Ubuntu Manpage: cnid_dbd — CNID database access daemon

Name

       cnid_dbd — CNID database access daemon

Synopsis

       cnid_dbd

       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 Berkeley 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 Berkeley 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
Berkeley 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 Berkeley 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 the transactional
database changes. They will be removed regularly, unless the logfile_autoremove option is specified in
the db_param configuration file (see below) with a value of 0 (default 1).

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 regular 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 Berkeley DB can help you
determine whether 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 hard disk 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

       Starting with Netatalk 2.1.1, automatic Berkeley DB updates are supported, as long as Netatalk  2.1.0  or
       later was used to create the database.

       In  order  to update between older Netatalk releases using different Berkeley DB library versions, follow
       these steps:

       • Stop the to be upgraded old version of Netatalk

       • Using the old Berkeley DB utilities run db_recover -h path/to/.AppleDB

       • Using the new Berkeley DB utilities run db_upgrade -v -h path/to/.AppleDB -f cnid2.db

       • Again using the new Berkeley DB utilities run db_checkpoint -1 -h path/to/.AppleDB

       • Start the the new version of Netatalk

Author

       Contributors to the Netatalk Project (https://netatalk.io/contributors)

Netatalk 4.2.3                                                                                       CNID_DBD(8)