Open Source

Tech Tip: Monitor logs in Linux with LogSurfer+

Learn how to use the LogSurfer+ tool to monitor logs in Linux, and find out how to create rules that are relevant to your network.

A number of tools exist for monitoring log files. One well-known and commonly used tool is swatch, which can send out alerts based on certain strings that show up in a log file.

But due to some of its limitations, developers created another tool called LogSurfer. Based on swatch, LogSurfer yields a lot more power. LogSurfer+ is a version of LogSurfer that adds even more capabilities.

Setting up LogSurfer+ can take a little work because you need to create rules that are relevant to your network. To begin, download the tool from the LogSurfer and LogSurfer+ Resources Web page; then, compile and install it.

After installation, you can begin creating rules. Rules are based on regular expressions matching various actions that you can assign, such as "ignore," "exec" (run a program), "rule" (dynamically create a new rule), and more.

Here's a simple example of a rule to ignore log messages of "last message repeated xx times":

'last message repeated' - - - 0
  ignore

Here's the syntax for a rule:

match_regex not_match_regex stop_regex not_stop_regex timeout [continue] \ action

For example, to log ssh logins on any host, you could use a rule like the following:

'^.{15,} (.*) sshd\[.* session opened for user (.*)' - - - 0
  open "$2 sshd login" - 500 1200 600
  report "/usr/local/bin/mailop \"ssh login on $2 for $4\" \"$2 sshd login\"

While a little more complicated, this rule will run the /usr/local/bin/mailop script to send a message indicating that an ssh login occurred on the particular host and from a particular user.

The variables you see (i.e., $2, $4, etc.) stand for matched regular expressions So, $2 corresponds to the second matched regexp, and $4 corresponds to the fourth matched regexp, which corresponds to the machine name and username in the matched log line rule. This is an example of a rule making a new context rule.

LogSurfer+ can be a little difficult to set up initially, especially if you're unfamiliar with regular expressions. For other samples and in-use rules, check out emf's LogSurfer configuration Web page, which contains a number of example rules.

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