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LVMSYSTEMID(7)                                                                                         LVMSYSTEMID(7)



NAME
       lvmsystemid — LVM system ID


DESCRIPTION
       Local  VGs may exist on shared storage where they are visible to multiple hosts.  These VGs are intended to be
       used by only a single machine, even though they are visible to many.  A system_id identifying  a  single  host
       can  be assigned to a VG to indicate the VGs owner.  The VG owner can use the VG as usual, and all other hosts
       will ignore it.  This protects the VG from accidental use by other hosts.

       The system_id is not a dynamic property, and can only be changed in very limited circumstances  (see  vgexport
       and  vgimport).   Even  limited  changes to the VG system_id are not perfectly reflected across hosts.  A more
       coherent view of shared storage requires using an inter-host locking system to coordinate  access  and  update
       caches.

       The  system_id is a string uniquely identifying a host.  It can be manually set to a custom value or it can be
       assigned automatically by lvm using a unique identifier already available on  the  host,  e.g.  machine-id  or
       uname.

       In  vgcreate,  the local system_id is saved in the new VG metadata.  The local host owns the new VG, and other
       hosts cannot use it.

       A VG without a system_id can be used by any host, and a VG with a system_id can only be used by a host with  a
       matching  system_id.  A foreign VG is a VG with a system_id as viewed by a host with a system_id that does not
       match the VGs system_id.  (Or from a host without a system_id.)

       Valid system_id characters are the same as valid VG name characters.  If a system_id contains invalid  charac‐
       ters, those characters are omitted and remaining characters are used.  If a system_id is longer than the maxi‐
       mum name length, the characters up to the maximum length are used.  The maximum length of a system_id  is  128
       characters.


   Limitations and warnings
       To  benefit fully from system_id, all hosts must have system_id set, and VGs must have system_id set.  A VG on
       shared storage can be damaged or destroyed in some cases which the user must be careful to avoid.


       · A VG without a system_id can be used without restriction from any host, even from hosts  that  have  a  sys‐
         tem_id.   Many  VGs will not have a system_id and are unprotected.  Verify that a VG has a system_id by run‐
         ning the command 'vgs -o+systemid'

         A VG will not have a system_id if it was created before this feature was added to lvm, or if it was  created
         by a host that did not have a system_id defined.  A system_id can be assigned to these VGs by using vgchange
         --systemid (see below).


       · Two hosts should not be assigned the same system_id.  Doing so defeats the purpose of the system_id which is
         to distinguish different hosts.


       · Orphan  PVs (or unused devices) on shared storage are completely unprotected by the system_id feature.  Com‐
         mands that use these PVs, such as vgcreate or vgextend, are not prevented from performing conflicting opera‐
         tions and corrupting the PVs.  See the orphans section for more information.


       · A  host  using an old version of lvm without the system_id feature will not recognize a new system_id in VGs
       These can be further distinguished as:

       Unrestricted: A local VG that has no system_id.  This VG type is unprotected and accessible to any host.

       Owned: A local VG that has a system_id set, as viewed from the one host with a matching system_id (the owner).
       This VG type is by definition acessible.

       Foreign: A local VG that has a system_id set, as viewed from any host with an unmatching system_id (or no sys‐
       tem_id).  It is owned by another host.  This VG type is by definition not accessible.

       Exported: A local VG that has been exported with vgexport and has no system_id.  This  VG  type  can  only  be
       accessed by vgimport which will change it to owned.

       Shared:  A shared or "lockd" VG has lock_type set and no system_id.  A shared VG is meant to be used on shared
       storage from multiple hosts, and is only accessible to hosts using lvmlockd. Applicable only if  LVM  is  com‐
       piled with lockd support.

       Clustered:  A  clustered or "clvm" VG has the clustered flag set and no system_id.  A clustered VG is meant to
       be used on shared storage from multiple hosts, and is only accessible to hosts using clvmd.


   system_id_source
       A host's own system_id can be defined in a number  of  ways.   lvm.conf  global/system_id_source  defines  the
       method lvm will use to find the local system_id:


       none

              lvm  will  not  use a system_id.  lvm is allowed to access VGs without a system_id, and will create new
              VGs without a system_id.  An undefined system_id_source is equivalent to none.

              lvm.conf
              global {
                  system_id_source = "none"
              }


       machineid

              The content of /etc/machine-id is used as the system_id if available.  See machine-id(5)  and  systemd-
              machine-id-setup(1) to check if machine-id is available on the host.

              lvm.conf
              global {
                  system_id_source = "machineid"
              }


       uname

              The string utsname.nodename from uname(2) is used as the system_id.  A uname beginning with "localhost"
              is ignored and equivalent to none.

              lvm.conf
              }

              lvmlocal.conf
              local {
                  system_id = "example_name"
              }


       file

              The system_id is defined in a file specified by lvm.conf global/system_id_file.

              lvm.conf
              global {
                  system_id_source = "file"
                  system_id_file = "/path/to/file"
              }


       Changing system_id_source will often cause the system_id to change, which may prevent the host from using  VGs
       that it previously used (see extra_system_ids below to handle this.)

       If  a  system_id_source  other  than none fails to resolve a system_id, the host will be allowed to access VGs
       with no system_id, but will not be allowed to access VGs with a defined system_id.


   extra_system_ids
       In some cases, it may be useful for a host to access VGs with different system_id's, e.g.  if  a  host's  sys‐
       tem_id changes, and it wants to use VGs that it created with its old system_id.  To allow a host to access VGs
       with other system_id's, those other system_id's can be listed in lvmlocal.conf local/extra_system_ids.

       lvmlocal.conf
       local {
           extra_system_ids = [ "my_other_name" ]
       }


   vgcreate
       In vgcreate, the host running the command assigns its own system_id to the new VG.  To override this  and  set
       another system_id:

       vgcreate --systemid SystemID VG Devices

       Overriding  the system_id makes it possible for a host to create a VG that it may not be able to use.  Another
       host with a system_id matching the one specified may not recognize the  new  VG  without  manually  rescanning
       devices.

       If  the --systemid argument is an empty string (""), the VG is created with no system_id, making it accessible
       to other hosts (see warnings above.)


   report/display
       The system_id of a VG is displayed with the "systemid" reporting option.


       Other  hosts  will  continue  to  see a newly exported VG as foreign because of local caching (when lvmetad is
       used).  Manually updating the local lvmetad cache with pvscan --cache will allow a host to recognize the newly
       exported VG.

       vgimport  sets  the  VG system_id to the local system_id as determined by lvm.conf system_id_source.  vgimport
       automatically scans storage for newly exported VGs.

       After vgimport, the exporting host will continue to see the VG as exported, and not owned  by  the  new  host.
       Manually  updating the local cache with pvscan --cache will allow a host to recognize the newly imported VG as
       foreign.


   vgchange
       A host can change the system_id of its own VGs, but the command requires confirmation  because  the  host  may
       lose access to the VG being changed:

       vgchange --systemid SystemID VG

       The  system_id  can  be removed from a VG by specifying an empty string ("") as the new system_id.  This makes
       the VG accessible to other hosts (see warnings above.)

       A host cannot directly change the system_id of a foreign VG.

       To move a VG from one host to another, vgexport and vgimport should be used.

       To forcibly gain ownership of a foreign VG, a host can add the foreign system_id to its extra_system_ids list,
       change  the system_id of the foreign VG to its own, and remove the foreign system_id from its extra_system_ids
       list.


   shared VGs
       A shared/lockd VG has no system_id set, allowing multiple hosts to use it via lvmlockd.  Changing a  VG  to  a
       lockd type will clear the existing system_id. Applicable only if LVM is compiled with lockd support.


   clustered VGs
       A clustered/clvm VG has no system_id set, allowing multiple hosts to use it via clvmd.  Changing a VG to clus‐
       tered will clear the existing system_id.  Changing a VG to not clustered will set the system_id  to  the  host
       running the vgchange command.


   creation_host
       In  vgcreate,  the  VG  metadata field creation_host is set by default to the host's uname.  The creation_host
       cannot be changed, and is not used to control access.  When system_id_source is  "uname",  the  system_id  and
       creation_host will be the same.


   orphans
       Orphan PVs are unused devices; they are not currently used in any VG.  Because of this, they are not protected
       by a system_id, and any host can use them.  Coordination of changes to orphan PVs is beyond the scope of  sys‐
       tem_id.  The same is true of any block device that is not a PV.

       The  effects of this are especially evident when lvm uses lvmetad caching.  For example, if multiple hosts see

Red Hat, Inc                           LVM TOOLS 2.02.166(2)-RHEL7 (2016-11-16)                        LVMSYSTEMID(7)