Linux Network Administratoramp;#039;s Guide (3rd Edition) [Electronic resources] نسخه متنی

12.8. Tips and Tricks

There are a number of things you
can do to make managing a sendmail site efficient. A number of
management tools are provided in the sendmail package;
let's look at the most important of these.

12.8.1. Managing the Mail Spool

Mail is queued in the
/var/spool/mqueue directory before being transmitted. This
directory is called the mail spool. The sendmail program provides the
mailq command as a means of displaying a
formatted list of all spooled mail messages and their status. The
/usr/bin/mailq command is a symbolic link to the
sendmail executable and behaves identically to:

# sendmail -bp

The output of the mailq command displays the
message ID, its size, the time it was placed in the queue, who sent
it, and a message indicating its current status. The following
example shows a mail message stuck in the queue with a problem:

$ mailq
Mail Queue (1 request)
--Q-ID-- --Size-- -----Q-Time----- ------------Sender/Recipient------------
RAA00275      124 Wed Dec  9 17:47 root
(host map: lookup (tao.linux.org.au): deferred)
terry@tao.linux.org.au

This message is still in the mail queue because the destination host
IP address could not be resolved.

To force sendmail to immediately process the queue, issue the
/usr/bin/runq command. sendmail will process the
mail queue in the background. The runq command
produces no output, but a subsequent mailq
command will tell you if the queue is clear.

12.8.2. Forcing a Remote Host to Process Its Mail Queue

If you use a
temporary dial-up Internet connection with a fixed IP address and
rely on an MX host to collect your mail while you are disconnected,
you will find it useful to force the MX host to process its mail
queue soon after you establish your connection.

A small
perl program is included with the sendmail
distribution that makes this simple for mail hosts that support it.
The etrn script has much the same effect on a
remote host as the runq command has on the local
server. If we invoke the command as shown in this example:

# etrn vstout.vbrew.com

we force the host vstout.vbrew.com
to process any mail queued for our local machine.

Typically you'd add this command to your PPP startup
script so that it is executed soon after your network connection is
established.

12.8.3. Mail Statistics

sendmail collects data on the volume of mail traffic and some
information on the hosts to which it has delivered mail. There are
two commands available to display this information,
mailstats and hoststat.

12.8.3.1 mailstats

The
mailstats command displays statistics on the
volume of mail processed by sendmail. The time at which data
collection commenced is printed first, followed by a table with one
row for each configured mailer and one showing a summary total of all
mail. Each line presents eight items of information, which are
described in Table 12-5.

A sample of the output of the mailstats command
is shown in Example 12-7.

Example 12-7. Sample output of the mailstats command

# /usr/sbin/mailstats
Statistics from Sun Dec 20 22:47:02 1998
M   msgsfr  bytes_from   msgsto    bytes_to  msgsrej msgsdis  Mailer
0        0          0K       19        515K        0       0  prog
3       33        545K        0          0K        0       0  local
5       88        972K      139       1018K        0       0  esmtp
=  =  =  =  =  =  =  =  =  =  =  =  =  =  =  =  =  =  =  =  =  =  =  =  =  =  =  =  =  
=  =  =  =  =  =  =  =  =  =  =  =  =  =  =  =  =  =  =  =  =  =  =  =  =  =  =  =  =  =  
T      121       1517K      158       1533K        0       0

This data is collected if the
StatusFile option is enabled in the
sendmail.cf file and the status file exists. The
StatusFile option is defined in the generic Linux
configuration and therefore defined in the
vstout.cf file we built from the generic
configuration, as shown below:

$ grep StatusFile vstout.cf
O StatusFile=/etc/mail/statistics

To restart
the statistics collection, make the statistics file zero length and
restart sendmail.

12.8.3.2 hoststat

The
hoststat command displays information about the
status of hosts to which sendmail has attempted to deliver mail. The
hoststat command is equivalent to invoking
sendmail as:

sendmail -bh

The output presents each host on a line of its own, and for each the
time since delivery was attempted to it, and the status message
received at that time.

Persistent host status is maintained only
if a path for the status directory is defined by the
HostStatusDirectory option, which in turn is
defined in the m4 macro configuration file by
confHOST_STATUS_DIRECTORY. By default, no path is
defined for the host status directory and no persistent host status
is maintained.

Example 12-8 shows the sort of output you can expect
from the hoststat command. Note that most of the
results indicate successful delivery. The result for earthlink.net, on the other hand, indicates
that delivery was unsuccessful. The status message can sometimes help
determine the cause of the failure. In this case, the connection
timed out, probably because the host was down or unreachable at the
time delivery was attempted.

Example 12-8. Sample Output of the hoststat Command

# hoststat
-------------- Hostname ---------- How long ago ---------Results---------
mail.telstra.com.au                    04:05:41 250 Message accepted for
scooter.eye-net.com.au              81+08:32:42 250 OK id=0zTGai-0008S9-0
yarrina.connect.com.a               53+10:46:03 250 LAA09163 Message acce
happy.optus.com.au                  55+03:34:40 250 Mail accepted
mail.zip.com.au                        04:05:33 250 RAA23904 Message acce
kwanon.research.canon.com.au        44+04:39:10 250 ok 911542267 qp 21186
linux.org.au                        83+10:04:11 250 IAA31139 Message acce
albert.aapra.org.au                    00:00:12 250 VAA21968 Message acce
field.medicine.adelaide.edu.au      53+10:46:03 250 ok 910742814 qp 721
copper.fuller.net                   65+12:38:00 250 OAA14470 Message acce
amsat.org                            5+06:49:21 250 UAA07526 Message acce
mail.acm.org                        53+10:46:17 250 TAA25012 Message acce
extmail.bigpond.com                 11+04:06:20 250 ok
earthlink.net                       45+05:41:09 Deferred: Connection time

The
purgestat command flushes the collected host
data and is equivalent to invoking sendmail as:

# sendmail -bH

The statistics will continue to grow
until you purge them. You might want to periodically run the
purgestat command to make it easier to search
and find recent entries, especially if you have a busy site. You
could put the command into a crontab file so it
runs automatically, or just do it yourself occasionally.