RRDCACHED(1) rrdtool RRDCACHED(1)
NAME
rrdcached - Data caching daemon for rrdtool
SYNOPSIS
rrdcached [-P permissions] [-l address] [-s group] [-w timeout]
[-z delay] [-f timeout] [-p pid_file] [-t write_threads]
[-j journal_dir] [-F] [-g] [-b base_dir [-B]]
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 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/tcp. 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.
-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 0750) 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 a network 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 $MORE_ARGUMENTS
The -P option affects the following socket addresses (the following
-l options) or the default socket (if no -l options have been
specified). In the following example, only the IPv4 network socket
(address 10.0.0.1) will be restricted to the "FLUSH" and "PENDING"
commands:
rrdcached -l unix:/some/path -P FLUSH,PENDING -l 10.0.0.1
A complete list of available commands can be found in the section
"Valid Commands" below. There are two minor special exceptions:
o The "HELP" and "QUIT" commands are always allowed.
o If the "BATCH" command is accepted, the . command will
automatically be accepted, too.
Please also read "SECURITY CONSIDERATIONS" below.
-w timeout
Data is written to disk every timeout seconds. If this option is
not specified the default interval of 300 seconds will be used.
-z delay
If specified, rrdcached will delay writing of each RRD for a random
number of seconds in the range [0,delay). This will avoid too many
writes being queued simultaneously. This value should be no
greater than the value specified in -w. By default, there is no
delay.
-f timeout
Every timeout seconds the entire cache is searched for old values
which are written to disk. This only concerns files to which
updates have stopped, so setting this to a high value, such as
3600 seconds, is acceptable in most cases. This timeout defaults to
3600 seconds.
-p file
Sets the name and location of the PID-file. If not specified, the
default, "$localststedir/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.
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:
o dump
o fetch
o flush
o graph
o graphv
o info
o last
o lastupdate
o update
o xport
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:
o Files/values are stored in a (balanced) tree.
o Tree nodes and entries in the update queue are the same data
structure.
o The local time ("First") and the time specified in updates ("Time")
may differ.
o Timed out values are inserted at the "tail".
o Explicitly flushed values are inserted at the "head".
o 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.
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
o Security is the job of the administrator.
o We recommend to allow write access via UNIX domain sockets only.
o 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.
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
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.
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
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 AT rufus.net>
1.4.8 2013-05-23 RRDCACHED(1)
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