1MIMEDEFANG-MULTIPLEXOR(8) System Manager's Manual MIMEDEFANG-MULTIPLEXOR(8)
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6 mimedefang-multiplexor - Process pool controller for mail filters.
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9 mimedefang-multiplexor [options]
10
13 mimedefang-multiplexor manages a pool of Perl processes for scanning e-
14 mail. It is designed to work in conjunction with mimedefang(8) and
15 mimedefang.pl(8).
16 mimedefang-multiplexor opens a UNIX-domain socket and listens for
18 requests for work from mimedefang. As requests come in, mimedefang-
19 multiplexor creates Perl processes as needed to scan mail. The Perl
20 processes are not killed when scanning is completed, but continue to
21 run in a loop. Perl processes are re-used for subsequent e-mail mes‐
22 sages. This eliminates the large overhead of starting a new Perl
23 process for each incoming message.
24 To avoid memory leaks, the Perl processes are killed after they have
26 handled some number of scans.
27
30 -U user
31 Runs the multiplexor as user rather than root. This option is
32 mandatory, and must match the -U option supplied to mimedefang.
33 -m minSlaves
36 The minimum number of Perl processes to keep running at all
37 times. The default is zero.
38 -x maxSlaves
41 The maximum number of Perl processes to run simultaneously. If
42 a request comes in and all processes are busy, a temporary fail‐
43 ure is signalled to the SMTP peer. The default is 2.
44 -r maxRequests
47 The maximum number of requests a given process handles before it
48 is killed and a replacement started. The default is 500.
49 -i idleTime
52 The idle time in seconds after which to kill of excess Perl pro‐
53 cesses. That is, if the process is idle for longer than this
54 time, and there are more than minSlaves running, the process is
55 killed. Note that this is implemented as a timer which ticks
56 every idleTime seconds; therefore, processes may be idle for up
57 to twice this time before they are killed. The default for
58 idleTime is 300 seconds.
59 -b busyTime
62 The longest a Perl process is allowed to spend scanning an e-
63 mail before it is declared hung up and killed. The default is
64 120 seconds.
65 -Z This option specifies that the multiplexor should accept and
68 process "status updates" from busy slaves. Note that this con‐
69 sumes one extra file descriptor per slave, plus a small amount
70 of CPU time per status update.
71 -c cmdTime
74 The timeout for communication between mimedefang-multiplexor and
75 mimedefang, or between mimedefang-multiplexor and a Perl scan‐
76 ning process. The default is 10 seconds. This timeout should
77 be kept quite short.
78 -w waitTime
81 When mimedefang-multiplexor starts the initial slaves, or needs
82 to bring the number of running slaves up to the number defined
83 by the -m option, it does not start all the slaves at once,
84 because this could overload your server. Instead, it starts one
85 slave every waitTime seconds. The default value for waitTime is
86 3.
87 -W waitTime
90 If you use this option, mimedefang-multiplexor will never acti‐
91 vate a slave until waitTime seconds have elapsed since the last
92 slave activation. This could result in mail being tempfailed if
93 slave activations do not keep pace with incoming mail. However,
94 it may be preferable to tempfail mail rather than allow the load
95 on your server to spike up too quickly. The default value for
96 this option is 0, meaning that mimedefang-multiplexor will start
97 slaves as quickly as necessary to keep up with incoming mail.
98 -z spooldir
101 Set the spool directory to spooldir. If this option is omitted,
102 the spool directory defaults to /var/spool/MIMEDefang.
103 -s pathName
106 The UNIX-domain socket on which mimedefang-multiplexor listens
107 for requests. This should be specified as an absolute pathname.
108 If this option is not supplied, it defaults to mimedefang-multi‐
109 plexor.sock under the spool directory.
110 -a socket
113 A socket for listening for requests. This is similar to the -s
114 socket, except that a restricted set of requests are processed.
115 On this socket, the multiplexor will only process requests ask‐
116 ing for status; it will not accept any commands to do scanning
117 or that would consume a slave. See the SOCKET SPECIFICATION
118 section for the format of socket.
119 -p fileName
122 Causes mimedefang-multiplexor to write its process-ID (after
123 becoming a daemon) to the specified file.
124 -f filter_path
127 Normally, mimedefang-multiplexor executes a Perl filter script
128 called mimedefang.pl to scan the e-mail. However, you can have
129 it execute any program you like by specifying the full path to
130 the program with the -f option. This program must obey the pro‐
131 tocol documented in mimedefang-protocol(7); see that manual page
132 for details.
133 Note that the -f option does not specify the "filter" to use
135 with mimedefang.pl; instead, it specifies the program for
136 mimedefang-multiplexor to execute. You almost certainly should
137 not use this option unless you wish to replace mimedefang.pl
138 with your own program.
139 -F rules_path
142 Specifies the path to the filter rules. By default,
143 /etc/mail/mimedefang-filter is used. If you use the -F option,
144 its value is passed to the underlying Perl filter program using
145 -f.
146 -l Log certain events, including the output of the Perl slaves'
149 standard-error, using syslog. Normally, the multiplexor does
150 not log much information.
151 -d Write debugging information about event-handling code in
154 /var/log/mimedefang-event-debug.log. This is only of use to
155 people debugging mimedefang-multiplexor.
156 -R kbytes
159 Limits the resident-set size of the slave filter processes to
160 kbytes kilobytes. This limit is not supported on all operating
161 systems; it is known to work on Linux.
162 -M kbytes
165 Limits the total memory space of slave filter processes to
166 kbytes kilobytes. This limit is supported on all operating sys‐
167 tems which support the setrlimit(2) system call. This should
168 include most modern UNIX systems.
169 We recommend that you monitor your slave filter processes and
171 get a feel for how much memory they use. You should then limit
172 the memory to two or three times the worst-case that you have
173 observed. This can help mitigate denial-of-service attacks
174 which use complicated MIME messages to force mimedefang.pl to
175 consume lots of memory.
176 -h Print usage information and exit.
179 -t filename
182 Log statistical information to filename. See the section STA‐
183 TISTICS for more information.
184 -T Log statistical information using syslog(2). You may use any -t
187 and -T together, in which case statistical information is logged
188 in a file and using syslog.
189 -u Flush the statistics file after every write. Normally, mimede‐
192 fang-multiplexor does not flush the file; this is the best
193 choice for minimizing disk I/O on a busy mail server. However,
194 if you wish to watch statistics entries in real-time, you should
195 enable flushing.
196 -D Do not fork into the background and become a daemon. Instead,
199 stay in the foreground. Useful mainly for debugging or if you
200 have a supervisory process managing mimedefang-multiplexor.
201 -q queue_size
204 Normally, if all slaves are busy and mimedefang-multiplexor
205 receives another request, it fails it with the error "No free
206 slaves." However, if you use the -q option, then up to
207 queue_size requests will be queued. As soon as a slave becomes
208 free, the queued requests will be handed off in FIFO order. If
209 the queue is full and another request comes in, then the request
210 is failed with "No free slaves".
211 -Q queue_timeout
214 Queued requests should not stay on the queue indefinitely. If a
215 queued request cannot be processed within queue_timeout (default
216 30) seconds of being placed on the queue, it is failed with a
217 "Queued request timed out" message. See the section "QUEUEING
218 REQUESTS" for more discussion.
219 -O sock
222 Listen on a notification socket for connections from listeners.
223 mimedefang-multiplexor can inform external programs of state
224 changes by sending messages over a notification socket. The
225 external programs connect to this socket and then listen for
226 notifications. See the section SOCKET SPECIFICATION for the
227 format of sock.
228 See the mimedefang-notify(7) man page for details of the notifi‐
230 cation protocol.
231 -N map_sock
234 Listen on a map socket for Sendmail SOCKETMAP connections. As
235 of Sendmail 8.13, you can define a Sendmail map type that talks
236 to a daemon over a socket. mimedefang-multiplexor implements
237 that protocol; consult the mimedefang-filter(5) man page for
238 detils (see the SOCKET MAPS section).
239 See the section SOCKET SPECIFICATION for the format of map_sock.
241 -I backlog
246 When mimedefang-multiplexor creates a listening socket, it cal‐
247 culates the "backlog" argument to listen(2) based on the maximum
248 number of slaves. However, you can explicitly set this backlog
249 with the -I option. Setting the backlog to a high value (around
250 30-50) may help on a very busy server. If you see mail log mes‐
251 sages saying "MXCommand: socket: Connection refused" during busy
252 periods, then that's an indication you need a higher listen
253 backlog.
254 -L interval
257 Log the slave status every interval seconds. This logs a line
258 using syslog; the line looks like this:
259 Slave status: Stopped=s Idle=i Busy=b Killed=k Queued=q Msgs=m Activations=a
262 Here, "Stopped" is the number of non-running slaves, "Idle" is
264 the number of idle slaves, "Busy" is the number of busy slaves,
265 "Killed" is the number of killed slaves yet to be reaped,
266 "Queued" is the number of queued requests, "Msgs" is the total
267 number of messages processed since the multiplexor began run‐
268 ning, and "Activations" is the number of times a Perl process
269 has been started since the multiplexor began running.
270 If you supply an interval of 0 (which is the default), no peri‐
272 odic status logging is performed. If you supply an interval of
273 less than 5 seconds, it is silently reset to 5 seconds.
274 -S facility
277 Specifies the syslog facility for log messages. The default is
278 mail. See openlog(3) for a list of valid facilities. You can
279 use either the short name ("mail") or long name ("LOG_MAIL") for
280 the facility name.
281 -E Specifies that the multiplexor should create an embedded Perl
284 interpreter. This can improve performance dramatically. But
285 see the section "EMBEDDING PERL" for more information.
286 -X n Specifies that the multiplexor should initiate a "tick" request
289 every n seconds. This causes your filter_tick function (if
290 defined) to be called. Note that you have no control over which
291 slave executes filter_tick. If all slaves are busy when a tick
292 occurs, that tick request is skipped and a warning message is
293 logged.
294 -P n Specifies that the multiplexor should run n tick requests in
297 parallel. Each tick is run as often as specified with the -X
298 argument. (If you omit the -P option, then the multiplexor
299 behaves as if -P 1 had been specified.)
300 If you run parallel ticks, each tick is assigned an integer
302 identifying its "type". The type ranges from 0 to n-1. While
303 there may be as many as n tick requests running at a time, only
304 one tick of each type will be active at any time.
305 -Y label
308 Sets the tag used in the multiplexor's syslog messages to label
309 instead of mimedefang-multiplexor.
310
313 The -a, -N and -O options take a socket as an argument. This socket
314 can be specified as:
315 /path/to/socket
318 A UNIX-domain socket
319 inet:portnum
322 A TCP socket bound to port portnum, but which accepts connec‐
323 tions only from the IPv4 loopback address (127.0.0.1).
324 inet_any:portnum
327 A TCP socket bound to port portnum which will accept connections
328 from any address. Use inet_any with caution!
329
332 Normally, if all slaves are busy, any additional requests are failed
333 immediately. However, the -q and -Q options allow you to queue
334 requests for a short amount of time. This facility is intended to
335 gracefully handle a temporary overload; most of the time, your queue
336 should be empty.
337 Because mimedefang checks the number of free slaves when a connection
339 is opened and fails the connection if there are no free slaves, the
340 intent of the queue is to allow SMTP transactions that are already
341 underway to continue if there is a slight overload. Any new connec‐
342 tions will be failed if all slaves are busy, but existing connections
343 are allowed to continue. Queuing requests may improve throughput on
344 extremely busy servers.
345 Note that if you supply the -q option to mimedefang, then even new con‐
347 nections are allowed to queue. This may improve throughput by keeping
348 the slave utilization higher.
349 The -R option to mimedefang can be used to reserve a specified number
351 of slaves for connections from the loopback address. Using the -R
352 option has the side-effect of permitting new connections from the loop‐
353 back address to queue.
354
357 Normally, when mimedefang-multiplexor activates a slave, it forks and
358 execs mimedefang.pl. However, if the multiplexor was compiled with
359 embedded Perl support, and you supply the -E command-line option, the
360 multiplexor works like this:
361 1 It creates an embedded Perl interpreter, and sources mimede‐
364 fang.pl with a special command-line argument telling it to read
365 the filter, but not to enter the main loop.
366 2 Each time a slave is activated, the multiplexor calls fork() and
369 runs the mimedefang.pl main loop. This invokes filter_initial‐
370 ize and then runs the main loop.
371 On some platforms (for example, Red Hat Linux 7.3 with Perl 5.6.1), it
374 is not safe to destroy and recreate a Perl interpreter without causing
375 a memory leak. On those platforms, if you attempt to reread the filter
376 file (by sending the multiplexor a HUP signal or reread command), the
377 filter will not be re-read, and a message will be logged to syslog. On
378 those platforms, you must kill and restart MIMEDefang if you change the
379 filter file.
380 On most platforms, however, a filter reread is accomplished by destroy‐
383 ing and re-creating the embedded interpreter, re-sourcing mimedefang.pl
384 and killing slaves as soon as they are idle.
385 WARNING: If you use the embedded Perl interpreter, the Perl variable
388 "$$" will not be updated with the process ID of each slave. Instead,
389 it will reflect the process ID of the master multiplexor. This is a
390 limitation of embedded Perl; we have no plans to fix it.
391
394 With the -t option, mimedefang-multiplexor logs certain events to a
395 file. This file can be post-processed to gather statistics about the
396 multiplexor. You can use it to tune the number of slaves you run,
397 adjust timeouts, and so on.
398 Each line of the file looks like this:
401 YYYY/MM/DD:HH:MM:SS timestamp event key=val key=val...
403 Here, YYYY/MM/DD:HH:MM:SS is the local time of day. Timestamp is the
405 number of seconds since January 1, 1970. Event is the name of an
406 event. The valid events are:
407 StartSlave
410 A slave process has been started.
411 KillSlave
414 A slave process has been killed.
415 ReapSlave
418 A dead slave process has been reaped. It is possible to have a
419 ReapSlave event without a previous KillSlave event if the slave
420 process terminated abnormally.
421 StartFilter
424 A slave process has begun filtering an e-mail message.
425 EndFilter
428 A slave process has finished filtering an e-mail message.
429 The possible keys in the key=value pairs are:
432 slave=n
435 The slave involved in the event. Every slave is identified by a
436 small integer.
437 nslaves=n
440 The total number of running slaves immediately after the event
441 happened.
442 nbusy=n
445 The number of busy slaves (slaves which are processing an e-mail
446 message) immediately after the event happened.
447 reason="string"
450 The reason for a StartSlave or KillSlave event. (Present only
451 for these events.)
452 numRequests=n
455 The number of e-mails processed by the slave. Present only for
456 an EndFilter event.
457 If you send the mimedefang-multiplexor process a SIGHUP signal (kill -1
460 pid), it closes and reopens the statistics file. This is useful during
461 log file rotation.
462 If you send the mimedefang-multiplexor process a SIGINT signal (kill
465 -INT pid), it terminates all active-but-idle slaves. Also, any active-
466 and-busy slaves terminate as soon as they finish filtering the current
467 message. This is useful to force a reread of the filter rules file
468 without stopping and restarting Sendmail.
469 If you send the mimedefang-multiplexor process a SIGTERM signal (kill
472 pid), it terminates all slaves and exits immediately.
473
476 mimedefang-mulitplexor was written by David F. Skoll <dfs@roaringpen‐
477 guin.com>. The mimedefang home page is http://www.mimedefang.org/.
478
481 mimedefang.pl(8), mimedefang-filter(5), mimedefang(8), mimedefang-pro‐
482 tocol(7)
4834th Berkeley Distribution 8 February 2005 MIMEDEFANG-MULTIPLEXOR(8)