NAME

CellServDB - Lists the database server machines in AFS cells

DESCRIPTION

There are two versions of the CellServDB file, both of which have the same format. One version is used by an AFS client and lists all of the database server machines in the local cell and any foreign cell that is to be accessible from the local client machine. The other version is used on servers and need list only the database servers in the local cell; in some configurations it can be a link to the same file the client uses.

Client CellServDB

Along with AFSDB and SRV entries in DNS, the client version of the CellServDB file lists the database server machines in the local cell and any foreign cell that is to be accessible from the local client machine. Database server machines run the Authentication Server (optional), Backup Server (optional), Protection Server, and Volume Location (VL) Server (the kaserver, buserver, ptserver, and vlserver) processes, which maintain the cell's administrative AFS databases.

The Cache Manager and other processes running on a client machine use the list of a cell's database server machines when performing several common functions, including:

The Cache Manager reads the CellServDB file into kernel memory as it initializes, and not again until the machine next reboots or the client service restarts. To enable users on the local machine to continue accessing the cell correctly, update the file whenever a database server machine is added to or removed from a cell. To update the kernel-resident list of database server machines without rebooting, use the fs newcell command.

If the client attempts to access an AFS cell not listed in CellServDB and afsd was started with the -afsdb option, the Cache Manager will attempt a DNS SRV or AFSDB record lookup and dynamically add the database server locations for that cell based on the result of the DNS query. If the -afsdb option was not used, all AFS cells that will be accessed by a client machine must either be listed in CellServDB or added with the fs newcell command.

The CellServDB file is in ASCII format and must reside in the /usr/vice/etc directory on each AFS client machine. Use a text editor to create and maintain it.

The client version of the CellServDB file is distinct from the server version, which resides in the /usr/afs/etc directory on each AFS server machine. The client version lists the database server machines in every AFS cell that the cell administrator wants the machine's users to be able to access, whereas the server version lists only the local cell's database server machines.

Server CellServDB

The server version of the CellServDB file lists the local cell's database server machines. These machines run the Authentication Server (optional), Backup Server (optional), Protection Server, and Volume Location (VL) Server (the kaserver, buserver, ptserver, and vlserver) processes, which maintain the cell's administrative AFS databases. The initial version of the file is created with the bos setcellname command during the installation of the cell's server machine, which is automatically recorded as the cell's first database server machine. When adding or removing database server machines, be sure to update this file appropriately. It must reside in the /usr/afs/etc directory on each AFS server machine. The database server processes, in addition to the usual configuration allowing each to be elected synchronization site and coordinate updates, can be set up as readonly database clone servers. Such servers can never be elected as the synchronization site.

The database server processes consult the CellServDB file to learn about their peers, with which they must maintain constant connections in order to coordinate replication of changes across the multiple copies of each database. The other AFS server processes consult the file to learn which machines to contact for information from the databases when they need it.

Although the server CellServDB file is in ASCII format, do not use a text editor to alter it. Instead always use the appropriate commands from the bos command suite:

In cells that use the Update Server to distribute the contents of the /usr/afs/etc directory, it is customary to edit only the copy of the file stored on the system control machine. Otherwise, edit the file on each server machine individually. For instructions on adding and removing database server machine, see the OpenAFS Quick Start chapter on installing additional server machines. Updates to the server CellServDB will trigger reloading the cell server configurations automatically in the AFS server processes.

CellServDB Format

Both CellServDB files have the same format:

No extra blank lines or newline characters are allowed in the file, even after the last entry. Their presence can prevent the Cache Manager from reading the file into kernel memory, resulting in an error message.

For the client CellServDB, it may be desirable to make the client aware of a cell (so that it's listed by default in /afs when the -dynroot flag to afsd is in use, for instance) without specifying the database server machines for that cell. This can be done by including only the cell line (starting with >) and omitting any following database server machine lines. afsd must be configured with the -afsdb option to use DNS SRV or AFSDB record lookups to locate database server machines. If the cell has such records and the client is configured to use them, this configuration won't require updates to the client CellServDB file when the IP addresses of the database server machines change.

grand.central.org maintains a list of the database server machines in all cells that have registered themselves as receptive to access from foreign cells. When a cell's administrators change its database server machines, it is customary to register the change with grand.central.org for inclusion in this file. The file conforms to the required CellServDB format, and so is a suitable basis for the CellServDB file on a client machine. You can download this file from http://grand.central.org/.

EXAMPLES

The following example shows entries for two cells in a client CellServDB file and illustrates the required format.

   >example.com         # Example Corporation
   192.12.105.2         #db1.example.com
   192.12.105.3         #db2.example.com
   [192.12.107.3]       #db3.example.com
   >test.example.com example.com   # Example Corporation Test Cell
   192.12.108.57        #testdb1.example.com
   192.12.108.55        #testdb2.example.com

The following example shows entries for two linked cells in a client CellServDB file. The a.example.com cell is linked to the b.example.com cell.

   >b.example.com # B cell
   192.12.108.57 # db1.b.example.com
   >a.example.com b.example.com # A cell
   192.12.105.2 # db1.a.example.com

In such a setup, if a client is looking for a volume in cell a.example.com and that volume doesn't exist, the client will try to find that volume again in cell b.example.com. The order is important. You must list the cell being linked before the cell doing the linking.

The Windows client supports linking in two directions. The UNIX client does not allow bidirectional linkage.

SEE ALSO

afsd(8), bos_addhost(8), bos_listhosts(8), bos_removehost(8), bos_setcellname(8), buserver(8), fs_newcell(1), kaserver(8), klog(1), ptserver(8), vlserver(8), upclient(8), upserver(8)

OpenAFS Quick Start

COPYRIGHT

IBM Corporation 2000. <http://www.ibm.com/> All Rights Reserved.

This documentation is covered by the IBM Public License Version 1.0. It was converted from HTML to POD by software written by Chas Williams and Russ Allbery, based on work by Alf Wachsmann and Elizabeth Cassell.