Dirty Harry Wiki: Lxc

lxc#

lxc
Resources
Install and setup
Creating your first container
Operating the container
Show what is running
Starting the container
Stopping the container
Cloning the container
Destroying a container
control groups
Networking
TODO => how to get network access to the container(s) from other hosts than the "hypervisor" host.

Linux containers is a kernel based lightweight virtual system mechanism sometimes described as “chroot on steroids”.
It is part of the mainstream kernel, and is based on kernel cgroups.

Resources#

Install and setup#

First install the package lxc. This will introduce some new directories and files :

/etc/lxc/lxc.conf - the main configuration file for lxc
/etc/init/lxc.conf - two upstart scripts
/usr/lib/lxc/templates - contains the `templates' which can be used to create new containers.
/var/lib/lxc - is where containers and their configuration information are stored.
/var/cache/lxc - is where caches of distribution data are stored to speed up multiple container creations.

Creating your first container#

Well, this is very simple :

lxc-create -t ubuntu -n ubuntu1

Which means: use template ubuntu and name the new container ubuntu1
A new directory is created and has contents for a minimal ubuntu system:

athena ~ # ls -l /var/lib/lxc/ubuntu1/
total 12
-rw-r--r--  1 root root 1304 Feb  3 17:35 config
-rw-r--r--  1 root root  110 Feb  3 15:17 fstab
drwxr-xr-x 21 root root 4096 Feb  4 20:55 rootfs
-rw-------  1 root root    0 Feb  3 15:17 rootfs.hold
athena ~ # ls -l /var/lib/lxc/ubuntu1/rootfs
total 76
drwxr-xr-x  2 root root 4096 Feb  3 15:17 bin
drwxr-xr-x  2 root root 4096 Apr 19  2012 boot
drwxr-xr-x  8 root root 4096 Feb  4 20:55 dev
drwxr-xr-x 62 root root 4096 Feb  4 20:55 etc
drwxr-xr-x  3 root root 4096 Feb  3 15:17 home
drwxr-xr-x 12 root root 4096 Feb  3 15:16 lib
drwxr-xr-x  2 root root 4096 Feb  3 15:14 media
drwxr-xr-x  2 root root 4096 Apr 19  2012 mnt
drwxr-xr-x  2 root root 4096 Feb  3 15:14 opt
drwxr-xr-x  2 root root 4096 Apr 19  2012 proc
drwx------  2 root root 4096 Feb  3 18:43 root
drwxr-xr-x  6 root root 4096 Feb  3 15:17 run
drwxr-xr-x  2 root root 4096 Feb  3 15:17 sbin
drwxr-xr-x  2 root root 4096 Mar  5  2012 selinux
drwxr-xr-x  2 root root 4096 Feb  3 15:14 srv
drwxr-xr-x  2 root root 4096 Apr 14  2012 sys
drwxrwxrwt  2 root root 4096 Feb  4 21:17 tmp
drwxr-xr-x 10 root root 4096 Feb  3 15:14 usr
drwxr-xr-x 11 root root 4096 Feb  3 18:52 var

Operating the container#

Show what is running#

athena ~ # lxc-list 
RUNNING

FROZEN

STOPPED
  ubuntu1

And (after starting a conainer) :

athena ~ # lxc-info -n ubuntu1
state:   RUNNING
pid:     12945

Starting the container#

athena ~ # lxc-start -n ubuntu1 -d

The -d option is for daemonize. If you omit this option you get a console

You can also grab a console afterwards

lxc-console -n ubuntu1

(press <Ctrl-a q> to quit the console).

Stopping the container#

You can, of course, shutdown the container itself when you are logged by issuing the shutdown command.
From the host you can issue:

lxc-shutdown -n ubuntu1

Cloning the container #

Cloning container ubuntu1 to ubuntu2 :

athena ~ # lxc-clone -o ubuntu1 -n ubuntu2
Tweaking configuration
Copying rootfs...
Updating rootfs...
'ubuntu2' created

Destroying a container#

athena ~ # lxc-destroy -n ubuntu2
Container ubuntu2 is running, aborting the deletion.
athena ~ # lxc-destroy -n ubuntu2 -f
athena ~ # lxc-list
RUNNING
  ubuntu1

FROZEN

STOPPED

control groups#

The lxc-cgroup allows you to set controls (constraints) on the container.
From the man page:

DESCRIPTION
       lxc-cgroup  get  or set value from the control group associated with the container name. 
       If no [value] is specified, the value of the subsystem is displayed, otherwise it is set. 
       The lxc-cgroup does not assume the correctness of the  subsystem name, it is up to the user to specify 
       the right subsystem name.

A few examples :

show cpus:

athena ~ # lxc-cgroup -n ubuntu1 cpuset.cpu_exclusive
0
athena ~ # lxc-cgroup -n ubuntu1 cpuset.cpus
0

More documentation/explanation needed here

limit/show blkio read bytes per second:

athena ~ # lxc-cgroup -n ubuntu1 blkio.throttle.read_bps_device "8:0 10000000"
athena ~ # lxc-cgroup -n ubuntu1 blkio.throttle.read_bps_device
8:0 10000000

The funny thing is that you can set these things on the fly. So for example try to do a ls -l / while logged in the container, and the set the blkio.throttle.read_bps_device to something like 1000, you immediately see the thing slowing down dramatically.

You can see the available subsystem in /sys/fs/cgroup filesystem :

athena cgroup # find .|grep lxc/ubuntu1
./perf_event/lxc/ubuntu1
./perf_event/lxc/ubuntu1/cgroup.clone_children
./perf_event/lxc/ubuntu1/cgroup.event_control
./perf_event/lxc/ubuntu1/notify_on_release
./perf_event/lxc/ubuntu1/cgroup.procs
./perf_event/lxc/ubuntu1/tasks
./blkio/lxc/ubuntu1
./blkio/lxc/ubuntu1/blkio.io_queued
./blkio/lxc/ubuntu1/blkio.io_merged
./blkio/lxc/ubuntu1/blkio.io_wait_time
./blkio/lxc/ubuntu1/blkio.io_service_time
./blkio/lxc/ubuntu1/blkio.io_serviced
./blkio/lxc/ubuntu1/blkio.io_service_bytes
./blkio/lxc/ubuntu1/blkio.sectors
./blkio/lxc/ubuntu1/blkio.time
./blkio/lxc/ubuntu1/blkio.weight
./blkio/lxc/ubuntu1/blkio.weight_device
./blkio/lxc/ubuntu1/blkio.throttle.io_serviced
./blkio/lxc/ubuntu1/blkio.throttle.io_service_bytes
./blkio/lxc/ubuntu1/blkio.throttle.write_iops_device
./blkio/lxc/ubuntu1/blkio.throttle.read_iops_device
./blkio/lxc/ubuntu1/blkio.throttle.write_bps_device
./blkio/lxc/ubuntu1/blkio.throttle.read_bps_device
./blkio/lxc/ubuntu1/blkio.reset_stats
./blkio/lxc/ubuntu1/cgroup.clone_children
./blkio/lxc/ubuntu1/cgroup.event_control
./blkio/lxc/ubuntu1/notify_on_release
./blkio/lxc/ubuntu1/cgroup.procs
./blkio/lxc/ubuntu1/tasks
./freezer/lxc/ubuntu1
./freezer/lxc/ubuntu1/freezer.state
./freezer/lxc/ubuntu1/cgroup.clone_children
./freezer/lxc/ubuntu1/cgroup.event_control
./freezer/lxc/ubuntu1/notify_on_release
./freezer/lxc/ubuntu1/cgroup.procs
./freezer/lxc/ubuntu1/tasks
./devices/lxc/ubuntu1
./devices/lxc/ubuntu1/devices.list
./devices/lxc/ubuntu1/devices.deny
./devices/lxc/ubuntu1/devices.allow
./devices/lxc/ubuntu1/cgroup.clone_children
./devices/lxc/ubuntu1/cgroup.event_control
./devices/lxc/ubuntu1/notify_on_release
./devices/lxc/ubuntu1/cgroup.procs
./devices/lxc/ubuntu1/tasks
./memory/lxc/ubuntu1
./memory/lxc/ubuntu1/memory.memsw.failcnt
./memory/lxc/ubuntu1/memory.memsw.limit_in_bytes
./memory/lxc/ubuntu1/memory.memsw.max_usage_in_bytes
./memory/lxc/ubuntu1/memory.memsw.usage_in_bytes
./memory/lxc/ubuntu1/memory.oom_control
./memory/lxc/ubuntu1/memory.move_charge_at_immigrate
./memory/lxc/ubuntu1/memory.swappiness
./memory/lxc/ubuntu1/memory.use_hierarchy
./memory/lxc/ubuntu1/memory.force_empty
./memory/lxc/ubuntu1/memory.stat
./memory/lxc/ubuntu1/memory.failcnt
./memory/lxc/ubuntu1/memory.soft_limit_in_bytes
./memory/lxc/ubuntu1/memory.limit_in_bytes
./memory/lxc/ubuntu1/memory.max_usage_in_bytes
./memory/lxc/ubuntu1/memory.usage_in_bytes
./memory/lxc/ubuntu1/cgroup.clone_children
./memory/lxc/ubuntu1/cgroup.event_control
./memory/lxc/ubuntu1/notify_on_release
./memory/lxc/ubuntu1/cgroup.procs
./memory/lxc/ubuntu1/tasks
./cpuacct/lxc/ubuntu1
./cpuacct/lxc/ubuntu1/cpuacct.stat
./cpuacct/lxc/ubuntu1/cpuacct.usage_percpu
./cpuacct/lxc/ubuntu1/cpuacct.usage
./cpuacct/lxc/ubuntu1/cgroup.clone_children
./cpuacct/lxc/ubuntu1/cgroup.event_control
./cpuacct/lxc/ubuntu1/notify_on_release
./cpuacct/lxc/ubuntu1/cgroup.procs
./cpuacct/lxc/ubuntu1/tasks
./cpu/lxc/ubuntu1
./cpu/lxc/ubuntu1/cpu.rt_period_us
./cpu/lxc/ubuntu1/cpu.rt_runtime_us
./cpu/lxc/ubuntu1/cpu.stat
./cpu/lxc/ubuntu1/cpu.cfs_period_us
./cpu/lxc/ubuntu1/cpu.cfs_quota_us
./cpu/lxc/ubuntu1/cpu.shares
./cpu/lxc/ubuntu1/cgroup.clone_children
./cpu/lxc/ubuntu1/cgroup.event_control
./cpu/lxc/ubuntu1/notify_on_release
./cpu/lxc/ubuntu1/cgroup.procs
./cpu/lxc/ubuntu1/tasks
./cpuset/lxc/ubuntu1
./cpuset/lxc/ubuntu1/cpuset.memory_spread_slab
./cpuset/lxc/ubuntu1/cpuset.memory_spread_page
./cpuset/lxc/ubuntu1/cpuset.memory_pressure
./cpuset/lxc/ubuntu1/cpuset.memory_migrate
./cpuset/lxc/ubuntu1/cpuset.sched_relax_domain_level
./cpuset/lxc/ubuntu1/cpuset.sched_load_balance
./cpuset/lxc/ubuntu1/cpuset.mem_hardwall
./cpuset/lxc/ubuntu1/cpuset.mem_exclusive
./cpuset/lxc/ubuntu1/cpuset.cpu_exclusive
./cpuset/lxc/ubuntu1/cpuset.mems
./cpuset/lxc/ubuntu1/cpuset.cpus
./cpuset/lxc/ubuntu1/cgroup.clone_children
./cpuset/lxc/ubuntu1/cgroup.event_control
./cpuset/lxc/ubuntu1/notify_on_release
./cpuset/lxc/ubuntu1/cgroup.procs
./cpuset/lxc/ubuntu1/tasks

Networking#

A virtual bridge is used for networking :

athena ~ # ifconfig 
eth0      Link encap:Ethernet  HWaddr e8:03:9a:e8:75:86  
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:41921 errors:0 dropped:0 overruns:0 frame:0
          TX packets:41921 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:37262180 (37.2 MB)  TX bytes:37262180 (37.2 MB)

lxcbr0    Link encap:Ethernet  HWaddr fe:e8:17:00:6d:05  
          inet addr:10.0.3.1  Bcast:10.0.3.255  Mask:255.255.255.0
          inet6 addr: fe80::d046:f4ff:feb8:f8c0/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:1041 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1530 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:190653 (190.6 KB)  TX bytes:164137 (164.1 KB)

vethYMtsPw Link encap:Ethernet  HWaddr fe:e8:17:00:6d:05  
          inet6 addr: fe80::fce8:17ff:fe00:6d05/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:6 errors:0 dropped:0 overruns:0 frame:0
          TX packets:25 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:468 (468.0 B)  TX bytes:5186 (5.1 KB)

wlan0     Link encap:Ethernet  HWaddr c4:85:08:52:76:78  
          inet addr:10.0.0.164  Bcast:10.255.255.255  Mask:255.0.0.0
          inet6 addr: fe80::c685:8ff:fe52:7678/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:24077 errors:0 dropped:0 overruns:0 frame:0
          TX packets:19514 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:18875484 (18.8 MB)  TX bytes:5204192 (5.2 MB)