Introduction
============

The Log File Navigator, **lnav**, is an advanced log file viewer for the
terminal.  It provides an :ref:`easy-to-use interface<ui>` for monitoring and
analyzing your log files with little to no setup.  Simply point **lnav** at
your log files and it will automatically detect the :ref:`log_formats`, index
their contents, and display a combined view of all log messages.  You can
navigate through your logs using a variety of :ref:`hotkeys<hotkeys>`.
:ref:`Commands<commands>` give you additional control over **lnav**'s behavior
for doing things like applying filters, tagging messages, and more.  You can
then analyze your log messages using the :ref:`sql-ext`.

.. figure:: lnav-intro-screen.png
   :align: center
   :alt: Screenshot of lnav showing a mix of syslog and web access_log messages.

   Screenshot of **lnav** viewing syslog and web access_log messages.

Development
-----------

Development of lnav is hosted on `GitHub <https://github.com/tstack/lnav/>`_.

`Issues <https://github.com/tstack/lnav/issues>`_ should be used for bugs
and feature requests.

`Discussions <https://github.com/tstack/lnav/discussions>`_ should be used
for asking questions and sharing tips.

Downloads
---------

Binaries and source code for lnav can be downloaded from the
`releases page <https://github.com/tstack/lnav/releases>`_.

When building from source, follow the steps below.

Dependencies
^^^^^^^^^^^^

When compiling from source, the following dependencies are required:

* `NCurses <http://www.gnu.org/s/ncurses/>`_
* `PCRE2 <http://www.pcre.org>`_
* `SQLite <http://www.sqlite.org>`_
* `ZLib <http://wwww.zlib.net>`_
* `Bzip2 <http://www.bzip.org>`_
* `Readline <http://www.gnu.org/s/readline>`_
* `libcurl <https://curl.haxx.se>`_
* `libarchive <https://libarchive.org>`_

Installation
^^^^^^^^^^^^

Check the `downloads page <http://lnav.org/downloads>`_ to see if there are
packages for your operating system.  To compile from source, use the following
commands:

.. prompt:: bash

   ./configure
   make
   sudo make install


Viewing Logs
------------

The arguments to **lnav** are the log files, directories, or URLs to be viewed.
For example, to view all of the CUPS logs on your system:

.. prompt:: bash

   lnav /var/log/cups

The formats of the logs are determined automatically and indexed on-the-fly.
See :ref:`log_formats` for a listing of the predefined formats and how to
define your own.

If no arguments are given, **lnav** will try to open the syslog file on your
system:

.. prompt:: bash

   lnav


Setup
-----

After starting **lnav**, you might want to set the
:ref:`configuration options<Configuration>` mentioned below.  Configuration in
**lnav** is done using the :code:`:config` command.  To change a configuration
option, start by pressing :kbd:`:` to enter the command prompt.  Then,
type "config" followed by the option name and value.

.. note::

   Tab-completion is available for these configuration options and, in some
   cases, their values as well.


Keymap
^^^^^^

The keymap defines the mapping from :ref:`hotkeys<hotkeys>` to commands to
execute. The default mapping is for "U.S." keyboards.  The following command
can be used to change the keymap:

.. code-block:: lnav

   :config /ui/keymap <keymap-name>

The builtin keymaps are:

  :de: `German <https://github.com/tstack/lnav/blob/master/src/keymaps/de-keymap.json>`_
  :fr: `French <https://github.com/tstack/lnav/blob/master/src/keymaps/fr-keymap.json>`_
  :sv: `Swedish <https://github.com/tstack/lnav/blob/master/src/keymaps/sv-keymap.json>`_
  :uk: `United Kingdom <https://github.com/tstack/lnav/blob/master/src/keymaps/uk-keymap.json>`_
  :us: `United States <https://github.com/tstack/lnav/blob/master/src/keymaps/us-keymap.json>`_

To create or customize a keymap, consult the :ref:`keymaps` section.


Theme
^^^^^

The visual styling of **lnav** can be customized using a theme.  The following
command can be used to the change the theme:

.. code-block:: lnav

   :config /ui/theme <theme-name>

The builtin themes are:
`default <https://github.com/tstack/lnav/blob/master/src/themes/default-theme.json>`_,
`eldar <https://github.com/tstack/lnav/blob/master/src/themes/eldar.json>`_,
`grayscale <https://github.com/tstack/lnav/blob/master/src/themes/grayscale.json>`_,
`monocai <https://github.com/tstack/lnav/blob/master/src/themes/monocai.json>`_,
`night-owl <https://github.com/tstack/lnav/blob/master/src/themes/night-owl.json>`_,
`solarized-dark <https://github.com/tstack/lnav/blob/master/src/themes/solarized-dark.json>`_,
and
`solarized-light <https://github.com/tstack/lnav/blob/master/src/themes/default-theme.json>`_.

To create or customize a theme, consult the :ref:`themes` section.


Cursor Mode (v0.11.2+)
^^^^^^^^^^^^^^^^^^^^^^

The default mode for scrolling in **lnav** is to move the contents of the
main view when the arrow keys are pressed.  Any interactions, such as
jumping to a search hit, are then focused on the top line in the view.
Alternatively, you can enable "cursor" mode where there is a cursor line
in the view that is moved by the arrow keys and other interactions.  You
can enable cursor mode with the following command:

.. code-block:: lnav

   :config /ui/movement/mode cursor

Log Formats
^^^^^^^^^^^

In order for **lnav** to understand your log files, it needs to told how to
parse the log messages using a log format definition.  There are many log
formats builtin and **lnav** will automatically determine the best format to
use.  In case your log file is not recognized, consult the :ref:`log_formats`
section for information on how to create a format.