path: root/tools/rsyslogd.8

.\" Copyright 2004-2014 Rainer Gerhards and Adiscon for the rsyslog modifications
.\" May be distributed under the GNU General Public License
.\"
.TH RSYSLOGD 8 "28 May 2014" "Version 8.1905.0" "Linux System Administration"
.SH NAME
rsyslogd \- reliable and extended syslogd 
.SH SYNOPSIS
.B rsyslogd
.RB [ " \-d " ]
.RB [ " \-D " ]
.RB [ " \-f "
.I config file
]
.RB [ " \-i "
.I pid file
]
.RB [ " \-n " ]
.RB [ " \-N "
.I level
]
.RB [ " \-o "
.I fullconf
]
.RB [ " \-C " ]
.RB [ " \-v " ]
.LP
.SH DESCRIPTION
.B 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.

.B 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
.B need
to look at the HTML documentation, because the man pages only covers
basic aspects of operation.
.B For details and configuration examples, see the rsyslog.conf (5)
.B man page and the online documentation at https://www.rsyslog.com/doc/

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

.B 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
.B 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
.I /etc/rsyslog.conf
or an alternative file, given with the 
.B "\-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.

.LP
.SH OPTIONS
.TP
.B "\-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 originally targeted towards developers.
.TP
.B "\-d"
Turns on debug mode. See the DEBUGGING section for more information.
.TP
.BI "\-f " "config file"
Specify an alternative configuration file instead of
.IR /etc/rsyslog.conf ","
which is the default.
.TP
.BI "\-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".
.TP
.B "\-n"
Avoid auto-backgrounding.  This is needed especially if the
.B rsyslogd
is started and controlled by
.BR init (8).
.TP
.B "\-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).
.TP
.B "\-o " "fullconf"
Generates a consolidated config file
.I 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.
.TP
.BI "\-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.
.TP
.B "\-v"
Print version and exit.
.LP
.SH SIGNALS
.B Rsyslogd
reacts to a set of signals.  You may easily send a signal to
.B rsyslogd
using the following:
.IP
.nf
kill -SIGNAL $(cat /var/run/rsyslogd.pid)
.fi
.PP
Note that -SIGNAL must be replaced with the actual signal
you are trying to send, e.g. with HUP. So it then becomes:
.IP
.nf
kill -HUP $(cat /var/run/rsyslogd.pid)
.fi
.PP
.TP
.B HUP
This lets
.B rsyslogd
perform close all open files.
.TP
.B TERM ", " INT ", " QUIT
.B Rsyslogd
will die.
.TP
.B USR1
Switch debugging on/off.  This option can only be used if
.B rsyslogd
is started with the
.B "\-d"
debug option.
.TP
.B CHLD
Wait for children if some were born, because of wall'ing messages.
.LP
.SH 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:
.IP 1.
Implement kernel firewalling to limit which hosts or networks have
access to the 514/UDP socket.
.IP 2.
Logging can be directed to an isolated or non-root filesystem which,
if filled, will not impair the machine.
.IP 3.
The ext2 filesystem can be used which can be configured to limit a
certain percentage of a filesystem to usage by root only.  \fBNOTE\fP
that this will require rsyslogd to be run as a non-root process.
\fBALSO NOTE\fP that this will prevent usage of remote logging on the default port since
rsyslogd will be unable to bind to the 514/UDP socket.
.IP 4.
Disabling inet domain sockets will limit risk to the local machine.
.SS 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.
.LP
.SH DEBUGGING
When debugging is turned on using the
.B "\-d"
option,
.B rsyslogd
produces debugging information according to the
.B 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
.B RSYSLOG_DEBUGLOG
environment variable.
.SH FILES
.PD 0
.TP
.I /etc/rsyslog.conf
Configuration file for
.BR rsyslogd .
See
.BR rsyslog.conf (5)
for exact information.
.TP
.I /dev/log
The Unix domain socket to from where local syslog messages are read.
.TP
.I /var/run/rsyslogd.pid
The file containing the process id of 
.BR rsyslogd .
.TP
.I prefix/lib/rsyslog
Default directory for
.B rsyslogd
modules. The
.I prefix
is specified during compilation (e.g. /usr/local).
.SH ENVIRONMENT
.TP
.B RSYSLOG_DEBUG
Controls runtime debug support. It contains an option string with the
following options possible (all are case insensitive):

.RS
.IP Debug
Turns on debugging and prevents forking. This is processed earlier
in the startup than command line options (i.e. -d) and as such
enables earlier debugging output. Mutually exclusive with DebugOnDemand.
.IP DebugOnDemand
Enables debugging but turns off debug output. The output can be toggled
by sending SIGUSR1. Mutually exclusive with Debug.
.IP LogFuncFlow
Print out the logical flow of functions (entering and exiting them)
.IP 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"
.IP PrintFuncDB
Print the content of the debug function database whenever debug
information is printed (e.g. abort case)!
.IP PrintAllDebugInfoOnExit
Print all debug information immediately before rsyslogd exits
(currently not implemented!)
.IP PrintMutexAction
Print mutex action as it happens. Useful for finding deadlocks and
such.
.IP NoLogTimeStamp
Do not prefix log lines with a timestamp (default is to do that).
.IP NoStdOut
Do not emit debug messages to stdout. If RSYSLOG_DEBUGLOG is not
set, this means no messages will be displayed at all.
.IP Help
Display a very short list of commands - hopefully a life saver if
you can't access the documentation...
.RE

.TP
.B RSYSLOG_DEBUGLOG
If set, writes (almost) all debug message to the specified log file
in addition to stdout.
.TP
.B RSYSLOG_MODDIR
Provides the default directory in which loadable modules reside.
.PD
.SH BUGS
Please review the file BUGS for up-to-date information on known
bugs and annoyances.
.SH Further Information
Please visit
.BR https://www.rsyslog.com/doc/
for additional information, tutorials and a support forum.
.SH SEE ALSO
.BR rsyslog.conf (5),
.BR logger (1),
.BR syslog (2),
.BR syslog (3),
.BR services (5),
.BR savelog (8)
.LP
.SH COLLABORATORS
.B rsyslogd
is derived from sysklogd sources, which in turn was taken from
the BSD sources. Special thanks to Greg Wettstein (greg@wind.enjellic.com)
and Martin Schulze (joey@linux.de) for the fine sysklogd package.

.PD 0
.TP
Rainer Gerhards
.TP
Adiscon GmbH
.TP
Grossrinderfeld, Germany
.TP
rgerhards@adiscon.com
.PD