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sensord(8) Linux System Administration sensord(8)


sensord – Sensor information logging daemon.


sensord [ options ] [ chips ]


Sensord is a daemon that can be used to periodically log sensor read‐
ings from hardware health-monitoring chips to syslog(3) or a round-
robin database (RRD) and to alert when a sensor alarm is signalled; for
example, if a fan fails, a temperature limit is exceeded, etc.


-i, –interval time
Specify the interval between scanning for sensor alarms; the
default is to scan every minute.

The time should be specified as a raw integer (seconds) or with
a suffix `s’ for seconds, `m’ for minutes or `h’ for hours; for
example, the default interval is `60′ or `1m’.

Specify an interval of zero to suppress scanning explicitly for

-l, –log-interval time
Specify the interval between logging all sensor readings; the
default is to log all readings every half hour.

The time is specified as before; e.g., `30m’.

Specify an interval of zero to suppress logging of regular sen‐
sor readings.

-t, –rrd-interval time
Specify the interval between logging all sensor readings to a
round-robin database; the default is to log all readings every
five minutes if a round-robin database is configured.

The time is specified as before; e.g., `5m’.

-T, –rrd-no-average
Specify that the round-robin database should not be averaged.

-r, –rrd-file file
Specify a round-robin database into which to log all sensor
readings; e.g., `/var/log/sensord.rrd’. This database will be
created if it does not exist. By default, no round-robin data‐
base is used.

See the section ROUND ROBIN DATABASES below for more details.

-c, –config-file file
Specify a libsensors configuration file. If no file is speci‐
fied, the libsensors default configuration file is used.

-p, –pid-file file
Specify what PID file to write; the default is to write the file
`/var/run/’. You should always specify an absolute
path here. The file is removed when the daemon exits.

-f, –syslog-facility facility
Specify the syslog(3) facility to use when logging sensor read‐
ings and alarms; the default is to use daemon.

Other possible facilities include local0 through local7, and

-g, –rrd-cgi directory
Prints out a sample rrdcgi(1) CGI script that can be used to
display graphs of recent sensor information in a Web page, and
exits. You must specify the world-writable, Web-accessible
directory where the graphs should be stored; the CGI script
assumes that this will be accessed under the `/sensord/’ direc‐
tory on the Webserver. See the section ROUND ROBIN DATABASES
below for more details.

-a, –load-average
Include the load average in the RRD database. You should also
specify this flag when you create the CGI script.

-d, –debug
Prints a small amount of additional debugging information.

-h, –help
Prints a help message and exits.

-v, –version
Displays the program version and exits.

To restrict the devices that are scanned by this daemon, you may
optionally specify a list of chip names. By default, all available
chips are scanned.

A typical chip name would be `w83782d-*’ (you may want to escape the
`*’ for your shell) which would scan any W83782D chips on any bus. See
sensors.conf(5) for more details. Another option is to simply not load
the sensor modules for chips in which you have no interest.

Upon receipt of a SIGTERM (see signal(7) for details) this daemon
should gracefully shut down.

Upon receipt of a SIGHUP, this daemon will rescan the kernel interface
for chips and features, and reload the libsensors configuration file.

All messages from this daemon are logged to syslog(3) under the program
name `sensord’ and facility daemon, or whatever is specified on the
command line.

Regular sensor readings are logged at the level info. Alarms are
logged at the level alert. Inconsequential status messages are logged
at the minimum level, debug, when debugging is enabled.

You can use an appropriate `/etc/syslog.conf’ file to direct these mes‐
sages in a useful manner. See syslog.conf(5) for full details. Assuming
you set the logging facility to local4, the following is a sample con‐

# Sample syslog.conf entries
*.info;…;local4.none;local4.warn /var/log/messages -/var/log/sensors
local4.alert /dev/console
local4.alert *

The first line ensures that regular sensor readings do not clutter
`/var/log/messages’; we first say `local4.none’ to eliminate informa‐
tional messages; then `local4.warn’ to enable warnings and above. The
second line says to log all regular sensor readings to `/var/log/sen‐
sors’; the leading hyphen `-‘ means that this file is not flushed after
every message. The final two lines ensure that alarms are printed to
the system console as well as to all connected users (in addition to
`/var/log/messages’ and `/var/log/sensors’).

On a typical system with a good sensor chip, expect about 2KB per sen‐
sor reading in the log file. This works out at about 3MB per month. You
should be rotating your syslog files anyway, but just to be sure you’ll
want to use something like logrotate(8) or equivalent. You might, for
example, want an entry in `/etc/logrotate.d/syslog’ containing:

# Sample logrotate.d entry
/var/log/sensors {
/usr/sbin/killall -HUP syslogd

Note, of course, that you want to restart syslogd(8) and not sensord(8)

Alarms generally indicate a critical condition; for example, a fan
failure or an unacceptable temperature or voltage. However, some sensor
chips do not support alarms, while others are incorrectly configured
and may signal alarms incorrectly.

Note that some drivers may lack support for alarm reporting even though
the chips they support do have alarms. As of Linux 2.6.23, many drivers
still don’t report alarms in a format suitable for libsensors 3.

If you see `(beep)’ beside any sensor reading, that just means that
your system is configured to issue an audio warning from the mother‐
board if an alarm is signalled on that sensor.

Sensord(8) provides support for storing sensor readings in a round-
robin database. This may be a useful alternative to the use of sys‐

Round-robin databases are constant-size databases that can be used to
store, for example, a week’s worth of sensor readings. Subsequent read‐
ings stored in the database will overwrite readings that are over a
week old. This capability is extremely useful because it allows useful
information to be stored in an easily-accessible manner for a useful
length of time, without the burden of ever-growing log files.

The rrdtool(1) utility and its associated library provide the basic
framework for the round-robin database beneath sensord(8). In addi‐
tion, the rrdcgi(1) and rrdgraph(1) utilities provide support for gen‐
erating graphs of these data for display in a Web page.

If you wish to use the default configuration of round-robin database,
which holds one week of sensor readings at five-minute intervals, then
simply start sensord(8) and specify where you want the database stored.
It will automatically be created and configured using these default

If you wish readings to be stored for a longer period, or want multiple
readings to be averaged into each database entry, then you must manu‐
ally create and configure the database before starting sensord(8).
Consult the rrdcreate(1) manual for details. Note that the database
must match exactly the names and order of sensors read by sensord(8).
It is recommended that you create the default database and then use
rrdinfo to obtain this information, and/or rrdtune(1) to change it.

After creating the round-robin database, you must then configure your
Web server to display the sensor information. This assumes that you
have a Web server preconfigured and functioning on your machine. Sen‐
sord(8) provides a command-line option –rrd-cgi to generate a basic
CGI script to display these graphs; you can then customize this script
as desired. Consult the rrdcgi(1) manual for details. This CGI script
requires a world-writable, Web-accessible directory into which to write
the graphs that it generates.

An example of how to set up Web-accessible graphs of recent sensor
readings follows:

sensord –log-interval 0 \
–load-average \
–rrd-file /var/log/sensord.rrd

Here, we start sensord(8) and configure it to store readings in a
round-robin database; note that we disable logging of sensor readings
to syslog(3), and enable logging of the load average.

mkdir /var/www/html/sensord
chown www-data:staff /var/www/html/sensord
chmod a=rwxs /var/www/html/sensord

Here, we create a world-writable, Web-accessible directory in which
graphs will be stored; we set the ownership and permissions on this
directory appropriately. You will have to determine the location and
ownership that is appropriate for your machine.

sensord –load-average \
–rrd-file /var/log/sensord.rrd \
–rrd-cgi /var/www/html/sensord \
> /usr/lib/cgi-bin/sensord.cgi
chmod a+rx /usr/lib/cgi-bin/sensord.cgi

Here, we create a CGI script that will display sensor readings from the
database. You must specify the location of the round-robin database,
the location of the directory where the images should be stored, and
whether you want the load average displayed. The –rrd-cgi command-line
parameter causes sensord(8) to display a suitable CGI script on stdout
and then to exit. You will need to write this script to the CGI bin
directory of your Web server, and edit the script if the image direc‐
tory you chose is not the `/sensord/’ directory of your Web server.

Finally, you should be able to view your sensor readings from the URL

It is expected that all required sensor modules are loaded prior to
this daemon being started. This can either be achieved with a system
specific module loading scheme (e.g., listing the required modules in
the file `/etc/modules’ under Debian).

Errors encountered by this daemon are logged to syslogd(8) after which
the daemon will exit.


Round-robin database support doesn’t cope with multiple sensor chips
having duplicate sensor labels.

The system-wide libsensors configuration file. See sen‐
sors.conf(5) for further details.
The system-wide syslog(3) / syslogd(8) configuration file. See
syslog.conf(5) for further details.



Sensord was written by Merlin Hughes . Basics of
round-robin databases were misappropriated from Mark D. Studebaker.

lm-sensors 3 October 2007 sensord(8)

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