Difference between revisions of "LXC"

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(Prepare network on host)
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Create a network configuration template for the guests, ''/etc/lxc/lxc.conf'':
Create a network configuration template for the guests, ''/etc/lxc/default.conf'':
lxc.network.type = veth
lxc.network.type = veth

Revision as of 10:37, 8 March 2018

Linux Containers (LXC) provides containers similar BSD Jails, Linux VServer and Solaris Zones. It gives the impression of virtualization, but shares the kernel and resources with the "host".


Install the required packages:

apk add lxc bridge

If you want to create containers other than alpine you will need lxc-templates:

apk add lxc-templates

Prepare network on host

Set up a bridge on the host. Example /etc/network/interfaces:

auto br0
iface br0 inet dhcp
    bridge-ports eth0

Create a network configuration template for the guests, /etc/lxc/default.conf:

lxc.network.type = veth
lxc.network.link = br0
lxc.network.flags = up
lxc.network.hwaddr = fe:xx:xx:xx:xx:xx

Grsecurity restrictions

Some restrictions will be applied when using a grsecurity kernel (Alpine Linux default kernel). The most notable is the use of lxc-attach which will not be allowed because of GRKERNSEC_CHROOT_CAPS. To solve this we will have to disable this grsec restriction by creating a sysctl profile for lxc. Create the following file /etc/sysctl.d/10-lxc.conf and add:

kernel.grsecurity.chroot_caps = 0

There are a few other restrictions that can prevent proper container functionality. When things do not work as expected always check the kernel log with dmesg to see if grsec prevented things from happening.

Other possible restrictions are:

kernel.grsecurity.chroot_deny_chroot = 0
kernel.grsecurity.chroot_deny_mount = 0
kernel.grsecurity.chroot_deny_mknod = 0
kernel.grsecurity.chroot_deny_chmod = 0

When you finished creating your new sysctl profile you can apply it by restarting sysctl service

rc-service sysctl restart

NOTE: Always consult the Grsecurity documentation before applying these settings.

Create a guest

Alpine Template

lxc-create -n guest1 -f /etc/lxc/lxc.conf -t alpine

This will create a /var/lib/lxc/guest1 directory with a config file and a rootfs directory.

Note that by default alpine template does not have networking service on, you will need to add it using lxc-console

If running on x86_64 architecture, it is possible to create a 32bit guest:

lxc-create -n guest1 -f /etc/lxc/lxc.conf -t alpine -- --arch x86

Debian template

In order to create a debian template container you will need to install some packages:

apk add debootstrap rsync

Also you will need to turn off some grsecurity chroot options otherwise the debootstrap will fail:

echo 0 > /proc/sys/kernel/grsecurity/chroot_caps echo 0 > /proc/sys/kernel/grsecurity/chroot_deny_chroot echo 0 > /proc/sys/kernel/grsecurity/chroot_deny_mount echo 0 > /proc/sys/kernel/grsecurity/chroot_deny_mknod echo 0 > /proc/sys/kernel/grsecurity/chroot_deny_chmod

Please remember to turn them back on, or just simply reboot the system.

Now you can run:

SUITE=wheezy lxc-create -n guest1 -f /etc/lxc/lxc.conf -t debian

Ubuntu template

In order to create an ubuntu template container you will need to turn off some grsecurity chroot options:

echo 0 > /proc/sys/kernel/grsecurity/chroot_caps echo 0 > /proc/sys/kernel/grsecurity/chroot_deny_chroot echo 0 > /proc/sys/kernel/grsecurity/chroot_deny_mount echo 0 > /proc/sys/kernel/grsecurity/chroot_deny_mknod echo 0 > /proc/sys/kernel/grsecurity/chroot_deny_chmod

Please remember to turn them back on, or just simply reboot the system.

Now you can run (replace %MIRROR% with the actual hostname, for example: http://us.archive.ubuntu.com/ubuntu/)

lxc-create -n guest2 -f /etc/lxc/default.conf -t ubuntu -- -r xenial -a amd64 -u user --password secretpassword --mirror $MIRROR

Unprivileged LXC images (Debian / Ubuntu / Centos etc..)

apk add gnupg xz lxc-create -n container-name -t download

& choose the Distribution | Release | Architecture.

To be able to login to a Debian container you currently need to:

rm /lib/systemd/system/container-getty\@.service

You can also remove Systemd from the container.

Starting/Stopping the guest

Create a symlink to the /etc/init.d/lxc script for your guest.

ln -s lxc /etc/init.d/lxc.guest1

You can start your guest with:

/etc/init.d/lxc.guest1 start

Stop it with:

/etc/init.d/lxc.guest1 stop

Make it autostart on boot up with:

rc-update add lxc.guest1

You can also add to the container config: lxc.start.auto = 1


rc-update add lxc

to autostart containers by the lxc service only.

Connecting to the guest

By default sshd is not installed, so you will have to attach to the container or connect to the virtual console. This is done with:

Attach to container

lxc-attach -n guest1

Just type exit to detach the container again (please do check the grsec notes above)

Connect to virtual console

lxc-console -n guest1

To disconnect from it, press Ctrl+a q

Deleting a guest

Make sure the guest is stopped and run:

lxc-destroy -n guest1

This will erase everything, without asking any questions. It is equivalent to:

rm -r /var/lib/lxc/guest1


Creating a LXC container without modifying your network interfaces

The problem with bridging is that the interface you bridge gets replaced with your new bridge interface. That is to say that say you have an interface eth0 that you want to bridge, your eth0 interface gets replaced with the br0 interface that you create. It also means that the interface you use needs to be placed into promiscuous mode to catch all the traffic that could de destined to the other side of the bridge, which again may not be what you want.

The solution is to create a dummy network interface, bridge that, and set up NAT so that traffic out of your bridge interface gets pushed through the interface of your choice.

So, first, lets create that dummy interface (thanks to ncopa for talking me out of macvlan and pointing out the dummy interface kernel module)

modprobe dummy

This will create a dummy interface called dummy0 on your host.

Now we will create a bridge called br0

brctl addbr br0 brctl setfd br0 0

and then make that dummy interface one end of the bridge

brctl addif br0 dummy0

Next, let's give that bridged interface a reason to exists

ifconfig br0 netmask up

Create a file for your container, let's say /etc/lxc/bridgenat.conf, with the following settings.

lxc.network.type = veth
lxc.network.flags = up
lxc.network.link = br0
lxc.network.name = eth1
lxc.network.ipv4 =

and build your container with that file

lxc-create -n alpine -f /etc/lxc/bridgenat.conf -t alpine

You should now be able to ping your container from your hosts, and your host from your container.

Your container needs to know where to push traffic that isn't within it's subnet. To do so, we tell the container to route through the bridge interface br0 From inside the container run

route add default gw

The next step is you push the traffic coming from your private subnet over br0 out through your internet facing interface, or any interface you chose

We are messing with your IP tables here, so make sure these settings don't conflict with anything you may have already set up, obviously.

Say eth0 was your internet facing network interface, and br0 is the name of the bridge you made earlier, we'd do this:

echo 1 > /proc/sys/net/ipv4/ip_forward iptables --table nat --append POSTROUTING --out-interface eth0 -j MASQUERADE iptables --append FORWARD --in-interface br0 -j ACCEPT

Now you should be able to route through your bridge interface to the internet facing interface of your host from your container, just like at home!

You could also have a dhcp server running on your host, and set it up to give IP addresses from your private subnet to any container that requests it, and then have one template for multiple alpine LXC containers, perfect for alpine development :)

Using static IP

If you're using static IP, you need to configure this properly on guest's /etc/network/interfaces. To stay on the above example, modify /var/lib/lxc/guest1/rootfs/etc/network/interfaces


#auto lo
    iface lo inet loopback
auto eth0
    iface eth0 inet dhcp


#auto lo
    iface lo inet loopback
auto eth0
    iface eth0 inet static
    address <lxc-container-ip>   # IP which the lxc container should use
    gateway <gateway-ip>         # IP of gateway to use, mostly same as on lxc-host
    netmask <netmask>

mem and swap

vim /boot/extlinux.conf

APPEND initrd=initramfs-3.10.13-1-grsec root=UUID=7cd8789f-5659-40f8-9548-ae8f89c918ab modules=sd-mod,usb-storage,ext4 quiet cgroup_enable=memory swapaccount=1



Kernel configuration not found at /proc/config.gz; searching... Kernel configuration found at /boot/config-3.10.13-1-grsec --- Namespaces --- Namespaces: enabled Utsname namespace: enabled Ipc namespace: enabled Pid namespace: enabled User namespace: missing 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: missing Cgroup cpuset: enabled --- Misc --- Veth pair device: enabled Macvlan: enabled Vlan: enabled File capabilities: enabled Note : Before booting a new kernel, you can check its configuration usage : CONFIG=/path/to/config /usr/bin/lxc-checkconfig


In order for network to work on containers you need to set "Promiscuous Mode" to "Allow All" in VirtualBox settings for the network adapter.



Inside the container run:

chmod go+w /dev/null

to fix

rc-service postgresql start


see Setting_up_a_OpenVPN_server#openVPN_and_LXC

LXC 1.0 Additional information

Some info regarding new features in LXC 1.0


See also