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Problem

You may be affected by that:

To visualize a graph, Checkmk is using RRD. The RRD needs by nature two files:

rw-rw---- 1 master master      93 Jun  2 07:21 CPU_Utilization_Packet_CPU_2.info
-rw-r--r-- 1 master master  384952 Jun  2 11:22 CPU_Utilization_Packet_CPU_2.rrd

The .rrd file stores all the data and the .info file defines the service metrics. If one of the file is missing, you will face the message above. This message will also be displayed in the cmc.log:

OMD[mysite]:~$ tail -f var/log/cmc.log
2022-06-02 12:09:41 [4] [main] [rrd] [rrdcached at /omd/sites/master/tmp/run/rrdcached.sock] >> -1 No such file: /opt/omd/sites/master/var/check_mk/rrd/<HOSTNAME>/CPU_Utilization_Packet_CPU_1.rrd
2022-06-02 12:10:41 [4] [main] [rrd] [rrdcached at /omd/sites/master/tmp/run/rrdcached.sock] >> -1 No such file: /opt/omd/sites/master/var/check_mk/rrd/<HOSTNAME>/CPU_Utilization_Mgmt_CPU.rrd
2022-06-02 12:10:41 [4] [main] [rrd] [rrdcached at /omd/sites/master/tmp/run/rrdcached.sock] >> -1 No such file: /opt/omd/sites/master/var/check_mk/rrd/<HOSTNAME>/CPU_Utilization_Packet_CPU_0.rrd

Solution

Unfortunately, for some reasons one of the file is missing. In that case it is the .rrd file. So to make the graphs working again, you need to  stop the site, find all the .info files with a missing .rrd file and to delete them manually: 

OMD[mysite]:~$ for i in $(find ~/var/check_mk/rrd -name *.info); do test -e ${i%info}rrd || echo $i; done
/omd/sites/mysite/var/check_mk/rrd/<HOSTNAME>/PING.info
/omd/sites/mysite/var/check_mk/rrd/<HOSTNAME>/CPU_Utilization_Mgmt_CPU.info
/omd/sites/mysite/var/check_mk/rrd/<HOSTNAME>/CPU_Utilization_Packet_CPU_1.info
/omd/sites/mysite/var/check_mk/rrd/<HOSTNAME>/CPU_Utilization_Packet_CPU_0.info

Now you have a list with files to delete. Please replace echo $i with rm $i in order to delete those files.

After you deleted the affected files, you need to start the site, so the new files are created.

Checkmk does not delete any .rrd file. So it could be deleted by a custom cleaning job!