[lxc-devel] `top` within unprivileged container breaks host
Stéphane Graber
stgraber at ubuntu.com
Sat Jan 24 19:56:44 UTC 2015
On Sat, Jan 24, 2015 at 02:45:52PM -0500, S.Çağlar Onur wrote:
> On Sat, Jan 24, 2015 at 2:29 PM, Stéphane Graber <stgraber at ubuntu.com> wrote:
> > On Sat, Jan 24, 2015 at 02:14:15PM -0500, S.Çağlar Onur wrote:
> >> Hey Stéphane,
> >>
> >> On Fri, Jan 23, 2015 at 1:47 PM, Stéphane Graber <stgraber at ubuntu.com> wrote:
> >> > On Fri, Jan 23, 2015 at 06:19:46PM +0000, Serge Hallyn wrote:
> >> >> Quoting Mathias Gibbens (mathias at calenhad.com):
> >> >> > On Fri, 2015-01-23 at 00:48 +0000, Mathias Gibbens wrote:
> >> >> > > Hello,
> >> >> > >
> >> >> > > I've been testing LXC 1.1-rc1 on a Debian jessie system. Specifically,
> >> >> > > since all the pieces are now in place to support systemd in unprivileged
> >> >> > > containers, I've been testing running Debian jessie within an
> >> >> > > unprivileged container.
> >> >> > >
> >> >> > > The jessie container successfully starts (there are some errors along
> >> >> > > the way, but that's another issue), and I can do a `lxc-attach`, add a
> >> >> > > user and log in. However, if I run `top` within the container I only get
> >> >> > > two lines of output:
> >> >> > >
> >> >> > > top - 00:13:25 up 4 min, 0 users, load average: 0.01, 0.05, 0.05
> >> >> > > Tasks: 10 total, 1 running, 9 sleeping, 0 stopped, 0 zombie
> >> >> > >
> >> >> > > Furthermore, the host system breaks spectacularly:
> >> >> > >
> >> >> > > lxc at lxc:~$ top
> >> >> > > Error, do this: mount -t proc proc /proc
> >> >> > > lxc at lxc:~$ /sbin/ifconfig
> >> >> > > Warning: cannot open /proc/net/dev (No such file or directory). Limited
> >> >> > > output.
> >> >> > > lxc at lxc:~$ mount
> >> >> > > mount: failed to read mtab: No such file or directory
> >> >> > > lxc at lxc:~$ df
> >> >> > > df: cannot read table of mounted file systems: No such file or directory
> >> >> > > lxc at lxc:~$ sudo reboot
> >> >> > > Running in chroot, ignoring request.
> >> >> > >
> >> >> > > It seems that /proc is being unmounted somehow on the host. I can
> >> >> > > re-mount /proc on the host, and things seem to work again. (I haven't
> >> >> > > tested too much after re-mounting, instead opting to just reboot the
> >> >> > > host back to a known good state.)
> >> >> > >
> >> >> > > Any idea what is causing this to happen? I have also tried running
> >> >> > > Ubuntu Vivid as an unprivileged container and see the same results. I
> >> >> > > have not yet tried a different Linux distro for the host system.
> >> >> > >
> >> >> > > Host system details: Debian jessie with kernel 3.16.7-ckt2-1 x86_64,
> >> >> > > systemd-215, LXC-1.1-rc1 and lxcfs built from current git checkout,
> >> >> > > cgmanager-0.35 as packaged from the sid repository.
> >> >> > >
> >> >> > > Thanks for any ideas,
> >> >> > > Mathias
> >> >> >
> >> >> > This morning I setup a host running Ubuntu Vivid with cgmanager, lxc,
> >> >> > and lxcfs packages installed from the daily PPA. I setup two
> >> >>
> >> >> But did you install the systemd-sysv package?
> >> >>
> >> >> > unprivileged containers, Debian jessie and Ubuntu Vivid, and ran `top`
> >> >> > within each one. On the Vivid host, `top` runs properly and the host
> >> >> > system does not break.
> >> >> >
> >> >> > So, it seems that the breakage is due to running jessie on the host
> >> >> > system. Any ideas why this is happening, or where I could begin looking
> >> >> > to debug this problem?
> >> >>
> >> >> No, I've just reproduced it, but it requires systemd to do so.
> >> >>
> >> >> Note that you'll have to manually chown your name=systemd cgroup
> >> >> to your user for the lxc-start to succeed.
> >> >
> >> >
> >> > Hey,
> >> >
> >> > So we've just tracked down that bug and it's a critical flaw in lxcfs
> >> > which we've now fixed upstream. I tagged LXCFS 0.4 with the fix and am
> >> > publishing it now on our website and uploading it to Ubuntu.
> >>
> >> https://launchpad.net/~ubuntu-lxc/+archive/ubuntu/daily still shows
> >> the old lxcfs version. Should I be tracking some other repo?
> >
> > Oops, no. I uploaded to vivid but forgot to refresh the PPA. Doing that now.
>
> Thanks! Restarting lxcfs breaks running containers, is this expected?
> This happened just after upgrade;
It unfortunately is and I haven't found a good way around this.
The mount disappearing on the host causes all the bind mounts to break.
I tried working around this by running lxcfs in a sub-directory of
/var/lib/lxcfs, bind-mounting the whole directory and then bind-mounting
symlinks but even that didn't work since the kernel followed the
symlinks at the time of the bind-mount...
>
> [caglar at qop:~/go/src/gopkg.in/lxc/go-lxc.v2/examples] sudo apt-get dist-upgrade
> Reading package lists... Done
> Building dependency tree
> Reading state information... Done
> Calculating upgrade... Done
> The following packages will be upgraded:
> lxcfs
> 1 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
> Need to get 19.1 kB of archives.
> After this operation, 0 B of additional disk space will be used.
> Do you want to continue? [Y/n] y
> Get:1 http://ppa.launchpad.net/ubuntu-lxc/daily/ubuntu/ trusty/main
> lxcfs amd64 0.4-0ubuntu1~ubuntu14.04.1~ppa1 [19.1 kB]
> Fetched 19.1 kB in 0s (42.2 kB/s)
> (Reading database ... 204049 files and directories currently installed.)
> Preparing to unpack .../lxcfs_0.4-0ubuntu1~ubuntu14.04.1~ppa1_amd64.deb ...
> lxcfs stop/waiting
> Unpacking lxcfs (0.4-0ubuntu1~ubuntu14.04.1~ppa1) over
> (0.3-0ubuntu1~ubuntu14.04.1~ppa1) ...
> Processing triggers for man-db (2.6.7.1-1ubuntu1) ...
> Processing triggers for ureadahead (0.100.0-16) ...
> Setting up lxcfs (0.4-0ubuntu1~ubuntu14.04.1~ppa1) ...
> lxcfs start/running, process 24251
>
> [caglar at qop:~/go/src/gopkg.in/lxc/go-lxc.v2/examples] ./attach
> 2015/01/24 14:41:56 AttachShell
> root at rubik:/# free -m
> Error: /proc must be mounted
> To mount /proc at boot you need an /etc/fstab line like:
> proc /proc proc defaults
> In the meantime, run "mount proc /proc -t proc"
> root at rubik:/# exit
>
> and I can reproduce it by just restarting the lxcfs service
>
> [caglar at qop:~/go/src/gopkg.in/lxc/go-lxc.v2/examples] ./attach
> 2015/01/24 14:42:24 AttachShell
> root at rubik:/# free -m
> total used free shared buffers cached
> Mem: 128 10 117 5 0 0
> -/+ buffers/cache: 10 117
> Swap: 975 0 975
> root at rubik:/# exit
> 2015/01/24 14:42:29 RunCommand
> uid=0(root) gid=0(root) groups=0(root)
> [caglar at qop:~/go/src/gopkg.in/lxc/go-lxc.v2/examples] sudo restart lxcfs
> lxcfs start/running, process 26069
> [caglar at qop:~/go/src/gopkg.in/lxc/go-lxc.v2/examples] ./attach
> 2015/01/24 14:42:37 AttachShell
> root at rubik:/# free -m
> Error: /proc must be mounted
> To mount /proc at boot you need an /etc/fstab line like:
> proc /proc proc defaults
> In the meantime, run "mount proc /proc -t proc"
> root at rubik:/#
>
>
> >>
> >> > Thanks for reporting this!
> >> >
> >> > --
> >> > Stéphane Graber
> >> > Ubuntu developer
> >> > http://www.ubuntu.com
> >> >
> >> > _______________________________________________
> >> > lxc-devel mailing list
> >> > lxc-devel at lists.linuxcontainers.org
> >> > http://lists.linuxcontainers.org/listinfo/lxc-devel
> >> >
> >>
> >> --
> >> S.Çağlar Onur <caglar at 10ur.org>
> >> _______________________________________________
> >> lxc-devel mailing list
> >> lxc-devel at lists.linuxcontainers.org
> >> http://lists.linuxcontainers.org/listinfo/lxc-devel
> >
> > --
> > Stéphane Graber
> > Ubuntu developer
> > http://www.ubuntu.com
> >
> > _______________________________________________
> > lxc-devel mailing list
> > lxc-devel at lists.linuxcontainers.org
> > http://lists.linuxcontainers.org/listinfo/lxc-devel
> >
>
>
>
> --
> S.Çağlar Onur <caglar at 10ur.org>
> _______________________________________________
> lxc-devel mailing list
> lxc-devel at lists.linuxcontainers.org
> http://lists.linuxcontainers.org/listinfo/lxc-devel
--
Stéphane Graber
Ubuntu developer
http://www.ubuntu.com
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