bionic (8) cnid_dbd.8.gz

Provided by: netatalk_2.2.6-1ubuntu0.18.04.2_amd64 bug

NAME

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

SYNOPSIS

       cnid_dbd volpath ctrlfd clntfd logconfig_string
                        cnid_dbd -v | -V

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 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
       unexpectedly.

       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) with a value of 0 (default 1).

       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.

OPTIONS

       -v, -V
           Show version and exit.

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
           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.

       cachesize
           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 information.

       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.

       fd_table_size
           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.

       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.

UPDATING

       Note that the first version to appear after Netatalk 2.1 i.e. 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.

       In order to update between older 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 .AppleDB>

       •   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

SEE ALSO

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