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4. How to Run sendmail

One way to run sendmail is to provide it with the name of a recipient as the only command-line argument. For example, the following sends a mail message to george : [1]

[1] For now, you can do this only with the system-supplied sendmail . It requires a configuration file that we have not yet written for our freshly compiled version.


/usr/lib/sendmail george

Multiple recipients can also be given. For example, the following sends a mail message to george , truman , and teddy :


/usr/lib/sendmail george,truman,teddy

The sendmail program accepts two different kinds of command-line arguments. Arguments that do not begin with a - character (such as george ) are assumed to be recipients. Arguments that do begin with a - character are taken as switches that determine the behavior of sendmail . In this chapter we will cover only a few of these switch-style command-line arguments (see Table 4.1 ). The complete list of command-line switches, along with an explanation of each, is presented in the reference part of this book ( Chapter 36, The Command Line ).

Table 4.1: Some Command-Line Switches
Flag Description
-b Set operating mode
-v Run in verbose mode
-d Run in debugging mode

4.1 Become a Mode (-b)

The sendmail program can function in a number of different ways depending on which form of -b argument you use. One form, for example, causes sendmail to display the contents of the queue. Another causes sendmail to rebuild the aliases database. A complete list of the -b command-line mode-setting switches is shown in Table 4.2 . We will cover only a few in this chapter and will present the others as this tutorial proceeds.

Table 4.2: Forms of the -b Command-Line Switch
Form Description
-ba Use ARPAnet (Grey Book) protocols
-bD Run as a daemon, but don't fork
-bd Run as a daemon
-bH Purge persistent host status
-bh Print persistent host status
-bi Rebuild alias database
-bm Be a mail sender
-bp Print the queue
-bs Run SMTP on standard input
-bt Test mode: resolve addresses only
-bv Verify: don't collect or deliver
-bz Freeze the configuration file (obsolete)

The effects of some of the options in Table 4.2 can also be achieved by running the sendmail executable using different names. Those names and a description of their results are shown in Table 4.3 . Each name can be a hard link with, a symbolic link to, or a copy of sendmail .

Table 4.3: Other Names for sendmail
Name Form Description
hoststat -bh Print persistent host status
mailq -bp Display the queue
newaliases -bi Initialize alias database
purgestat -bH Purge persistent host status
smtpd -bd Run as a daemon

4.1.1 Daemon Mode (-bd)

The sendmail program can run as a daemon in the background, listening for incoming mail from other machines. The sendmail program reads its configuration file only once, when it first starts as a daemon. It then continues to run forever, never reading the configuration file again. As a consequence, it will never see any changes to that configuration file.

When you change something in the sendmail.cf configuration file, you always need to kill and restart the sendmail daemon. But before you can kill the daemon, you need to know how to correctly restart it. This information is in the /etc/sendmail.pid file or one of your system rc files.

On a Berkeley UNIX-based system, for example, the daemon is usually started like this:

/usr/lib/sendmail -bd -q1h

The -bd command-line switch specifies daemon mode. The -q switch tells sendmail how often to look in its queue to process pending mail. The -q1h switch says to process the queue at one ( 1 ) hour ( h ) intervals.

The actual command to start the sendmail daemon on your system may be different from what we've shown. If you manage many different brands of systems, you'll need to know how to start the daemon on all of them. Kill and restart, beginning with V8.7

Killing and restarting the sendmail daemon became easier beginning with V8.7. A single command [2] will kill and restart the daemon:

[2] Provided that the daemon was originally started with a full pathname.


kill -HUP `head -1 /etc/sendmail.pid`

This single command has the same effect as the two commands shown for V8.6 below. Kill and restart, with V8.6

Before you can start the sendmail daemon, you need to make sure there is not a daemon running already. Beginning with V8.6, the pid of the currently running daemon is found in the first line of the /etc/sendmail.pid file. The processes of killing the daemon looks like this:


kill `head -1 /etc/sendmail.pid`

After killing the currently running daemon, you can start a new daemon with the following simple command:


`tail -1 /etc/sendmail.pid` Kill and restart, old versions

Under old versions of sendmail you need to use the ps (1) program to find the pid of the daemon. How you run ps is different on BSD UNIX and System V UNIX. For BSD UNIX the command that you use and the output that it produces resemble the following:


ps ax | grep sendmail | grep -v grep

   99    ?  IW    0:07 /usr/lib/sendmail -bd -q1h


kill 99

Here the leftmost number printed by ps (the 99 ) was used to kill the daemon.

For System V-based systems you use different arguments for the ps command, and its output differs:


ps -ae | grep sendmail

   99 ?         0:01 sendmail


kill 99

Under old versions of sendmail you must look in your system rc files for the way to restart sendmail . We showed how to find this information in Chapter 3, The Roles of sendmail (see Section 3.4, "Role as a Daemon" ). If you forget to kill the daemon

If you forget to kill the daemon before starting a new one, you may see a stream of messages similar to the following, one printed every 5 seconds (probably to your console window):

getrequests: cannot bind: Address already in use
getrequests: cannot bind: Address already in use
getrequests: cannot bind: Address already in use
getrequests: cannot bind: Address already in use
getrequests: cannot bind: Address already in use
getrequests: cannot bind: Address already in use
getrequests: cannot bind: Address already in use
getrequests: cannot bind: Address already in use
getrequests: cannot bind: Address already in use
getrequests: cannot bind: Address already in use
getrequests: cannot bind: Address already in use
opendaemonsocket: server SMTP socket wedged: exiting

This shows that the attempt to run a second daemon failed. [3]

[3] Note that some multicast-capable versions of UNIX allow multiple sendmail daemons to run simultaneously. This is a known bug in the SO_REUSEADDR ioctl (2) call for TCP under multicasting. Contact your vendor for a fix.

4.1.2 Show Queue Mode (-bp)

The sendmail program can also display the contents of its queue directory. It can do this in two ways: by running as a program named mailq or by being run as sendmail with the -bp command-line switch. Whichever way you run it, the contents of the queue directory are printed. If the queue is empty, sendmail prints the following:

Mail queue is empty

If, on the other hand, there is mail waiting in the queue, the output is far more verbose, possibly containing lines similar to these:

.ps 8
                Mail Queue (1 requests)
-Q-ID-- -Size- --Q-Time--- ------Sender/Recipient------
GAA29775*     702 Thu Mar 12 16:51 <you@here.us.edu>
            Deferred: Host fbi.dc.gov is down

Here, the output produced with the -bp switch shows that there is only one mail message in the queue. If there were more, each entry would look pretty much the same as this. Each message results in at least two lines of output.

The first line shows details about the message and the sender. The GAA29775 identifies this message in the queue. The * shows that this message is locked and currently being processed. The 702 is the size of the message body in bytes (the size of the df file as mentioned in Section 3.1.2, "The Queue Directory" ). The date shows when this message was originally queued. The address shown is the name of the sender.

A second line may appear giving a reason for failure (if there was one). A message may be queued intentionally or because it couldn't be delivered.

The third and possibly subsequent lines show the addresses of the recipients.

The output produced by the -bp switch is more fully covered in Chapter 23, The Queue .

4.1.3 Rebuild Aliases Mode (-bi)

Because sendmail may have to search through thousands of names in the aliases file, a version of the file is stored in a separate dbm (3) or db (3) database format file. The use of a database significantly improves lookup speed.

Although sendmail can automatically update the database whenever the aliases file is changed, there will be times when you will want to rebuild it yourself. You do this either by running sendmail using the command newaliases or with the -bi command-line switch. The following two commands do the same thing:




/usr/lib/sendmail -bi

There will be a delay while sendmail rebuilds the aliases database; then a summary of what it did is printed:

/etc/aliases: 859 aliases, longest 615 bytes, 28096 bytes total

This line shows that the database was successfully rebuilt. Beginning with V8.6 sendmail , multiple alias files became possible, so each line (and there might be many) begins with the name of an alias file. The information then displayed is the number of aliases processed, the size of the biggest entry to the right of the : in the aliases file, and the total number of bytes entered into the database. Any mistakes in an alias file will also be printed here.

The aliases file and how to manipulate it are covered in Chapter 24, Aliases .

4.1.4 Verify Mode (-bv)

A handy tool for checking aliases is the -bv command-line switch. It causes sendmail to recursively look up an alias and report the ultimate real name that it found.

To illustrate, consider the following aliases file:

animals:      farmanimals,wildanimals

bill-eats:    redmeat

birds:        farmbirds,wildbirds

bob-eats:     seafood,whitemeat

farmanimals:  pig,cow

farmbirds:    chicken,turkey

fish:         cod,tuna

redmeat:      animals

seafood:      fish,shellfish

shellfish:    crab,lobster

ted-eats:     bob-eats,bill-eats

whitemeat:    birds

wildanimals:  deer,boar

wildbirds:    quail

Although you can figure out what the name ted-eats ultimately expands to, it is far easier to have sendmail do it for you. By using sendmail , you have the added advantage of being assured accuracy, which is especially important in large and complex aliases files.

In addition to expanding aliases, the -bv switch performs another important function. It verifies whether or not the expanded aliases are in fact deliverable. Consider the following one-line aliases file:

root:       fred,larry

Assume that the user fred is the system administrator and has an account on the local machine. The user larry , however, has left, and his account has been removed. You can run sendmail with the -bv switch to find out whether both names are valid:


/usr/lib/sendmail -bv root

This tells sendmail to verify the name root from the aliases file. Since larry (one of root 's aliases) doesn't exist, the output produced looks like this:

larry... User unknown
fred... deliverable: mailer local, user fred