Initramfs Prompt – Fix ‘Can’t Read /etc/fstab’ and ‘No Init Found’

Cause

In version 23, the mkinitcpio resolve_device() function is called only once. When at execution time the drive labels are not yet read, blkid can't lookup the kernel drive (/dev/...) name for the requested label.

Solution

By adding the "without-udev" hook, as listed below, the resolve_device function is left untouched. Though standard available mkinitcpio functionality to override the mount_handler add a run_hook is used to poll until blkid returns a value, or (a timeout of) 10 seconds has passed. Thus the "udev" hook can be removed from mkinitcpio config.

Notes

• This solution was created with the help of falconindy.
• There was an error message in the early boot phase involving fsck. To remove that message the without-udev hook has been rewritten to use a run_hook instead of a mount_handler. The newer code is even shorter.

$ cat /usr/lib/initcpio/hooks/without-udev
#!/bin/ash
# Minimal initramfs files are created without udev.
# This hooks provides a polling disk mount replacement for udev.
# Udev hook can be removed, resulting in smaller initramfs files.

run_hook () {
    local dev timeout sleepval device=$root
    # if udev is running then exit
    [ "$udevd_running" -eq 1 ] && return
    # try for (timeout * sleepval =) 10 seconds to handle slow (USB) devices
    timeout=1000
    sleepval=0.01

    case $device in
        # label to resolve, when resolved the kernel block device also exists
        UUID=*|LABEL=*|PARTUUID=*|PARTLABEL=*)
            while [ $timeout -gt 0 ]; do
                timeout=$((timeout - 1))
                dev=$(blkid -lt "$device" -o device)
                [ -n "$dev" ] && timeout=0 || sleep $sleepval
            done
            ;;
        # kernel named block device, poll for existence
        /dev/*)
            while [ $timeout -gt 0 ]; do
                timeout=$((timeout -1))
                if [ -b "$device" ]; then
                    dev=$device
                    timeout=0
                else
                    sleep $sleepval
                fi
            done
            ;;
    esac
}

# vim:set syntax=sh:

$ cat /usr/lib/initcpio/install/without-udev
#!/bin/bash

build() {
    add_runscript
}

help() {
    cat <<HELPEOF
This hook provides support for booting without the "udev" hook,
including support for UUID, LABEL, PARTUUID, PARTLABEL.
HELPEOF
}

# vim: set ft=sh ts=4 sw=4 et: