Linux containers (LXC), is a lightweight operating system-level virtualization method that allows us to run multiple isolated Linux systems (containers) on a single host. LXC does not provide all the features of standard virtualization software such as VMware, VirtualBox, and KVM but rather it provides a virtual environment that has its own CPU, memory, blocks I/O, network. LXC creates a Linux environment as close as to a standard Linux installation but without the need for the separate kernel.
LXC is free software, and it is released under GNU LGPLv2.1+ license. The LXC project is sponsored by Canonical Ltd who is behind Ubuntu OS.
In this guide, I will show you how to install LXC, and how to create and manage LXC using the command line as well as using LXC Web Portal.
Prerequisites
LXC is not available on Base repo. So we need to add EPEL repository to the server using the following command.
# yum -y install epel-release
LXC containers use bridge networking to have access to/from an external network, before starting the container we must create a network bridge on CentOS 7 / RHEL 7. The name of the network bridge should be “virbr0”
Install LXC on CentOS 7
Once you have completed prerequisites, it’s a time to install LXC. Install the LXC and other important packages required for the containers to work properly.
# yum -y install lxc lxc-templates libcap-devel libcgroup busybox wget bridge-utils lxc-extra
Run the following command to check everything is fine to run containers.
# lxc-checkconfig Kernel configuration not found at /proc/config.gz; searching... Kernel configuration found at /boot/config-3.10.0-327.el7.x86_64 --- 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 CONFIG_NF_NAT_IPV4: enabled CONFIG_NF_NAT_IPV6: enabled CONFIG_IP_NF_TARGET_MASQUERADE: enabled CONFIG_IP6_NF_TARGET_MASQUERADE: enabled CONFIG_NETFILTER_XT_TARGET_CHECKSUM: enabled --- Checkpoint/Restore --- checkpoint restore: enabled CONFIG_FHANDLE: enabled CONFIG_EVENTFD: enabled CONFIG_EPOLL: enabled CONFIG_UNIX_DIAG: enabled CONFIG_INET_DIAG: enabled CONFIG_PACKET_DIAG: enabled CONFIG_NETLINK_DIAG: 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 Linux Containers
LXC comes with ready-made templates for easy installation of containers, and you can list down the available templates using the following command.
# ls /usr/share/lxc/templates/ lxc-alpine lxc-archlinux lxc-centos lxc-debian lxc-fedora lxc-openmandriva lxc-oracle lxc-sshd lxc-ubuntu-cloud lxc-altlinux lxc-busybox lxc-cirros lxc-download lxc-gentoo lxc-opensuse lxc-plamo lxc-ubuntu
To create a container, issue the following command.
# lxc-create -n centos_lxc -t centos
Where,
-n <container name>
-t <template>
Once you have issued the above command, LXC will start creating the container with name “centos_lxc“.
Sample output:
Host CPE ID from /etc/os-release: cpe:/o:centos:centos:7 Checking cache download in /var/cache/lxc/centos/x86_64/7/rootfs ... Downloading centos minimal ... Loaded plugins: fastestmirror base | 3.6 kB 00:00:00 updates | 3.4 kB 00:00:00 Determining fastest mirrors . . . . Complete! Download complete. Copy /var/cache/lxc/centos/x86_64/7/rootfs to /var/lib/lxc/centos_lxc/rootfs ... Copying rootfs to /var/lib/lxc/centos_lxc/rootfs ... sed: can't read /var/lib/lxc/centos_lxc/rootfs/etc/init/tty.conf: No such file or directory Storing root password in '/var/lib/lxc/centos_lxc/tmp_root_pass' Expiring password for user root. passwd: Successsed: can't read /var/lib/lxc/centos_lxc/rootfs/etc/rc.sysinit: No such file or directory sed: can't read /var/lib/lxc/centos_lxc/rootfs/etc/rc.d/rc.sysinit: No such file or directory Container rootfs and config have been created. Edit the config file to check/enable networking setup. The temporary root password is stored in: '/var/lib/lxc/centos_lxc/tmp_root_pass' The root password is set up as expired and will require it to be changed at first login, which you should do as soon as possible. If you lose the root password or wish to change it without starting the container, you can change it from the host by running the following command (which will also reset the expired flag): chroot /var/lib/lxc/centos_lxc/rootfs passwd
Please note the above login details, and you must require this information to login to the containers.
Containers Credentials
To log into the container (centos_lxc), either use the temporary root password stored in the following location. In our case, “Root-centos_lxc-KRzJLy” is the root password of the centos_lxc.
# cat /var/lib/lxc/centos_lxc/tmp_root_pass Root-centos_lxc-KRzJLy
or
Reset the root password using the following command.
# chroot /var/lib/lxc/centos_lxc/rootfs passwd
PS: You are yet to start the containers.
Starting Linux Containers
After creating the containers, start it using the following command, runs in the background.
# lxc-start -n centos_lxc -d
Now, take the console of the container using the following command.
Note: I use “-t” with “0” to connect the container with tty0, just because tty1 was not responding to me.
# lxc-console -n centos_lxc -t 0
Enter the username and password to log in. You can find the credential at the end of the output during the creation of a container. You must change the root password at the first login.
Sample output:
Connected to tty 0
Type <Ctrl+a q> to exit the console, <Ctrl+a Ctrl+a> to enter Ctrl+a itself
CentOS Linux 7 (Core)
Kernel 3.10.0-327.el7.x86_64 on an x86_64
centos_lxc login: root
Password:
You are required to change your password immediately (root enforced)
Changing password for root.
(current) UNIX password:
New password:
Retype new password:
[root@centos_lxc ~]#
Once you logged in, you can perform all the work in this container as like you do on a normal Linux server.
To exit from the container’s console, press “Ctrl+a” followed by “q”. Now, you will be returned back to host computer’s terminal.
If you want to connect to the container again ( the container is still running), run the following command.
# lxc-console -n centos_lxc -t 0
Working with Linux Containers
To list down the containers on the host computer, use the following command.
# lxc-ls centos_lxc
Also, list down the containers that are currently active and running on the host computer.
# lxc-ls --active centos_lxc
Since I have only one container which is currently running, that’s why you could see the same output for both of the commands.
If you want to get the full information of the running container, then issue the following command.
# lxc-info -n centos_lxc Name: centos_lxc State: RUNNING PID: 4047 IP: 192.168.12.16 CPU use: 0.47 seconds BlkIO use: 6.32 MiB Memory use: 4.19 MiB KMem use: 0 bytes Link: vethM3N48G TX bytes: 1.53 KiB RX bytes: 1.94 KiB Total bytes: 3.47 KiB
The above command gives you detailed information (name, state, IP address, CPU, memory, I/O and network usage) of “centos_lxc” container.
You can also use IP address to connect to the containers instead of LXC console.
You can stop a running container using “lxc-stop” command, use the following command to stop a “centos_lxc” container.
# lxc-stop -n centos_lxc
Cloning Linux containers
LXC has a future of cloning a container from the existing container, run the following command to clone an existing “centos_lxc” container to a new container “centos_lxc_clone”.
Note: You must stop a running container before initiating the clone.
# lxc-clone centos_lxc centos_lxc_clone Created container centos_lxc_clone as copy of centos_lxc
Check out whether a container is created successfully.
# lxc-ls centos_lxc centos_lxc_clone
You can start working with a new container as usual.
# lxc_start -n centos_lxc_clone -d
# lxc_console -n centos_lxc_clone -t 0 Connected to tty 0 Type <Ctrl+a q> to exit the console, <Ctrl+a Ctrl+a> to enter Ctrl+a itself CentOS Linux 7 (Core) Kernel 3.10.0-327.el7.x86_64 on an x86_64 centos_lxc_clone login: root Password: Last login: Sat Mar 26 14:11:17 from 192.168.12.1 [root@centos_lxc_clone ~]#
Power off the container from inside console.
[root@centos_lxc_clone ~]# poweroff
Taking a Snapshot
LXC also has another future called snapshot, use the following commands.
Note: You must stop a container before taking a snapshot.
# lxc-stop -n centos_lxc_clone
For a demo, I am taking the snapshot of centos_lxc_clone.
# lxc-snapshot -n centos_lxc_clone
Sample output:
lxc_container: lxccontainer.c: lxcapi_snapshot: 2879 Snapshot of directory-backed container requested. lxc_container: lxccontainer.c: lxcapi_snapshot: 2880 Making a copy-clone. If you do want snapshots, then lxc_container: lxccontainer.c: lxcapi_snapshot: 2881 please create an aufs or overlayfs clone first, snapshot that lxc_container: lxccontainer.c: lxcapi_snapshot: 2882 and keep the original container pristine.
To know where the snapshot is being saved, run the following command.
# lxc-snapshot -L -n centos_lxc_clone snap0 (/var/lib/lxcsnaps/centos_lxc_clone) 2016:03:26 10:59:10
In Centos 7, LXC snapshots are stored in “/var/lib/lxcsnaps/”
Restoring Snapshot
To restore a container from the snapshot, use the following command.
# lxc-snapshot -r snap0 -n centos_lxc_clone
Removing Containers
To remove a container completely, use the following command.
# lxc-destroy -n centos_lxc_clone
Running an Ubuntu Container on CentOS 7
I came across multiple issues when I was trying to run an Ubuntu container on CentOS, was able to run Ubuntu with the help of some tweaks shared on other websites.
Install the below packages for Debian based containers.
# yum -y install debootstrap perl # cd /usr/sbin ; ln -sf debootstrap qemu-debootstrap
Run the following command to replace Debian mirror to ubuntu mirror.
# sed -i 's/DEF_HTTPS_MIRROR="https:\/\/mirrors.kernel.org\/debian"/DEF_HTTPS_MIRROR="https:\/\/mirrors.kernel.org\/ubuntu"/g' /usr/sbin/debootstrap
Thanks to unix.stackexchange.com
Get the Ubuntu precise keyring and place it in the keyrings directory.
# cd /tmp # wget "http://archive.ubuntu.com/ubuntu/pool/main/u/ubuntu-keyring/ubuntu-keyring_2011.11.21.tar.gz" # tar xzf ubuntu-keyring_2011.11.21.tar.gz # mkdir /usr/share/keyrings/ # cp /tmp/ubuntu-keyring-2011.11.21/keyrings/ubuntu-archive-keyring.gpg /usr/share/keyrings/
Thanks to blog.toxa.de
Create an Ubuntu container using the following command.
# lxc-create -n ubuntu_lxc -t ubuntu
Checking cache download in /var/cache/lxc/precise/rootfs-amd64 ...
Installing packages in template: ssh,vim,language-pack-en
Downloading ubuntu precise minimal ...
I: Retrieving Release
I: Retrieving Release.gpg
I: Checking Release signature
I: Valid Release signature (key id 630239CC130E1A7FD81A27B140976EAF437D05B5)
I: Retrieving Packages
I: Validating Packages
I: Retrieving Packages
Generation complete.
Setting up libdevmapper1.02.1 (2:1.02.48-4ubuntu7.4) ...
Setting up dmsetup (2:1.02.48-4ubuntu7.4) ...
update-initramfs: deferring update (trigger activated)
Processing triggers for libc-bin ...
ldconfig deferred processing now taking place
Processing triggers for initramfs-tools ...
Processing triggers for resolvconf ...
invoke-rc.d: policy-rc.d denied execution of start.
Download complete
Copy /var/cache/lxc/precise/rootfs-amd64 to /var/lib/lxc/ubuntu_lxc/rootfs ...
Copying rootfs to /var/lib/lxc/ubuntu_lxc/rootfs ...
Generating locales...
en_US.UTF-8... up-to-date
Generation complete.
Creating SSH2 RSA key; this may take some time ...
Creating SSH2 DSA key; this may take some time ...
Creating SSH2 ECDSA key; this may take some time ...
Timezone in container is not configured. Adjust it manually.
##
# The default user is 'ubuntu' with password 'ubuntu'!
# Use the 'sudo' command to run tasks as root in the container.
##
From the above output, you can see that default user is “ubuntu”, and the password for the user is “ubuntu”.
Take a console of Ubuntu container with the following command.
# lxc_console -n ubuntu_lxc Ubuntu 12.04.5 LTS ubuntu_lxc console ubuntu_lxc login: ubuntu Password: Welcome to Ubuntu 12.04.5 LTS (GNU/Linux 3.10.0-327.10.1.el7.x86_64 x86_64) * Documentation: https://help.ubuntu.com/ The programs included with the Ubuntu system are free software; the exact distribution terms for each program are described in the individual files in /usr/share/doc/*/copyright. Ubuntu comes with ABSOLUTELY NO WARRANTY, to the extent permitted by applicable law. Would you like to enter a security context? [N] ubuntu@ubuntu_lxc:~$
PS: I have not checked the functionality of the server except login, please do post here for any issues.
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