'\" t .\" Title: cnid_dbd .\" Author: [FIXME: author] [see http://docbook.sf.net/el/author] .\" Generator: DocBook XSL Stylesheets v1.74.3 .\" Date: 2 Dec 2003 .\" Manual: Netatalk 2.0.4 .\" Source: Netatalk 2.0.4 .\" Language: English .\" .TH "CNID_DBD" "8" "2 Dec 2003" "Netatalk 2\&.0\&.4" "Netatalk 2.0.4" .\" ----------------------------------------------------------------- .\" * set default formatting .\" ----------------------------------------------------------------- .\" disable hyphenation .nh .\" disable justification (adjust text to left margin only) .ad l .\" ----------------------------------------------------------------- .\" * MAIN CONTENT STARTS HERE * .\" ----------------------------------------------------------------- .SH "NAME" cnid_dbd \- implement access to CNID databases through a dedicated daemon process .SH "SYNOPSIS" .HP \w'\fBcnid_dbd\fR\fB\fR\fB\fR\fB\fR\ 'u \fBcnid_dbd\fR\fB\fR\fB\fR\fB\fR \fIdbdir\fR \fIctrlfd\fR \fIclntfd\fR .SH "DESCRIPTION" .PP \fBcnid_dbd\fR provides an interface for storage and retrieval of catalog node IDs (CNIDs) and related information to the \fBafpd\fR 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\&. \fBcnid_dbd\fR is part of the \fBCNID backend\fR framework of \fBafpd\fR and implements the \fBdbd\fR backend\&. .PP \fBcnid_dbd\fR is never started via the command line or system startup scripts but only by the \fBcnid_metad\fR daemon\&. There is at most one instance of \fBcnid_dbd\fR per netatalk volume\&. .PP \fBcnid_dbd\fR uses the \fBBerkleley DB\fR database library and optionally supports transactionally protected updates if the netatalk package is compiled with the appropriate options\&. Using the \fBdbd\fR backend without transactions will protect the CNID database against unexpected crashes of the \fBafpd\fR daemon\&. Using the \fBdbd\fR backend with transactions will avoid corruption of the CNID database even if the system crashes unexpectedly\&. .PP \fBcnid_dbd\fR uses the same on\-disk database format as the \fBcdb\fR backend\&. It is therefore possible to switch between the two backends as necessary\&. .PP \fBcnid_dbd\fR inherits the effective userid and groupid from \fBcnid_metad\fR on startup, which is normally caused by \fBafpd\fR serving a netatalk volume to a client\&. It changes to the \fBBerkleley DB\fR database home directory \fIdbdir\fR that is associated with the volume\&. If the userid inherited from \fBcnid_metad\fR is 0 (root), \fBcnid_dbd\fR will change userid and groupid to the owner and group of the database home directory\&. Otherwise, it will continue to use the inherited values\&. \fBcnid_dbd\fR will then attempt to open the database and start serving requests using filedescriptor \fIclntfd\fR\&. Subsequent instances of \fBafpd\fR that want to access the same volume are redirected to the running \fBcnid_dbd\fR process by \fBcnid_metad\fR via the filedescriptor \fIctrlfd\fR\&. .PP \fBcnid_dbd\fR can be configured to run forever or to exit after a period of inactivity\&. If \fBcnid_dbd\fR receives a TERM or an INT signal it will exit cleanly after flushing dirty database buffers to disk and closing \fBBerkleley DB\fR database environments\&. It is safe to terminate \fBcnid_dbd\fR 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)\&. .PP If transactions are used the \fBBerkleley DB\fR database subsystem will create files named log\&.xxxxxxxxxx in the database home directory \fIdbdir\fR, where xxxxxxxxxx is a monotonically increasing integer\&. These files contain information to replay database changes and are not automatically removed, unless the \fBlogfile_autoremove\fR option is specified in the \fIdb_param\fR configuration file (see below)\&. Please see the sections \fBDatabase and log file archival\fR, \fB Log file removal\fR and the documentation of the \fB db_archive\fR command line utility in the Berkeley DB Tutorial and Reference for information when and how it is safe to remove these files manually\&. .PP Do not use \fBcnid_dbd\fR 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 \fBAppleVolumes\fR configuration file to put the database onto a local disk\&. .SH "CONFIGURATION" .PP \fBcnid_dbd\fR reads configuration information from the file \fIdb_param\fR in the database directory \fIdbdir\fR 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: .PP \fBlogfile_autoremove\fR .RS 4 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 \fBcnid_dbd\fR\&. This is usually safe if the content of the database directory is backed up on a regular basis\&. Default: 0\&. .RE .PP \fBcachesize\fR .RS 4 Determines the size of the Berkeley DB cache in kilobytes\&. Default: 1024\&. Each \fBcnid_dbd\fR process grabs that much memory on top of its normal memory footprint\&. It can be used to tune database performance\&. The \fBdb_stat\fR utility with the \fB\-m\fR 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 \fBBerkeley DB Tutorial and Reference Guide\fR has a section \fBSelecting a cache size\fR that gives more detailed information\&. .RE .PP \fBnosync\fR .RS 4 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 \fBTransaction Throughput\fR in the Berkeley DB Tutorial for more information\&. Default: 0\&. .RE .PP \fBflush_frequency\fR, \fBflush_interval\fR .RS 4 \fIflush_frequency\fR (Default: 100) and \fIflush_interval\fR (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 \fIflush_frequency\fR requests have been received or ii) more than \fIflush_interval\fR seconds have elapsed since the last save/checkpoint\&. If you use transactions with \fInosync\fR set to zero these parameters only influence how long recovery takes after a crash, there should never be any lost data\&. If \fInosync\fR 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\&. .RE .PP \fBfd_table_size\fR .RS 4 is the maximum number of connections (filedescriptors) that can be open for \fBafpd\fR client processes in \fBcnid_dbd\&.\fR Default: 16\&. If this number is exceeded, one of the existing connections is closed and reused\&. The affected \fBafpd\fR process will transparently reconnect later, which causes slight overhead\&. On the other hand, setting this parameter too high could affect performance in \fBcnid_dbd\fR since all descriptors have to be checked in a \fBselect()\fR 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 \fBafpd\fR client process is expected to run, e\&.g\&. home directories\&. .RE .PP \fBidle_timeout\fR .RS 4 is the number of seconds of inactivity before an idle \fBcnid_dbd\fR exits\&. Default: 600\&. Set this to 0 to disable the timeout\&. .RE .PP \fBcheck\fR .RS 4 is a flag value\&. If set \fBcnid_dbd\fR will automatically check the database indexes\&. Default: 0\&. Set this to 1 to enable checking\&. .RE .SH "SEE ALSO" .PP \fBcnid_metad\fR(8), \fBafpd\fR(8)