Frequently Asked Questions


  1. What does NARC have to offer over other System Activity Reporters?

    NARC is the Network Activity Reporting Chimp. NARC is the graphing engine for NAR, which monitors and collects network traffic volume data.

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  3. What type of data does NARC collect?

    NARC collects information about the traffic volume and the errors that have occured on all configured network devices on the system.

    Network Device Traffic - NARC monitors the number of bits, packets, broadcast packets, and multicast packets that travel in and out of the network devices.

    Network Device Errors - NARC watches for transmission and reception errors, collisions and queue length.

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  1. What system requirements are needed to run NARC?

    This is dependent on the number of systems being monitored and other tasks the central system is running. A dedicated Intel PIII 1.0 GHZ with 512 MB RAM was able to monitor 35 systems without problems.

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  3. What is required to run NARC?

    Perl Version 5.8.x or greater.

    Perl Modules: (


    Web server (Apache)

    RRDTool ( Installed with Perl module.

    NAR - 'nar' installed on each system to be monitored.

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  5. How much space should I allocate for data collection?

    Roughly 3 MB per host per year for data storage, and another 1 MB per host for graph display. Systems with a large number of disk drives may require an additional 3 MB of space.

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  7. What Operating Systems are supported?

    The following table shows the operating systems support status as of Feb 2007.

    Operating SystemSupport
    Mac OSXSupported

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  1. If a machine is off the network, will the data still be collected and graphed? depends on what's "down".

    If the remote system is down, then no nar data is being collected and can't be graphed.

    If the remote system is unreachable due to a network problem, NARC will attempt to collect the previous 3 hours of data automatically. Anything beyond that will be lost.

    If the NARC data collection server is down for a significant length of time (a few days), historcal data can be collected using the the "loadall" script. (Be sure to turn off the crontab call to NARC while doing this.)

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  3. Can you control how much data is collected and how long it is kept?

    Not easily.

    RRDTool requires data to be collected as specific intervals, or else the data is considered invalid. RRDTool also requires that storage is pre-allocated for the predicted size. These constraints also aid in the small processing over head of RRDTool.

    Five minute data collection intervals and storage of one year of data per host were chosen as the NARC limits based on input from colleagues and years of running monitoring tools.

    The intrepid programmer can dive into the NARC code to change these, if desired. This is not recommeneded. Or supported.

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  5. Does NARC run continually in the background on the server? What about the clients?

    No. The central server collects data from monitored systems every 15 minutes. Each remote system collects data locally every 5 minutes.

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  7. Does NARC use up a lot of system resources on the clients?

    Resources on the clients (i.e., systems being monitored) are neglible (< 1% CPU utilitazation).

    Resource use on the central server depends on the number of clients being monitored. Our operational server spikes to approximately 30% CPU usage for a minute every 15 minutes during data collection periods.

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  9. What about firewalls and the operation of NARC?

    Data collection from clients will work as long as correct ports (port 514 for rsh, port 22 for ssh) are open and the 'narc' user can perform data collection without a password.

    Graph display is via a web interface (port 80 for http).

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  11. Why can't I load historical data?

    Is there data to be loaded? NAR data is pruned by crontab entries (see na2) every few weeks to avoid filling disks.

    Is there already data in the RRDTool database? RRDTool is a "forward only" database, not a random access database. This means that only data with newer time stamps may be inserted into the database. Attempts to load old data will raise RRDTool errors.

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Data Collection

  1. No data is being collected on the client. What's wrong?

    Make sure that NAR is enabled.

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  1. Data appears to be collecting, why aren't the graphs displaying?

    Run "webgen" and see what happens.

    If that doesn't work, it's possible that there is a problem with the nar data being entered into RRDTool. RRDTool is a forward only database and some versions of nar have been known to enter data with timestamps in the future. We've tried to correct for this, but haven't been able to do so in all cases.

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  3. The default screen shows "-24h" in Start and "now" in the End boxes, why doesn't it show a date?

    The default display period is 'the last 24 hours.' This is the method RRDTool specifies this period.

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  5. How do I make the graphs bigger/smaller?

    Re-run "webgen" with the "-p <percent>" option. The default size is 75%.

    Ex - Smaller: ./webgen -p 50

    Ex - Larger: ./webgen -p 150

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  7. Can I change the limits of the graphs?

    Again, not easily. RRDTool needs to have limits chosen at the time the databases are created. The limits chosen seem reasonable and are based on years of experience with NAR data and performance monitoring.

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