How to create unprivileged LXC container on Ubuntu Linux 14.04 LTS


ow 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

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:

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:

Create a new user for lxc.

Set password for for lxc.

Find out allocated subuids and subgids for the lxc user.

Create a default container configuration file for lxc user

Create a new container.

Start a new container.

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



$ 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:

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


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.



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