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<h2><code>courierd</code> daemon process</h2>
<h3>Configuration files</h3>The following files are present in
the <code>local/config</code> subdirectory.
<p>The following configuration files are specific to the main
<code>courierd</code> daemon. Module-specific configuration files
are defined elsewhere.</p>
<p><code>me</code> - if present, specifies the hostname of the
machine, and used instead of <code>gethostname()</code>. Note
that this is also used by submit. If The <em>Courier</em> mail server's
installation directory is exported to clusters, you must arrange
for a different <code>local/config/me</code> file for each
machine in the cluster. One way to do so is to have
<code>local/config/me</code> set as a soft link to /etc/HOSTNAME,
which on each machine contains its host name.</p>
<p><code>locals</code> - all the possible domains that are
recognized as local. Text file, one domain per line. Defaults to
me. This is used by the locals module, and by submit.</p>
<p><code>queuetime</code> - how long The <em>Courier</em> mail server
keeps trying to deliver a message, before returning it as
undeliverable. Default is one week.</p>
<p><code>warntime</code> - if a message is undeliverable for this
long, send a warning message to the sender. Set to 0, in order to
disable. Default is four hours.</p>
<p><code>sizelimit</code> - maximum size of a message, in bytes.
<code>submit</code> rejects longer messages.</p>
<p><code>sizecheck</code> - contains three numbers: b i s. submit
will return a temporary error indication and reject a submission
if there are less than b free blocks, or i free inodes, on the
mail filesystem. As submit receives the message, it will check
the status of the filesystem every s bytes, and will immediately
stop if the available free space falls below the set limits. If
not specified, the limits are 500 blocks, 20 inodes, and 128K
bytes. Also note that sometimes the actual amount of free disk
blocks has to be twice as much, if <code>submit</code> decides to
rewrite the message to convert to/from quoted printable encoding,
or to add MIME headers.</p>
<p><code>batchsize</code> - maximum number of recipients per
message. submit splits longer recipient lists into separate
messages. If absent, defaults to 100.</p>
<p><code>queuelo</code> - <code>courierd</code> output queue low
watermark. If absent, defaults to the sum of <b>MAXDELS</b> of
all output modules. This number should be the minimum value for
queuelo. The minimum value for <code>queuelo</code> is 20.</p>
<p><code>queuehi</code> - <code>courierd</code> output queue high
watermark. If absent, defaults to <b>queuelo</b> * 2, not to
exceed <b>queuelo</b> + 1000. Must greater than
<b>queuelo</b>.</p>
<p><code>respawnlo</code> - do not respawn <code>courierd</code>
second process more often than this time interval. The contents
of this file is a single number following by 'h' for hours or 'd'
for days. If this file does not exist, the <code>respawnlo</code>
is set for one hour.</p>
<p><code>respawnhi</code> - respawn <code>courierd</code> at
least this often. Helps to cut down on memory fragmentation. The
contents of this file is a single number following by 'h' for
hours or 'd' for days. If this file does not exist, the
<code>respawnhi</code> is set for seven days.</p>
<p><code>bouncefrom</code> - what to put in the From: header on
bounces</p>
<h2><code>courierd</code> - process A - startup process</h2>
<h3><code>courierd</code> startup activity</h3>A) chdirs to
${COURIER_HOME}. Disassociates from controlling terminal. Closes
stdin/stdout/stderr, reopens stdin to <code>/dev/null</code>,
stdout to <code>/dev/console</code>., and stderror to
<code>logger</code>, Resets umask to 007. Forks, parent exits,
child continues to run, becomes the first <code>courierd</code>
daemon process, process A.
<p>B) main starts all output modules. A separate pipe to each
output module's stdin. Shared pipe from all output modules'
stdout.</p>
<p>C) main setgids and setuids itself to mail.</p>
<p>D) main creates another pipe, then forks the second
<code>courierd</code> daemon process, process B.</p>
<p>E) main waits for any child process to terminate. If main
receives a SIGHUP, main sighups process B.</p>
<p>F) if process B terminates with a zero exit, main respawns it
again, and logs the event to syslog.</p>
<p>G) All other signals are logged to syslog, resulting in
termination.</p>
<p>H) Non-zero exit codes are logged, process A waits a minute,
then respawns process B.</p>
<p>I) each time main forks process B, main executes tmp directory
cleanup (see submit process).</p>
<h3><code>courierd</code> - process B</h3>A) Receipt of a SIGHUP
sets a boolean flag called 'termination_flag'. This is logged.
<p>B) Allocate queuehi msgq structures.</p>
<p>C) Open all shared module libraries.</p>
<p>D) Open <code>queue/trigger</code> for reading.</p>
<p>E) Remove all empty directories in <code>local/msgq</code> and
<code>local/msgs</code>.</p>
<p>F) <b>Queue scan</b>.</p>
<blockquote>
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<div align="center">
Queue scan
</div>A) Obtain current time
<p>B) Read all directories in <code>local/msgq</code>,
sort it in chronological order.</p>
<p>C) Read each directory, skip control files which are
already in the queue (check using inodes), sort the
remaining ones in chronological order. Perform
the following steps for each remaining control
file.</p>
<p>D) <b>Add this control file to the queue</b>. Stop
queue scan if the control file wasn't added.</p>
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Add control file to the queue
</div>A) Read the control file.
<p>B) Initialize the msgq structure, and all the
rcptinfos. If there are no rcptinfos, <b>remove control
file from the queue</b>.</p>
<p>C) If the msgq array is not full, go to step E.</p>
<p>D) Scan the msgq array, by nextdel, starting with
the latest nextdel. Stop at the first msgq whose
rcptinfos all have non-null pending pointers. If we
don't find one, stop. Use pendingpos to remove the
rcptinfo * from pending->recipient_list. If the
resulting recipient_list is NULL: if hostp is not null,
set hostp->pendinglist to NULL; remove this
pendelinfo structure from drvp->pendelinfo_list.
Remove this msgq.</p>
<p>E) Add the msgq structure to the queue list, sorted
by nextdel. For each rcptinfo, search delmodule's
hdlvrpfirst/last list for this host. If found, go to
step F. If not found, check pendelinfo_list. If found
there, add this rcptinfo * to pendelinfo's
recipient_list (sorted by nextdel). Otherwise, search
hdlvrpfirst/last list from the tail end, looking for a
host with a 0 dlvrcount and either a null pendinglist
pointer, or whose pendelinfo's first recipient has a
later timestamp than the new control file. If all hosts
have a non-0 dlvrcount, create a new pendelinfo, add it
to pendelinfo_list, add this rcptinfo * to pendelinfo's
recipient_list (sorted by nextdel). If found one with a
0 dlvrcount, set pendelinfo->hostp to null (if
pendelinfo is not null).</p>
<p>F) If delinfo's delpfreefirst is null, add this
rcptinfo * to dlrvrhost's
pendelinfo->recipient_list, otherwise remove the
first delinfo from delpfreefirst's list, initialize it,
increment dlvrhost's dlvrcount, send the message to the
device module.<br />
</p>
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<div align="center">
Remove control file from the queue
</div>A) Read the control file and check if every
recipient has a succesfull delivery.
<p>B) Unless every recipient has a succesful delivery,
generate a bounce message.</p>
<p>C) Remove the message file, and both links to the
control file. Deallocate the msgq structure. If
the msgq list falls below respawnlo, set the queue scan
flag.</p>
</td>
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</blockquote>
<h3><code>courierd</code> - process B - main loop</h3>A)
<code>courierd</code> scans tmp directory for new messages (see
submit process, above). When a new message is found, the message
and control files are moved to local/msgs, and the control file
is linked to local/msgq, with the current time set as the next
scheduled delivery time. If the termination flag is NOT set,
<b>add this control file to the queue</b>.
<p>B) If the termination flag is not set, and there are no
pending deliveries, check the process starting time. If the
process has been running for at least respawnlo period of time,
set the termination flag.</p>
<p>C) If the process has been running for at least respawnhi
period of time, set the termination flag unconditionally.</p>
<p>D) If the termination flag is not set, and the queue scan flag
is set, do a <b>queue scan</b>. If there are any control files in
the local/tmp directory, go back to step A.</p>
<p>E) If the termination flag is set, wait until a <b>delivery
completion notice is received</b>. If there are no pending
deliveries, terminate the process normally.</p>
<p>F) Wait until any of the following events: <b>delivery
completion notice</b>, new message notification from
queue/trigger, if there are delivery attempts scheduled for a
future time, wait until the timer expires. Check the time this
process was started. If respawnlo interval has not passed, wait
until respawnlo interval passes.</p>
<p>G) End of file indication from process A causes an immediate
termination.</p>
<h3>Delivery completion notice</h3>A) Get delid of the completed
delivery.
<p>B) Decrement delinfo->rcptlist->dlvrcount. If it's zero,
recycle the msgq, reread the control file. If all recipients have
a delivery completion or failure on file, or if the message's
expiration time has expired, r<b>emove control file from the
queue</b>.</p>
<p>C) Put the delinfo back on the delpfreefirst list. Move the
delinfo's dlvrhost to the top of the MRU list.</p>
<p>D) As long as the delpfreefirst list is not empty, do this.
Scan the MRU list, from top to bottom. If we find a dlvrhost with
a pending list, remove the first rcptinfo from the rcptinfo_list
(if it's empty, remove the pendelinfo structure), remove the
first delinfo from delpfreefirst's list, initialize it, increment
dlvrhost's dlvrcount, send the message to the device module. If
all dlvrhosts have null pending lists, go through the drvinfo's
pendelinfo_list.<br />
</p>
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