Shell Monitor

This agent monitor plugin periodically executes a specified shell command, and records the output. It can be used to monitor any information that can be retrieved via a shell command. Shell commands are run from the Scalyr Agent, and execute as the same user as the agent.

An agent monitor plugin is a component of the Scalyr Agent. To use a plugin, simply add it to the monitors section of the Scalyr Agent configuration file (/etc/scalyr/agent.json). For more information, see Agent Plugins.

Sample Configuration

Here is a simple configuration fragment showing use of the shell_monitor plugin. This sample will record the version of the Linux kernel in use on the machine where the agent is running.

monitors: [
  {
    module:  "scalyr_agent.builtin_monitors.shell_monitor",
    id:      "kernel-version",
    command: "uname -r"
  }
]

To record output from more than one command, use several copies of the shell_monitor plugin in your configuration.

Viewing Data

After adding this plugin to the agent configuration file, wait one minute for data to begin recording. Then go to the Search page and search for $monitor = 'shell_monitor'. This will show all data collected by this plugin, across all servers. You can use the Refine search by dropdown to narrow your search to specific servers and monitors.

The Search overview page describes the tools you can use to view and analyze log data. Query Language lists the operators you can use to select specific metrics and values. You can also use this data in Dashboards and Alerts.

Configuration Reference

Option	Usage
module	Always scalyr_agent.builtin_monitors.shell_monitor
id	Included in each log message generated by this monitor, as a field named instance. Allows you to distinguish between values recorded by different monitors.
command	The shell command to execute.
extract	Optional: a regular expression to apply to the command output. If defined, this expression must contain a matching group (i.e. a subexpression enclosed in parentheses). The monitor will record only the content of that matching group. This allows you to discard unnecessary portions of the command output and extract the information you need.
log_all_lines	Optional (defaults to false). If true, the monitor will record the entire command output; otherwise, it only records the first line.
max_characters	Optional (defaults to 200). At most this many characters of output are recorded. You may specify a value up to 10000, but the Scalyr server currently truncates all fields to 3500 characters.

Log Reference

Each event recorded by this plugin will have the following fields:

Field	Meaning
monitor	Always shell_monitor
metric	Always output
instance	The id value from the monitor configuration, e.g. kernel-version
command	The shell command for this plugin instance, e.g. uname -r
value	The output of the shell command, e.g. 3.4.73-64.112.amzn1.x86_64