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NAME

rsyslogd - reliable and extended syslogd

SYNOPSIS

rsyslogd [ -d ] [ -D ] [ -f config file ] [ -i pid file ] [ -n ] [ -N level ] [ -o fullconf ] [ -C ] [ -v ]

DESCRIPTION

Rsyslogd is a system utility providing support for message logging. Support of both internet and unix domain sockets enables this utility to support both local and remote logging.

Note that this version of rsyslog ships with extensive documentation in HTML format. This is provided in the ./doc subdirectory and probably in a separate package if you installed rsyslog via a packaging system. To use rsyslog’s advanced features, you need to look at the HTML documentation, because the man pages only covers basic aspects of operation. For details and configuration examples, see the rsyslog.conf (5) man page and the online documentation at https://www.rsyslog.com/doc/

Rsyslogd(8) is derived from the sysklogd package which in turn is derived from the stock BSD sources.

Rsyslogd provides a kind of logging that many modern programs use. Every logged message contains at least a time and a hostname field, normally a program name field, too, but that depends on how trusty the logging program is. The rsyslog package supports free definition of output formats via templates. It also supports precise timestamps and writing directly to databases. If the database option is used, tools like phpLogCon can be used to view the log data.

While the rsyslogd sources have been heavily modified a couple of notes are in order. First of all there has been a systematic attempt to ensure that rsyslogd follows its default, standard BSD behavior. Of course, some configuration file changes are necessary in order to support the template system. However, rsyslogd should be able to use a standard syslog.conf and act like the original syslogd. However, an original syslogd will not work correctly with a rsyslog-enhanced configuration file. At best, it will generate funny looking file names. The second important concept to note is that this version of rsyslogd interacts transparently with the version of syslog found in the standard libraries. If a binary linked to the standard shared libraries fails to function correctly we would like an example of the anomalous behavior.

The main configuration file /etc/rsyslog.conf or an alternative file, given with the -f option, is read at startup. Any lines that begin with the hash mark (’’#’’) and empty lines are ignored. If an error occurs during parsing the error element is ignored. It is tried to parse the rest of the line.

OPTIONS

-f config file

Specify an alternative configuration file instead of /etc/rsyslog.conf, which is the default.

-i pid file

Specify an alternative pid file instead of the default one. This option must be used if multiple instances of rsyslogd should run on a single machine. To disable writing a pid file, use the reserved name "NONE" (all upper case!), so "-iNONE".

-N level

Do a config check. Do NOT run in regular mode, just check configuration file correctness. This option is meant to verify a config file. To do so, run rsyslogd interactively in foreground, specifying -f <config-file> and -N level. The level argument modifies behaviour. Currently, 0 is the same as not specifying the -N option at all (so this makes limited sense) and 1 actually activates the code. Later, higher levels will mean more verbosity (this is a forward-compatibility option).

-o fullconf

Generates a consolidated config file fullconf that contains all of rsyslog’s configuration in a single file. Include files are exploded into that file in exactly the way rsyslog sees them. This option is useful for troubleshooting, especially if problems with the order of action processing is suspected. It may also be used to check for "unexepectedly" included config content.

SIGNALS

Rsyslogd reacts to a set of signals. You may easily send a signal to rsyslogd using the following:

kill -SIGNAL $(cat /var/run/rsyslogd.pid)

Note that -SIGNAL must be replaced with the actual signal you are trying to send, e.g. with HUP. So it then becomes:

kill -HUP $(cat /var/run/rsyslogd.pid)

TERM , INT , QUIT

Rsyslogd will die.

SECURITY THREATS

There is the potential for the rsyslogd daemon to be used as a conduit for a denial of service attack. A rogue program(mer) could very easily flood the rsyslogd daemon with syslog messages resulting in the log files consuming all the remaining space on the filesystem. Activating logging over the inet domain sockets will of course expose a system to risks outside of programs or individuals on the local machine.

There are a number of methods of protecting a machine:

Message replay and spoofing
If remote logging is enabled, messages can easily be spoofed and replayed. As the messages are transmitted in clear-text, an attacker might use the information obtained from the packets for malicious things. Also, an attacker might replay recorded messages or spoof a sender’s IP address, which could lead to a wrong perception of system activity. These can be prevented by using GSS-API authentication and encryption. Be sure to think about syslog network security before enabling it.

DEBUGGING

When debugging is turned on using the -d option, rsyslogd produces debugging information according to the RSYSLOG_DEBUG environment variable and the signals received. When run in foreground, the information is written to stdout. An additional output file can be specified using the RSYSLOG_DEBUGLOG environment variable.

FILES

/etc/rsyslog.conf

Configuration file for rsyslogd. See rsyslog.conf(5) for exact information.

/dev/log

The Unix domain socket to from where local syslog messages are read.

/var/run/rsyslogd.pid

The file containing the process id of rsyslogd.

prefix/lib/rsyslog

Default directory for rsyslogd modules. The prefix is specified during compilation (e.g. /usr/local).

ENVIRONMENT

RSYSLOG_DEBUG

Controls runtime debug support. It contains an option string with the following options possible (all are case insensitive):

DebugOnDemand

Enables debugging but turns off debug output. The output can be toggled by sending SIGUSR1. Mutually exclusive with Debug.

LogFuncFlow

Print out the logical flow of functions (entering and exiting them)

FileTrace

Specifies which files to trace LogFuncFlow. If not set (the default), a LogFuncFlow trace is provided for all files. Set to limit it to the files specified.FileTrace may be specified multiple times, one file each (e.g. export RSYSLOG_DEBUG="LogFuncFlow FileTrace=vm.c FileTrace=expr.c"

PrintFuncDB

Print the content of the debug function database whenever debug information is printed (e.g. abort case)!

PrintAllDebugInfoOnExit

Print all debug information immediately before rsyslogd exits (currently not implemented!)

PrintMutexAction

Print mutex action as it happens. Useful for finding deadlocks and such.

NoLogTimeStamp

Do not prefix log lines with a timestamp (default is to do that).

NoStdOut

Do not emit debug messages to stdout. If RSYSLOG_DEBUGLOG is not set, this means no messages will be displayed at all.

RSYSLOG_DEBUGLOG

If set, writes (almost) all debug message to the specified log file in addition to stdout.

RSYSLOG_MODDIR

Provides the default directory in which loadable modules reside.

BUGS

Please review the file BUGS for up-to-date information on known bugs and annoyances.

Further Information

Please visit https://www.rsyslog.com/doc/ for additional information, tutorials and a support forum.

SEE ALSO

rsyslog.conf(5), logger(1), syslog(2), syslog(3), services(5), savelog(8)

COLLABORATORS

rsyslogd is derived from sysklogd sources, which in turn was taken from the BSD sources. Special thanks to Greg Wettstein (greg [AT] wind.com) and Martin Schulze (joey [AT] linux.de) for the fine sysklogd package.
Rainer Gerhards
Adiscon GmbH
Grossrinderfeld, Germany
rgerhards [AT] adiscon.com