Multitech MultiModem iSMS SF100-G Manual de usuario descargar pdf (Pagina 5)

Apache

I initially had multiple overlapping “Directory” statements

in the Nagios section of the Apache configuration file.

The net effect was a “Permission denied” when the CGI

was being run. I figured this out by using the method

described below and by looking at the Apache access_log

and error_log files.

Network Capture

If you think there is some communication problem with

the script, you can monitor the traffic between Nagios,

Apache and the iSMS by listening on the network.

I used tcpdump to capture the HTTP traffic and see

error messages:

% tcpdump -v -s 0 -w /tmp/cap host 192.168.1.50

In this example, I used the

-v

option for verbose output,

the

-s 0

option to capture as much of the packet as possible

and the

-w

option to write the captured traffic to the /tmp/cap

file. The “host” keyword indicates that I want all traffic to

and from the IP address of the iSMS (192.168.1.50). I ran this

command on the machine hosting both Nagios and Apache,

so it should see all communication between these services

and the iSMS. I then generated some SMS messages traffic

by causing Nagios to send out a “PROBLEM” message,

which I then acknowledged via my mobile phone. You

should see the number following “Got” incrementing as

packets are being captured:

tcpdump: listening on eth0, link-type EN10MB (Ethernet),

capture size 65535 bytes

Got 22

I then interrupted the capture and converted the captured

data to plain text:

% tcpdump -A -r /tmp/cap > /tmp/txt

The

-A

option writes out ASCII text, and the

-r

option

reads capture data from a file. Examining the /tmp/txt file

allows you to see the entire HTTP transaction between Nagios,

the iSMS and the CGI script:

12:50:09.434851 IP nagios.46058 > smsgw.http:

P 1:266(265) ack 1 win 46

<nop,nop,timestamp 2801435752 1987587011>

GET /sendmsg?user=nagios&passwd=secret...text=ACKNOWLEDGEMENT...

12:50:09.501524 IP smsgw.http > nagios.46058:

P 1:29(28) ack 266 win 6432

<nop,nop,timestamp 1987587017 2801435752>

HTTP/1.0 200 OK

ID: 2078

In this capture, you can see that the sendsms.pl script

invoked by Nagios (hostname nagios) has sent an HTTP

GET to the iSMS (hostname smsgw) containing the Nagios

“ACKNOWLEDGEMENT” message. The “ID: 2078”

response from the iSMS back to Nagios indicates that the

message has been queued for sending and that the ID for

this SMS message is 2078. You also might note that the

user name and password for the iSMS “nagios” account

is being sent in the clear—not perfect, but I think this is

a pretty low security risk, as this transaction is internal to

the company network.

Firmware Version of iSMS

My original iSMS came with version 1.20 firmware. This

worked fine with the original Perl script, but it had a

problem in that it was somewhat “single user”. For example,

if you happened to be logged in to the iSMS Web user

interface while the check_smsfinder.pl script ran, it would

return a bad status, and Nagios would create an alert for

the device. Upgrading to the newer firmware fixed this

problem, but broke the check_smsfinder.pl script. The

Perl script has been updated, but the version of the script

now is tied to the firmware version running on the iSMS.

Because this is a Perl script, it can be modified easily. If

you do not like the format of the message being sent out

by Nagios, you can change this in the Nagios “command”

definition—for example, “notify-host-by-sms” and also

change the Perl script to parse whatever format of a

message you want to send back from your phone. The

script authors have changed their message format over

time to make it easier to parse, as problems were discovered

with whitespace in service names and host alerts that

would change format depending on whether the host

definition contained an IP address (such as in the case

of DHCP clients).

Conclusion

I am very pleased with how this alerting service has worked

out. The iSMS has been solid since the moment I installed it,

and the associated script has worked perfectly once I tweaked

my Nagios setup to match it. I have high confidence that I will

get alerts regardless of the nature of the problem.

Acknowledgements

Thanks to Birger Schmidt and his colleagues from

NETWAYS GmbH (www.netways.de) for writing the

original script, updating it and taking the time to review

this article, and to Chris Reilley (www.reilleydesign.com)

for Figure 2.

Eric Pearce is the IT Lead for AmberPoint, Inc., an Application Management and Governance

software company based in Oakland, California. He has authored several books on UNIX and

Windows system administration for O’Reilly & Associates.

6 |

march 2010 www.linuxjournal.com

FEATURE Using an SMS Server to Provide a Robust Alerting Service for Nagios

To read more Linux Journal or start your subscription, please visit http://www.linuxjournal.com.

The iSMS can send helpful

debugging messages to

a remote host via syslog.

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