pmxcfs.adoc

   1 Proxmox Cluster file system (pmxcfs)
   2 ====================================
   3
   4 The Proxmox Cluster file system (pmxcfs) is a database-driven file
   5 system for storing configuration files, replicated in real time to all
   6 cluster nodes using corosync. We use this to store all PVE related
   7 configuration files.
   8
   9 Although the file system stores all data inside a persistent database
  10 on disk, a copy of the data resides in RAM. That imposes restriction
  11 on the maximal size, which is currently 30MB. This is still enough to
  12 store the configuration of several thousand virtual machines.
  13
  14 Advantages
  15 ----------
  16
  17 * seamless replication of all configuration to all nodes in real time
  18 * provides strong consistency checks to avoid duplicate VM IDs
  19 * read-only when a node looses quorum
  20 * automatic updates of the corosync cluster configuration to all nodes
  21 * includes a distributed locking mechanism
  22
  23 POSIX Compatibility
  24 ~~~~~~~~~~~~~~~~~~~
  25
  26 The file system is based on FUSE, so the behavior is POSIX like. But
  27 some feature are simply not implemented, because we do not need them:
  28
  29 * you can just generate normal files and directories, but no symbolic
  30   links, ...
  31
  32 * you can't rename non-empty directories (because this makes it easier
  33   to guarantee that VMIDs are unique).
  34
  35 * you can't change file permissions (permissions are based on path)
  36
  37 * `O_EXCL` creates were not atomic (like old NFS)
  38
  39 * `O_TRUNC` creates are not atomic (FUSE restriction)
  40
  41
  42 File access rights
  43 ~~~~~~~~~~~~~~~~~~
  44
  45 All files and directories are owned by user 'root' and have group
  46 'www-data'. Only root has write permissions, but group 'www-data' can
  47 read most files. Files below the following paths:
  48
  49  /etc/pve/priv/
  50  /etc/pve/nodes/${NAME}/priv/
  51
  52 are only accessible by root.
  53
  54 Technology
  55 ----------
  56
  57 We use the http://www.corosync.org[Corosync Cluster Engine] for
  58 cluster communication, and http://www.sqlite.org[SQlite] for the
  59 database file. The filesystem is implemented in user space using
  60 http://fuse.sourceforge.net[FUSE].
  61
  62 File system layout
  63 ------------------
  64
  65 The file system is mounted at:
  66
  67  /etc/pve
  68
  69 Files
  70 ~~~~~
  71
  72 [width="100%",cols="m,d"]
  73 |=======
  74 |corosync.conf  |corosync cluster configuration file (previous to {pve} 4.x this file was called cluster.conf)
  75 |storage.cfg   |{pve} storage configuration
  76 |datacenter.cfg   |{pve} datacenter wide configuration (keyboard layout, proxy, ...)
  77 |user.cfg      |{pve} access control configuration (users/groups/...)
  78 |domains.cfg   |{pve} Authentication domains
  79 |authkey.pub   | public key used by ticket system
  80 |priv/shadow.cfg  | shadow password file
  81 |priv/authkey.key | private key used by ticket system
  82 |nodes/<NAME>/pve-ssl.pem                 | public ssl key for web server
  83 |nodes/<NAME>/priv/pve-ssl.key            | private ssl key
  84 |nodes/<NAME>/qemu-server/<VMID>.conf    | VM configuration data for KVM VMs
  85 |nodes/<NAME>/lxc/<VMID>.conf         | VM configuration data for LXC containers
  86 |firewall/cluster.fw | Firewall config applied to all nodes
  87 |firewall/<NAME>.fw  | Firewall config for individual nodes
  88 |firewall/<VMID>.fw  | Firewall config for VMs and Containers
  89 |=======
  90
  91 Symbolic links
  92 ~~~~~~~~~~~~~~
  93
  94 [width="100%",cols="m,m"]
  95 |=======
  96 |local         |nodes/<LOCAL_HOST_NAME>
  97 |qemu-server   |nodes/<LOCAL_HOST_NAME>/qemu-server/
  98 |lxc           |nodes/<LOCAL_HOST_NAME>/lxc/
  99 |=======
 100
 101 Special status files for debugging (JSON)
 102 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 103
 104 [width="100%",cols="m,d"]
 105 |=======
 106 | .version    |file versions (to detect file modifications)
 107 | .members    |Info about cluster members
 108 | .vmlist     |List of all VMs
 109 | .clusterlog |Cluster log (last 50 entries)
 110 | .rrd        |RRD data (most recent entries)
 111 |=======
 112
 113 Enable/Disable debugging
 114 ~~~~~~~~~~~~~~~~~~~~~~~~
 115
 116 You can enable verbose syslog messages with:
 117
 118  echo "1" >/etc/pve/.debug
 119
 120 And disable verbose syslog messages with:
 121
 122  echo "0" >/etc/pve/.debug
 123
 124
 125 Recovery
 126 --------
 127
 128 If you have major problems with your Proxmox VE host, e.g. hardware
 129 issues, it could be helpful to just copy the pmxcfs database file
 130 /var/lib/pve-cluster/config.db and move it to a new Proxmox VE
 131 host. On the new host (with nothing running), you need to stop the
 132 pve-cluster service and replace the config.db file (needed permissions
 133 0600). Second, adapt '/etc/hostname' and '/etc/hosts' according to the
 134 lost Proxmox VE host, then reboot and check. (And don´t forget your
 135 VM/CT data)
 136
 137 Remove Cluster configuration
 138 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 139
 140 The recommended way is to reinstall the node after you removed it from
 141 your cluster. This makes sure that all secret cluster/ssh keys and any
 142 shared configuration data is destroyed.
 143
 144 In some cases, you might prefer to put a node back to local mode
 145 without reinstall, which is described here:
 146
 147 * stop the cluster file system in '/etc/pve/'
 148
 149  # systemctl stop pve-cluster
 150
 151 * start it again but forcing local mode
 152
 153  # pmxcfs -l
 154
 155 * remove the cluster config
 156
 157  # rm /etc/pve/cluster.conf
 158  # rm /etc/cluster/cluster.conf
 159  # rm /var/lib/pve-cluster/corosync.authkey
 160
 161 * stop the cluster file system again
 162
 163  # service pve-cluster stop
 164
 165 * restart pve services (or reboot)
 166
 167  # service pve-cluster start
 168  # service pvedaemon restart
 169  # service pveproxy restart
 170  # service pvestatd restart
 171