What’s LXCFS?

LXCFS is a side project of LXC and LXD. It’s basically a tiny FUSE filesystem which gets mounted in your containers and mask a number of proc files.

At present, it supports the following files:

  • /proc/cpuinfo
    Only returns the CPUs listed in your cpuset
  • /proc/diskstats
    Returns I/O usage from the container
  • /proc/meminfo
    Only shows the amount of memory and SWAP the container can use
  • /proc/stat
    Related to cpuinfo, only lists the right CPUs
  • /proc/swaps
    Related to meminfo, only shows your container’s swap consumption
  • /proc/uptime
    Shows the container uptime instead of the host’s

It’s basically a userspace workaround to changes which were deemed unreasonable to do in the kernel. It makes containers feel much more like separate systems than they would without it.

On top of the proc virtualization feature, lxcfs also supports rendering a partial cgroupfs view which can then be mounted into a container on top of /sys/fs/cgroup, allowing processes in the container to interact with the cgroups in a safe way.

This part is only enabled on kernels that do not support the cgroup namespace, as newer kernels (4.6 upstream, 4.4 Ubuntu) no longer need this.

Why do I need it?

lxcfs isn’t absolutely needed to run LXC or LXD containers.

That being said, you will want it if:

  • You want proper resource consumption reporting inside your container
  • You need to start a systemd based container on a system running a kernel older than 4.6 upstream (or 4.4 Ubuntu)

LXD in Ubuntu actually depends on LXCFS as we think it’s a critical part of offering a good container experience on Ubuntu.

How to get it?

LXCFS is available in quite a few distributions, so chances are you can just grab it with your package manager. It may take a few days/weeks for 2.0 to be available though.

Ubuntu users have had lxcfs available for a few years now and the 2.0 release is now in the Ubuntu development release. Up to date packages for all Ubuntu releases can also be found in our PPAs.

Install fuse

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yum install fuse fuse-devel
yum install pam-devel
modprobe fuse

Building and running lxcfs from git

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git clone git://github.com/lxc/lxcfs
cd lxcfs
./bootstrap.sh
./configure
make
sudo mkdir -p /var/lib/lxcfs
sudo ./lxcfs -s -f -o allow_other /var/lib/lxcfs/

note:
After the last step is started, if the report can not find the liblxcfs.so file.

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# ./lxcfs -s -f -o allow_other /var/lib/lxcfs/
lxcfs.c: 99: do_reload: Failed to open liblxcfs.so: /usr/local/lib/lxcfs/liblxcfs.so: cannot open shared object file: No such file or directory.

execute:

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# cp .libs/liblxcfs.so /usr/lib/lxcfs/liblxcfs.so

Start LXCFS in the background and detect the process state automatically pull up, the content is as follows:

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#!/bin/bash
a=`ps -ef|grep /var/lib/lxcfs|grep -v grep|wc -l`
if [ $a -eq 0 ];then
b=`mount|grep /var/lib/lxc|wc -l`
if [ $b -ne 0 ];then
    umount /var/lib/lxcfs/
fi
rm -rf /var/lib/lxcfs/*
cd /home/wangxigang/lxcfs/lxcfs
nohup  ./lxcfs -s -f -o allow_other /var/lib/lxcfs/ > /root/lxcfs_startup.log  2>&1 &
fi

Test

create and run docker container:

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docker run -it --rm --privileged=true --cpuset-cpus=2-9 -m 1024m -v /var/lib/lxcfs/proc/uptime:/proc/uptime:rw -v /var/lib/lxcfs/proc/cpuinfo:/proc/cpuinfo:rw -v /var/lib/lxcfs/proc/stat:/proc/stat -v /var/lib/lxcfs/cgroup/:/cgroup/:rw  -v /var/lib/lxcfs/proc/meminfo:/proc/meminfo -v /var/lib/lxcfs/proc/swaps:/proc/swaps -v /var/lib/lxcfs/proc/diskstats:/proc/diskstats  -v /home/wangxigang/go/src/runtime:/root/ ubuntu:14.04 /bin/bash

lxcfs

Project information