Case study:
EMG at Mblox (PDF)
EMG Watchdog Print
Sunday, 29 March 2015

EMG Watchdog is a perl script ( that is run as a background process on the same server as EMG and which can monitor and control the emgd process. It is released with EMG 7 but can be used to control EMG 6 as well.

It implements a simple API based on HTTP and JSON for starting, stopping EMG and reading EMG server log files.

EMG Watchdog can be used from EMG Portal to control the EMG process via the web-based interface.


The script provided is named "". It is intended to be copied to "" and can be run in the background with "perl &" as the same user that runs the "emgd" process, normally "emg".

It depends on several CPAN modules that need to be installed before the script can be run.

cpan Email::Sender::Simple Email::Sender::Transport::SMTP Email::Simple Email::Simple::Creator \
Filesys::Df HTTP::Daemon HTTP::Status IPC::Shareable JSON Net::Subnet URI::QueryParam

Before running the watchdog the configuration variables described below must be modified to match the local environment.

The latest version of the EMG Watchdog can be found on the URL below:


The most important variables below are "$emg_dir", "@notify_recipients" and "$mail_from".

Configuration variables in the script:

Variable Default Description
$emg_dir /home/emg/etc Directory where EMG configuration (server.cfg) is located
$logfile $emg_dir/log/emg_watchdog.log Log file for EMG watchdog
$emg_quickstop 1 Use "quick stop" for stopping emgd (signal emgd to stop, wait a few seconds and then kill it)
$check_interval 60 Specifies how often (in seconds) checks should be run
$notify_interval 21600 Specifies how often (in seconds) notifications should be sent for persistent error (21600 secs = 6 hours)
$fs_to_check / File system to check for used space
$fs_limit 80 File system usage limit (in %), notification will be sent when limit exceeded
$listen_port 3000 Port on which integrated web server listens for incoming requests
@notify_recipients ('') Array with recipients for e-mail notifications (empty by default)
$mail_from This e-mail address is being protected from spambots. You need JavaScript enabled to view it E-mail notification "From" address
$mail_subject_prefix 'EMG watchdog' E-mail notification subject prefix (consider adding hostname for easier identification)
$smtp_server IP address of SMTP server to use for sending e-mails
$smtp_port 25 Port of SMTP server to use for sending e-mails
$smtp_username undef Username for SMTP server authentication (undef = no auth)
$smtp_password undef Password for SMTP server authentication (undef = no auth)
$allowed_client_ips Allowed client ip addresses / subnets for web server access


When specific events occur the watchdog will send e-mail notifications to the addresses configured ($notify_recipients).

  • Monitor detected EMG was not running
  • EMG manual stop requested via API
  • EMG stopped
  • EMG manual startup requested via API
  • EMG started
  • EMG startup failed
  • Used disk space in monitored file system ($fs_to_check) exceeds configured percent (fs_limit)

Using the watchdog API

The watchdog features a built-in web server that by default listens on port 3000 which implements an api.

Web server port must be protected in order to make sure it cannot be accessed directly via the internet. Access must be protected either by a local firewall in the server (iptables) or by an external firewall in front of the EMG server.

URI Description and parameters (M - Mandatory, O - Optional)
/api/ping Check server status
/api/emg_start Start EMG server
/api/emg_stop Stop EMG server
/api/emg_status Get status of EMG server
/api/get_log_file_list Get list of log files
/api/get_log_file Get contents of log file
Parameters: file - Log file name (M)
maxrows - Max number of rows to return (O, default: 100)
search_string - Only return rows that include search_string, multiple terms can be separated by space (O)

Sample http request using wget

wget -q -O -

should return