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.
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/udp. 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>
If the -l option is not specified the default address, "unix:/tmp/rrdcached.sock", will be used.
This option affects the following UNIX socket addresses (the following -l options), 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.
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), 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.
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). 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:
Please also read ``SECURITY CONSIDERATIONS'' below.
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.
+------------------------+------------------------+ ! 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
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.
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:
The client/server protocol does not yet have any authentication mechanism. It is likely that authentication and encryption will be added in a future version, but for the time being it is the administrator's responsibility to secure the traffic from/to the daemon!
It is 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 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.
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!
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!
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>
<num_vals> <file>
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
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.
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
Both rrdcached and this manual page have been written by Florian.