Kernel Parameters

This section documents kernel command-line parameters supported by Asterinas.

Inherited from Linux

rdinit

Run the specified initramfs binary as the first userspace process.

Example:

rdinit=/bin/busybox

Notes:

• The value is the path to the executable in the initramfs root.
• If omitted, Asterinas will try to execute /init from the initramfs root.
• If the specified path cannot be accessed, Asterinas ignores it and proceeds with root filesystem initialization. It does not fall back to /init in this case.

root

Mount the specified block device as the root filesystem.

Example:

root=/dev/vda2

Notes:

• The value currently must name a registered block device under /dev, such as /dev/vda2.
• Asterinas first determines the boot source. If the path specified by rdinit is accessible, or if rdinit is absent and /init exists, it boots from the initramfs and ignores root. Otherwise, it boots from the rootfs, for which root is required: Asterinas mounts the specified device as the root filesystem and panics if the parameter is absent.

rootfstype

Select the filesystem type used for the root filesystem.

Example:

root=/dev/vda2 rootfstype=ext2

Valid values:

• ext2

ro

Mount the root filesystem read-only. This is the default when Asterinas mounts the root filesystem via root.

Example:

root=/dev/vda2 ro

Notes:

• This parameter has no effect when Asterinas boots from the initramfs.
• If both ro and rw are specified, the last one takes precedence.

rw

Mount the root filesystem read-write.

Example:

root=/dev/vda2 rw

Notes:

• This parameter has no effect when Asterinas boots from the initramfs.
• rw overrides the default read-only root mount.
• If both ro and rw are specified, the last one takes precedence.

init

Run the specified executable as the first userspace process from the root filesystem.

Example:

root=/dev/vda2 rootfstype=ext2 init=/nix/var/nix/profiles/system/init

Notes:

• init is used only after Asterinas mounts the root filesystem via root=.
• If omitted, Asterinas tries /sbin/init, /etc/init, /bin/init, and /bin/sh, in that order.

console

Select console devices for kernel messages. This parameter may be specified multiple times. Kernel messages are delivered to each listed console.

Valid values:

• tty0
• ttyS0
• hvc0

Examples:

console=ttyS0
console=ttyS0 console=hvc0

virtio_mmio.device

Register a VirtIO-MMIO device from the kernel command line. This parameter may be specified multiple times.

Format:

virtio_mmio.device=<size>@<base>:<irq>[:<id>]

Notes:

• size and base may be decimal or hexadecimal with a 0x prefix.
• size may use K, M, G, or T suffixes.
• irq must be nonzero.
• The optional id field is accepted for Linux compatibility but ignored.

Examples:

virtio_mmio.device=0x200@0x5950f000:10
virtio_mmio.device=1K@0x1001e000:74

earlycon

Enable the early console to output logs during the early stages of system boot. The name follows Linux’s earlycon parameter. Asterinas currently supports a simplified form.

Example:

earlycon

Notes:

• If omitted, the early console stays disabled.
• Only the bare earlycon token is supported; complex Linux forms such as earlycon=uart8250,io,0x3f8,115200 are not supported yet.

loglevel

Control how verbose kernel log output is on the console. Set either a numeric value (0 to 8) or a lowercase level name.

Each value acts as a cutoff: messages at that severity and all more urgent levels are printed. For example, loglevel=4 shows emergencies through errors, but not warnings or routine info.

This uses the same 0–8 scale as the Linux kernel loglevel parameter, with string aliases for convenience.

Example:

loglevel=4
loglevel=error

Notes:

• Level names are case-sensitive; use lowercase names.
• If omitted, the default is 8 (debug). Invalid values are ignored.
• Use warn for normal operation, info/debug when troubleshooting, and error or lower for a quieter console.

Asterinas-specific

i8042.exist

Override ACPI’s indication of whether a PS/2 (i8042) controller exists.

Valid values:

• 1, on, yes, true or no value — treat the i8042 controller as present (force probing)
• 0, off, no, false - treat the i8042 controller as absent (skip probing)

Examples:

i8042.exist
i8042.exist=1
i8042.exist=0