libvirt users - Nov 2013 - Failed to access the console after starting the lxc container

Hello,

I am starting the system container without "/"  directory So that it
can
share the host /bin /sbin /lib and /lib64 and i have sepeartely mounted
/var, /etc and /usr directory for the container
Below is xml file
 <domain type='lxc'>
<name>test6</name>
<memory>102400</memory>
<os>
  <type>exe</type>
  <init>/sbin/init</init>
</os>
<vcpu>1</vcpu>
<clock offset='utc'/>
<on_poweroff>destroy</on_poweroff>
<on_reboot>restart</on_reboot>
<on_crash>destroy</on_crash>

<devices>
  <console type='pty'/>
  <emulator>/usr/libexec/libvirt_lxc</emulator>
  <filesystem type='mount' accessmode='passthrough'>
    <source dir='/lxc/test6/etc'/>
    <target dir='/etc'/>
  </filesystem>

  <filesystem type='mount' accessmode='passthrough'>
    <source dir='/lxc/test6/var'/>
    <target dir='/var'/>
  </filesystem>
  <filesystem type='mount' accessmode='passthrough'>
    <source dir='/lxc/test6/usr'/>
     <target dir='/usr'/>
  </filesystem>

  <filesystem type='mount' accessmode='passthrough'>
    <source dir='/pg_data/'/>
    <target dir='/pg_data'/>
  </filesystem>

  <filesystem type='ram' accessmode='passthrough'>
    <source usage='0' units='KiB'/>
    <target dir='/dev/shm'/>
   </filesystem>
   <interface type='bridge'>
     <source bridge='br0' />
   </interface>
</devices>
</domain>


when i start the container it get start , but when i try to access console
it get stuck

virsh # list
 Id    Name                           State
----------------------------------------------------
 18238 test4                          running
 20435 test6                          running


virsh #

virsh # start test6
Domain test6 started

virsh # console test6
Connected to domain test6
Escape character is ^]


But when i mount the "/" in xml it works, i have also share host
/bin,/sbin, /lib and /lib64.

<domain type='lxc'>
<name>test4</name>
<memory>102400</memory>
<os>
  <type>exe</type>
  <init>/sbin/init</init>
</os>
<vcpu>1</vcpu>
<clock offset='utc'/>
<on_poweroff>destroy</on_poweroff>
<on_reboot>restart</on_reboot>
<on_crash>destroy</on_crash>

<devices>
  <console type='pty'/>
  <emulator>/usr/libexec/libvirt_lxc</emulator>
<filesystem type='mount' accessmode='passthrough'>
    <source dir='/lxc/test4/'/>
    <target dir='/'/>
  </filesystem>
  <filesystem type='mount' accessmode='passthrough'>
    <source dir='/bin'/>
    <target dir='/bin'/>
  </filesystem>

  <filesystem type='mount' accessmode='passthrough'>
    <source dir='/sbin'/>
    <target dir='/sbin'/>
  </filesystem>
  <filesystem type='mount' accessmode='passthrough'>
    <source dir='/lib'/>
     <target dir='/lib'/>
  </filesystem>
  </filesystem>
  <filesystem type='mount' accessmode='passthrough'>
    <source dir='/lib64'/>
     <target dir='/lib64'/>
  </filesystem>
  <filesystem type='mount' accessmode='passthrough'>
    <source dir='/pg_data/'/>
    <target dir='/pg_data'/>
  </filesystem>

  <filesystem type='ram' accessmode='passthrough'>
    <source usage='0' units='KiB'/>
    <target dir='/dev/shm'/>
   </filesystem>
   <interface type='bridge'>
     <source bridge='br0' />
   </interface>
</devices>
</domain>

as i am new , can anyone explain me why my test6 container get stuck?
And in system container if we need to share host filesystem y we need to
mount them explicitly?

Thanks,
Aarti Sawant
NTTDATA OSS Center Pune

On Wed, Nov 20, 2013 at 05:28:29PM +0530, Aarti Sawant
wrote:
> Hello,
> 
> I am starting the system container without "/"  directory So that
it can
> share the host /bin /sbin /lib and /lib64 and i have sepeartely mounted
> /var, /etc and /usr directory for the container
> Below is xml file
>  <domain type='lxc'>
> <name>test6</name>
> <memory>102400</memory>
> <os>
>   <type>exe</type>
>   <init>/sbin/init</init>
Ok, so you're starting a real "init" process. By default this
won't respond to any input on the console. You need to make
sure that your init system is setup to start a mingtty process
on the console.

Typically if you're trying to share the '/' diretory between
the host & container though, you don't want to run a full
"init" system. Instead you'd want to just run a specific
application binary instead. In fact I'd go as far to
recommend against running 'init' if you're sharing '/'.
That said, I see you're setting up private /etc & /var
so you should be mostly OK from a writable file clash
POV.

If you want a full OS container installed to a new location
though, I've got a guide for this

 
https://www.berrange.com/posts/2013/08/12/running-a-full-fedora-os-inside-a-libvirt-lxc-guest/

> </os>
> <vcpu>1</vcpu>
> <clock offset='utc'/>
> <on_poweroff>destroy</on_poweroff>
> <on_reboot>restart</on_reboot>
> <on_crash>destroy</on_crash>
> 
> <devices>
>   <console type='pty'/>
>   <emulator>/usr/libexec/libvirt_lxc</emulator>
>   <filesystem type='mount' accessmode='passthrough'>
>     <source dir='/lxc/test6/etc'/>
>     <target dir='/etc'/>
>   </filesystem>
> 
>   <filesystem type='mount' accessmode='passthrough'>
>     <source dir='/lxc/test6/var'/>
>     <target dir='/var'/>
>   </filesystem>
>   <filesystem type='mount' accessmode='passthrough'>
>     <source dir='/lxc/test6/usr'/>
>      <target dir='/usr'/>
>   </filesystem>
> 
>   <filesystem type='mount' accessmode='passthrough'>
>     <source dir='/pg_data/'/>
>     <target dir='/pg_data'/>
>   </filesystem>
> 
>   <filesystem type='ram' accessmode='passthrough'>
>     <source usage='0' units='KiB'/>
>     <target dir='/dev/shm'/>
>    </filesystem>
>    <interface type='bridge'>
>      <source bridge='br0' />
>    </interface>
> </devices>
> </domain>
> 
> 
> when i start the container it get start , but when i try to access console
> it get stuck
Basically you need to see why the mingetty processes aren't being
started. On F19 with systemd, it should all 'just work' from a
console POV, aside from needing to edit /etc/securetty to allow
root login per my blog above.
> 
> virsh # list
>  Id    Name                           State
> ----------------------------------------------------
>  18238 test4                          running
>  20435 test6                          running
> 
> 
> virsh #
> 
> virsh # start test6
> Domain test6 started
> 
> virsh # console test6
> Connected to domain test6
> Escape character is ^]
> 
> 
> But when i mount the "/" in xml it works, i have also share host
> /bin,/sbin, /lib and /lib64.
That should not make any difference, at least with a fairly
recent libvirt. If you don't have any <filesystem> listed
with a target of '/', then libvirt will secretly add one
using source=/ and target=/.

You don't mention what version of libvirt / kernel, or host
OS you have here btw. That would be generally useful info
for troubleshooting this.

Regards,
Daniel
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