[Devel] Re: LXC container, unmounting unneeded mount points (from the container namespace)

[Daniel Lezcano]

Michael H. Warfield wrote:
> Added lxc-devel to the cc list since this seems to be more appropriate
> over there (maybe) and I've just joined that one as well.
>
> On Fri, 2010-01-08 at 15:35 +0100, Daniel Lezcano wrote: 
>   
>> Ciprian Dorin, Craciun wrote:
>>     
>>> On Fri, Jan 8, 2010 at 4:17 PM, Daniel Lezcano <daniel.lezcano at free.fr> wrote:
>>>   
>>>       
>>>> Ciprian Dorin, Craciun wrote:
>>>>     
>>>>         
>>>>>    Hy all!
>>>>>
>>>>>    Today I've started to play with the LXC containers, and I've got a
>>>>> question: when starting a container (with it's own mount point
>>>>> namespace), and I do a `cat /proc/mounts` I also see the mount points
>>>>> from my host system.
>>>>>
>>>>>    So the question is: how can I force `lxc-create` to remove any
>>>>> uneeded mount points (maybe all)?
>>>>>
>>>>>       
>>>>>           
>>>> Committed today :)
>>>>
>>>> http://git.lab.toulouse-stg.fr.ibm.com/?p=lxc.git;a=commit;h=ed83715df7666879116d1657b1dd54a8fc6513f6
>>>>     
>>>>         
>
>   
>> Oops, this one:
>>     
>
>   
>> http://lxc.git.sourceforge.net/git/gitweb.cgi?p=lxc/lxc;a=commit;h=bf601689a9e0cea1ceaf17e4f7f853f5392c2827
>>     
>
> Nice.  This is EXACTLY what I've been looking for as well.  Only problem
> is...  It didn't work.  It complains about:
>
> lxc-start: could not umount 1 mounts"
>
> Then terminates saying it can't start the container.
>
> When I throw in some debugging prints, I find out that it's complaining
> that it can't umount {pivotdir}/dev.  Commented out the return -1's in
> that routine so it starts the container anyways and jump into the
> running container and I discover that {pivotdir}/dev/shm is still
> mounted even though it thinks it umounted it.  I can see from the
> debugging prints that it seems to have successfully umount it (the
> debugging message indicates that it umounted it - so it saw it had it
> and tried and got a good return from the attempt) but it's apparently
> still mount.  If I umount that {pivotdir}/dev/shm inside the container,
> I can then umount {pivotdir}/dev and {pivotdir}. 
>
> Tried it both by defining lxc.pivotdir and by letting it choose a
> temporary one.  Tried two different containers.  Same result.
>
> This is what I get with the "return -1"'s commented out in the function
> and laced with my own debugging prints to print each step of the umount
> loop (this is with lxc.pivotdir = /rootfs):
>
> ===
> [root at Berserker-Base ~]# lxc-start -n 1009
> still mounted '/rootfs/dev'
> umounted '/rootfs/dev/pts'
> umounted '/rootfs/dev/shm'
> still mounted '/rootfs/proc'
> umounted '/rootfs/proc/bus/usb'
> umounted '/rootfs/proc/sys/fs/binfmt_misc'
> umounted '/rootfs/sys'
> umounted '/rootfs/home'
> still mounted '/rootfs/var'
> umounted '/rootfs/var/lib/cgroup'
> umounted '/rootfs/var/lib/nfs/rpc_pipefs'
> umounted '/rootfs/usr'
> umounted '/rootfs/boot'
> still mounted '/rootfs/srv'
> umounted '/rootfs/misc'
> umounted '/rootfs/net'
> still mounted '/rootfs/srv/lxc/root/1009'
> umounted '/rootfs/srv/lxc/root/1009/export'
> umounted '/rootfs/srv/lxc/root/1009/srv/shared'
> umounted '/rootfs/srv/lxc/root/1009/dev/pts'
> umounted '/rootfs/srv/lxc/root/1009/proc'
> umounted '/rootfs/srv/lxc/root/1009/sys'
> umounted '/rootfs/srv/lxc/root/1009/dev/shm'
> umounted '/rootfs/srv/lxc/root/1009/dev/console'
> umounted '/rootfs/srv/lxc/root/1009/dev/tty1'
> umounted '/rootfs/srv/lxc/root/1009/dev/tty2'
> umounted '/rootfs/srv/lxc/root/1009/dev/tty3'
> umounted '/rootfs/srv/lxc/root/1009/dev/tty4'
> umounted '/rootfs/srv/lxc/root/1009/dev/tty5'
> umounted '/rootfs/srv/lxc/root/1009/dev/tty6'
> still mounted '/rootfs/dev'
> umounted '/rootfs/proc'
> umounted '/rootfs/var'
> still mounted '/rootfs/srv'
> umounted '/rootfs/srv/lxc/root/1009'
> still mounted '/rootfs/dev'
> umounted '/rootfs/srv'
> still mounted '/rootfs/dev'
> lxc-start: could not umount 1 mounts
> lxc-start: Device or resource busy - could not unmount old rootfs
> INIT: version 2.86 booting
> ===
>
> Container now continues to boot, since I commented out the error
> returns.  Jumping into that container:
>
> === 
> [root at Berserker ~]# df
> Filesystem           1K-blocks      Used Available Use% Mounted on
> rootfs               288433504 240305660  33476248  88% /
> /dev/sda6              2063504    662116   1296568  34% /rootfs
> udev                   1031280       200   1031080   1% /rootfs/dev
> /dev/shm               1031280         0   1031280   0% /rootfs/dev/shm
> /dev/mapper/VolGroup00-LogVol00
>                      288433504 240305660  33476248  88% /
> /dev/sda6              2063504    662116   1296568  34% /export
> /dev/sda7            693727244 554704408 103783460  85% /srv/shared
> none                   1031280         0   1031280   0% /dev/shm
> [root at Berserker ~]# umount /rootfs/dev/shm
> [root at Berserker ~]# umount /rootfs/dev    
> [root at Berserker ~]# umount /rootfs    
> [root at Berserker ~]# df
> Filesystem           1K-blocks      Used Available Use% Mounted on
> rootfs               288433504 240305672  33476236  88% /
> /dev/mapper/VolGroup00-LogVol00
>                      288433504 240305672  33476236  88% /
> /dev/sda6              2063504    662116   1296568  34% /export
> /dev/sda7            693727244 554704408 103783460  85% /srv/shared
> none                   1031280         0   1031280   0% /dev/shm
> ===
>
> Of course we also have the strange "rootfs" entry there as well.
>
> Host system is Fedora 12.
> Host kernel is: 2.6.31.9-174.fc12.i686
> Guest system in each case is CentOS 5.4
>   

I added in the Cc Michael Holzt.

Thanks for reporting this.

  -- Daniel

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