Libguestfs - Aug 2011 - building a supermin appliance with febootstrap...

Rich,

So, I tried to build the simple supermin app. from your blog. I can confirm that
I did get
to the shell when I invoked qemu-kvm.


I used the standard qemu-kvm cmdline (but appended a serial console). This boots
fine.
########################################################
[root at moon appliance-test]# qemu-kvm -kernel kernel -append
"console=tty0
console=ttyS0,115200" -initrd initrd -hda root -nographic
.
.
.
insmod: error inserting 'ideapad-laptop.ko': -1 Unknown symbol in module
insmod: wait: File exists
febootstrap: insmod sym53c8xx.ko
febootstrap: picked /sys/block/sda/dev as root device
febootstrap: creating /dev/root as block special 8:0
febootstrap: mounting new root on /root
febootstrap: chroot
/proc/uptime: No such file or directory
Welcome to my world
bash: cannot set terminal process group (-1): Inappropriate ioctl for device
bash: no job control in this shell
bash-4.2# [    1.103034] input: ImExPS/2 Generic Explorer Mouse as 
/devices/platform/i8042/serio1/input/input2
[    1.334183] Refined TSC clocksource calibration: 1995.006 MHz.

bash-4.2#
########################################################


But when I try to 'exit', I notice a kernel panic. And it just seems to
hung there, no
more budging. I had to do 'ctl a + x' to get out of the serial console.
Is this expected?
########################################################
bash-4.2# exit
exit
[  153.520309] Kernel panic - not syncing: Attempted to kill init!
[  153.523584] Pid: 1, comm: init Not tainted 2.6.40-4.fc15.x86_64 #1
[  153.526990] Call Trace:
[  153.529039]  [<ffffffff814ae2cd>] panic+0x91/0x19c
[  153.531914]  [<ffffffff810580a2>] do_exit+0xb9/0x77b
[  153.534798]  [<ffffffff810589e9>] do_group_exit+0x7a/0xa2
[  153.537835]  [<ffffffff81058a28>] sys_exit_group+0x17/0x17
[  153.540924]  [<ffffffff814bd7c2>] system_call_fastpath+0x16/0x1b
########################################################

-- 
/kashyap

* Kashyap Chamarthy:
> So, I tried to build the simple supermin app. from your blog. I can
> confirm that I did get to the shell when I invoked qemu-kvm.
>
> I used the standard qemu-kvm cmdline (but appended a serial console). This
boots fine.
> [...]
>
> But when I try to 'exit', I notice a kernel panic. And it just
seems
> to hung there, no more budging. I had to do 'ctl a + x' to get out
of
> the serial console.
> Is this expected?
This is normal behavior. The demo system as described by Rich has no
regular init process. The shell has been started via exec, so it is PID
1. PID 1 has a special role on Unix and Linux, the first processs that
is started by the kernel is normally /sbin/init which is responsible for
bringing up the rest of the system. Something must have gone horribly
wrong with the system if this process exits.

And this is what the kernel panic message you posted is all about:
> bash-4.2# exit
> exit
> [  153.520309] Kernel panic - not syncing: Attempted to kill init!
> [  153.523584] Pid: 1, comm: init Not tainted 2.6.40-4.fc15.x86_64 #1
-Hilko

On Wed, Aug 17, 2011 at 11:34:54AM +0530, Kashyap Chamarthy
wrote:
> But when I try to 'exit', I notice a kernel panic. And it just
seems
> to hung there, no more budging. I had to do 'ctl a + x' to get out
> of the serial console.
> Is this expected?
As Hilko says, this is normal behaviour when the init process dies:

http://lxr.linux.no/#linux+v3.0.2/kernel/exit.c#L728

In libguestfs, our "init process" is the guestfsd daemon.  We
configure the kernel to reboot instead of panicking by adding the
kernel command line option "panic=1".

If you use a real init or systemd then this won't be an issue because
init will issue a reboot system call instead of exiting.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming blog: http://rwmj.wordpress.com
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