28.1. The System and Server Status Module
This module allows you to monitor the status of various servers and daemons running on your system, so you can easily see which ones are running properly and which are down. It can also be configured to check the status of servers on a regular schedule, and to email you or run a command if something goes down. This can be useful if your system runs critical servers that other people depend upon, such as web or DNS servers.
The module can also monitor servers running on other hosts. This can be done in two ways—by making a TCP or HTTP connection to the port on which the server runs or by communicating with the Webmin server on the remote host and asking it to check the status of the server. The latter method is more powerful because it can be used to monitor things such as disk space and daemons that do not accept any network connections.
Each server or service that you want to watch, using the module, must have a monitor defined. Every monitor has a type that indicates what kind of server it is supposed to check, such as Apache or BIND. Monitors also have additional parameters, some of which are specific to their type. The module allows you to create many different types of monitors, for things like checking to see if Sendmail or Squid is running, watching for excessive network traffic or a shortage of disk space, or pinging or connecting to some host.
A monitor can run either on the system on which you are using the module or another server running Webmin. In the latter case, the server must be defined in the Webmin Servers Index module, explained in Chapter 53. You can also check another system that does not have Webmin installed using the remote TCP, HTTP, and ping monitor types.
Many monitors use other Webmin modules to find the locations of the servers and daemons that they check. For this reason, those other modules must be configured and working properly for the associated monitor to work as well. For example, if you have compiled and installed Apache in a different directory from the standard for your Linux distribution, the module configuration for Apache Web server will have to be adjusted to use the correct paths. If not, this module will not know where to look for the Apache PID file.
When you enter the System and Server Status module from the Others category on the Webmin menu, its main page will display a table of all configured monitors. Several monitors for common servers and services will be defined by default, but you can edit, delete, or add to them as you wish. Figure 28.1 shows an example of the module's main page.
Figure 28.1. The System and Server Status module.
For each monitor, a description, the Webmin server that it runs on, and its current status are shown. A monitor can be in one of the following three states:
Up Means that the monitored server or service is running correctly. This state is indicated by a green tick on the main page.
Down Means that the monitored server is down. This state is indicated by a red “X” on the module's main page.
Webmin down Means that Webmin on the remote system is down, and so the monitor cannot be run. Indicated by a red “W” on the module's main page.
Timed out6 Means that the monitor did not return a result within 60 seconds, perhaps because it ran a command that never completed. Indicated by a red clock symbol on the main page.
Not installed Means that the server being monitored is not installed on your system. This state is indicated by a black circle with a line through it.
By default, the status of every monitor is queried every time you view the module's main page. Because this may take a long time, if you have many monitors or are checking the status of servers on remote hosts, there is a module configuration option that can be used to display the status from the last scheduled check instead.