cookbook.rst

Cookbook

This chapter contains recipes for common tasks that can be done in lnav. These recipes can be used as a starting point for your own needs after some adaptation.

Log Formats

TBD

Defining a New Format

TBD

Annotating Logs

Log messages can be annotated in a couple of different ways in lnav to help you get organized.

Create partitions for Linux boots

When digging through logs that can be broken up into multiple sections, lnav's :ref:`partitioning feature<taking_notes>` can be used to keep track of which section you are in. For example, if a collection of Linux logs covered multiple boots, the following script could be used to create partitions for each boot. After the partition name is set for the log messages, the current name will show up in the top status bar next to the current time.

.. literalinclude:: ../../src/scripts/partition-by-boot.lnav
   :language: custsqlite
   :caption: partition-by-boot.lnav
   :linenos:

Tagging SSH log messages

Log messages can be tagged interactively with the :ref:`:tag<tag>` command or programmatically using the :ref:`sql-ext`. This example uses a script to search for interesting SSH messages and automatically adds an appropriate tag.

.. literalinclude:: ../../example-scripts/tag-ssh-msgs.lnav
   :language: custsqlite
   :caption: tag-ssh-msgs.lnav
   :linenos:

Log Analysis

Most log analysis within lnav is done through the :ref:`sql-ext`. The following examples should give you some ideas to start leveraging this functionality. One thing to keep in mind is that if a query gets to be too large or multiple statements need to be executed, you can create a .lnav script that contains the statements and execute it using the | command prompt.

Count client IPs in web access logs

To count the occurrences of an IP in web access logs and order the results from highest to lowest:

;SELECT c_ip, count(*) as hits FROM access_log GROUP BY c_ip ORDER BY hits DESC

Show only lines where a numeric field is in a range

The :ref:`:filter-expr<filter_expr>` command can be used to filter web access logs to only show lines where the number of bytes transferred to the client is between 10,000 and 40,000 bytes like so:

:filter-expr :sc_bytes BETWEEN 10000 AND 40000

Generating a Report

Reports can be generated by writing an lnav :ref:`script<scripts>` that uses SQL queries and commands to format a document. A basic script can simply execute a SQL query that is shown in the DB view. More sophisticated scripts can use the following commands to generate customized output for a report:

• The :ref:`:echo<echo>` command to write plain text
• :ref:`SQL queries<sql-ext>` followed by a "write" command, like :ref:`:write-table-to<write_table_to>`.

.. literalinclude:: ../../example-scripts/report-demo.lnav
   :language: custsqlite
   :caption: report-demo.lnav
   :linenos: