Merge pull request #250 from brauner/2018-07-30/improve_error_message

[mirror_lxcfs.git] / README.md

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 # lxcfs
 
-FUSE filesystem for LXC, offering the following features:
- - a cgroupfs compatible view for unprivileged containers
- - a set of cgroup-aware files:
-   - cpuinfo
-   - meminfo
-   - stat
-   - uptime
+## 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.
 
-### Usage
+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 -s -f -d -o allow_other /var/lib/lxcfs
+    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:
 
-We recommend -s to avoid threading;  -o allow_other is needed to
-allow users other than root to use the filesystem.
+    kill -s USR1 $(pidof lxcfs)