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 ] [ -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
26 derived from the stock BSD sources.
27 Rsyslogd provides a kind of logging that many modern programs use.
29 Every logged message contains at least a time and a hostname field,
30 normally 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
38 ensure 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
61 towards 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 -C This prevents rsyslogd from changing to the root directory. This
90 is almost never a good idea in production use. This option was
91 introduced in support of the internal testbed.
92 -v Print version and exit.
94
96 Rsyslogd reacts to a set of signals. You may easily send a signal to
97 rsyslogd using the following:
98 kill -SIGNAL $(cat /var/run/rsyslogd.pid)
100 Note that -SIGNAL must be replaced with the actual signal you are try‐
102 ing to send, e.g. with HUP. So it then becomes:
103 kill -HUP $(cat /var/run/rsyslogd.pid)
105 HUP This lets rsyslogd perform close all open files.
107 TERM , INT , QUIT
109 Rsyslogd will die.
110 USR1 Switch debugging on/off. This option can only be used if rsys‐
112 logd is started with the -d debug option.
113 CHLD Wait for childs if some were born, because of wall'ing messages.
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117 There is the potential for the rsyslogd daemon to be used as a conduit
118 for a denial of service attack. A rogue program(mer) could very easily
119 flood the rsyslogd daemon with syslog messages resulting in the log
120 files consuming all the remaining space on the filesystem. Activating
121 logging over the inet domain sockets will of course expose a system to
122 risks outside of programs or individuals on the local machine.
123 There are a number of methods of protecting a machine:
125 1. Implement kernel firewalling to limit which hosts or networks
127 have access to the 514/UDP socket.
128 2. Logging can be directed to an isolated or non-root filesystem
130 which, if filled, will not impair the machine.
131 3. The ext2 filesystem can be used which can be configured to limit
133 a certain percentage of a filesystem to usage by root only.
134 NOTE that this will require rsyslogd to be run as a non-root
135 process. ALSO NOTE that this will prevent usage of remote log‐
136 ging on the default port since rsyslogd will be unable to bind
137 to the 514/UDP socket.
138 4. Disabling inet domain sockets will limit risk to the local
140 machine.
141 Message replay and spoofing
143 If remote logging is enabled, messages can easily be spoofed and
144 replayed. As the messages are transmitted in clear-text, an attacker
145 might use the information obtained from the packets for malicious
146 things. Also, an attacker might replay recorded messages or spoof a
147 sender's IP address, which could lead to a wrong perception of system
148 activity. These can be prevented by using GSS-API authentication and
149 encryption. Be sure to think about syslog network security before
150 enabling it.
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153 When debugging is turned on using the -d option, rsyslogd produces
154 debugging information according to the RSYSLOG_DEBUG environment vari‐
155 able and the signals received. When run in foreground, the information
156 is written to stdout. An additional output file can be specified using
157 the RSYSLOG_DEBUGLOG environment variable.
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160 /etc/rsyslog.conf
161 Configuration file for rsyslogd. See rsyslog.conf(5) for exact
162 information.
163 /dev/log
164 The Unix domain socket to from where local syslog messages are
165 read.
166 /var/run/rsyslogd.pid
167 The file containing the process id of rsyslogd.
168 prefix/lib/rsyslog
169 Default directory for rsyslogd modules. The prefix is specified
170 during compilation (e.g. /usr/local).
172 RSYSLOG_DEBUG
173 Controls runtime debug support. It contains an option string
174 with the following options possible (all are case insensitive):
175 Debug Turns on debugging and prevents forking. This is pro‐
177 cessed earlier in the startup than command line options
178 (i.e. -d) and as such enables earlier debugging output.
179 Mutually exclusive with DebugOnDemand.
180 DebugOnDemand
181 Enables debugging but turns off debug output. The output
182 can be toggled by sending SIGUSR1. Mutually exclusive
183 with Debug.
184 LogFuncFlow
185 Print out the logical flow of functions (entering and
186 exiting them)
187 FileTrace
188 Specifies which files to trace LogFuncFlow. If not set
189 (the default), a LogFuncFlow trace is provided for all
190 files. Set to limit it to the files specified.FileTrace
191 may be specified multiple times, one file each (e.g.
192 export RSYSLOG_DEBUG="LogFuncFlow FileTrace=vm.c File‐
193 Trace=expr.c"
194 PrintFuncDB
195 Print the content of the debug function database whenever
196 debug information is printed (e.g. abort case)!
197 PrintAllDebugInfoOnExit
198 Print all debug information immediately before rsyslogd
199 exits (currently not implemented!)
200 PrintMutexAction
201 Print mutex action as it happens. Useful for finding
202 deadlocks and such.
203 NoLogTimeStamp
204 Do not prefix log lines with a timestamp (default is to
205 do that).
206 NoStdOut
207 Do not emit debug messages to stdout. If RSYSLOG_DEBUGLOG
208 is not set, this means no messages will be displayed at
209 all.
210 Help Display a very short list of commands - hopefully a life
211 saver if you can't access the documentation...
212 RSYSLOG_DEBUGLOG
214 If set, writes (almost) all debug message to the specified log
215 file in addition to stdout.
216 RSYSLOG_MODDIR
217 Provides the default directory in which loadable modules reside.
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220 Please review the file BUGS for up-to-date information on known bugs
221 and annoyances.
222
224 Please visit https://www.rsyslog.com/doc/ for additional information,
225 tutorials and a support forum.
226
228 rsyslog.conf(5), logger(1), syslog(2), syslog(3), services(5),
229 savelog(8)
230
232 rsyslogd is derived from sysklogd sources, which in turn was taken from
233 the BSD sources. Special thanks to Greg Wettstein (greg@wind.enjel‐
234 lic.com) and Martin Schulze (joey@linux.de) for the fine sysklogd pack‐
235 age.
236 Rainer Gerhards
238 Adiscon GmbH
239 Grossrinderfeld, Germany
240 rgerhards@adiscon.com
241Version 8.6.0 02 Dec 2014 RSYSLOGD(8)