Guralp Systems CMG-DCM - Manual (Page 43)

Operator's guide
The DCM receives streams, but 2-minute gaps appear in the data
at 4-hour intervals.
After a reboot, the DCM takes around 2 minutes to begin transmitting.
The DCM runs a guardian process which monitors the health of the
system. In some circumstances guardian will need to reboot the DCM
to attempt to resolve a problem. If the reboot does not help, the DCM
will soon find itself in the same position, and guardian will reboot it
again.
You can check the time since the last reboot with the command
uptime, which will respond with a line like
14:30:32 up 34 min, load average: 1.24, 1.32, 1.10
In this example, the DCM last rebooted 34 minutes ago.
The most common circumstance where guardian will reboot a DCM
is when the operator has instructed it to record data, but it cannot do
so. This may be because
•
the Flash memory is full, and all connected USB disks are also
full,
•
the Flash memory is full, and no USB disk is present;
•
the Flash memory is full, and a USB disk is inaccessible for
some other reason ( e.g. it is unformatted, incorrectly partitioned,
or faulty); or
•
the Flash memory is being filled up faster than the DCM can
empty it. This may happen if the individual files are longer than
25% of the total Flash memory in each of the two memory banks
( e.g. 16 Mb, for DCMs with 128 Mb of storage.) If you encounter
this problem, try making the watch files shorter by changing the
value of disk.recordinterval (see Section 6.3, page 86.)
3.6 CMG-AM Authentication Modules
The CMG-AM is a variant of the CMG-DCM which includes strong
cryptographic capabilities, including an on-boad Spyrus crypto-token.
This token can be used to sign all outgoing data at source. The
signature matches the data as produced, so if anyone alters the data,
the signature will no longer be correct.
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