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       cnid_dbd - implement access to CNID databases through a dedicated
       daemon process


       cnid_dbd dbdir ctrlfd clntfd logconfig_string


       cnid_dbd provides an interface for storage and retrieval of catalog
       node IDs (CNIDs) and related information to the afpd daemon. CNIDs are
       a component of Macintosh based file systems with semantics that map not
       easily onto Unix file systems. This makes separate storage in a
       database necessary.  cnid_dbd is part of the CNID backend framework of
       afpd and implements the dbd backend.

       cnid_dbd is never started via the command line or system startup
       scripts but only by the cnid_metad daemon. There is at most one
       instance of cnid_dbd per netatalk volume.

       cnid_dbd uses the Berkleley DB database library and uses
       transactionally protected updates. The dbd backend with transactions
       will avoid corruption of the CNID database even if the system crashes

       cnid_dbd uses the same on-disk database format as the cdb backend. It
       is therefore possible to switch between the two backends as necessary.

       cnid_dbd inherits the effective userid and groupid from cnid_metad on
       startup, which is normally caused by afpd serving a netatalk volume to
       a client. It changes to the Berkleley DB database home directory dbdir
       that is associated with the volume. If the userid inherited from
       cnid_metad is 0 (root), cnid_dbd will change userid and groupid to the
       owner and group of the database home directory. Otherwise, it will
       continue to use the inherited values.  cnid_dbd will then attempt to
       open the database and start serving requests using filedescriptor
       clntfd. Subsequent instances of afpd that want to access the same
       volume are redirected to the running cnid_dbd process by cnid_metad via
       the filedescriptor ctrlfd.

       cnid_dbd uses logconfig_string which is passed from cnid_metad to
       configure its logging output.

       cnid_dbd can be configured to run forever or to exit after a period of
       inactivity. If cnid_dbd receives a TERM or an INT signal it will exit
       cleanly after flushing dirty database buffers to disk and closing
       Berkleley DB database environments. It is safe to terminate cnid_dbd
       this way, it will be restarted when necessary. Other signals are not
       handled and will cause an immediate exit, possibly leaving the CNID
       database in an inconsistent state (no transactions) or losing recent
       updates during recovery (transactions).

       The Berkleley DB database subsystem will create files named
       log.xxxxxxxxxx in the database home directory dbdir, where xxxxxxxxxx
       is a monotonically increasing integer. These files contain ithe
       transactional database changes. They will be removed regularily, unless
       the logfile_autoremove option is specified in the db_param
       configuration file (see below).

       Do not use cnid_dbd for databases on NFS mounted file systems. It makes
       the whole point of securing database changes properly moot. Use the
       dbdir: Option in the appropriate AppleVolumes configuration file to put
       the database onto a local disk.


       cnid_dbd reads configuration information from the file db_param in the
       database directory dbdir on startup. If the file does not exist or a
       parameter is not listed, suitable default values are used. The format
       for a single parameter is the parameter name, followed by one or more
       spaces, followed by the parameter value, followed by a newline. The
       following parameters are currently recognized:

           If set to 0, unused Berkeley DB transactional logfiles
           (log.xxxxxxxxxx in the database home directory) are not removed on
           startup of cnid_dbd and on a reqular basis. Default: 1.

           Determines the size of the Berkeley DB cache in kilobytes. Default:
           8192. Each cnid_dbd process grabs that much memory on top of its
           normal memory footprint. It can be used to tune database
           performance. The db_stat utility with the -m option that comes with
           Berkely DB can help you determine wether you need to change this
           value. The default is pretty conservative so that a large
           percentage of requests should be satisfied from the cache directly.
           If memory is not a bottleneck on your system you might want to
           leave it at that value. The Berkeley DB Tutorial and Reference
           Guide has a section Selecting a cache size that gives more detailed

       flush_frequency, flush_interval
           flush_frequency (Default: 1000) and flush_interval (Default: 1800)
           control how often changes to the database are checkpointed. Both of
           these operations are performed if either i) more than
           flush_frequency requests have been received or ii) more than
           flush_interval seconds have elapsed since the last save/checkpoint.
           Be careful to check your harddisk configuration for on disk cache
           settings. Many IDE disks just cache writes as the default
           behaviour, so even flushing database files to disk will not have
           the desired effect.

           is the maximum number of connections (filedescriptors) that can be
           open for afpd client processes in cnid_dbd.  Default: 512. If this
           number is exceeded, one of the existing connections is closed and
           reused. The affected afpd process will transparently reconnect
           later, which causes slight overhead. On the other hand, setting
           this parameter too high could affect performance in cnid_dbd since
           all descriptors have to be checked in a select() system call, or
           worse, you might exceed the per process limit of open file
           descriptors on your system. It is safe to set the value to 1 on
           volumes where only one afpd client process is expected to run, e.g.
           home directories.

           is the number of seconds of inactivity before an idle cnid_dbd
           exits. Default: 600. Set this to 0 to disable the timeout.


       In order to update between Netatalk releases using different BerkeleyDB
       library versions, follow this steps:

       ·   Stop the to be upgraded old version of Netatalk

       ·   Using the old BerkeleyDB utilities run db_recover -h <path to

       ·   Using the new BerkeleyDB utilities run db_upgrade -v -h <path to
           .AppleDB> -f cnid2.db

       ·   Again using the new BerkeleyDB utilities run db_checkpoint -1 -h
           <path to .AppleDB>

       ·   Start the the new version of Netatalk

       Note that the first version to appear after Netatalk 2.1 ie Netatalk
       2.1.1, will support BerkeleyDB updates on the fly without manual
       intervention. In other words Netatalk 2.1 does contain code to prepare
       the BerkeleyDB database for upgrades and to upgrade it in case it has
       been prepared before. That means it can´t upgrade a 2.0.x version
       because that one didn´t prepare the database.


       cnid_metad(8), afpd(8), dbd(1)