Re: udev on real Linux from scratch

[Alex Smith <alex@alex-smith.me.uk>]

Gabor Z. Papp wrote:
> Hello,
> 
> the udev FAQ pointed me to this list.
> 
> Time hit me too, and started to migrating from 2.4 kernels to 2.6. :-P
> 
> I have some questions that not really clear to me, I think this part
> of documentation could be expanded too. :-)
> 
> First of all, someone could take a look at this init process and
> confirm me its ok, or something still wrong. Finally got working /dev
> directory with this setup, but I'm not sure its correct:
> 
>    mount -n -t proc proc /proc
> 
>    mount -n -t sysfs sysfs /sys
> 
>    echo "" > /proc/sys/kernel/hotplug
> 
>    mount -n -o mode\a55 -t tmpfs tmpfs /dev
> 
>    mkdir -p /dev/pts
> 
>    mount -n -o mode\x0620 -t devpts devpts /dev/pts
> 
>    udevd --daemon
> 
>    udevstart

IMO it would be wiser to use udevtrigger and udevsettle here rather than 
udevstart because AFAIK udevstart is deprecated and will be removed soon.

> 
> My /etc/udev dir is mostly empty (only the default udev.conf exist)
> and will fill up the rules.d/ dir depending on my needs.
> I'm not starting any other udev* related program.
> The original /dev/ directory has only console device. 
> 
> Well, my another important question is, that starting udevd --daemon
> gives me a "cannot open /dev/null" error message.
> 
> I have found this message in the udevd.c file around line 1018:
> 
>         /* make sure std{in,out,err} fd's are in a sane state */
>         fd = open("/dev/null", O_RDWR);
>         if (fd < 0) {
>                 fprintf(stderr, "cannot open /dev/null\n");
>                 err("cannot open /dev/null");
>         }
> 
> Should I create /dev/null after mounting tmpfs on /dev/?

Yes, after mounting tmpfs you should create some initial device nodes 
that udevd needs and does not create. This is what I do on Frugalware:

# Create initial device nodes.
mknod -m 600 /dev/console c 5 1
mknod -m 666 /dev/null c 1 3

# Create extra links that Udev does not create for us
ln -snf /proc/self/fd /dev/fd
ln -snf /proc/self/fd/0 /dev/stdin
ln -snf /proc/self/fd/1 /dev/stdout
ln -snf /proc/self/fd/2 /dev/stderr
ln -snf /proc/kcore /dev/core


HTH, Alex
-- 
Alex Smith
Frugalware Linux developer - http://www.frugalware.org

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