rsyslogd
reliable and extended syslogd
see also :
logger - savelog
Synopsis
rsyslogd
[ -4 ] [ -6 ] [ -A ]
[ -d ] [ -f config file ]
[ -i pid file ] [ -l
hostlist ] [ -n ] [ -N
level ]
[ -q ] [ -Q ] [ -s
domainlist ] [ -u userlevel ] [
-v ] [ -w ] [ -x
]
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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 cover
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
Note that in
version 3 of rsyslog a number of command line options have
been deprecated and replaced with config file directives.
The -c option controls the backward compatibility mode in
use.
-A
When sending UDP messages, there are potentially
multiple paths to the target destination. By default,
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 duplication. This option should be enabled
only if it is fully understood.
-4
Causes rsyslogd to listen to IPv4 addresses only.
If neither -4 nor -6 is given, rsyslogd listens to
all configured addresses of the system.
-6
Causes rsyslogd to listen to IPv6 addresses only.
If neither -4 nor -6 is given, rsyslogd listens to
all configured addresses of the system.
-c
version
Selects the desired backward
compatibility mode. It must always be the first option on
the command line, as it influences processing of the other
options. To use the rsyslog v3 native interface, specify
-c3. To use compatibility mode , either do not use -c at all
or use -c<version> where version is the rsyslog
version that it shall be compatible with. Using -c0 tells
rsyslog to be command-line compatible to sysklogd, which is
the default if -c is not given. Please note that rsyslogd
issues warning messages if the -c3 command line option is
not given. This is to alert you that your are running in
compatibility mode. Compatibility mode interferes with your
rsyslog.conf commands and may cause some undesired
side-effects. It is meant to be used with a plain old
rsyslog.conf - if you use new features, things become messy.
So the best advice is to work through this document, convert
your options and config file and then use rsyslog in native
mode. In order to aid you in this process, rsyslog logs
every compatibility-mode config file directive it has
generated. So you can simply copy them from your logfile and
paste them to the config.
-d
Turns on debug mode. Using this the daemon will not
proceed a 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.
-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.
-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.
-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).
-q add hostname
if DNS fails during ACL processing
During ACL processing,
hostnames are resolved to IP addresses 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.
-Q do not
resolve hostnames during ACL processing
Do not resolve hostnames to IP
addresses during ACL processing.
-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
-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: -s
north.de:infodrom.north.de.
-u
userlevel
This is a "catch all"
option for some very seldomly-used user settings. The
"userlevel" variable selects multiple things. Add
the specific values to get the combined effect of them. A
value of 1 prevents rsyslogd from parsing hostnames and tags
inside messages. A value of 2 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. To combine these two
features, use a userlevel of 3 (1+2). Whenever you use an -u
option, make sure you really understand what you do and why
you do it.
-v
Print version and exit.
-w
Suppress warnings issued when messages are received from
non-authorized machines (those, that are in no AllowedSender
list).
-x
Disable DNS for remote messages.
collaborators
rsyslogd is derived from sysklogd sources, which in turn
was taken from the BSD sources. Special thanks to Greg Wettstein
(greg[:at:]wind.enjellic[:dot:]com) and Martin Schulze
(joey[:at:]linux[:dot:]de) for the fine sysklogd package.
Rainer Gerhards
Adiscon GmbH
Grossrinderfeld, Germany
rgerhards[:at:]adiscon[:dot:]com
debugging
When debugging is turned on using -d option then
rsyslogd will be very verbose by writing much of what it
does on stdout.
environment
RSYSLOG_DEBUG
Controls runtime debug support.It contains an option string with
the following options possible (all are case insensitive):
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.
Help
Display a very short list of commands - hopefully a life saver if
you can’t access the documentation...
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.
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.
hup
This lets rsyslogd perform close all open files. Also, in
v3 a full restart will be done in order to read changed
configuration files. Note that this means a full rsyslogd restart
is done. This has, among others, the consequence that TCP and
other connections are torn down. Also, if any queues are not
running in disk assisted mode or are not set to persist data on
shutdown, queue data is lost. HUPing rsyslogd is an extremely
expensive operation and should only be done when actually
necessary. Actually, it is a rsyslgod stop immediately followed
by a restart. Future versions will remove this restart
functionality of HUP (it will go away in v5). So it is advised to
use HUP only for closing files, and a "real restart" (e.g.
/etc/rc.d/rsyslogd restart) to activate configuration changes.
TERM , INT , QUIT
Rsyslogd will die.
USR1
Switch debugging on/off. This option can only be used if
rsyslogd is started with the -d debug option.
CHLD
Wait for childs if some were born, because of wall’ing messages.
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.
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)
bugs
Please review
the file BUGS for up-to-date information on known bugs and
annoyances.
see also
rsyslog.conf,
logger , syslog, syslog,
services, savelog