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fetchlog(1) fetchlog documentation fetchlog(1)
NAME
fetchlog - fetch and convert new messages of a logfile
SYNOPSIS
fetchlog -f first:last:len:conv logfile bookmarkfile [ pattern .. ]
fetchlog -F first:last:len:conv logfile bookmarkfile [ pattern .. ]
fetchlog [-h|-V]
DESCRIPTION
The fetchlog utility displays the last new messages of a logfile. It is
similar like tail(1) but offers some extra functionality for output
formatting. To show only the new messages appeared since the last call
fetchlog uses a bookmark to remember which messages have been fetched.
fetchlog scans backwards logfile and collects all messages, optionally
only those matching any of the given regex-style patterns. Then
fetchlog converts found message lines for output. It stops scanning
when one of these conditions become true: The bookmark from
bookmarkfile is reached, or len characters are ready for output, or an
error occurs. fetchlog knows about rotated and uncompressed logfiles
and continues scanning in rotated logfiles by appending '.0', if that
file does not exist '.1', then upto '.9' to logfile when scanning in
rotated logfiles. Scanning stops without error when a rotated logfile
does not exist.
OPTIONS
-f do not update bookmark in bookmarkfile.
-F update bookmark in bookmarkfile : set bookmark to the very last
line fetched from logfile
first The first column of text fetchlog will read from logfile. Lines
shorter than first will be show up as a single newline. The
column count starts with 1.
last The maximum last column fetchlog will read from logfile. Lines
longer than last will be cut off and a `~` will be set at column
last for output. The column count starts with 1.
len The maximum number of characters fetchlog will output. If more
than len characters are available after cutting and conversion,
the first line put out will start with '...'.
conv Conversion: one ore more of characters 'bpsno3'.
b [brackets] convert '<' and '>' to '(' and ')' for safe HTML
output.
p [percent] convert '%' to 'p' for safe printf(1) output.
s [shell] convert '$', '^', and the three quotes (backquote,
doublequote, singlequote) and '|' to '_' and '\' to '/'. This
conversion is useful when passing the result of fetchlog to a
shell command as a parameter.
n [newline] convert newline characters to '\n' sequence to get a
single line of output.
o [ok message] Show 'OK: no messages' if no new messages are
available for output.
3 [Nagios3] output in multiline format required for plugins
since Nagios3.
logfile
Absolute path to the unrotated logfile to fetch data from. The
user needs read access to logfile.
bookmarkfile
Absolute path to the file holding the bookmark. The user needs
read access to the file when using option -f and write access
plus permission to create files in the directory of bookarkfile
when using option -F (update bookmark).
If bookmarkfile does not exist fetchlog assumes an infinite old
bookmark.
pattern
A extended regular expression pattern, see re_format(7) for
details. If one or more pattern are defined, fetchlog will only
pick lines where any of these pattern match. Pattern matching is
done after trimming the lines with respect to first and last and
before any conversions takes place. In other words: pattern
matching operates on data that fetchlog shows when no conversion
is set.
-h print help message
-V print version
MULTIPLE FETCHING
Fetching the same logfile with different bookmarks works without
problem. Simultanously fetching with option -F (update mode) using the
same bookmark file works too, but unpredictable results will occur. For
safety reasons bookmarkfile will never be opened for writing directly,
instead a temporary file will be used and renamed to bookmarkfile when
writing has finished.
PERFORMANCE
Before opening logfiles for scanning fetchlog first checks the
modification time of logfile and compares this time with the
modification time stored in bookmarkfile. If both timestamps are the
same then fetchlog exits with 0 (no messages). Otherwise the
logfile(s) get mapped to memory step by step and are scanned backwards
line by line until one of the end conditions become true. fetchlog
uses the logfiles inode to distinguish different logs.
NAGIOS
fetchlog may be used as a local plugin for the Nagios network
monitoring system to monitor a local logfile. It follows the calling
convention for Nagios plugins if at least conversions on are set and
len is 'short' enough for Nagios (330 prior to Nagios 3, 4000 since
Nagios 3). It is recommended to use conversion s also because shell
metacharacters in fetched messages may confuse Nagios' notification
system.
Nagios 3 introduces a new interface for plugins sending out multiline
output as fetchlog does. Even with conversion 'n' Nagios reads this as
a multiline message. To be compatible with Nagios 3 plugin format
enable conversion '3' also. Output format is then:
SHORT_MESSAGE|\nMESSAGE_LINE_1\n...\nMESSAGE_LINE_N where SHORT_MESSAGE
will be the last line fetched MESSAGE_LINE_N. Please see README.Nagios
for details.
When using fetchlog as a local plugin for Nagios then exit status is as
follows:
OK No new messages in logfile where found. The single line 'OK: no
messages' will be send to stdout.
WARNING
fetchlog detected an internal error while fetching. A one line
error message starting with 'ERROR: fetchlog:' is send to
stdout.
CRITICAL
New messages in logfile where found. A single line with the last
new messages will be send to stdout.
UNKNOWN
fetchlog was called with wrong parameters. A multiline usage
message is send to stdout.
Nagios can monitor remote logfiles together with NET-SNMP and fetchlog
using the check-snmp plugin. Please read the README files coming with
fetchlog how to setup this.
SNMP
The motivation for fetchlog was to create a helper tool for NET-SNMP's
snmpd to enable monitoring of remote kernel syslogs using SNMP. If
configured properly, snmpd replies to a specific SNMP request with the
output of an external helper program. With fetchlog using update mode
-F and conversions on one can peek at a remote syslog file and gets
either 'OK: no messages' or one line with the new syslog messages
appeared since the last SNMP request.
Because of some limitiations of SNMP itself and the monitoring
applications using SNMP, the length of the SNMP reply must not exceed a
specific size. To ease the integration of SNMP in monitoring software
it is useful to have the SNMP reply only consist of a single line of
text rather than multiple lines.
COMPRESSING OUTPUT
The syslog messages fetched can be compressed by increasing first to
skip the timestamp and host entry from syslog. Lowering last gives
even more compression for long syslog lines. As a result one gets a
very short message that gives an idea of what is going wrong.
DIAGNOSTICS
fetchlog sends all output and error messages to stdout. Exit codes:
0 No new messages in logfile were found. If conversion o is set,
the single line 'OK: no messages' will be send to stdout.
1 An internal error in fetchlog occured. A one line error message
will be send to stdout. The error message starts with 'ERROR:
fetchlog:' and shows detailed information about what went wrong.
Length limitation by parameter len is applied, if an error
message is too long the last part will be cut off and a '~' is
appended.
2 New messages in logfile were found. The new messages will be
send to stdout. If conversion n is set, a single line of text is
send, else zero or more lines of converted syslog messages are
send.
3 fetchlog was called with wrong parameters, a multiline usage
message is print to stdout.
Note: Since version 0.93 the meanings of exit code 1 and 2 have been
exchanged.
AUTHOR
Alexander Haderer, LoeScap Technology GmbH, Berlin - Germany
SEE ALSO
tail(1), cat(1), head(1), sed(1), re_format(7), syslogd(8),
newsyslog(8)
NET-SNMP - Various tools relating to the Simple Network Management
Protocol SNMP (NET-SNMP: formerly known as UCD-SNMP)
http://www.net-snmp.org
Nagios - A Network monitoring system
http://www.nagios.org
Nagios Plugins - Plugins for Nagios
http://nagiosplug.sourceforge.net
fetchlog homepage - download, support and bugtracking
http://fetchlog.sourceforge.net
BUGS
Bookmarkfiles are not portable across plattforms or fetchlog versions.
Logfiles are expected not to shrink.
fetchlog does not work with compressed logfiles.
Fetching when logfile rotation takes place may result in some messages
to appear twice.
If an regex error occurs during pattern matching this error is silently
ignored and will be handled as non-match.
LEGAL
Nagios is a registered trademark of Ethan Galstad.
fetchlog(1) 23 Nov 2008 (1.2) fetchlog(1)