lxc complains about cgroup not available

[Ritesh Raj Sarraf]

I have been trying to work with lxc to make use of my uml image. My config is as follows:

12:21:05 rrs@champaran:~$ cat /var/lib/lxc/test/config
lxc.utsname = test
lxc.rootfs = /home/rrs/Debian-Wheezy-AMD64-root_fs
lxc.rootfs.mount = /tmp/foo

lxc.cgroup.cpuset.cpus = 0,1
lxc.cgroup.cpu.shares = 1234
lxc.cgroup.devices.deny = a
lxc.cgroup.devices.allow = c 1:3 rw
lxc.cgroup.devices.allow = b 8:0 rw
#lxc.mount = /etc/fstab.complex
lxc.mount.entry = /lib /root/myrootfs/lib none ro,bind 0 0
lxc.cap.drop = sys_module mknod setuid net_raw
lxc.cap.drop = mac_override

When I try to start the instance, I get the following error:

12:16:04 rrs@champaran:~$ sudo lxc-start -n test
lxc-start: cgroup is not mounted
lxc-start: failed to setup the cgroups for 'test'
lxc-start: failed to setup the container
lxc-start: invalid sequence number 1. expected 2
lxc-start: failed to spawn 'test'

But as you can see below, cgroup is already mounted.

12:16:49 rrs@champaran:~$ mount
/dev/sda6 on / type ext4 (rw,errors=remount-ro,commit=600)
proc on /proc type proc (rw,noexec,nosuid,nodev)
sysfs on /sys type sysfs (rw,noexec,nosuid,nodev)
none on /sys/fs/fuse/connections type fusectl (rw)
none on /sys/kernel/debug type debugfs (rw)
none on /sys/kernel/security type securityfs (rw)
udev on /dev type devtmpfs (rw,mode=0755)
devpts on /dev/pts type devpts (rw,noexec,nosuid,gid=5,mode=0620)
tmpfs on /run type tmpfs (rw,noexec,nosuid,size=10%,mode=0755)
none on /run/lock type tmpfs (rw,noexec,nosuid,nodev,size=5242880)
none on /run/shm type tmpfs (rw,nosuid,nodev)
/dev/sda2 on /boot type ext4 (rw,commit=600)
binfmt_misc on /proc/sys/fs/binfmt_misc type binfmt_misc (rw,noexec,nosuid,nodev)
cgroups on /sys/fs/cgroup type tmpfs (rw,uid=0,gid=0,mode=0755)
gvfs-fuse-daemon on /home/rrs/.cache/gvfs type fuse.gvfs-fuse-daemon (rw,nosuid,nodev,user=rrs)

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: lxc 0.7.5-3ubuntu28
ProcVersionSignature: Ubuntu 3.2.0-17.26-generic 3.2.6
Uname: Linux 3.2.0-17-generic x86_64
ApportVersion: 1.91-0ubuntu1
Architecture: amd64
Date: Mon Feb 20 12:17:21 2012
SourcePackage: lxc
UpgradeStatus: Upgraded to precise on 2012-01-24 (26 days ago)
mtime.conffile..etc.default.lxc: 2012-01-25T01:58:25.599609

[Ritesh Raj Sarraf (rrs)]

actually, this must be a problem at my end. I just tried with lxc-create, and it was able to create a container. Sorry for the noise.

[Serge Hallyn (serge-hallyn)]

@Ritesh,

actually lxc-create doesn't need the cgroups, so that doesn't mean there is no problem. However, your mount output only shows that a tmpfs called cgroup is mounted under /sys/fs/cgroup. It doesn't show that actual cgroup filesystems are mounted under there. Take a look at /proc/self/mounts, and you should see something like:

serge@ubuntu:~$ grep cgroup /proc/self/mounts
cgroup /sys/fs/cgroup tmpfs rw,relatime,mode=755 0 0
cgroup /sys/fs/cgroup/cpuset cgroup rw,relatime,cpuset 0 0
cgroup /sys/fs/cgroup/cpu cgroup rw,relatime,cpu 0 0
cgroup /sys/fs/cgroup/cpuacct cgroup rw,relatime,cpuacct 0 0
cgroup /sys/fs/cgroup/memory cgroup rw,relatime,memory 0 0
cgroup /sys/fs/cgroup/devices cgroup rw,relatime,devices 0 0
cgroup /sys/fs/cgroup/freezer cgroup rw,relatime,freezer 0 0
cgroup /sys/fs/cgroup/blkio cgroup rw,relatime,blkio 0 0
cgroup /sys/fs/cgroup/perf_event cgroup rw,relatime,perf_event 0 0

[Arie Skliarouk (skliarie)]

kernel 3.2.0-30-generic
cgroup-bin 0.37.1-1ubuntu10

After boot cgroup fs is mounted onto /sys/fs/cgroup

# df | grep cgroup
 cgroups 4088656 0 4088656 0% /sys/fs/cgroup
# mount | grep cgroup
cgroups on /sys/fs/cgroup type tmpfs (rw,uid=0,gid=0,mode=0755)
#

and lxc-start complains on "lxc-start: cgroup is not mounted"

To workaround the problem following had to be done:
/etc/init.d/cgconfig stop
mkdir -p /cgroup
mount none -t cgroup /cgroup

After that lxc-start worked properly...

[Stéphane Graber (stgraber)]

Remove cgroup-bin from your system and replace it with cgroup-lite.

cgroup-bin is known to have a variety of issues and is in the process of getting killed to replace by the much simpler and much more reliable cgroup-lite.

[eval- (eval-)]

I had to remove cgroup-lite and install cgroup-bin in order to avoid this error. cgroup-lite was not mounting /sys/fs/cgroup which lxc-execute required. Once I installed cgroup-bin and invoked /etc/init.d/cgconfig everything worked fine on my 12.04.3 LTS

[Serge Hallyn (serge-hallyn)]

Ah, are you running a saucy or trusty backport kernel?

the precise cgroup-lite still is 'start on mounted MOUNTPOINT=/sys', whereas later it had to become 'MOUNTPOINT=/sys/fs/cgroup',

It sounds like we need to update the precise job to handle both cases.

[Serge Hallyn (serge-hallyn)]

Filed bug 1304538 for the cgroup-lite bug.