DMA: 96 pages in unavailable ranges
[ 0.205634] On node 0, zone DMA32: 29696 pages in unavailable ranges
[ 0.219647] ACPI: PM-Timer IO Port: 0x608
[ 0.221859] IOAPIC[0]: apic_id 0, version 17, address 0xfec00000, GSI 0-23
[ 0.221966] ACPI: INT_SRC_OVR (bus 0 bus_irq 4 global_irq 4 dfl dfl)
[ 0.222070] ACPI: Using ACPI (MADT) for SMP configuration information
[ 0.222074] TSC deadline timer available
[ 0.222088] CPU topo: Max. logical packages: 1
[ 0.222091] CPU topo: Max. logical dies: 1
[ 0.222093] CPU topo: Max. dies per package: 1
[ 0.222106] CPU topo: Max. threads per core: 1
[ 0.222109] CPU topo: Num. cores per package: 1
[ 0.222111] CPU topo: Num. threads per package: 1
[ 0.222112] CPU topo: Allowing 1 present CPUs plus 0 hotplug CPUs
[ 0.222647] kvm-guest: APIC: eoi() replaced with kvm_guest_apic_eoi_write()
[ 0.224591] [mem 0x10c00000-0xe7ffffff] available for PCI devices
[ 0.224597] Booting paravirtualized kernel on KVM
[ 0.224601] clocksource: refined-jiffies: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 7645519600211568 ns
[ 0.277248] setup_percpu: NR_CPUS:240 nr_cpumask_bits:1 nr_cpu_ids:1 nr_node_ids:1
[ 0.341619] percpu: Embedded 45 pages/cpu s154776 r0 d29544 u2097152
[ 0.342594] Kernel command line: panic=-1 console=ttyS0 root=fs0 rw rootfstype=virtiofs ip=172.17.0.5::172.17.0.1:255.255.0.0:urunc:eth0:off retain_initrd URUNIT_CONFIG=/sys/firmware/initrd init=/urunit -- /bin/sh
[ 0.347646] Unknown kernel command line parameters "URUNIT_CONFIG=/sys/firmware/initrd", will be passed to user space.
[ 0.347985] random: crng init done
[ 0.355525] Dentry cache hash table entries: 32768 (order: 6, 262144 bytes, linear)
[ 0.360088] Inode-cache hash table entries: 16384 (order: 5, 131072 bytes, linear)
[ 0.361521] Fallback order for Node 0: 0
[ 0.361531] Built 1 zonelists, mobility grouping on. Total pages: 68511
[ 0.361621] Policy zone: DMA32
[ 0.361625] mem auto-init: stack:off, heap alloc:off, heap free:off
[ 0.375573] SLUB: HWalign=64, Order=0-3, MinObjects=0, CPUs=1, Nodes=1
[ 0.376783] Kernel/User page tables isolation: enabled
[ 0.384848] rcu: Hierarchical RCU implementation.
[ 0.385018] rcu: RCU restricting CPUs from NR_CPUS=240 to nr_cpu_ids=1.
[ 0.385106] Tracing variant of Tasks RCU enabled.
[ 0.385272] rcu: RCU calculated value of scheduler-enlistment delay is 25 jiffies.
[ 0.385277] rcu: Adjusting geometry for rcu_fanout_leaf=16, nr_cpu_ids=1
[ 0.385611] RCU Tasks Trace: Setting shift to 0 and lim to 1 rcu_task_cb_adjust=1 rcu_task_cpu_ids=1.
[ 0.385619] NR_IRQS: 15616, nr_irqs: 256, preallocated irqs: 0
[ 0.387097] rcu: srcu_init: Setting srcu_struct sizes based on contention.
[ 0.391045] Console: colour dummy device 80x25
[ 0.393527] printk: legacy console [ttyS0] enabled
[ 5.660123] ACPI: Core revision 20240827
[ 5.694810] APIC: Switch to symmetric I/O mode setup
[ 5.759187] x2apic enabled
[ 5.799065] APIC: Switched APIC routing to: physical x2apic
[ 5.854074] clocksource: tsc-early: mask: 0xffffffffffffffff max_cycles: 0xb6a8c3c985, max_idle_ns: 440795235827 ns
[ 5.948377] Calibrating delay loop (skipped) preset value.. 1583.99 BogoMIPS (lpj=3167996)
[ 5.952375] x86/cpu: User Mode Instruction Prevention (UMIP) activated
[ 5.952375] Last level iTLB entries: 4KB 0, 2MB 0, 4MB 0
[ 5.952375] Last level dTLB entries: 4KB 0, 2MB 0, 4MB 0, 1GB 0
[ 5.952375] Spectre V1 : Vulnerable: __user pointer sanitization and usercopy barriers only; no swapgs barriers
[ 5.952375] Spectre V2 : User space: Vulnerable
[ 5.952375] Speculative Store Bypass: Vulnerable
[ 5.952375] MDS: Vulnerable
[ 5.952375] MMIO Stale Data: Vulnerable
[ 5.952375] SRBDS: Unknown: Dependent on hypervisor status
[ 5.952375] ITS: Vulnerable
[ 5.952375] x86/fpu: Supporting XSAVE feature 0x001: 'x87 floating point registers'
[ 5.952375] x86/fpu: Supporting XSAVE feature 0x002: 'SSE registers'
[ 5.952375] x86/fpu: Supporting XSAVE feature 0x004: 'AVX registers'
[ 5.952375] x86/fpu: Supporting XSAVE feature 0x008: 'MPX bounds registers'
[ 5.952375] x86/fpu: Supporting XSAVE feature 0x010: 'MPX CSR'
[ 5.952375] x86/fpu: xstate_offset[2]: 576, xstate_sizes[2]: 256
[ 5.952375] x86/fpu: xstate_offset[3]: 832, xstate_sizes[3]: 64
[ 5.952375] x86/fpu: xstate_offset[4]: 896, xstate_sizes[4]: 64
[ 5.952375] x86/fpu: Enabled xstate features 0x1f, context size is 960 bytes, using 'compacted' format.
[ 5.952375] Freeing SMP alternatives memory: 36K
[ 5.952375] pid_max: default: 32768 minimum: 301
[ 5.952375] LSM: initializing lsm=capability,selinux
[ 5.952375] SELinux: Initializing.
[ 5.952375] Mount-cache hash table entries: 512 (order: 0, 4096 bytes, linear)
[ 5.952375] Mountpoint-cache hash table entries: 512 (order: 0, 4096 bytes, linear)
[ 5.952375] smpboot: CPU0: Intel(R) Core(TM) i7-8700T CPU @ 2.40GHz (family: 0x6, model: 0x9e, stepping: 0xa)
[ 5.962188] Performance Events: Skylake events, full-width counters, Intel PMU driver.
[ 5.964942] ... version: 2
[ 5.968459] ... bit width: 48
[ 5.972451] ... generic registers: 4
[ 5.976457] ... value mask: 0000ffffffffffff
[ 5.980456] ... max period: 00007fffffffffff
[ 5.984456] ... fixed-purpose events: 3
[ 5.988457] ... event mask: 000000070000000f
[ 5.995161] signal: max sigframe size: 1616
[ 5.997446] rcu: Hierarchical SRCU implementation.
[ 6.000536] rcu: Max phase no-delay instances is 1000.
[ 6.012202] smp: Bringing up secondary CPUs ...
[ 6.012471] smp: Brought up 1 node, 1 CPU
[ 6.016465] smpboot: Total of 1 processors activated (1583.99 BogoMIPS)
[ 6.023582] Memory: 240104K/274044K available (12288K kernel code, 1050K rwdata, 2336K rodata, 1148K init, 2576K bss, 31980K reserved, 0K cma-reserved)
[ 6.032620] devtmpfs: initialized
[ 6.038971] x86/mm: Memory block size: 128MB
[ 6.045559] clocksource: jiffies: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 7645041785100000 ns
[ 6.048470] futex hash table entries: 256 (order: 2, 16384 bytes, linear)
[ 6.058276] NET: Registered PF_NETLINK/PF_ROUTE protocol family
[ 6.061189] audit: initializing netlink subsys (disabled)
[ 6.066652] thermal_sys: Registered thermal governor 'step_wise'
[ 6.066707] audit: type=2000 audit(1784735314.253:1): state=initialized audit_enabled=0 res=1
[ 6.073044] cpuidle: using governor menu
[ 6.077870] acpiphp: ACPI Hot Plug PCI Controller Driver version: 0.5
[ 6.084328] PCI: ECAM [mem 0xe8000000-0xe80fffff] (base 0xe8000000) for domain 0000 [bus 00-00]
[ 6.084460] PCI: ECAM [mem 0xe8000000-0xe80fffff] reserved as E820 entry
[ 6.090785] PCI: Using configuration type 1 for base access
[ 6.103278] HugeTLB: registered 1.00 GiB page size, pre-allocated 0 pages
[ 6.106404] HugeTLB: 16380 KiB vmemmap can be freed for a 1.00 GiB page
[ 6.108582] HugeTLB: registered 2.00 MiB page size, pre-allocated 0 pages
[ 6.112458] HugeTLB: 28 KiB vmemmap can be freed for a 2.00 MiB page
[ 6.120542] cryptd: max_cpu_qlen set to 1000
[ 6.133641] ACPI: Added _OSI(Module Device)
[ 6.136454] ACPI: Added _OSI(Processor Device)
[ 6.140464] ACPI: Added _OSI(Processor Aggregator Device)
[ 6.147844] ACPI: 1 ACPI AML tables successfully acquired and loaded
[ 6.150859] ACPI: Interpreter enabled
[ 6.152697] ACPI: PM: (supports S0 S5)
[ 6.156483] ACPI: Using IOAPIC for interrupt routing
[ 6.160853] PCI: Using host bridge windows from ACPI; if necessary, use "pci=nocrs" and report a bug
[ 6.164462] PCI: Using E820 reservations for host bridge windows
[ 6.185453] ACPI: PCI Root Bridge [PC00] (domain 0000 [bus 00])
[ 6.188661] acpi PNP0A08:00: _OSC: OS supports [ExtendedConfig ASPM ClockPM Segments MSI HPX-Type3]
[ 6.192492] acpi PNP0A08:00: _OSC: OS requested [PCIeHotplug SHPCHotplug PME PCIeCapability LTR]
[ 6.196467] acpi PNP0A08:00: _OSC: platform willing to grant [PCIeHotplug SHPCHotplug PME PCIeCapability LTR]
[ 6.200466] acpi PNP0A08:00: _OSC: platform retains control of PCIe features (AE_NOT_FOUND)
[ 6.206311] acpiphp: Slot [0] registered
[ 6.210633] acpiphp: Slot [1] registered
[ 6.212902] acpiphp: Slot [2] registered
[ 6.217795] acpiphp: Slot [3] registered
[ 6.222529] acpiphp: Slot [4] registered
[ 6.224923] acpiphp: Slot [5] registered
[ 6.229298] acpiphp: Slot [6] registered
[ 6.232819] acpiphp: Slot [7] registered
[ 6.237008] acpiphp: Slot [8] registered
[ 6.240948] acpiphp: Slot [9] registered
[ 6.244930] acpiphp: Slot [10] registered
[ 6.249058] acpiphp: Slot [11] registered
[ 6.252811] acpiphp: Slot [12] registered
[ 6.257153] acpiphp: Slot [13] registered
[ 6.261837] acpiphp: Slot [14] registered
[ 6.264951] acpiphp: Slot [15] registered
[ 6.269064] acpiphp: Slot [16] registered
[ 6.274183] acpiphp: Slot [17] registered
[ 6.276802] acpiphp: Slot [18] registered
[ 6.281213] acpiphp: Slot [19] registered
[ 6.284825] acpiphp: Slot [20] registered
[ 6.288810] acpiphp: Slot [21] registered
[ 6.292868] acpiphp: Slot [22] registered
[ 6.297945] acpiphp: Slot [23] registered
[ 6.301470] acpiphp: Slot [24] registered
[ 6.304879] acpiphp: Slot [25] registered
[ 6.308865] acpiphp: Slot [26] registered
[ 6.312807] acpiphp: Slot [27] registered
[ 6.316845] acpiphp: Slot [28] registered
[ 6.320823] acpiphp: Slot [29] registered
[ 6.325076] acpiphp: Slot [30] registered
[ 6.329000] acpiphp: Slot [31] registered
[ 6.334055] PCI host bridge to bus 0000:00
[ 6.336518] pci_bus 0000:00: root bus resource [mem 0xe8000000-0xe80fffff]
[ 6.341065] pci_bus 0000:00: root bus resource [mem 0xc0000000-0xe7ffffff window]
[ 6.345030] pci_bus 0000:00: root bus resource [mem 0x100000000-0x7effffffff window]
[ 6.348460] pci_bus 0000:00: root bus resource [io 0x0000-0x0cf7 window]
[ 6.352460] pci_bus 0000:00: root bus resource [io 0x0d00-0xffff window]
[ 6.356537] pci_bus 0000:00: root bus resource [bus 00]
[ 6.362836] pci 0000:00:00.0: [8086:0d57] type 00 class 0x060000 conventional PCI endpoint
[ 6.386576] pci 0000:00:01.0: [1af4:1041] type 00 class 0x020000 conventional PCI endpoint
[ 6.393335] pci 0000:00:01.0: BAR 0 [mem 0x7efff80000-0x7effffffff 64bit]
[ 6.434993] pci 0000:00:02.0: [1af4:1044] type 00 class 0xffff00 conventional PCI endpoint
[ 6.440732] pci 0000:00:02.0: BAR 0 [mem 0x7efff00000-0x7efff7ffff 64bit]
[ 6.479619] pci 0000:00:03.0: [1af4:105a] type 00 class 0xffff00 conventional PCI endpoint
[ 6.484780] pci 0000:00:03.0: BAR 0 [mem 0x7effe80000-0x7effefffff 64bit]
[ 6.527239] iommu: Default domain type: Translated
[ 6.529162] iommu: DMA domain TLB invalidation policy: lazy mode
[ 6.535259] SCSI subsystem initialized
[ 6.536543] pps_core: LinuxPPS API ver. 1 registered
[ 6.540455] pps_core: Software ver. 5.3.6 - Copyright 2005-2007 Rodolfo Giometti <giometti@linux.it>
[ 6.544480] PTP clock support registered
[ 6.553130] PCI: Using ACPI for IRQ routing
[ 6.559830] vgaarb: loaded
[ 6.560568] clocksource: Switched to clocksource kvm-clock
[ 6.622626] pnp: PnP ACPI init
[ 6.665023] system 00:00: [mem 0xe8000000-0xe80fffff] has been reserved
[ 6.723476] pnp: PnP ACPI: found 2 devices
[ 6.783252] clocksource: acpi_pm: mask: 0xffffff max_cycles: 0xffffff, max_idle_ns: 2085701024 ns
[ 6.888976] NET: Registered PF_INET protocol family
[ 6.929731] IP idents hash table entries: 4096 (order: 3, 32768 bytes, linear)
[ 6.997971] tcp_listen_portaddr_hash hash table entries: 256 (order: 0, 4096 bytes, linear)
[ 7.076770] Table-perturb hash table entries: 65536 (order: 6, 262144 bytes, linear)
[ 7.142445] TCP established hash table entries: 2048 (order: 2, 16384 bytes, linear)
[ 7.222051] TCP bind hash table entries: 2048 (order: 4, 65536 bytes, linear)
[ 7.298470] TCP: Hash tables configured (established 2048 bind 2048)
[ 7.342384] UDP hash table entries: 256 (order: 1, 8192 bytes, linear)
[ 7.401551] UDP-Lite hash table entries: 256 (order: 1, 8192 bytes, linear)
[ 7.478758] NET: Registered PF_UNIX/PF_LOCAL protocol family
[ 7.524216] pci_bus 0000:00: resource 4 [mem 0xe8000000-0xe80fffff]
[ 7.580384] pci_bus 0000:00: resource 5 [mem 0xc0000000-0xe7ffffff window]
[ 7.642785] pci_bus 0000:00: resource 6 [mem 0x100000000-0x7effffffff window]
[ 7.716448] pci_bus 0000:00: resource 7 [io 0x0000-0x0cf7 window]
[ 7.776938] pci_bus 0000:00: resource 8 [io 0x0d00-0xffff window]
[ 7.835332] PCI: CLS 0 bytes, default 64
[ 7.872770] clocksource: tsc: mask: 0xffffffffffffffff max_cycles: 0xb6a8c3c985, max_idle_ns: 440795235827 ns
[ 7.969122] platform rtc_cmos: registered platform RTC device (no PNP device found)
[ 8.052788] workingset: timestamp_bits=40 max_order=16 bucket_order=0
[ 8.111519] fuse: init (API version 7.41)
[ 8.150225] SGI XFS with security attributes, no debug enabled
[ 8.204607] 9p: Installing v9fs 9p2000 file system support
[ 8.263060] NET: Registered PF_ALG protocol family
[ 8.318149] Block layer SCSI generic (bsg) driver version 0.4 loaded (major 249)
[ 8.407498] shpchp: Standard Hot Plug PCI Controller Driver version: 0.4
[ 8.561479] input: Power Button as /devices/LNXSYSTM:00/LNXSYBUS:00/PNP0C0C:00/input/input0
[ 8.603607] ACPI: button: Power Button [PWRB]
[ 8.673702] virtio-pci 0000:00:01.0: enabling device (0000 -> 0002)
[ 8.735737] virtio-pci 0000:00:02.0: enabling device (0000 -> 0002)
[ 8.806268] virtio-pci 0000:00:03.0: enabling device (0000 -> 0002)
[ 8.911519] virtiofs virtio2: virtio_fs_setup_dax: No cache capability
[ 8.975027] Serial: 8250/16550 driver, 4 ports, IRQ sharing disabled
[ 9.054062] 00:01: ttyS0 at I/O 0x3f8 (irq = 24, base_baud = 115200) is a 16550A
[ 9.173927] brd: module loaded
[ 9.230349] loop: module loaded
[ 9.271085] tun: Universal TUN/TAP device driver, 1.6
[ 9.353195] VFIO - User Level meta-driver version: 0.3
[ 9.396348] intel_pstate: CPU model not supported
[ 9.442350] xt_time: kernel timezone is -0000
[ 9.489025] IPVS: Registered protocols (TCP, UDP, SCTP, AH, ESP)
[ 9.552260] IPVS: Connection hash table configured (size=4096, memory=32Kbytes)
[ 9.625192] IPVS: ipvs loaded.
[ 9.651401] IPVS: [rr] scheduler registered.
[ 9.706384] IPVS: [wrr] scheduler registered.
[ 9.752473] IPVS: [lc] scheduler registered.
[ 9.797556] IPVS: [wlc] scheduler registered.
[ 9.843066] IPVS: [fo] scheduler registered.
[ 9.880032] IPVS: [ovf] scheduler registered.
[ 9.925436] IPVS: [lblc] scheduler registered.
[ 9.975981] IPVS: [lblcr] scheduler registered.
[ 10.018093] IPVS: [dh] scheduler registered.
[ 10.058270] IPVS: [sh] scheduler registered.
[ 10.102977] IPVS: [sed] scheduler registered.
[ 10.149162] IPVS: [nq] scheduler registered.
[ 10.180484] IPVS: [sip] pe registered.
[ 10.219394] Initializing XFRM netlink socket
[ 10.259616] NET: Registered PF_INET6 protocol family
[ 10.321002] Segment Routing with IPv6
[ 10.356287] In-situ OAM (IOAM) with IPv6
[ 10.394563] NET: Registered PF_PACKET protocol family
[ 10.440017] 9pnet: Installing 9P2000 support
[ 10.475929] NET: Registered PF_VSOCK protocol family
[ 10.526902] IPI shorthand broadcast: enabled
[ 10.573419] AES CTR mode by8 optimization enabled
[ 10.632154] registered taskstats version 1
[ 10.705613] Demotion targets for Node 0: null
[ 10.763207] alg: No test for fips(ansi_cprng) (fips_ansi_cprng)
[ 10.857513] IP-Config: Complete:
[ 10.878472] device=eth0, hwaddr=06:04:1f:fb:f3:ab, ipaddr=172.17.0.5, mask=255.255.0.0, gw=172.17.0.1
[ 10.954430] host=urunc, domain=, nis-domain=(none)
[ 10.995883] bootserver=255.255.255.255, rootserver=255.255.255.255, rootpath=
[ 11.005958] VFS: Mounted root (virtiofs filesystem) on device 0:19.
[ 11.092069] devtmpfs: mounted
[ 11.123282] Freeing unused kernel image (initmem) memory: 1148K
[ 11.153063] Write protecting the kernel read-only data: 16384k
[ 11.242246] Freeing unused kernel image (rodata/data gap) memory: 1760K
[ 11.272242] Run /urunit as init process
Read configuration file: No such file or directory
Could not read file /sys/firmware/initrd
/bin/sh: can't access tty; job control turned off
~ #
$ ps aux | grep cloud
cmainas 179533 18.0 0.7 1809572 29508 pts/3 Sl+ 15:48 0:02 docker run --rm -it --runtime io.containerd.urunc.v2 harbor.nbfc.io/nubificus/urunc/busybox-cloud-hypervisor-linux-raw:latest
root 179578 53.5 0.9 287928 38128 ? Ssl 15:48 0:05 /opt/urunc/bin/cloud-hypervisor --memory size=268M,shared=on --cpus boot=1 --kernel /cntrRootfs/.boot/kernel --console off --serial tty --seccomp true --net tap=tap0_urunc,mac=06:04:1f:fb:f3:ab,mtu=1500 --fs tag=fs0,socket=/tmp/vhostqemu --cmdline panic=-1 console=ttyS0 root=fs0 rw rootfstype=virtiofs ip=172.17.0.5::172.17.0.1:255.255.0.0:urunc:eth0:off retain_initrd URUNIT_CONFIG=/sys/firmware/initrd init=/urunit -- /bin/sh
cmainas 179649 0.0 0.0 9144 2272 pts/2 S+ 15:48 0:00 grep --color=auto cloud
Urunc makes use of the initrd to pass information to Linux based guests. In more details, if the rootfs is not initrd based, then the urunit configuration is passed as the initrd of the VM and urunit reads it. While the above works correctly for Qemu and Firecracker, it does not for cloud-hypervisor.
This can be seen by running the
harbor.nbfc.io/nubificus/urunc/busybox-cloud-hypervisor-linux-raw:latestimage from Sample images.Note the
Could not read file /sys/firmware/initrdline.Also, looking at the cloud-hypervisor command