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:

+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.

-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:

+o dump

+o fetch

+o flush

+o graph

+o graphv

+o info

+o first

+o last

+o lastupdate

+o update

+o xport

+o create

+o 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:

+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.

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

+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.

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>

1.8.0 2022-03-14 RRDCACHED(1)