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
/sys/devices/system/cpu/online
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.
Building
Build lxcfs as follows:
yum install fuse fuse-lib fuse-devel
git clone git://github.com/lxc/lxcfs
cd lxcfs
./bootstrap.sh
./configure
make
make install
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