udev on real Linux from scratch

Gabor Z. Papp

author

2007-05-06 07:55 UTC #0 lore raw

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 mode55 -t tmpfs tmpfs /dev

mkdir -p /dev/pts

mount -n -o mode20 -t devpts devpts /dev/pts

   udevd --daemon

udevstart

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/?

Thanks for the help.

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Alex Smith

2007-05-06 08:34 UTC #1 lore raw

Quoted 21 lines · Gabor Z. Papp

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 mode55 -t tmpfs tmpfs /dev

Quoted 7 lines

mkdir -p /dev/pts
mount -n -o mode20 -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.

Quoted 11 lines

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:

Quoted 8 lines

        /* 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

Signature · 12 lines

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

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control of your XML. No limits. Just data. Click to get it now.
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Bryan Kadzban

2007-05-06 11:57 UTC #2 lore raw