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 |user.cfg      |{pve} access control configuration (users/groups/...)
  77 |domains.cfg   |{pve} Authentication domains
  78 |authkey.pub   | public key used by ticket system
  79 |priv/shadow.cfg  | shadow password file
  80 |priv/authkey.key | private key used by ticket system
  81 |nodes/<NAME>/pve-ssl.pem                 | public ssl key for web server
  82 |nodes/<NAME>/priv/pve-ssl.key            | private ssl key
  83 |nodes/<NAME>/qemu-server/<VMID>.conf    | VM configuration data for KVM VMs
  84 |nodes/<NAME>/lxc/<VMID>.conf         | VM configuration data for LXC containers
  85 |firewall/cluster.fw | Firewall config applied to all nodes
  86 |firewall/<NAME>.fw  | Firewall config for individual nodes
  87 |firewall/<VMID>.fw  | Firewall config for VMs and Containers
  88 |=======
  89
  90 Symbolic links
  91 ~~~~~~~~~~~~~~
  92
  93 [width="100%",cols="m,m"]
  94 |=======
  95 |local         |nodes/<LOCAL_HOST_NAME>
  96 |qemu-server   |nodes/<LOCAL_HOST_NAME>/qemu-server/
  97 |lxc           |nodes/<LOCAL_HOST_NAME>/lxc/
  98 |=======
  99
 100 Special status files for debugging (JSON)
 101 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 102
 103 [width="100%",cols="m,d"]
 104 |=======
 105 | .version    |file versions (to detect file modifications)
 106 | .members    |Info about cluster members
 107 | .vmlist     |List of all VMs
 108 | .clusterlog |Cluster log (last 50 entries)
 109 | .rrd        |RRD data (most recent entries)
 110 |=======
 111
 112 Enable/Disable debugging
 113 ~~~~~~~~~~~~~~~~~~~~~~~~
 114
 115 You can enable verbose syslog messages with:
 116
 117  echo "1" >/etc/pve/.debug
 118
 119 And disable verbose syslog messages with:
 120
 121  echo "0" >/etc/pve/.debug
 122
 123
 124 Recovery
 125 --------
 126
 127 If you have major problems with your Proxmox VE host, e.g. hardware
 128 issues, it could be helpful to just copy the pmxcfs database file
 129 /var/lib/pve-cluster/config.db and move it to a new Proxmox VE
 130 host. On the new host (with nothing running), you need to stop the
 131 pve-cluster service and replace the config.db file (needed permissions
 132 0600). Second, adapt '/etc/hostname' and '/etc/hosts' according to the
 133 lost Proxmox VE host, then reboot and check. (And don´t forget your
 134 VM/CT data)
 135
 136 Remove Cluster configuration
 137 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 138
 139 The recommended way is to reinstall the node after you removed it from
 140 your cluster. This makes sure that all secret cluster/ssh keys and any
 141 shared configuration data is destroyed.
 142
 143 In some cases, you might prefer to put a node back to local mode
 144 without reinstall, which is described here:
 145
 146 * stop the cluster file system in '/etc/pve/'
 147
 148  # systemctl stop pve-cluster
 149
 150 * start it again but forcing local mode
 151
 152  # pmxcfs -l
 153
 154 * remove the cluster config
 155
 156  # rm /etc/pve/cluster.conf
 157  # rm /etc/cluster/cluster.conf
 158  # rm /var/lib/pve-cluster/corosync.authkey
 159
 160 * stop the cluster file system again
 161
 162  # service pve-cluster stop
 163
 164 * restart pve services (or reboot)
 165
 166  # service pve-cluster start
 167  # service pvedaemon restart
 168  # service pveproxy restart
 169  # service pvestatd restart
 170