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     rrdcached - Data caching daemon for rrdtool

     rrdcached [-a alloc_size] [-b base_dir [-B]] [-F]
     [-f timeout] [-G group]] [-g] [-j journal_dir] [-L]
     [-l address] [-m mode] [-O] [-P permissions] [-p pid_file]
     [-R] [-s group] [-t write_threads] [-U user]] [-V log_level]
     [-w timeout] [-z delay]

     rrdcached is a daemon that receives updates to existing RRD
     files, accumulates them and, if enough have been received or
     a defined time has passed, writes the updates to the RRD
     file. A flush command may be used to force writing of values
     to disk, so that graphing facilities and similar can work
     with up-to-date data.

     The daemon was written with big setups in mind. Those setups
     usually run into IO related problems sooner or later for
     reasons that are beyond the scope of this document. Check
     the wiki at the RRDtool homepage for details. Also check
     "SECURITY CONSIDERATIONS" below before using this daemon! A
     detailed description of how the daemon operates can be found
     in the "HOW IT WORKS" section below.

     -l address
         Tells the daemon to bind to address and accept incoming
         TCP connections on that socket. If address begins with
         "unix:", everything following that prefix is interpreted
         as the path to a UNIX domain socket. Otherwise the
         address or node name are resolved using "getaddrinfo()".

         For network sockets, a port may be specified by using
         the form "[address]:port". If the address is an IPv4
         address or a fully qualified domain name (i. e. the
         address contains at least one dot (".")), the square
         brackets can be omitted, resulting in the (simpler)
         "address:port" pattern. The default port is 42217. If
         you specify a network socket, it is mandatory to read
         the "SECURITY CONSIDERATIONS" section.

         The following formats are accepted. Please note that the
         address of the UNIX domain socket must start with a
         slash in the second case!


         Given a port without a host (e.g. "-l :42217") the
         daemon will listen on that port on all network
         interfaces.  Use "-L" to avoid the need to explicitly
         provide the port if the default port is desired.

         If no -l option is not specified the default address,
         "unix:/tmp/rrdcached.sock", will be used.  Multiple -l
         options may be provided.

     -L  Tells the daemon to bind to the default TCP port on all
         available interfaces.  It is equivalent to "-l `'"
         without the confusion of the empty string parameter.

     -s group_name|gid
         Set the group permissions of a UNIX domain socket. The
         option accepts either a numeric group id or group name.
         That group will then have both read and write
         permissions (the socket will have file permissions 0760)
         for the socket and, therefore, is able to send commands
         to the daemon. This may be useful in cases where you
         cannot easily run all RRD processes with the same user
         privileges (e.g. graph generating CGI scripts that
         typically run in the permission context of the web

         This option affects the following UNIX socket addresses
         (the following -l options) or the default socket (if no
         -l options have been specified), i.e., you may specify
         different settings for different sockets.

         The default is not to change ownership or permissions of
         the socket and, thus, use the system default.

     -m mode
         Set the file permissions of a UNIX domain socket. The
         option accepts an octal number representing the bit
         pattern for the mode (see chmod(1) for details).

         Please note that not all systems honor this setting. On
         Linux, read/write permissions are required to connect to
         a UNIX socket. However, many BSD-derived systems ignore
         permissions for UNIX sockets. See unix(7) for details.

         This option affects the following UNIX socket addresses
         (the following -l options) or the default socket (if no
         -l options have been specified), i.e., you may specify
         different settings for different sockets.

         The default is not to change ownership or permissions of
         the socket and, thus, use the system default.

     -P command[,command[,...]]

         Specifies the commands accepted via both a network and a
         UNIX socket. This allows administrators of RRDCacheD to
         control the actions accepted from various sources.

         The arguments given to the -P option is a comma
         separated list of commands.  For example, to allow the
         "FLUSH" and "PENDING" commands one could specify:

           rrdcached -P FLUSH,PENDING $MORE_ARGUMENTS

         The -P option affects the following socket addresses
         (the following -l options) or the default socket (if no
         -l options have been specified). In the following
         example, only the IPv4 network socket (address
         will be restricted to the "FLUSH" and "PENDING"

           rrdcached -l unix:/some/path -P FLUSH,PENDING -l

         A complete list of available commands can be found in
         the section "Valid Commands" below. There are two minor
         special exceptions:

         *   The "HELP" and "QUIT" commands are always allowed.

         *   If the "BATCH" command is accepted, the . command
             will automatically be accepted, too.

         Please also read "SECURITY CONSIDERATIONS" below.

     -V log_level
         rrdcached under load can severely flood the logs. This
         command line option specifies the maximum log_level to
         be used, meaning that a message with verbosity higher
         than log_level is muted (LOG_EMERG being the lowest and
         LOG_DEBUG highest).

         Accepted values for "log_level" (lowest to highest
         verbosity):  LOG_EMERG, LOG_ALERT, LOG_CRIT, LOG_ERR,

         Default log level when this flag is NOT present: LOG_ERR

         See also: syslog.h

     -w timeout
         Data is written to disk every timeout seconds.  An
         optional suffix may be used (e.g. "5m" instead of 300
         seconds).  If this option is not specified the default
         interval of 300 seconds will be used.

     -z delay

         If specified, rrdcached will delay writing of each RRD
         for a random number of seconds in the range [0,delay).
         This will avoid too many writes being queued
         simultaneously.  This value should be no greater than
         the value specified in -w.  An optional suffix may be
         used (e.g. "3m" instead of 180 seconds).  By default,
         there is no delay.

     -f timeout
         Every timeout seconds the entire cache is searched for
         old values which are written to disk. This only concerns
         files to which updates have stopped, so setting this to
         a high value, such as 3600 seconds, is acceptable in
         most cases.  An optional suffix may be used (e.g. "1h"
         instead of 3600 seconds).  This timeout defaults to
         3600 seconds.

     -p file
         Sets the name and location of the PID-file. If not
         specified, the default,
         "$localstatedir/run/rrdcached.pid" will be used.

     -t write_threads
         Specifies the number of threads used for writing RRD
         files.  The default is 4.  Increasing this number will
         allow rrdcached to have more simultaneous I/O requests
         into the kernel.  This may allow the kernel to re-order
         disk writes, resulting in better disk throughput.

     -j dir
         Write updates to a journal in dir.  In the event of a
         program or system crash, this will allow the daemon to
         write any updates that were pending at the time of the

         On startup, the daemon will check for journal files in
         this directory.  If found, all updates therein will be
         read into memory before the daemon starts accepting new

         The journal will be rotated with the same frequency as
         the flush timer given by -f.

         When journaling is enabled, the daemon will use a fast
         shutdown procedure.  Rather than flushing all files to
         disk, it will make sure the journal is properly written
         and exit immediately.  Although the RRD data files are
         not fully up-to-date, no information is lost; all
         pending updates will be replayed from the journal next
         time the daemon starts up.

         To disable fast shutdown, use the -F option.

     -F  ALWAYS flush all updates to the RRD data files when the
         daemon is shut down, regardless of journal setting.

     -g  Run in the foreground.  The daemon will not fork().

     -b dir
         The daemon will change into a specific directory at
         startup. All files passed to the daemon, that are
         specified by a relative path, will be interpreted to be
         relative to this directory. If not given the default,
         "/tmp", will be used.

           ! Command line           ! File updated           !
           ! foo.rrd                ! /tmp/foo.rrd           !
           ! foo/bar.rrd            ! /tmp/foo/bar.rrd       !
           ! /var/lib/rrd/foo.rrd   ! /var/lib/rrd/foo.rrd   !
           Paths given on the command  line and paths actually
           updated by the daemon,  assuming the base directory

         WARNING: The paths up to and including the base
         directory MUST NOT BE symbolic links.  In other words,
         if the base directory is specified as:

             -b /base/dir/somewhere

         ... then NONE of the following should be symbolic links:


     -B  Only permit writes into the base directory specified in
         -b (and any sub-directories).  This does NOT detect
         symbolic links.  Paths containing "../" will also be

     -R  Permit recursive subdirectory creation in the base
         directory specified in -b (and any sub-directories). Can
         only be used when -B is also set.

     -a alloc_size
         Allocate value pointers in chunks of alloc_size.  This
         may improve CPU utilization on machines with slow
         "realloc()" implementations, in exchange for slightly
         higher memory utilization.  The default is 1.  Do not
         set this more than the -w value divided by your average
         RRD step size.

     -O  Prevent the CREATE command from overwriting existing
         files, even when it is instructed to do so.  This is for
         added security.

     -G -group
         When running as daemon and invoked from a privileged
         account, reset group privileges to those of group.  The
         group may be specified as a name or as a group ID.  The
         daemon will exit with a diagnostic if it cannot
         successfully transition to the specified group.

     -U -user
         When running as daemon and invoked from a privileged
         account, reset user privileges to those of user.  The
         user may be specified as a name or as a user ID.  The
         daemon will exit with a diagnostic if it cannot
         successfully transition to the specified user.

Affected Rrdtool Commands
     The following commands may be made aware of the rrdcached
     using the command line argument --daemon or the environment
     variable RRDCACHED_ADDRESS:

     *   dump

     *   fetch

     *   flush

     *   graph

     *   graphv

     *   info

     *   first

     *   last

     *   lastupdate

     *   update

     *   xport

     *   create

     *   list

     The update command can send values to the daemon instead of
     writing them to the disk itself. All other commands can send
     a FLUSH command (see below) to the daemon before accessing
     the files, so they work with up-to-date data even if the
     cache timeout is large.

Error Reporting
     The daemon reports errors in one of two ways: During
     startup, error messages are printed to "STDERR". One of the
     steps when starting up is to fork to the background and
     closing "STDERR" - after this writing directly to the user
     is no longer possible. Once this has happened, the daemon
     will send log messages to the system logging daemon using
     syslog(3). The facility used is "LOG_DAEMON".

How it Works
     When receiving an update, rrdcached does not write to disk
     but looks for an entry for that file in its internal tree.
     If not found, an entry is created including the current time
     (called "First" in the diagram below). This time is not the
     time specified on the command line but the time the
     operating system considers to be "now". The value and time
     of the value (called "Time" in the diagram below) are
     appended to the tree node.

     When appending a value to a tree node, it is checked whether
     it's time to write the values to disk. Values are written to
     disk if "now() - First >= timeout", where "timeout" is the
     timeout specified using the -w option, see "OPTIONS". If the
     values are "old enough" they will be enqueued in the "update
     queue", i. e. they will be appended to the linked list shown
     below.  Because the tree nodes and the elements of the
     linked list are the same data structures in memory, any
     update to a file that has already been enqueued will be
     written with the next write to the RRD file, too.

     A separate "update thread" constantly dequeues the first
     element in the update queue and writes all its values to the
     appropriate file. So as long as the update queue is not
     empty files are written at the highest possible rate.

     Since the timeout of files is checked only when new values
     are added to the file, "dead" files, i. e. files that are
     not updated anymore, would never be written to disk.
     Therefore, every now and then, controlled by the -f option,
     the entire tree is walked and all "old" values are enqueued.
     Since this only affects "dead" files and walking the tree is
     relatively expensive, you should set the "flush interval" to
     a reasonably high value. The default is 3600 seconds (one

     The downside of caching values is that they won't show up in
     graphs generated from the RRD files. To get around this, the
     daemon provides the "flush command" to flush specific files.
     This means that the file is inserted at the head of the
     update queue or moved there if it is already enqueued. The
     flush command will return only after the file's pending
     updates have been written to disk.

      +------+   +------+                               +------+
      ! head !   ! root !                             ! tail !
      +---+--+   +---+--+                               +---+--+
          !         /\                       !
          !        /  \                      !
          !       /\  /\                       !
          !      /\/\ \ `----------------- ... --------,    !
          V     /      `-------,                     !    V
      +---+----+---+    +------+-----+             +---+----+---+
      ! File:  foo !    ! File:  bar !             ! File:  qux !
      ! First: 101 !    ! First: 119 !             ! First: 180 !
      ! Next:&bar -+--->! Next:&... -+---> ... --->! Next:NULL  !
      | Prev:NULL  !<---+-Prev:&foo  !<--- ... ----+-Prev: &... !
      +============+    +============+             +============+
      ! Time:  100 !    ! Time:  120 !             ! Time:  180 !
      ! Value:  10 !    ! Value: 0.1 !             ! Value: 2,2 !
      +------------+    +------------+             +------------+
      ! Time:  110 !    ! Time:  130 !             ! Time:  190 !
      ! Value:  26 !    ! Value: 0.1 !             ! Value: 7,3 !
      +------------+    +------------+             +------------+
      :            :    :            :        :            :
      +------------+    +------------+             +------------+
      ! Time:  230 !    ! Time:  250 !             ! Time:  310 !
      ! Value:  42 !    ! Value: 0.2 !             ! Value: 1,2 !
      +------------+    +------------+             +------------+

     The above diagram demonstrates:

     *   Files/values are stored in a (balanced) tree.

     *   Tree nodes and entries in the update queue are the same
         data structure.

     *   The local time ("First") and the time specified in
         updates ("Time") may differ.

     *   Timed out values are inserted at the "tail".

     *   Explicitly flushed values are inserted at the "head".

     *   ASCII art rocks.

Security Considerations
     If your rrdtool installation was built without libwrap there
     is no form of authentication for clients connecting to the
     rrdcache daemon!

     If your rrdtool installation was built with libwrap then you
     can use hosts_access to restrict client access to the
     rrdcache daemon (rrdcached).  For more information on how to
     use hosts_access to restrict access to the rrdcache daemon
     you should read the hosts_access(5) man pages.

     It is still highly recommended to install a packet filter or
     similar mechanism to prevent unauthorized connections.
     Unless you have a dedicated VLAN or VPN for this, using
     network sockets is probably a bad idea!

     There is minimal per-socket authorization.

     Authorization is currently done on a per-socket basis. That
     means each socket has a list of commands it will accept and
     it will accept. It will accept only those commands
     explicitly listed but it will (currently) accept these
     commands from anyone reaching the socket.

     If the networking sockets are to be used, it is necessary to
     restrict the accepted commands to those needed by external
     clients. If, for example, external clients want to draw
     graphs of the cached data, they should only be allowed to
     use the "FLUSH" command.

     Authorization does not work when rrcached is socket-
     activated by systemd.

     There is no encryption.

     Again, this may be added in the future, but for the time
     being it is your job to keep your private data private.
     Install a VPN or an encrypted tunnel if you statistics are

  Sanity checking
     There is no sanity checking.

     The daemon will blindly write to any file it gets told, so
     you really should create a separate user just for this
     daemon. Also it does not do any sanity checks, so if it gets
     told to write values for a time far in the future, your
     files will be messed up good!

     *   Security is the job of the administrator.

     *   We recommend to allow write access via UNIX domain
         sockets only.

     *   You have been warned.

     The daemon communicates with clients using a line based
     ASCII protocol which is easy to read and easy to type. This
     makes it easy for scripts to implement the protocol and
     possible for users to use telnet to connect to the daemon
     and test stuff "by hand".

     The protocol is line based, this means that each record
     consists of one or more lines. A line is terminated by the
     line feed character 0x0A, commonly written as "\n". In the
     examples below, this character will be written as "<LF>"
     ("line feed").

     After the connection has been established, the client is
     expected to send a "command". A command consists of the
     command keyword, possibly some arguments, and a terminating
     newline character. For a list of commands, see "Valid
     Commands" below.


       FLUSH /tmp/foo.rrd<LF>

     The daemon answers with a line consisting of a status code
     and a short status message, separated by one or more space
     characters. A negative status code signals an error, a
     positive status code or zero signal success. If the status
     code is greater than zero, it indicates the number of lines
     that follow the status line.


      0 Success<LF>

      2 Two lines follow<LF>
      This is the first line<LF>
      And this is the second line<LF>

  Valid Commands
     The following commands are understood by the daemon:

     FLUSH filename
         Causes the daemon to put filename to the head of the
         update queue (possibly moving it there if the node is
         already enqueued). The answer will be sent after the
         node has been dequeued.

         Causes the daemon to start flushing ALL pending values
         to disk.  This returns immediately, even though the
         writes may take a long time.

     PENDING filename
         Shows any "pending" updates for a file, in order.  The
         updates shown have not yet been written to the
         underlying RRD file.

     FETCH filename CF [start [end] [ds ...]]
         Calls "rrd_fetch" with the specified arguments and
         returns the result in text form. If necessary, the file
         is flushed to disk first. The client side function
         "rrdc_fetch" (declared in "rrd_client.h") parses the
         output and behaves just like "rrd_fetch_r" for easy
         integration of remote queries.  ds defines the columns
         to dump - if none are given then all are returned

     FETCHBIN filename CF [start [end] [ds ...]]
         Calls "rrd_fetch" with the specified arguments and
         returns the result in text/binary form to avoid
         unnecessary un/marshalling overhead.  If necessary, the
         file is flushed to disk first. The client side function
         "rrdc_fetch" (declared in "rrd_client.h") parses the
         output and behaves just like "rrd_fetch_r" for easy
         integration of remote queries.  ds defines the columns
         to dump - if none are given then all are returned

     FORGET filename
         Removes filename from the cache.  Any pending updates
         WILL BE LOST.

         Shows the files that are on the output queue.  Returns
         zero or more lines in the following format, where
         <num_vals> is the number of values to be written for the

             <num_vals> <file>

     HELP [command]
         Returns a short usage message. If no command is given,
         or command is HELP, a list of commands supported by the
         daemon is returned. Otherwise a short description,
         possibly containing a pointer to a manual page, is
         returned.  Obviously, this is meant for interactive
         usage and the format in which the commands and usage
         summaries are returned is not well defined.

         Returns a list of metrics which can be used to measure
         the daemons performance and check its status. For a
         description of the values returned, see "Performance
         Values" below.

         The format in which the values are returned is similar
         to many other line based protocols: Each value is
         printed on a separate line, each consisting of the name
         of the value, a colon, one or more spaces and the actual


          9 Statistics follow
          QueueLength: 0
          UpdatesReceived: 30
          FlushesReceived: 2
          UpdatesWritten: 13
          DataSetsWritten: 390
          TreeNodesNumber: 13
          TreeDepth: 4
          JournalBytes: 190
          JournalRotate: 0

         PING-PONG, this is very useful when using connection
         pool between user client and RRDCACHED.


          0 PONG

     UPDATE filename values [values ...]
         Adds more data to a filename. This is the operation the
         daemon was designed for, so describing the mechanism
         again is unnecessary. Read "HOW IT WORKS" above for a
         detailed explanation.

         Note that rrdcached only accepts absolute timestamps in
         the update values.  Updates strings like "N:1:2:3" are
         automatically converted to absolute time by the RRD
         client library before sending to rrdcached.

     WROTE filename
         This command is written to the journal after a file is
         successfully written out to disk.  It is used during
         journal replay to determine which updates have already
         been applied.  It is only valid in the journal; it is
         not accepted from the other command channels.

     FIRST filename [rranum]
         Return the timestamp for the first CDP in the specified
         RRA.  Default is to use RRA zero if none is specified.

     LAST filename
         Return the timestamp for the last update to the
         specified RRD. Note that the cache is not flushed before
         checking, as the client is expected to request this
         separately if it is required.

     INFO filename
         Return the configuration information for the specified
         RRD. Note that the cache is not flushed before checking,
         as the client is expected to request this separately if
         it is required.

         The information is returned, one item per line, with the

          I<keyname> I<type> I<value>

     CREATE filename [-s stepsize] [-b begintime] [-O] DSdefinitions
         This will create the RRD file according to the supplied
         parameters, provided the parameters are valid, and (if
         the -O option is given or if the rrdcached was started
         with the -O flag) the specified filename does not
         already exist.

         This command initiates the bulk load of multiple
         commands.  This is designed for installations with
         extremely high update rates, since it permits more than
         one command to be issued per read() and write().

         All commands are executed just as they would be if given
         individually, except for output to the user.  Messages
         indicating success are suppressed, and error messages
         are delayed until the client is finished.

         Command processing is finished when the client sends a
         dot (".") on its own line.  After the client has
         finished, the server responds with an error count and
         the list of error messages (if any).  Each error
         messages indicates the number of the command to which it
         corresponds, and the error message itself.  The first
         user command after BATCH is command number one.

             client:  BATCH
             server:  0 Go ahead.  End with dot `.' on its own line.
             client:  UPDATE x.rrd 1223661439:1:2:3            <--- command #1
             client:  UPDATE y.rrd 1223661440:3:4:5            <--- command #2
             client:  and so on...
             client:  .
             server:  2 Errors
             server:  1 message for command 1
             server:  12 message for command 12

     LIST [RECURSIVE] I/<path>
         This command allows to list directories and rrd
         databases as seen by the daemon.  The root "directory"
         is the base_dir (see `-b dir'). When invoked with `LIST
         RECURSIVE /<path>' it will behave similarly to `ls -R'
         but limited to rrd files (listing all the rrd bases in
         the subtree of <path>, skipping empty directories).

         Disconnect from rrdcached.

  Performance Values
     The following counters are returned by the STATS command:

     QueueLength (unsigned 64bit integer)
         Number of nodes currently enqueued in the update queue.

     UpdatesReceived (unsigned 64bit integer)
         Number of UPDATE commands received.

     FlushesReceived (unsigned 64bit integer)
         Number of FLUSH commands received.

     UpdatesWritten (unsigned 64bit integer)
         Total number of updates, i. e. calls to "rrd_update_r",
         since the daemon was started.

     DataSetsWritten (unsigned 64bit integer)
         Total number of "data sets" written to disk since the
         daemon was started. A data set is one or more values
         passed to the UPDATE command. For example:
         "1223661439:123:456" is one data set with two values.
         The term "data set" is used to prevent confusion whether
         individual values or groups of values are counted.

     TreeNodesNumber (unsigned 64bit integer)
         Number of nodes in the cache.

     TreeDepth (unsigned 64bit integer)
         Depth of the tree used for fast key lookup.

     JournalBytes (unsigned 64bit integer)
         Total number of bytes written to the journal since

     JournalRotate (unsigned 64bit integer)
         Number of times the journal has been rotated since

         The daemon exits normally on receipt of either of these
         signals.  Pending updates are handled in accordance with
         the -j and -F options.

         The daemon exits AFTER flushing all updates out to disk.
         This may take a while.

         The daemon exits immediately, without flushing updates
         out to disk.  Pending updates will be replayed from the
         journal when the daemon starts up again.  WARNING: if
         journaling (-j) is NOT enabled, any pending updates WILL
         BE LOST.

     No known bugs at the moment.

See Also
     rrdtool, rrdgraph

     Florian Forster <octo at verplant.org>

     Both rrdcached and this manual page have been written by

     kevin brintnall <kbrint@rufus.net> Steve Shipway
     <steve@steveshipway.org> Martin Sperl
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