1CNID_DBD(8) 3.1.14 CNID_DBD(8)
2
6 cnid_dbd - implement access to CNID databases through a dedicated
7 daemon process
8
10 cnid_dbd
11 cnid_dbd -v | -V
13
15 cnid_dbd provides an interface for storage and retrieval of catalog
16 node IDs (CNIDs) and related information to the afpd daemon. CNIDs are
17 a component of Macintosh based file systems with semantics that map not
18 easily onto Unix file systems. This makes separate storage in a
19 database necessary. cnid_dbd is part of the CNID backend framework of
20 afpd and implements the dbd backend.
21 cnid_dbd is never started via the command line or system startup
23 scripts but only by the cnid_metad daemon. There is one instance of
24 cnid_dbd per netatalk volume.
25 cnid_dbd uses the Berkeley DB database library and uses transactionally
27 protected updates. The dbd backend with transactions will avoid
28 corruption of the CNID database even if the system crashes
29 unexpectedly.
30 cnid_dbd inherits the effective userid and groupid from cnid_metad on
32 startup, which is normally caused by afpd serving a netatalk volume to
33 a client. It changes to the Berkeley DB database home directory dbdir
34 that is associated with the volume. If the userid inherited from
35 cnid_metad is 0 (root), cnid_dbd will change userid and groupid to the
36 owner and group of the database home directory. Otherwise, it will
37 continue to use the inherited values. cnid_dbd will then attempt to
38 open the database and start serving requests using filedescriptor
39 clntfd. Subsequent instances of afpd that want to access the same
40 volume are redirected to the running cnid_dbd process by cnid_metad via
41 the filedescriptor ctrlfd.
42 cnid_dbd can be configured to run forever or to exit after a period of
44 inactivity. If cnid_dbd receives a TERM or an INT signal it will exit
45 cleanly after flushing dirty database buffers to disk and closing
46 Berkeley DB database environments. It is safe to terminate cnid_dbd
47 this way, it will be restarted when necessary. Other signals are not
48 handled and will cause an immediate exit, possibly leaving the CNID
49 database in an inconsistent state (no transactions) or losing recent
50 updates during recovery (transactions).
51 The Berkeley DB database subsystem will create files named
53 log.xxxxxxxxxx in the database home directory dbdir, where xxxxxxxxxx
54 is a monotonically increasing integer. These files contain the
55 transactional database changes. They will be removed regularly, unless
56 the logfile_autoremove option is specified in the db_param
57 configuration file (see below) with a value of 0 (default 1).
58
60 -v, -V
61 Show version and exit.
62
64 cnid_dbd reads configuration information from the file db_param in the
65 database directory dbdir on startup. If the file does not exist or a
66 parameter is not listed, suitable default values are used. The format
67 for a single parameter is the parameter name, followed by one or more
68 spaces, followed by the parameter value, followed by a newline. The
69 following parameters are currently recognized:
70 logfile_autoremove
72 If set to 0, unused Berkeley DB transactional logfiles
73 (log.xxxxxxxxxx in the database home directory) are not removed on
74 startup of cnid_dbd and on a regular basis. Default: 1.
75 cachesize
77 Determines the size of the Berkeley DB cache in kilobytes. Default:
78 8192. Each cnid_dbd process grabs that much memory on top of its
79 normal memory footprint. It can be used to tune database
80 performance. The db_stat utility with the -m option that comes with
81 Berkley DB can help you determine whether you need to change this
82 value. The default is pretty conservative so that a large
83 percentage of requests should be satisfied from the cache directly.
84 If memory is not a bottleneck on your system you might want to
85 leave it at that value. The Berkeley DB Tutorial and Reference
86 Guide has a section Selecting a cache size that gives more detailed
87 information.
88 flush_frequency, flush_interval
90 flush_frequency (Default: 1000) and flush_interval (Default: 1800)
91 control how often changes to the database are checkpointed. Both of
92 these operations are performed if either i) more than
93 flush_frequency requests have been received or ii) more than
94 flush_interval seconds have elapsed since the last save/checkpoint.
95 Be careful to check your harddisk configuration for on disk cache
96 settings. Many IDE disks just cache writes as the default
97 behaviour, so even flushing database files to disk will not have
98 the desired effect.
99 fd_table_size
101 is the maximum number of connections (filedescriptors) that can be
102 open for afpd client processes in cnid_dbd. Default: 512. If this
103 number is exceeded, one of the existing connections is closed and
104 reused. The affected afpd process will transparently reconnect
105 later, which causes slight overhead. On the other hand, setting
106 this parameter too high could affect performance in cnid_dbd since
107 all descriptors have to be checked in a select() system call, or
108 worse, you might exceed the per process limit of open file
109 descriptors on your system. It is safe to set the value to 1 on
110 volumes where only one afpd client process is expected to run, e.g.
111 home directories.
112 idle_timeout
114 is the number of seconds of inactivity before an idle cnid_dbd
115 exits. Default: 600. Set this to 0 to disable the timeout.
116
118 Note that the first version to appear after Netatalk 2.1 ie Netatalk
119 2.1.1, will support BerkeleyDB updates on the fly without manual
120 intervention. In other words Netatalk 2.1 does contain code to prepare
121 the BerkeleyDB database for upgrades and to upgrade it in case it has
122 been prepared before. That means it can't upgrade a 2.0.x version
123 because that one didn't prepare the database.
124 In order to update between older Netatalk releases using different
126 BerkeleyDB library versions, follow this steps:
127 • Stop the to be upgraded old version of Netatalk
129 • Using the old BerkeleyDB utilities run db_recover -h <path to
131 .AppleDB>
132 • Using the new BerkeleyDB utilities run db_upgrade -v -h <path to
134 .AppleDB> -f cnid2.db
135 • Again using the new BerkeleyDB utilities run db_checkpoint -1 -h
137 <path to .AppleDB>
138 • Start the the new version of Netatalk
140
142 cnid_metad(8), afpd(8), dbd(1)
1433.1.14 10 Nov 2015 CNID_DBD(8)