Extracting Data¶
Note: This feature is still in BETA, you should expect bugs and incompatible changes in the future.
Log messages contain a good deal of useful data, but it’s not always easy to get
at. The log parser built into lnav is able to extract data as described by
Log Formats as well as discovering data in plain text messages. This data
can then be queried and processed using the SQLite front-end that is also
incorporated into lnav. As an example, the following Syslog message from
sudo can be processed to extract several key/value pairs:
Jul 31 11:42:26 Example-MacBook-Pro.local sudo[87024]: testuser : TTY=ttys004 ; PWD=/Users/testuser/github/lbuild ; USER=root ; COMMAND=/usr/bin/make install
The data that can be extracted by the parser is viewable directly in lnav by pressing the ‘p’ key. The results will be shown in an overlay like the following:
Current Time: 2013-07-31T11:42:26.000 Original Time: 2013-07-31T11:42:26.000 Offset: +0.000
Known message fields:
├ log_hostname = Example-MacBook-Pro.local
├ log_procname = sudo
├ log_pid = 87024
Discovered message fields:
├ col_0 = testuser
├ TTY = ttys004
├ PWD = /Users/testuser/github/lbuild
├ USER = root
└ COMMAND = /usr/bin/make install
Notice that the parser has detected pairs of the form ‘<key>=<value>’. The data parser will also look for pairs separated by a colon. If there are no clearly demarcated pairs, then the parser will extract anything that looks like data values and assign them keys of the form ‘col_N’. For example, two data values, an IPv4 address and a symbol, will be extracted from the following log message:
Apr 29 08:13:43 sample-centos5 avahi-daemon[2467]: Registering new address record for 10.1.10.62 on eth0.
Since there are no keys for the values in the message, the parser will assign ‘col_0’ for the IP address and ‘col_1’ for the symbol, as seen here:
Current Time: 2013-04-29T08:13:43.000 Original Time: 2013-04-29T08:13:43.000 Offset: +0.000
Known message fields:
├ log_hostname = sample-centos5
├ log_procname = avahi-daemon
├ log_pid = 2467
Discovered message fields:
├ col_0 = 10.1.10.62
└ col_1 = eth0
Now that you have an idea of how the parser works, you can begin to perform queries on the data that is being extracted. The SQLite database engine is embedded into lnav and its Virtual Table mechanism is used to provide a means to process this log data. Each log format has its own table that can be used to access all of the loaded messages that are in that format. For accessing log message content that is more free-form, like the examples given here, the logline table can be used. The logline table is recreated for each query and is based on the format and pairs discovered in the log message at the top of the display.
Queries can be performed by pressing the semi-colon (;) key in lnav. After pressing the key, the overlay showing any known or discovered fields will be displayed to give you an idea of what data is available. The query can be any SQL query supported by SQLite. To make analysis easier, lnav includes many extra functions for processing strings, paths, and IP addresses. See SQLite Interface for more information.
As an example, the simplest query to perform initially would be a “select all”, like so:
SELECT * FROM logline
When this query is run against the second example log message given above, the following results are received:
log_line log_part log_time log_idle_msecs log_level log_hostname log_procname log_pid col_0 col_1
292 p.0 2013-04-11T16:42:51.000 0 info localhost avahi-daemon 2480 fe80::a00:27ff:fe98:7f6e eth0
293 p.0 2013-04-11T16:42:51.000 0 info localhost avahi-daemon 2480 10.0.2.15 eth0
330 p.0 2013-04-11T16:47:02.000 0 info localhost avahi-daemon 2480 fe80::a00:27ff:fe98:7f6e eth0
336 p.0 2013-04-11T16:47:02.000 0 info localhost avahi-daemon 2480 10.1.10.75 eth0
343 p.0 2013-04-11T16:47:02.000 0 info localhost avahi-daemon 2480 10.1.10.75 eth0
370 p.0 2013-04-11T16:59:39.000 0 info localhost avahi-daemon 2480 10.1.10.75 eth0
377 p.0 2013-04-11T16:59:39.000 0 info localhost avahi-daemon 2480 10.1.10.75 eth0
382 p.0 2013-04-11T16:59:41.000 0 info localhost avahi-daemon 2480 fe80::a00:27ff:fe98:7f6e eth0
401 p.0 2013-04-11T17:20:45.000 0 info localhost avahi-daemon 4247 fe80::a00:27ff:fe98:7f6e eth0
402 p.0 2013-04-11T17:20:45.000 0 info localhost avahi-daemon 4247 10.1.10.75 eth0
735 p.0 2013-04-11T17:41:46.000 0 info sample-centos5 avahi-daemon 2465 fe80::a00:27ff:fe98:7f6e eth0
736 p.0 2013-04-11T17:41:46.000 0 info sample-centos5 avahi-daemon 2465 10.1.10.75 eth0
781 p.0 2013-04-12T03:32:30.000 0 info sample-centos5 avahi-daemon 2465 10.1.10.64 eth0
788 p.0 2013-04-12T03:32:30.000 0 info sample-centos5 avahi-daemon 2465 10.1.10.64 eth0
1166 p.0 2013-04-25T10:56:00.000 0 info sample-centos5 avahi-daemon 2467 fe80::a00:27ff:fe98:7f6e eth0
1167 p.0 2013-04-25T10:56:00.000 0 info sample-centos5 avahi-daemon 2467 10.1.10.111 eth0
1246 p.0 2013-04-26T06:06:25.000 0 info sample-centos5 avahi-daemon 2467 10.1.10.49 eth0
1253 p.0 2013-04-26T06:06:25.000 0 info sample-centos5 avahi-daemon 2467 10.1.10.49 eth0
1454 p.0 2013-04-28T06:53:55.000 0 info sample-centos5 avahi-daemon 2467 10.1.10.103 eth0
1461 p.0 2013-04-28T06:53:55.000 0 info sample-centos5 avahi-daemon 2467 10.1.10.103 eth0
1497 p.0 2013-04-29T08:13:43.000 0 info sample-centos5 avahi-daemon 2467 10.1.10.62 eth0
1504 p.0 2013-04-29T08:13:43.000 0 info sample-centos5 avahi-daemon 2467 10.1.10.62 eth0
Note that lnav is not returning results for all messages that are in this syslog file. Rather, it searches for messages that match the format for the given line and returns only those messages in results. In this case, that format is “Registering new address record for <IP> on <symbol>”, which corresponds to the parts of the message that were not recognized as data.
More sophisticated queries can be done, of course. For example, to find out the frequency of IP addresses mentioned in these messages, you can run:
SELECT col_0,count(*) FROM logline GROUP BY col_0
The results for this query are:
col_0 count(*)
10.0.2.15 1
10.1.10.49 2
10.1.10.62 2
10.1.10.64 2
10.1.10.75 6
10.1.10.103 2
10.1.10.111 1
fe80::a00:27ff:fe98:7f6e 6
Since this type of query is fairly common, lnav includes a “summarize” command that will compute the frequencies of identifiers as well as min, max, average, median, and standard deviation for number columns. In this case, you can run the following to compute the frequencies and return an ordered set of results:
:summarize col_0
Recognized Data Types¶
When searching for data to extract from log messages, lnav looks for the following set of patterns:
- Strings
Single and double-quoted strings. Example: “The quick brown fox.”
- URLs
URLs that contain the ‘://’ separator. Example: http://example.com
- Paths
File system paths. Examples: /path/to/file, ./relative/path
- MAC Address
Ethernet MAC addresses. Example: c4:2c:03:0e:e4:4a
- Hex Dumps
A colon-separated string of hex numbers. Example: e8:06:88:ff
- Date/Time
Date and time stamps of the form “YYYY-mm-DD” and “HH:MM:SS”.
- IP Addresses
IPv4 and IPv6 addresses. Examples: 127.0.0.1, fe80::c62c:3ff:fe0e:e44a%en0
- UUID
The common formatting for 128-bit UUIDs. Example: 0E305E39-F1E9-4DE4-B10B-5829E5DF54D0
- Version Numbers
Dot-separated version numbers. Example: 3.7.17
- Numbers
Numbers in base ten, hex, and octal formats. Examples: 1234, 0xbeef, 0777
- E-Mail Address
Strings that look close to an e-mail address. Example: gary@example.com
- Constants
Common constants in languages, like: true, false, null, None.
- Symbols
Words that follow the common conventions for symbols in programming languages. For example, containing all capital letters, or separated by colons. Example: SOME_CONSTANT_VALUE, namespace::value