NAME¶
rsyslogd - reliable and extended syslogd
SYNOPSIS¶
rsyslogd [
-4 ] [
-6 ] [
-A ] [
-d ] [
-D
] [
-f config file ]
[
-i pid file ] [
-l hostlist ] [
-n ] [
-N level ]
[
-q ] [
-Q ] [
-s domainlist ] [
-u
userlevel ] [
-v ] [
-w ] [
-x ]
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¶
- -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
- This option has been obsoleted and has no function any longer. It is still
accepted in order not to break existing scripts. However, future versions
may not support it.
- -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. 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.
- -S ip_addresslocal client source IP
- rsyslogd uses ip_address as local client address while connecting to
remote logserver. Currently used by omrelp only and only with tcp.
- -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.
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)
- HUP
- This lets rsyslogd perform close all open files.
- 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.
DEBUGGING¶
When debugging is turned on using
-d option then
rsyslogd will be
very verbose by writing much of what it does on stdout.
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):
- 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.
BUGS¶
Please review the file BUGS for up-to-date information on known bugs and
annoyances.
Please visit
http://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@wind.enjellic.com) and
Martin Schulze (joey@linux.de) for the fine sysklogd package.
- Rainer Gerhards
- Adiscon GmbH
- Grossrinderfeld, Germany
- rgerhards@adiscon.com