lxcfs

Introduction

LXCFS is a small FUSE filesystem written with the intention of making Linux containers feel more like a virtual machine. It started as a side-project of LXC but is useable by any runtime.

LXCFS will take care that the information provided by crucial files in procfs such as:

/proc/cpuinfo
/proc/diskstats
/proc/meminfo
/proc/stat
/proc/swaps
/proc/uptime

are container aware such that the values displayed (e.g. in /proc/uptime) really reflect how long the container is running and not how long the host is running.

Prior to the implementation of cgroup namespaces by Serge Hallyn LXCFS also provided a container aware cgroupfs tree. It took care that the container only had access to cgroups underneath it's own cgroups and thus provided additional safety. For systems without support for cgroup namespaces LXCFS will still provide this feature.

Usage

The recommended command to run lxcfs is:

sudo mkdir -p /var/lib/lxcfs
sudo lxcfs /var/lib/lxcfs

A container runtime wishing to use LXCFS should then bind mount the approriate files into the correct places on container startup.

LXC

In order to use lxcfs with systemd-based containers, you can either use LXC 1.1 in which case it should work automatically, or otherwise, copy the lxc.mount.hook and lxc.reboot.hook files (once built) from this tree to /usr/share/lxcfs, make sure it is executable, then add the following lines to your container configuration:

lxc.mount.auto = cgroup:mixed
lxc.autodev = 1
lxc.kmsg = 0
lxc.include = /usr/share/lxc/config/common.conf.d/00-lxcfs.conf

Upgrading LXCFS without breaking running containers

LXCFS is implemented using a simple shared library without any external dependencies other than FUSE. It is completely reloadable without having to umount it. This ensures that container can be kept running even when the shared library is upgraded.

To force a reload of the shared library at the next possible instance simply send SIGUSR1 to the pid of the running LXCFS process. This can be as simple as doing:

kill -s USR1 $(pidof lxcfs)

Using with Docker

docker run -it -m 256m --memory-swap 256m \
      -v /var/lib/lxcfs/proc/cpuinfo:/proc/cpuinfo:rw \
      -v /var/lib/lxcfs/proc/diskstats:/proc/diskstats:rw \
      -v /var/lib/lxcfs/proc/meminfo:/proc/meminfo:rw \
      -v /var/lib/lxcfs/proc/stat:/proc/stat:rw \
      -v /var/lib/lxcfs/proc/swaps:/proc/swaps:rw \
      -v /var/lib/lxcfs/proc/uptime:/proc/uptime:rw \
      ubuntu:18.04 /bin/bash

In a system with swap enabled, the parameter "-u" can be used to set all values in "meminfo" that refer to the swap to 0.

sudo lxcfs -u /var/lib/lxcfs

xiewen/lxcfs

lxcfs

Introduction

Usage

LXC

Upgrading LXCFS without breaking running containers

Using with Docker