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NAME

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

SYNOPSIS

       cnid_dbd dbdir ctrlfd clntfd

DESCRIPTION

       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 optionally supports
       transactionally protected updates if the netatalk package  is  compiled
       with   the   appropriate   options.   Using  the  dbd  backend  without
       transactions will protect the CNID database against unexpected  crashes
       of  the afpd daemon. Using the dbd backend with transactions will avoid
       corruption  of  the  CNID  database  even   if   the   system   crashes
       unexpectedly.

       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  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).

       If transactions are used  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   information   to   replay   database   changes  and  are  not
       automatically  removed,  unless  the   logfile_autoremove   option   is
       specified  in  the  db_param configuration file (see below). Please see
       the sections Database and log file archival, Log file removal  and  the
       documentation of the db_archive command line utility in the Berkeley DB
       Tutorial and Reference for information when  and  how  it  is  safe  to
       remove these files manually.

       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.

CONFIGURATION

       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:

       logfile_autoremove
              This  flag  is  ignored unless transactional support is enabled.
              If  set  to  1,  unused  Berkeley  DB   transactional   logfiles
              (log.xxxxxxxxxx  in  the database home directory) are removed on
              startup of cnid_dbd. This is usually safe if the content of  the
              database directory is backed up on a regular basis.  Default: 0.

       cachesize
              Determines the size of  the  Berkeley  DB  cache  in  kilobytes.
              Default:  1024.  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 information.

       nosync This flag is ignored unless transactional  support  is  enabled.
              If it is set to 1, transactional changes to the database are not
              synchronously written to disk when  the  transaction  completes.
              This  will  increase  performance  considerably  at  the risk of
              recent changes getting lost in case of  a  crash.  The  database
              will  still be consistent, though. See Transaction Throughput in
              the Berkeley DB Tutorial for more information. Default: 0.

       flush_frequency, flush_interval
              flush_frequency (Default: 100) and flush_interval (Default:  30)
              control  how  often  changes  to the database are written to the
              underlying database files if no transactions  are  used  or  how
              often  the  transaction system is checkpointed for transactions.
              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. If you use transactions with nosync set to zero
              these parameters only influence how long recovery takes after  a
              crash,  there  should  never  be  any lost data. If nosync is 1,
              changes might be lost, but only since the  last  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.

       fd_table_size
              is the maximum number of connections (filedescriptors) that  can
              be  open  for afpd client processes in cnid_dbd. Default: 16. 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.

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

       check  is  a  flag  value. If set cnid_dbd will automatically check the
              database indexes. Default: 0. Set this to 1 to enable  checking.

SEE ALSO

       cnid_metad(8), afpd(8)