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Proxmox Cluster file system (pmxcfs)
====================================

The Proxmox Cluster file system (pmxcfs) is a database-driven file
system for storing configuration files, replicated in real time to all
cluster nodes using corosync. We use this to store all PVE related
configuration files.

Although the file system stores all data inside a persistent database
on disk, a copy of the data resides in RAM. That imposes restriction
on the maximal size, which is currently 30MB. This is still enough to
store the configuration of several thousand virtual machines.

Advantages
----------

* seamless replication of all configuration to all nodes in real time
* provides strong consistency checks to avoid duplicate VM IDs
* read-only when a node loses quorum
* automatic updates of the corosync cluster configuration to all nodes
* includes a distributed locking mechanism

POSIX Compatibility
~~~~~~~~~~~~~~~~~~~

The file system is based on FUSE, so the behavior is POSIX like. But
some feature are simply not implemented, because we do not need them:

* you can just generate normal files and directories, but no symbolic
  links, ...

* you can't rename non-empty directories (because this makes it easier
  to guarantee that VMIDs are unique).

* you can't change file permissions (permissions are based on path)

* `O_EXCL` creates were not atomic (like old NFS)

* `O_TRUNC` creates are not atomic (FUSE restriction)


File access rights
~~~~~~~~~~~~~~~~~~

All files and directories are owned by user 'root' and have group
'www-data'. Only root has write permissions, but group 'www-data' can
read most files. Files below the following paths:

 /etc/pve/priv/
 /etc/pve/nodes/${NAME}/priv/

are only accessible by root.

Technology
----------

We use the http://www.corosync.org[Corosync Cluster Engine] for
cluster communication, and http://www.sqlite.org[SQlite] for the
database file. The filesystem is implemented in user space using
http://fuse.sourceforge.net[FUSE].

File system layout
------------------

The file system is mounted at:

 /etc/pve

Files
~~~~~

[width="100%",cols="m,d"]
|=======
|corosync.conf  |corosync cluster configuration file (previous to {pve} 4.x this file was called cluster.conf)
|storage.cfg   |{pve} storage configuration
|datacenter.cfg   |{pve} datacenter wide configuration (keyboard layout, proxy, ...)
|user.cfg      |{pve} access control configuration (users/groups/...)
|domains.cfg   |{pve} Authentication domains 
|authkey.pub   | public key used by ticket system
|pve-root-ca.pem | public certificate of cluster CA
|priv/shadow.cfg  | shadow password file
|priv/authkey.key | private key used by ticket system
|priv/pve-root-ca.key | private key of cluster CA
|nodes/<NAME>/pve-ssl.pem                 | public ssl certificate for web server (signed by cluster CA)
|nodes/<NAME>/pve-ssl.key            | private ssl key for pve-ssl.pem
|nodes/<NAME>/pveproxy-ssl.pem       | public ssl certificate (chain) for web server (optional override for pve-ssl.pem)
|nodes/<NAME>/pveproxy-ssl.key       | private ssl key for pveproxy-ssl.pem (optional)
|nodes/<NAME>/qemu-server/<VMID>.conf    | VM configuration data for KVM VMs
|nodes/<NAME>/lxc/<VMID>.conf         | VM configuration data for LXC containers
|firewall/cluster.fw | Firewall config applied to all nodes
|firewall/<NAME>.fw  | Firewall config for individual nodes
|firewall/<VMID>.fw  | Firewall config for VMs and Containers
|=======

Symbolic links
~~~~~~~~~~~~~~

[width="100%",cols="m,m"]
|=======
|local         |nodes/<LOCAL_HOST_NAME>
|qemu-server   |nodes/<LOCAL_HOST_NAME>/qemu-server/
|lxc           |nodes/<LOCAL_HOST_NAME>/lxc/
|=======

Special status files for debugging (JSON)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

[width="100%",cols="m,d"]
|=======
| .version    |file versions (to detect file modifications)
| .members    |Info about cluster members
| .vmlist     |List of all VMs
| .clusterlog |Cluster log (last 50 entries)
| .rrd        |RRD data (most recent entries)
|=======

Enable/Disable debugging
~~~~~~~~~~~~~~~~~~~~~~~~

You can enable verbose syslog messages with:

 echo "1" >/etc/pve/.debug 

And disable verbose syslog messages with:

 echo "0" >/etc/pve/.debug 


Recovery
--------

If you have major problems with your Proxmox VE host, e.g. hardware
issues, it could be helpful to just copy the pmxcfs database file
/var/lib/pve-cluster/config.db and move it to a new Proxmox VE
host. On the new host (with nothing running), you need to stop the
pve-cluster service and replace the config.db file (needed permissions
0600). Second, adapt '/etc/hostname' and '/etc/hosts' according to the
lost Proxmox VE host, then reboot and check. (And don´t forget your
VM/CT data)

Remove Cluster configuration
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The recommended way is to reinstall the node after you removed it from
your cluster. This makes sure that all secret cluster/ssh keys and any
shared configuration data is destroyed.

In some cases, you might prefer to put a node back to local mode
without reinstall, which is described here:

* stop the cluster file system in '/etc/pve/'

 # systemctl stop pve-cluster

* start it again but forcing local mode

 # pmxcfs -l

* remove the cluster config

 # rm /etc/pve/cluster.conf
 # rm /etc/cluster/cluster.conf
 # rm /var/lib/pve-cluster/corosync.authkey

* stop the cluster file system again

 # service pve-cluster stop

* restart pve services (or reboot)

 # service pve-cluster start
 # service pvedaemon restart
 # service pveproxy restart
 # service pvestatd restart