How to create unprivileged LXC container on Ubuntu Linux 14.04 LTS

​ Author: Vivek Gite Last updated: February 3, 2016 8 comments

How do I install, create and manage unprivileged LXC containers on Ubuntu Linux version 14.04 LTS server?

LXC is an acronym for Linux Containers. It is nothing but an operating system-level virtualization technology for running multiple isolated Linux distros (systems containers) on a single Linux host. In this tutorial you will learn how to install and manage LXC containers on Ubuntu Linux server.

Say hello to LXC

imgFig.01: Linux containers

Fig.01: Linux containers

The LXC often described as a lightweight virtualization technology. You can think LXC as chrooted jail on steroids. There is no guest operating system involved. You can only run Linux distros with LXC. You can not run Windows or BSD or any other operating system with LXC. You can run CentOS or Gentoo or any other Linux distro using LXC.

Traditional virtualization such as KVM/XEN/VMWARE and paravirtualization need a full operating system image for each instance. You can run any operating system using traditional virtualization.

Install the lxc on Ubuntu

Type the following apt-get command to install : $ sudo apt-get install lxc Sample outputs:

imgFig.02: Installing LXC on Ubuntu

Fig.02: Installing LXC on Ubuntu

LXC and networking

LXC creates a NATed bridge called lxcbr0 for you. Each container will have one veth NIC and all traffic routed using the lxcbr0 bridge. To view current settings, enter: $ sudo brctl show Sample outputs:

bridge name bridge id       STP enabled interfaces
lxcbr0      8000.fe09977d9e4f   no      vethH1OXMH

To see an IP address assigned to the lxcbr0, enter: $ sudo ifconfig lxcbr0 Sample outputs:

lxcbr0    Link encap:Ethernet  HWaddr fe:09:97:7d:9e:4f  
          inet addr:  Bcast:  Mask:
          inet6 addr: fe80::4820:9fff:fe01:4d52/64 Scope:Link
          RX packets:40 errors:0 dropped:0 overruns:0 frame:0
          TX packets:42 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:3553 (3.5 KB)  TX bytes:4383 (4.3 KB)

To see DHCP range used by containers, enter: $ ps aux | grep lxc-dns | grep -o 'dhcp-range.[0-9].* ' Sample outputs:

dhcp-range, --dhcp-lease-max=253 --dhcp-no-override --except-interface=lo --interface=lxcbr0 --dhcp-leasefile=/var/lib/misc/dnsmasq.lxcbr0.leases

To check the current kernel for lxc support, enter: $ lxc-checkconfig Sample outputs:

Kernel configuration not found at /proc/config.gz; searching...
Kernel configuration found at /boot/config-3.13.0-76-generic
--- Namespaces ---
Namespaces: enabled
Utsname namespace: enabled
Ipc namespace: enabled
Pid namespace: enabled
User namespace: enabled
Network namespace: enabled
Multiple /dev/pts instances: enabled

--- Control groups ---
Cgroup: enabled
Cgroup clone_children flag: enabled
Cgroup device: enabled
Cgroup sched: enabled
Cgroup cpu account: enabled
Cgroup memory controller: enabled
Cgroup cpuset: enabled

--- Misc ---
Veth pair device: enabled
Macvlan: enabled
Vlan: enabled
Bridges: enabled
Advanced netfilter: enabled

--- Checkpoint/Restore ---
checkpoint restore: enabled
File capabilities: enabled

Note : Before booting a new kernel, you can check its configuration
usage : CONFIG=/path/to/config /usr/bin/lxc-checkconfig

Creating unprivileged container

Unprivileged containers run the same way as privileged ones, simply without using sudo or root access. This is more secure as you can’t be root on the host even if you managed to escape container. The steps are as follows:

  1. Create a new user for lxc.
  2. Set password for for lxc.
  3. Find out allocated subuids and subgids for the lxc user.
  4. Create a default container configuration file for lxc user
  5. Create a new container.
  6. Start a new container.
  7. Deploy apps in newly created unprivileged container.

Step – 1: Create a new user for lxc

Type the following command to add a user called mylxcusr: $ sudo useradd -s /sbin/bash -c 'unprivileged lxc user' -m mylxcusr

Step – 2: Set password for for lxc

Set the password for mylxcusr $ sudo passwd mylxcusr

Step -3: Find out allocated subuids and subgids for the lxc user

Type the following command $ sudo grep mylxcusr /etc/sub{gid,uid} Sample outputs:


Note down the values.

Step – 4:Create a default container configuration file for lxc user

Make sure the user “mylxcusr” is allowed up to 10 veth type devices to be created and added to the bridge called lxcbr0. In other words networking will only work if you add the following lines: $ sudo vi /etc/lxc/lxc-usernet Append the following line:

mylxcusr veth lxcbr0 10

Save and close the file. Now switch to new user using su or just login using the ssh client: $ su - mylxcusr OR $ ssh $ ssh mylxcusr@ $ id Sample outputs:

uid=1002(mylxcusr) gid=1002(mylxcusr) groups=1002(mylxcusr)

Once logged into a remote machine, type the following command to create ~/.config/lxc/ director as follows: $ mkdir -p ~/.config/lxc Finally, create ~/.config/lxc/default.conf file as follows: $ cp /etc/lxc/default.conf ~/.config/lxc/default.conf Edit the file, enter: $ vi ~/.config/lxc/default.conf Append the configuration as follows (use mapped user and group id ranges 100000:65536 from step #3):

lxc.id_map = u 0 100000 65536
lxc.id_map = g 0 100000 65536

Step – 5:Create a new container

Let us create a new Ubuntu container called httpd, enter: $ lxc-create -t download -n httpd -- -d ubuntu -r trusty -a amd64 Sample outputs:

imgFig.03: Create an Ubuntu container

Fig.03: Create an Ubuntu container

That’s all it takes to create an Ubuntu container called httpd.

Step – 6:Start a new container

To start httpd container type: $ lxc -n httpd -d $ echo $? $ lxc-ls --fancy

httpd     RUNNING  -     NO

To start a process inside a running container or just to login, enter: $ lxc-attach -n httpd Sample session inside a httpd container:

root@httpd:/# id
uid=0(root) gid=0(root) groups=0(root)
root@httpd:/# ifconfig 
eth0      Link encap:Ethernet  HWaddr 00:16:3e:ea:ce:fa  
          inet addr:  Bcast:  Mask:
          inet6 addr: fe80::216:3eff:feea:cefa/64 Scope:Link
          RX packets:37 errors:0 dropped:0 overruns:0 frame:0
          TX packets:35 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:3502 (3.5 KB)  TX bytes:3362 (3.3 KB)
lo        Link encap:Local Loopback  
          inet addr:  Mask:
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  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:0 
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)
root@httpd:/# lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 14.04.3 LTS
Release:    14.04
Codename:   trusty

For security reason, container images ship without user accounts and without a root password. Setup a root password for httpd container: # passwd root To enable sshd for httpd container, run: # apt-get install openssh-server You can login from host to container using ssh: $ ssh user@

Step – 7:Deploy apps in newly created unprivileged container

You can now install nginx, php or any other application. Just attach to container and run commands or apps as per your need.

Important management commands

Here is a quick overview of useful commands:

How do I start a container?

$ lxc-start -n {container-name-here} -d $ lxc-start -n mysql -d

How do I stop a container?

$ lxc-stop -n {container-name-here} $ lxc-stop -n mysql 

How do I destroy (delete) a container?

$ lxc-destroy -n {container-name-here} $ lxc-destroy -n mysql

How do I list all containers?

$ lxc-ls $ lxc-ls --fancy

How do I update or patch my container?

Use the lxc-attach command to update your container that is powered by Ubuntu or Debian: $ lxc-attach -n mysql apt-get -- -qq update $ lxc-attach -n mysql apt-get -- -qq upgrade $ lxc-attach -n nginx yum -- -y update

How do I force DHCP to provide a persistent IP address to my container?

As a root on host run the following command: $ sudo vi /etc/lxc/dnsmasq.conf To give containers on lxcbr0 a persistent ip address based on domain name, you can add entries as follows:


Save and close the file.

How do I create CentOS/Gentoo/Fedora or any other flavour of LXC?

$ lxc-create -t download -n {container-name-here} -- -d {DISTRONAME} -r {RELEASE} -a {ARCH} $ lxc-create -t download -n bar -- -d centos -r 6 -a amd64 $ lxc-create -t download -n foo -- -d gentoo -r current -a amd64 $ lxc-create -t download -n db -- -d ubuntu -r precise -a i386 $ lxc-create -t download -n nginx -- -d debian -r jessie -a amd64 $ lxc-create -t download -n mysql -- -d fedora -r 22 -a amd64 $ lxc-create -t download -n maridb -- -d oracle -r 6.5 -a amd64 $ lxc-create -t download -n cahcing -- -d plamo -r 5.x -a amd64 The list of lxc flavour:

centos  6   amd64   default 20160203_02:16
centos  6   i386    default 20160203_02:16
centos  7   amd64   default 20160203_02:16
debian  jessie  amd64   default 20160202_22:42
debian  jessie  armel   default 20160111_22:42
debian  jessie  armhf   default 20160111_22:42
debian  jessie  i386    default 20160202_22:42
debian  sid amd64   default 20160202_22:42
debian  sid armel   default 20160111_22:42
debian  sid armhf   default 20160111_22:42
debian  sid i386    default 20160202_22:42
debian  squeeze amd64   default 20160202_22:42
debian  squeeze armel   default 20150826_22:42
debian  squeeze i386    default 20160202_22:42
debian  wheezy  amd64   default 20160202_22:42
debian  wheezy  armel   default 20160111_22:42
debian  wheezy  armhf   default 20160111_22:42
debian  wheezy  i386    default 20160202_22:42
fedora  21  amd64   default 20160203_01:27
fedora  21  armhf   default 20160112_01:27
fedora  21  i386    default 20160203_01:27
fedora  22  amd64   default 20160203_01:27
fedora  22  armhf   default 20160112_01:27
fedora  22  i386    default 20160203_01:27
gentoo  current amd64   default 20160203_14:12
gentoo  current armhf   default 20160111_14:12
gentoo  current i386    default 20160203_14:12
oracle  6.5 amd64   default 20160203_11:40
oracle  6.5 i386    default 20160203_11:40
plamo   5.x amd64   default 20160202_21:36
plamo   5.x i386    default 20160202_21:36
ubuntu  precise amd64   default 20160203_03:49
ubuntu  precise armel   default 20160112_03:49
ubuntu  precise armhf   default 20160203_03:49
ubuntu  precise i386    default 20160203_03:49
ubuntu  trusty  amd64   default 20160203_03:49
ubuntu  trusty  arm64   default 20150604_03:49
ubuntu  trusty  armhf   default 20160203_03:49
ubuntu  trusty  i386    default 20160203_03:49
ubuntu  trusty  ppc64el default 20160201_03:49
ubuntu  vivid   amd64   default 20160203_03:49
ubuntu  vivid   arm64   default 20150604_03:49
ubuntu  vivid   armhf   default 20160203_03:49
ubuntu  vivid   i386    default 20160203_03:49
ubuntu  vivid   ppc64el default 20160201_03:49
ubuntu  wily    amd64   default 20160203_03:49
ubuntu  wily    arm64   default 20150604_03:49
ubuntu  wily    armhf   default 20160203_03:49
ubuntu  wily    i386    default 20160203_03:49
ubuntu  wily    ppc64el default 20160201_03:49
ubuntu  xenial  amd64   default 20160203_03:49
ubuntu  xenial  armhf   default 20160203_03:49
ubuntu  xenial  i386    default 20160203_03:49


And, there you have it, a container running on Ubuntu Linux 14.04 LTS in unprivileged mode. I suggest you visit the official project home page and Ubuntu lxc wiki page for more information.