Dear LDM user,
Version 6.8.0 of the LDM is now available from the LDM homepage at
<http://www.unidata.ucar.edu/software/ldm/>
or from
<ftp://ftp.unidata.ucar.edu/pub/ldm/ldm-6.8.0.tar.gz>
This version features the following:
1) The way the top-level LDM server vets new client connections is
improved;
2) More information is printed by the "ldmadmin config"
command;
3) The accuracy of the system clock can be checked by
ldmadmin(1); and
4) LDM performance metrics can now be collected and plotted by the
ldmadmin(1) script if the requisite utilities are installed.
VETTING NEW CLIENT CONNECTIONS:
In this version, the way the top-level LDM server vets new client
connections is improved. Before, the LDM server would get the
hostname of the client system and then check both the IP address and
hostname of the client system against the ALLOW and ACCEPT entries
in the LDM configuration-file before fork(1)ing a child LDM process
to handle the connection. Now, the LDM server immediately and
unconditionally fork(2)s a child LDM process to handle the
connection and the child process uses a two-phase procedure to vet
the client system. First the IP address of the client is checked
against the ALLOW and ACCEPT entries. If that succeeds, then the
client connection is allowed; otherwise, the hostname of the client
system is obtained and that is then checked against the entries.
These changes were made to prevent a client whose hostname cannot be
found from suspending the LDM server until the hostname lookup
times-out.
As a consequence of these changes, there is now an upper limit on
the number of active client connections to an LDM server. The
default is 256. This value can be changed via the "$max_clients"
variable in the ldmadmin(1) configuration-file
(etc/ldmadmin-pl.conf).
CHECKING THE SYSTEM CLOCK:
As you may know, an accurate system clock is necessary for correct
operation by the LDM: an inaccurate clock can cause a delay in data
reception or even a loss of data. By default, this new feature
causes almost every ldmadmin(1) command to also check the accuracy
of the system clock. This new feature is also highly customizable:
everything from being disabled to causing it to *not* start the LDM
if the clock is off by a user-settable threshold. The default is to
check the system clock but to allow the LDM to start. To customize
this feature, pay close attention to the instructions on web-page
<http://www.unidata.ucar.edu/software/ldm/ldm-current/basics/vet-ldmadmin.html>.
Do a case-insensitive search for the word "time".
ACCUMULATING AND PLOTTING METRICS:
This feature deals with metrics for the LDM system such as the
number of LDM connections, the age of the oldest data-product in the
product-queue, CPU load average and modes, etc. This feature allows
the metrics to be periodically accumulated in a file and to be
displayed as time-series plots (great for figuring-out if your
product-queue is large enough). You will need to have the top(1),
uptime(1), netstat(1), and vmstat(1) utilities installed in order to
collect metrics, and you'll need to have the gnuplot(1) utility
installed in order to display them. To use this feature, pay close
attention to the web-pages
<http://www.unidata.ucar.edu/software/ldm/ldm-current/basics/platform.html>,
<http://www.unidata.ucar.edu/software/ldm/ldm-current/basics/vet-ldmadmin.html>,
<http://www.unidata.ucar.edu/software/ldm/ldm-current/basics/configuring.html>,
and
<http://www.unidata.ucar.edu/software/ldm/ldm-current/basics/monitoring.html>.
Do a case-insensitive search for the word "metric".
For an extensive history of changes to the LDM, see the file CHANGE_LOG
in the top-level source-directory.
As always, we are happy to install the LDM system for you if you grant
us root access to your system.
Regards,
Steve Emmerson
LDM Developer
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