The most common user complaint I receive is poor or unexpected performance by a user application, so I've been spending some time looking at tools that can help me understand what is happening on a server. A good place to start is with simple command-line applications that watch overall system performance. I chose command-line tools because I don't always have a nice GUI to the node, and sometimes I am left with just a simple SSH connection or a crash cart (the nodes likely don't have graphics cards). In this article, I'm going to examine a comprehensive tool that provides a quick glance at node performance from many perspectives (i.e., CPU, network, disk). The tool is called nmon [1].

Nmon Overview

Nmon is short for "Nigel's Monitor" and is a command-line tool that presents performance information about the system to the user. It started in the AIX world but has migrated to other *nix systems, including Linux. Nmon has lots of options for monitoring different aspects of the system, including:

• Machine (system) information
• CPU stats
• Memory stats
• Virtual memory stats
• Kernel internal stats
• Network stats (and errors)
• NFS information
• Disk I/O stats (and graphs)
• Disk busy information (Disk I/O map)
• Partition disk I/O stats
• Logical partition disk I/O stats

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