imfile: Text File Input Module

Module Name:	imfile
Author:	Rainer Gerhards <rgerhards@adiscon.com>

This module provides the ability to convert any standard text file into a syslog message. A standard text file is a file consisting of printable characters with lines being delimited by LF.

The file is read line-by-line and any line read is passed to rsyslog’s rule engine. The rule engine applies filter conditions and selects which actions needs to be carried out. Empty lines are not processed, as they would result in empty syslog records. They are simply ignored.

As new lines are written they are taken from the file and processed. Depending on the selected mode, this happens via inotify or based on a polling interval. Especially in polling mode, file reading doesn’t happen immediately. But there are also slight delays (due to process scheduling and internal processing) in inotify mode.

The file monitor supports file rotation. To fully work, rsyslogd must run while the file is rotated. Then, any remaining lines from the old file are read and processed and when done with that, the new file is being processed from the beginning. If rsyslogd is stopped during rotation, the new file is read, but any not-yet-reported lines from the previous file can no longer be obtained.

When rsyslogd is stopped while monitoring a text file, it records the last processed location and continues to work from there upon restart. So no data is lost during a restart (except, as noted above, if the file is rotated just in this very moment).

See Also

• presentation on using wildcards with imfile

Metadata

The imfile module supports message metadata. It supports the following data items

• filename

  Name of the file where the message originated from. This is most useful when using wildcards inside file monitors, because it then is the only way to know which file the message originated from. The value can be accessed using the %$!metadata!filename% property.

Metadata is only present if enabled. By default it is enabled for input() statements that contain wildcards. For all others, it is disabled by default. It can explicitly be turned on or off via the addMetadata input() parameter, which always overrides the default.

State Files

Rsyslog must keep track of which parts of the monitored file are already processed. This is done in so-called “state files”. These files are always created in the rsyslog working directory (configurable via $WorkDirectory).

To avoid problems with duplicate state files, rsyslog automatically generates state file names according to the following scheme:

• the string “imfile-state:” is added before the actual file name, which includes the full path
• the full name is prepended after that string, but all occurrences of “/” are replaced by “-” to facilitate handling of these files

As a concrete example, consider file /var/log/applog is being monitored. The corresponding state file will be named imfile-state:-var-log-applog.

Note that it is possible to set a fixed state file name via the deprecated “stateFile” parameter. It is suggested to avoid this, as the user must take care of name clashes. Most importantly, if “stateFile” is set for file monitors with wildcards, the same state file is used for all occurrences of these files. In short, this will usually not work and cause confusion. Upon startup, rsyslog tries to detect these cases and emit warning messages. However, the detection simply checks for the presence of “*” and as such it will not cover more complex cases.

Note that when $WorkDirectory is not set or set to a non-writable location, the state file will not be generated. In those cases, the file content will always be completely re-sent by imfile, because the module does not know that it already processed parts of that file.

Module Parameters

mode ["inotify"/"polling"]

Default: “inotify”

Available since: 8.1.5

This specifies if imfile is shall run in inotify (“inotify”) or polling (“polling”) mode. Traditionally, imfile used polling mode, which is much more resource-intense (and slower) than inotify mode. It is suggested that users turn on “polling” mode only if they experience strange problems in inotify mode. In theory, there should never be a reason to enable “polling” mode and later versions will most probably remove it.

PollingInterval seconds

Default: 10

This setting specifies how often files are to be polled for new data. For obvious reasons, it has effect only if imfile is running in polling mode. The time specified is in seconds. During each polling interval, all files are processed in a round-robin fashion.

A short poll interval provides more rapid message forwarding, but requires more system resources. While it is possible, we stongly recommend not to set the polling interval to 0 seconds. That will make rsyslogd become a CPU hog, taking up considerable resources. It is supported, however, for the few very unusual situations where this level may be needed. Even if you need quick response, 1 seconds should be well enough. Please note that imfile keeps reading files as long as there is any data in them. So a “polling sleep” will only happen when nothing is left to be processed.

We recommend to use inotify mode.

Input Parameters

File [/path/to/file]

(Required Parameter) The file being monitored. So far, this must be an absolute name (no macros or templates). Note that wildcards are supported at the file name level (see “Wildcards” above for more details).

Tag [tag:]

(Required Parameter) The tag to be used for messages that originate from this file. If you would like to see the colon after the tag, you need to specify it here (like ‘tag=”myTagValue:”’).

Facility [facility]

The syslog facility to be assigned to lines read. Can be specified in textual form (e.g. “local0”, “local1”, ...) or as numbers (e.g. 128 for “local0”). Textual form is suggested. Default  is “local0”.

Severity [syslogSeverity]

The syslog severity to be assigned to lines read. Can be specified in textual form (e.g. “info”, “warning”, ...) or as numbers (e.g. 4 for “info”). Textual form is suggested. Default is “notice”.

PersistStateInterval [lines]

Specifies how often the state file shall be written when processing the input file. The default value is 0, which means a new state file is only written when the monitored files is being closed (end of rsyslogd execution). Any other value n means that the state file is written every time n file lines have been processed. This setting can be used to guard against message duplication due to fatal errors (like power fail). Note that this setting affects imfile performance, especially when set to a low value. Frequently writing the state file is very time consuming.

startmsg.regex [POSIX ERE regex]

This permits the processing of multi-line messages. When set, a messages is terminated when the next one begins, and startmsg.regex contains the regex that identifies the start of a message. As this parameter is using regular expressions, it is more flexible than readMode but at the cost of lower performance. Note that readMode and startmsg.regex cannot both be defined for the same input.

This parameter is available since rsyslog v8.10.0.

readMode [mode]

This provides support for processing some standard types of multiline messages. It is less flexible than startmsg.regex but offers higher performance than regex processing. Note that readMode and startmsg.regex cannot both be defined for the same input.

The value can range from 0-2 and determines the multiline detection method.

0 - (default) line based (each line is a new message)

1 - paragraph (There is a blank line between log messages)

2 - indented (new log messages start at the beginning of a line. If a line starts with a space it is part of the log message before it)

escapeLF [on/off] (requires v7.5.3+)

This is only meaningful if multi-line messages are to be processed. LF characters embedded into syslog messages cause a lot of trouble, as most tools and even the legacy syslog TCP protocol do not expect these. If set to “on”, this option avoid this trouble by properly escaping LF characters to the 4-byte sequence “#012”. This is consistent with other rsyslog control character escaping. By default, escaping is turned on. If you turn it off, make sure you test very carefully with all associated tools. Please note that if you intend to use plain TCP syslog with embedded LF characters, you need to enable octet-counted framing. For more details, see Rainer’s blog posting on imfile LF escaping.

MaxLinesAtOnce [number]

This is a legacy setting that only is supported in polling mode. In inotify mode, it is fixed at 0 and all attempts to configure a different value will be ignored, but will generate an error message.

Please note that future versions of imfile may not support this parameter at all. So it is suggested to not use it.

In polling mode, if set to 0, each file will be fully processed and then processing switches to the next file. If it is set to any other value, a maximum of [number] lines is processed in sequence for each file, and then the file is switched. This provides a kind of mutiplexing the load of multiple files and probably leads to a more natural distribution of events when multiple busy files are monitored. For polling mode, the default is 10240.

MaxSubmitAtOnce [number]

This is an expert option. It can be used to set the maximum input batch size that imfile can generate. The default is 1024, which is suitable for a wide range of applications. Be sure to understand rsyslog message batch processing before you modify this option. If you do not know what this doc here talks about, this is a good indication that you should NOT modify the default.

deleteStateOnFileDelete [on/off] (requires v8.5.0+)

Default: on

This parameter controls if state files are deleted if their associated main file is deleted. Usually, this is a good idea, because otherwise problems would occur if a new file with the same name is created. In that case, imfile would pick up reading from the last position in the deleted file, which usually is not what you want.

However, there is one situation where not deleting associated state file makes sense: this is the case if a monitored file is modified with an editor (like vi or gedit). Most editors write out modifications by deleting the old file and creating a new now. If the state file would be deleted in that case, all of the file would be reprocessed, something that’s probably not intended in most case. As a side-note, it is strongly suggested not to modify monitored files with editors. In any case, in such a situation, it makes sense to disable state file deletion. That also applies to similar use cases.

In general, this parameter should only by set if the users knows exactly why this is required.

Ruleset <ruleset>

Binds the listener to a specific ruleset.

addMetadata [on/off]

Default: see intro section on Metadata

This is used to turn on or off the addition of metadata to the message object.

stateFile [name-of-state-file]

Default: unset

This paramater is deprecated. It still is accepted, but should no longer be used for newly created configurations.

This is the name of this file’s state file. This parameter should usually not be used. Check the section on “State Files” above for more details.

reopenOnTruncate [on/off] (requires v8.16.0+)

Default: off

This is an experimental feature that tells rsyslog to reopen input file when it was truncated (inode unchanged but file size on disk is less than current offset in memory).

trimLineOverBytes [number] (requires v8.17.0+)

Default: 0

This is used to tell rsyslog to truncate the line which length is greater than specified bytes. If it is positive number, rsyslog truncate the line at specified bytes. Default value of ‘trimLineOverBytes’ is 0, means never truncate line.

This option can be used when readMode is 0 or 2.

Caveats/Known Bugs

• currently, wildcards are only supported in inotify mode
• read modes other than “0” currently seem to have issues in inotify mode

Configuration Example

The following sample monitors two files. If you need just one, remove the second one. If you need more, add them according to the sample ;). This code must be placed in /etc/rsyslog.conf (or wherever your distro puts rsyslog’s config files). Note that only commands actually needed need to be specified. The second file uses less commands and uses defaults instead.

module(load="imfile" PollingInterval="10") #needs to be done just once

# File 1
input(type="imfile"
      File="/path/to/file1"
      Tag="tag1"
      Severity="error"
      Facility="local7")

# File 2
input(type="imfile"
      File="/path/to/file2"
      Tag="tag2")

# ... and so on ... #

Legacy Configuration

Note: in order to preserve compatibility with previous versions, the LF escaping in multi-line messages is turned off for legacy-configured file monitors (the “escapeLF” input parameter). This can cause serious problems. So it is highly suggested that new deployments use the new input() configuration object and keep LF escaping turned on.

Legacy Configuration Directives

$InputFileName /path/to/file

equivalent to “file”

$InputFileTag tag:

equivalent to: “tag” you would like to see the colon after the tag, you need to specify it here (as shown above).

$InputFileStateFile /path/to/state/file

equivalent to: “StateFile”

$InputFileFacility facility

equivalent to: “Facility”

$InputFileSeverity severity

equivalent to: “Severity”

$InputRunFileMonitor

This activates the current monitor. It has no parameters. If you forget this directive, no file monitoring will take place.

$InputFilePollInterval seconds

equivalent to: “PollingInterval”

$InputFilePersistStateInterval lines

equivalent to: “PersistStateInterval”

$InputFileReadMode mode

equivalent to: “ReadMode”

$InputFileMaxLinesAtOnce number

equivalent to: “MaxLinesAtOnce”

$InputFileBindRuleset ruleset

Equivalent to: Ruleset

Legacy Example

The following sample monitors two files. If you need just one, remove the second one. If you need more, add them according to the sample ;). Note that only non-default parameters actually needed need to be specified. The second file uses less directives and uses defaults instead.

$ModLoad imfile # needs to be done just once
# File 1
$InputFileName /path/to/file1
$InputFileTag tag1:
$InputFileStateFile stat-file1

$InputFileSeverity error
$InputFileFacility local7
$InputRunFileMonitor

# File 2
$InputFileName /path/to/file2
$InputFileTag tag2:

$InputFileStateFile stat-file2
$InputRunFileMonitor
# ... and so on ...
# check for new lines every 10 seconds $InputFilePollingInterval 10