RRDCACHED(1)                        rrdtool                       RRDCACHED(1)



NAME
       rrdcached - Data caching daemon for rrdtool

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

DESCRIPTION
       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.

OPTIONS
       -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!

              unix:</path/to/unix.sock>
              /<path/to/unix.sock>
              <hostname-or-ip>
              [<hostname-or-ip>]:<port>
              <hostname-or-ipv4>:<port>

           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 server).

           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 one 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 10.0.0.1) will be restricted to the "FLUSH" and "PENDING"
           commands:

             rrdcached -l unix:/some/path -P FLUSH,PENDING -l 10.0.0.1

           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, LOG_WARNING, LOG_NOTICE,
           LOG_INFO, LOG_DEBUG

           Default log level when this flag is NOT present: LOG_ERR

           See also: syslog.h

       -o log_file
           Log to the given file instead of syslog.

       -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 crash.

           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 connections.

           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
             "/tmp".

           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:

               /base
               /base/dir
               /base/dir/somewhere

       -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 blocked.

       -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 hour).

       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
   Authentication
       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!

   Authorization
       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 rrdcached is socket-activated by
       systemd.

   Encryption
       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 confidential!

   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!

   Conclusion
       •   Security is the job of the administrator.

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

       •   You have been warned.

PROTOCOL
       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.

       Example:

         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.

       Examples:

        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.

       FLUSHALL
           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.

       QUEUE
           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 <file>:

               <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.

       STATS
           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 value.

           Example:

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

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

           Example:

            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 format:

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

       CREATE filename [-s stepsize] [-b begintime] [-r sourcefile ...] [-t
       templatefile] [-O] DSdefinitions ... RRAdefinitions ...
           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.

       BATCH
           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).

       SUSPEND filename
           Suspend writing to an RRD file. While a file is suspended, all
           metrics for it are cached in memory until RESUME is called for that
           file or RESUMEALL is called.

       RESUME filename
           Resume writing to an RRD file previously suspended by SUSPEND or
           SUSPENDALL.

       SUSPENDALL
           Suspend writing to all RRD files. While a file is suspended, all
           metrics for it are cached in memory until RESUME is called for that
           file or RESUMEALL is called.

       RESUMEALL
           Resume writing to all RRD files previously suspended by SUSPEND or
           SUSPENDALL.

       QUIT
           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 startup.

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

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

       SIGUSR1
           The daemon exits AFTER flushing all updates out to disk.  This may
           take a while.

       SIGUSR2
           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.

BUGS
       No known bugs at the moment.

SEE ALSO
       rrdtool, rrdgraph

AUTHOR
       Florian Forster <octo at verplant.org>

       Both rrdcached and this manual page have been written by Florian.

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



1.9.0                             2024-07-29                      RRDCACHED(1)
