[ldm-users] LDM 6.8.0 released

• To: LDM-USERS <ldm-users@xxxxxxxxxxxxxxxx>
• Subject: [ldm-users] LDM 6.8.0 released
• From: Steve Emmerson <steve@xxxxxxxxxxxxxxxx>
• Date: Fri, 31 Jul 2009 14:32:23 -0600

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.ht
ml>.
    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.ht
ml>,

<http://www.unidata.ucar.edu/software/ldm/ldm-current/basics/configuring.htm
l>,
    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