SYNOPSIS

rsyslogd [ -d ] [ -D ] [ -f config file ] [ -i pid file ] [ -n ] [ -N level ] [ -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 http://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

-D

Runs the Bison config parser in debug mode. This may help when hard to find syntax errors are reported. Please note that the output generated is deeply technical and orignally targeted towards developers.

-d

Turns on debug mode. See the DEBUGGING section for more information.

-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.

-n

Avoid auto-backgrounding. This is needed especially if the rsyslogd is started and controlled by init(8).

-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). rsyslogd is started and controlled by init(8).

-C

This prevents rsyslogd from changing to the root directory. This is almost never a good idea in production use. This option was introduced in support of the internal testbed.

-v

Print version and exit.

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:

1.

Implement kernel firewalling to limit which hosts or networks have access to the 514/UDP socket.

2.

Logging can be directed to an isolated or non-root filesystem which, if filled, will not impair the machine.

3.

The ext2 filesystem can be used which can be configured to limit a certain percentage of a filesystem to usage by root only. NOTE that this will require rsyslogd to be run as a non-root process. ALSO NOTE that this will prevent usage of remote logging on the default port since rsyslogd will be unable to bind to the 514/UDP socket.

4.

Disabling inet domain sockets will limit risk to the local 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).

Further Information

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

COLLABORATORS

rsyslogd is derived from sysklogd sources, which in turn was taken from the BSD sources. Special thanks to Greg Wettstein ([email protected]) and Martin Schulze ([email protected]) for the fine sysklogd package.

Rainer Gerhards

Adiscon GmbH

Grossrinderfeld, Germany

[email protected]