1RSYSLOGD(8) Linux System Administration RSYSLOGD(8)
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6 rsyslogd - reliable and extended syslogd
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9 rsyslogd [ -d ] [ -D ] [ -f config file ] [ -i pid file ] [ -n ] [ -N
10 level ] [ -o fullconf ] [ -C ] [ -v ]
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13 Rsyslogd is a system utility providing support for message logging.
14 Support of both internet and unix domain sockets enables this utility
15 to support both local and remote logging.
16 Note that this version of rsyslog ships with extensive documentation in
18 HTML format. This is provided in the ./doc subdirectory and probably
19 in a separate package if you installed rsyslog via a packaging system.
20 To use rsyslog's advanced features, you need to look at the HTML docu‐
21 mentation, because the man pages only covers basic aspects of opera‐
22 tion. For details and configuration examples, see the rsyslog.conf (5)
23 man page and the online documentation at https://www.rsyslog.com/doc/
24 Rsyslogd(8) is derived from the sysklogd package which in turn is de‐
26 rived from the stock BSD sources.
27 Rsyslogd provides a kind of logging that many modern programs use. Ev‐
29 ery logged message contains at least a time and a hostname field, nor‐
30 mally a program name field, too, but that depends on how trusty the
31 logging program is. The rsyslog package supports free definition of
32 output formats via templates. It also supports precise timestamps and
33 writing directly to databases. If the database option is used, tools
34 like phpLogCon can be used to view the log data.
35 While the rsyslogd sources have been heavily modified a couple of notes
37 are in order. First of all there has been a systematic attempt to en‐
38 sure that rsyslogd follows its default, standard BSD behavior. Of
39 course, some configuration file changes are necessary in order to sup‐
40 port the template system. However, rsyslogd should be able to use a
41 standard syslog.conf and act like the original syslogd. However, an
42 original syslogd will not work correctly with a rsyslog-enhanced con‐
43 figuration file. At best, it will generate funny looking file names.
44 The second important concept to note is that this version of rsyslogd
45 interacts transparently with the version of syslog found in the stan‐
46 dard libraries. If a binary linked to the standard shared libraries
47 fails to function correctly we would like an example of the anomalous
48 behavior.
49 The main configuration file /etc/rsyslog.conf or an alternative file,
51 given with the -f option, is read at startup. Any lines that begin
52 with the hash mark (``#'') and empty lines are ignored. If an error
53 occurs during parsing the error element is ignored. It is tried to
54 parse the rest of the line.
55
58 -D Runs the Bison config parser in debug mode. This may help when
59 hard to find syntax errors are reported. Please note that the
60 output generated is deeply technical and orignally targeted to‐
61 wards developers.
62 -d Turns on debug mode. See the DEBUGGING section for more informa‐
64 tion.
65 -f config file
67 Specify an alternative configuration file instead of /etc/rsys‐
68 log.conf, which is the default.
69 -i pid file
71 Specify an alternative pid file instead of the default one.
72 This option must be used if multiple instances of rsyslogd
73 should run on a single machine. To disable writing a pid file,
74 use the reserved name "NONE" (all upper case!), so "-iNONE".
75 -n Avoid auto-backgrounding. This is needed especially if the
77 rsyslogd is started and controlled by init(8).
78 -N level
80 Do a config check. Do NOT run in regular mode, just check con‐
81 figuration file correctness. This option is meant to verify a
82 config file. To do so, run rsyslogd interactively in foreground,
83 specifying -f <config-file> and -N level. The level argument
84 modifies behaviour. Currently, 0 is the same as not specifying
85 the -N option at all (so this makes limited sense) and 1 actu‐
86 ally activates the code. Later, higher levels will mean more
87 verbosity (this is a forward-compatibility option).
88 -o fullconf
90 Generates a consolidated config file fullconf that contains all
91 of rsyslog's configuration in a single file. Include files are
92 exploded into that file in exactly the way rsyslog sees them.
93 This option is useful for troubleshooting, especially if prob‐
94 lems with the order of action processing is suspected. It may
95 also be used to check for "unexepectedly" included config con‐
96 tent.
97 -C This prevents rsyslogd from changing to the root directory. This
99 is almost never a good idea in production use. This option was
100 introduced in support of the internal testbed.
101 -v Print version and exit.
103
105 Rsyslogd reacts to a set of signals. You may easily send a signal to
106 rsyslogd using the following:
107 kill -SIGNAL $(cat /var/run/rsyslogd.pid)
109 Note that -SIGNAL must be replaced with the actual signal you are try‐
111 ing to send, e.g. with HUP. So it then becomes:
112 kill -HUP $(cat /var/run/rsyslogd.pid)
114 HUP This lets rsyslogd perform close all open files.
116 TERM , INT , QUIT
118 Rsyslogd will die.
119 USR1 Switch debugging on/off. This option can only be used if rsys‐
121 logd is started with the -d debug option.
122 CHLD Wait for children if some were born, because of wall'ing mes‐
124 sages.
125
127 There is the potential for the rsyslogd daemon to be used as a conduit
128 for a denial of service attack. A rogue program(mer) could very easily
129 flood the rsyslogd daemon with syslog messages resulting in the log
130 files consuming all the remaining space on the filesystem. Activating
131 logging over the inet domain sockets will of course expose a system to
132 risks outside of programs or individuals on the local machine.
133 There are a number of methods of protecting a machine:
135 1. Implement kernel firewalling to limit which hosts or networks
137 have access to the 514/UDP socket.
138 2. Logging can be directed to an isolated or non-root filesystem
140 which, if filled, will not impair the machine.
141 3. The ext2 filesystem can be used which can be configured to limit
143 a certain percentage of a filesystem to usage by root only.
144 NOTE that this will require rsyslogd to be run as a non-root
145 process. ALSO NOTE that this will prevent usage of remote log‐
146 ging on the default port since rsyslogd will be unable to bind
147 to the 514/UDP socket.
148 4. Disabling inet domain sockets will limit risk to the local ma‐
150 chine.
151 Message replay and spoofing
153 If remote logging is enabled, messages can easily be spoofed and re‐
154 played. As the messages are transmitted in clear-text, an attacker
155 might use the information obtained from the packets for malicious
156 things. Also, an attacker might replay recorded messages or spoof a
157 sender's IP address, which could lead to a wrong perception of system
158 activity. These can be prevented by using GSS-API authentication and
159 encryption. Be sure to think about syslog network security before en‐
160 abling it.
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163 When debugging is turned on using the -d option, rsyslogd produces de‐
164 bugging information according to the RSYSLOG_DEBUG environment variable
165 and the signals received. When run in foreground, the information is
166 written to stdout. An additional output file can be specified using the
167 RSYSLOG_DEBUGLOG environment variable.
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170 /etc/rsyslog.conf
171 Configuration file for rsyslogd. See rsyslog.conf(5) for exact
172 information.
173 /dev/log
174 The Unix domain socket to from where local syslog messages are
175 read.
176 /var/run/rsyslogd.pid
177 The file containing the process id of rsyslogd.
178 prefix/lib/rsyslog
179 Default directory for rsyslogd modules. The prefix is specified
180 during compilation (e.g. /usr/local).
182 RSYSLOG_DEBUG
183 Controls runtime debug support. It contains an option string
184 with the following options possible (all are case insensitive):
185 Debug Turns on debugging and prevents forking. This is pro‐
187 cessed earlier in the startup than command line options
188 (i.e. -d) and as such enables earlier debugging output.
189 Mutually exclusive with DebugOnDemand.
190 DebugOnDemand
191 Enables debugging but turns off debug output. The output
192 can be toggled by sending SIGUSR1. Mutually exclusive
193 with Debug.
194 LogFuncFlow
195 Print out the logical flow of functions (entering and ex‐
196 iting them)
197 FileTrace
198 Specifies which files to trace LogFuncFlow. If not set
199 (the default), a LogFuncFlow trace is provided for all
200 files. Set to limit it to the files specified.FileTrace
201 may be specified multiple times, one file each (e.g. ex‐
202 port RSYSLOG_DEBUG="LogFuncFlow FileTrace=vm.c File‐
203 Trace=expr.c"
204 PrintFuncDB
205 Print the content of the debug function database whenever
206 debug information is printed (e.g. abort case)!
207 PrintAllDebugInfoOnExit
208 Print all debug information immediately before rsyslogd
209 exits (currently not implemented!)
210 PrintMutexAction
211 Print mutex action as it happens. Useful for finding
212 deadlocks and such.
213 NoLogTimeStamp
214 Do not prefix log lines with a timestamp (default is to
215 do that).
216 NoStdOut
217 Do not emit debug messages to stdout. If RSYSLOG_DEBUGLOG
218 is not set, this means no messages will be displayed at
219 all.
220 Help Display a very short list of commands - hopefully a life
221 saver if you can't access the documentation...
222 RSYSLOG_DEBUGLOG
224 If set, writes (almost) all debug message to the specified log
225 file in addition to stdout.
226 RSYSLOG_MODDIR
227 Provides the default directory in which loadable modules reside.
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230 Please review the file BUGS for up-to-date information on known bugs
231 and annoyances.
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234 Please visit https://www.rsyslog.com/doc/ for additional information,
235 tutorials and a support forum.
236
238 rsyslog.conf(5), logger(1), syslog(2), syslog(3), services(5),
239 savelog(8)
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242 rsyslogd is derived from sysklogd sources, which in turn was taken from
243 the BSD sources. Special thanks to Greg Wettstein (greg@wind.enjel‐
244 lic.com) and Martin Schulze (joey@linux.de) for the fine sysklogd pack‐
245 age.
246 Rainer Gerhards
248 Adiscon GmbH
249 Grossrinderfeld, Germany
250 rgerhards@adiscon.com
251Version 8.1905.0 28 May 2014 RSYSLOGD(8)