Multitech MultiModem iSMS SF100-G Manual de usuario descargar pdf (Pagina 3)

Physical Location of iSMS

I wanted the iSMS and the Nagios server to be able to send

messages for as long as possible if there were a problem with

network connectivity or power. In my situation, this meant

locating the iSMS, the Nagios server and their shared Ethernet

switch all in the same computer room and plugged in to the

same redundant UPS. Of course, I could eliminate the switch

from this configuration by using an Ethernet crossover cable

to link the iSMS and the Nagios server directly, but that

would limit communication to the one server. It also would

eliminate most of the advantages over the hard-wired

GSM modems that I was trying to improve upon.

The smsfinder Perl Script

The Perl script can be found on the MonitoringExchange site

(www.monitoringexchange.org) or the Nagios Wiki

(www.nagioswiki.org). Searching for “smsfinder” should get

you to the correct place. The documentation for the script

includes installation instructions, example Nagios configuration

files and screenshots of the iSMS Web user interface. The

author used an interesting approach to create a single script

that serves three different purposes. The script checks to see

which filename was used to call the script and then performs

a completely different function depending on which name was

used. The script has three names:

I smssend.pl: a Nagios “command” used to send messages

about hosts and services via SMS.

I smsack.cgi: a CGI script used by the iSMS to acknowledge

alerts it has received via an SMS message sent by a

mobile phone.

I check_smsfinder.pl: a typical Nagios “plugin” or “check”

script invoked by Nagios on a scheduled basis to monitor

the health of the iSMS device itself.

Script Installation

I stored the actual script as /usr/local/nagios/smsack/smsack.cgi and

made two symbolic links to it with the following names/paths:

I /usr/local/nagios/smsack/sendsms.pl

I /usr/local/nagios/libexec/check_smsfinder.pl

Apache will want to execute an actual file as a CGI, while

Nagios will not care about the symbolic links. Figure 2 provides

an overview of how the script interacts with the other compo-

nents of the system.

The least complex use of the script is when it is called

check_smsfinder.pl. Nagios runs this check script at scheduled

intervals, and the script queries a status page on the iSMS via

HTTP to make sure it is running okay. The script returns the

exit status back to Nagios. The performance data includes

the signal level for the GSM modem, the model number

and the firmware version.

The next use of the script is when it is called as sendsms.pl

by Nagios. In this form, it is used to send host and service

alerts and acknowledgements to the iSMS for delivery to

mobile users. The script uses the “HTTP Send API” to request

that it transmit the SMS message. The iSMS queues the

request and returns a message ID. The end user can query the

iSMS with the message ID to find out if the SMS message was

sent successfully or failed for some reason. When invoked as

sendsms.pl, the script has a --noma option, which will query

the iSMS after queuing the message to get its status. This

takes slightly longer to execute, as the script has to wait for

confirmation that the message actually was sent (or failed).

The documentation refers to “NoMa” but does not explain

why the option was named that way.

The most complicated use of the script is when it runs as the

smsack.cgi CGI script under Apache. The recipient of an SMS

alert can send the entire message back to the iSMS with the

string “ACK” or “OK” prepended to the message text. When

this SMS message is received by the iSMS, it uses the “HTTP

Receive API” to call the smsack.cgi CGI script with the ACK

message. The smsack.cgi CGI script parses the message text,

determines whether it is a host or service being acknowledged,

verifies that the sender’s phone number is in the Nagios object

cache and then uses

the Nagios “external

command” interface to

signal Nagios. Nagios

then tries to match the

host or service name

with one it knows

about, and if this

match is successful,

it acknowledges the

problem. The script also

creates a note on the

host or service page

indicating that the

problem was acknowl-

edged by the sender’s

mobile number.

The acknowledge

feature expects the

entire SMS alert mes-

sage to be sent back

to the iSMS with the

4 | 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.

smsnder.log

check_smsnder.pl

sendsms.pl

smsack.cgi

Nagios

Nagios.log

Logging activity

MultiModem

iSMS

Logging activity

Internal or syslog

Mobile Phone

Apache

access_log

error_log

Logging activity

Figure 2. SMSFinder Method of Operation

Figure 3. Apple iPhone Screenshot

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