path: root/rsyslogd.8

.\" Copyright 2004-2008 Rainer Gerhards and Adiscon for the rsyslog modifications
.\" May be distributed under the GNU General Public License
.\"
.TH RSYSLOGD 8 "02 April 2008" "Version 3.14.0" "Linux System Administration"
.SH NAME
rsyslogd \- reliable and extended syslogd 
.SH SYNOPSIS
.B rsyslogd
.RB [ " \-4 " ]
.RB [ " \-6 " ]
.RB [ " \-A " ]
.RB [ " \-d " ]
.RB [ " \-f "
.I config file
]
.br
.RB [ " \-i "
.I pid file
]
.RB [ " \-l "
.I hostlist
]
.RB [ " \-n " ]
.br
.RB [ " \-q " ]
.RB [ " \-Q " ]
.RB [ " \-s "
.I domainlist
]
.RB [ " \-v " ]
.RB [ " \-w " ]
.RB [ " \-x " ]
.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 cover
basic aspects of operation.

.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 orginal 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.

For details and configuration examples, see the
.B rsyslog.conf (5)
man page.
.LP
.SH OPTIONS
.TP
.BI "\-A"
When sending UDP messages, there are potentially multiple pathes to
the target destination. By default,
.B rsyslogd
only sends to the first target it can successfully send to. If -A 
is given, messages are sent to all targets. This may improve
reliability, but may also cause message duplicaton. This option
should enabled only if it is fully understood.
.TP
.BI "\-4"
Causes
.B rsyslogd
to listen to IPv4 addresses only.
If neither -4 nor -6 is given,
.B rsyslogd
listens to all configured addresses of the system.
.TP
.BI "\-6"
Causes
.B rsyslogd
to listen to IPv6 addresses only.
If neither -4 nor -6 is given,
.B rsyslogd
listens to all configured addresses of the system.
.TP
.B "\-d"
Turns on debug mode.  Using this the daemon will not proceed a 
.BR fork (2)
to set itself in the background, but opposite to that stay in the
foreground and write much debug information on the current tty.  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.
.TP
.BI "\-l " "hostlist"
Specify a hostname that should be logged only with its simple hostname
and not the fqdn.  Multiple hosts may be specified using the colon
(``:'') separator.
.TP
.B "\-n"
Avoid auto-backgrounding.  This is needed especially if the
.B rsyslogd
is started and controlled by
.BR init (8).
.TP
.BI "\-q " "add hostname if DNS fails during ACL processing"
During ACL processing, hostnames are resolved to IP addreses for
performance reasons. If DNS fails during that process, the hostname
is added as wildcard text, which results in proper, but somewhat
slower operation once DNS is up again.
.TP
.BI "\-Q " "do not resolve hostnames during ACL processing"
Do not resolve hostnames to IP addresses during ACL processing.
.TP
.BI "\-s " "domainlist"
Specify a domainname that should be stripped off before
logging.  Multiple domains may be specified using the colon (``:'')
separator.
Please be advised that no sub-domains may be specified but only entire
domains.  For example if
.B "\-s north.de"
is specified and the host logging resolves to satu.infodrom.north.de
no domain would be cut, you will have to specify two domains like:
.BR "\-s north.de:infodrom.north.de" .
.TP
.B "\-v"
Print version and exit.
.TP
.B "\-w"
Supress warnings issued when messages are received from non-authorized
machines (those, that are in no AllowedSender list).
.TP
.B "\-x"
Disable DNS for remote messages.
.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/syslogd.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/syslogd.pid)
.fi
.PP
.TP
.B HUP
This lets
.B rsyslogd
perform a re-initialization.  All open files are closed, the
configuration file (default is 
.IR /etc/rsyslog.conf ")"
will be reread and the
.BR rsyslog (3)
facility is started again.
.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 childs if some were born, because of wall'ing messages.
.LP
.SH SUPPORT FOR REMOTE LOGGING
.B Rsyslogd
provides network support to the syslogd facility.
Network support means that messages can be forwarded from one node
running rsyslogd to another node running rsyslogd (or a
compatible syslog implementation).
actually logged to a disk file.

To enable this, proper configuration commands must
be entered in rsyslog.conf. See the rsyslog.conf html
documentation for details.

The strategy is to have rsyslogd listen on a unix domain socket for
locally generated log messages.  This behavior will allow rsyslogd to
inter-operate with the syslog found in the standard C library.  At the
same time rsyslogd listens on the standard syslog port for messages
forwarded from other hosts.

.SH OUTPUT TO DATABASES
.B Rsyslogd
has support for writing data to database tables. The exact specifics
are described in the
.B rsyslog.conf (5)
html documentation. Be sure to read it if you plan to use database logging.

.SH OUTPUT TO NAMED PIPES (FIFOs)
.B Rsyslogd
has support for logging output to named pipes
(fifos).  A fifo or named pipe can be used as a destination for log
messages by prepending a pipy symbol (``|'') to the name of the
file.  This is handy for debugging.  Note that the fifo must be created
with the mkfifo command before
.B rsyslogd
is started.
.IP
The following configuration file routes debug messages from the
kernel to a fifo:
.IP
.nf
	# Sample configuration to route kernel debugging
	# messages ONLY to /usr/adm/debug which is a
	# named pipe.
	kern.=debug			|/usr/adm/debug
.fi
.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 reply 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
.B "\-d"
option then
.B rsyslogd
will be very verbose by writing much of what it does on stdout.
.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 .
.PD
.SH BUGS
Please review the file BUGS for up-to-date information on known
bugs and annouyances.
.SH Further Information
Please visit
.BR http://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