Troubleshooting Linux Collectors

We’ve compiled some helpful tips for troubleshooting common Linux Collector issues.

Name Service Caching Daemon (NSCD)

The LogicMonitor Collector makes DNS queries to resolve the hosts it is monitoring and to determine which LogicMonitor servers to report data to.

If you are running an NSCD, you should make sure that it respects positive DNS TTLs. For example, on RedHat ES/CentOS glibc-2.5-24 and earlier does not respect DNS TTLs correctly, meaning that you will need to run a later version or disable NSCD.

If the NSCD returns a stale record for an hour, it would impact your ability to monitor devices and communication between LogicMonitor datacenters.

SE Linux

Some distributions of Linux (such as RedHat, CentOS, and Fedora) may have Security-Enhanced (SE) Linux enabled, which may restrict access and permissions that can impact the Collector’s ability to monitor.

Use the /usr/sbin/getenforce or /usr/sbin/sestatus commands to check the status of SELinux.

• The getenforce command returns Enforcing, Permissive, or Disabled. The command returns Enforcing when SE Linux is enabled.
• The sestatus command returns the SE Linux status (Enabled, Disabled) and the mode (Enforcing, Permissive, Passive) being used.

If you are having monitoring problems in your Linux server and SE Linux is enabled, you may be able to use Permissive mode to review the logs and identify the issue:

setenforce Permissive

In Permissive mode, more denials are logged because actions that would otherwise be denied in Enforcing mode are allowed.  After you run the Collector services in permissive mode and SE Linux logs to identify the permissions that need to be enabled, you should enable the necessary permissions.

To put SE Linux back into enforcing mode, run:

setenforce 1