(unknown),

(unknown),

[Renjun Qu]

Hello everyone:
         I am building a small embedded linux system right now. I
confused that why the default rootfs must has a "dev/console" node. I
have made a experiment as follow:
        1st, configure the kernel(2.6.32) to support the initramfs
and initrd, and set the source of the initramfs to a directory which
only has a "root" node.
        2nd, configure the kernel to support the root file system on
nfs, and rebuild the kernel. I have created all necessary files and
directories in the directory exported by the nfs server.
        3rd,  set the appropriate boot parameter, and boot my kernel.
        The result is, the kernel can successfully mount the root
file system, but the "/sbin/init" program can not print any
information to me. My "sbin/init" program is just a hello world
program which only print some greeting information.There is a
"dev/console" device node in the nfs exported directory.
        But if i set the source of the initramfs to empty, and redo
my experiment from the 2nd step,everything will be ok. So, i think
there must be a “dev/console” node in the rootfs. The real root file
system already has a "dev/console" node, why default rootfs must have
a dev/console node. Please help me.

                         Best regards,

                            Ren jun Qu

Re:

[Harald Hoyer]

On 25.10.2011 07:55, Renjun Qu wrote:
> Hello everyone:
>          I am building a small embedded linux system right now. I
> confused that why the default rootfs must has a "dev/console" node. I
> have made a experiment as follow:
>         1st, configure the kernel(2.6.32) to support the initramfs
> and initrd, and set the source of the initramfs to a directory which
> only has a "root" node.
>         2nd, configure the kernel to support the root file system on
> nfs, and rebuild the kernel. I have created all necessary files and
> directories in the directory exported by the nfs server.
>         3rd,  set the appropriate boot parameter, and boot my kernel.
>         The result is, the kernel can successfully mount the root
> file system, but the "/sbin/init" program can not print any
> information to me. My "sbin/init" program is just a hello world
> program which only print some greeting information.There is a
> "dev/console" device node in the nfs exported directory.
>         But if i set the source of the initramfs to empty, and redo
> my experiment from the 2nd step,everything will be ok. So, i think
> there must be a “dev/console” node in the rootfs. The real root file
> system already has a "dev/console" node, why default rootfs must have
> a dev/console node. Please help me.
> 
>                          Best regards,
> 
>                             Ren jun Qu
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Your small initramfs should have something like this in sbin/init:

mknod -m 0666 /dev/null c 1 3

mount -t proc  -o nosuid,noexec,nodev proc /proc
mount -t sysfs -o nosuid,noexec,nodev sysfs /sys

ismounted() {
    while read a m a; do
        [ "$m" = "$1" ] && return 0
    done < /proc/mounts
    return 1
}

_opt="-o mode=0755,nosuid,exec"; _fs="-t devtmpfs"
ismounted /dev && { _opt="$_opt,remount"; unset _fs; }
if ! mount $_fs $_opt devtmpfs /dev >/dev/null 2>&1; then
    # if it failed (remount can't fail - no need to redo $_opt), fall back to
    # normal tmpfs
    mount -t tmpfs $_opt tmpfs /dev >/dev/null 2>&1
    # Make some basic devices first, let udev handle the rest
    mknod -m 0666 /dev/null c 1 3
    mknod -m 0666 /dev/ptmx c 5 2
    mknod -m 0600 /dev/console c 5 1
    mknod -m 0660 /dev/kmsg c 1 11
fi

# prepare the /dev directory (note: newer udevd takes care of it automatically)
[ ! -h /dev/fd ] && ln -s /proc/self/fd /dev/fd >/dev/null 2>&1
[ ! -h /dev/stdin ] && ln -s /proc/self/fd/0 /dev/stdin >/dev/null 2>&1
[ ! -h /dev/stdout ] && ln -s /proc/self/fd/1 /dev/stdout >/dev/null 2>&1
[ ! -h /dev/stderr ] && ln -s /proc/self/fd/2 /dev/stderr >/dev/null 2>&1