The initial behavior of sendmail is determined largely by the command line used to invoke it. The command line can, for example, cause sendmail to use a different configuration file or to rebuild the aliases file rather than deliver mail. The command line can be typed at your keyboard, executed from a boot-time script, or even executed by an MUA when sending mail.
The format of the sendmail command line is:
argv switches recipients
argv is the name used to run sendmail.
switches, if any of them are present,
must always precede the list of recipients. The
is a list of zero or more recipient address expressions.
The sendmail program may exist in any of several places, depending on the version of the operating system you are running. Usually, it is located in the /usr/lib directory and is called sendmail,  but it can alternatively be located in the /etc, /usr/sbin, or /usr/etc directory. The location of the sendmail program can be found by examining the /etc/rc files for BSD UNIX or the /etc/init.d files for Sys V UNIX (see Section 3.4, "Role as a Daemon").
 On Sun systems you will find /usr/lib/sendmail.mx for use with the Domain Name System.
In addition to the name sendmail, other names (in other directories) can exist that alter the behavior of sendmail. Those alternative names are usually symbolic links to /usr/lib/sendmail. On some systems they may be hard links, and in rare cases you may actually find them to be copies. The complete list of other names is shown in Table 36.1.
|Name||Mode of Operation|
|hoststat||Section 36.1.1, "hoststat (V8.8 and Above)"|
Print persistent host status (V8.8 and above)
|mailq||Section 36.1.2, "mailq"|
Print the queue contents
|newaliases||Section 36.1.3, "newaliases"|
Rebuild the aliases file
|purgestat||Section 36.1.4, "purgestat (V8.8 and Above)"|
Purge persistent host status (V8.8 and above)
|smtpd||Section 36.1.5, "smtpd"|
Run in daemon mode
When sendmail looks for the name under which it is running, it strips any leading directory components from argv and compares the result (in a case-sensitive fashion) to its internal list of alternative names. If a match is found, its mode of operation is changed to conform to that of the alternative name. If no match is found (if, say, a link is named Mailq, note the uppercase M), sendmail does not change its mode.
The name that is found is used to build an argument list for use with process listings. For example, if the name was sendmail.mx (from SunOS), a process listing produced with ps(3) would look something like this:
root 1247 620 p0 S 07:22 0:00 -AA15186 (sendmail.mx)
(sendmail.mx) shows that sendmail was run
under the name sendmail.mx.
Note that sendmail uses the hard-coded name "sendmail" for logging purposes with syslog(3) (see Section 26.1.1, "syslog(3)"). Therefore logged errors and warnings always appear to come from sendmail, no matter what name was used to run it.
As a final note, be aware that command-line switches are processed immediately after the name but before sendmail finalizes its mode of operation. Thus the use of particular switches can completely cancel any special meaning given a name.
The hoststat command is a synonym for the
command-line switch. It causes sendmail to print its
persistent host status and exit.
Persistent host status is enabled with the
HostStatusDirectory option (see Section 34.8.31, HostStatusDirectory).
The output produced by this command begins with a heading like this:
------- Hostname -------- How long ago -----Results-----
Then for each host that has its status saved, sendmail prints this information:
This is the name of the host that was connected to. It may not be the hostname specified for the recipient. It could easily be an MX record instead. If a message has multiple recipients, a separate status line will be produced for each unique host that is tried. If this name is prefixed with an asterisk, the status file is locked and currently being updated.
How long ago
This shows how long ago this status record was updated. It is printed in the form:
DD is the number of days. If the status was updated less than
a day ago, the
DD+ is omitted. The
HH is hours, the
is minutes, and the
SS is seconds. The colons are literal.
This shows the result of the last connection attempt, failure, or success. If no reason was stored, this prints as:
No status available
If a result was stored, it will print in three parts:
smtp id msg
smtp is the SMTP reply code.
msg is the text of the message generated by the other end
or other program.
To illustrate, consider this output:
------- Hostname -------- How long ago -----Results----- there.ufoa.edu 00:00:51 250 PAA27153 Message acce *books.ora.com 07:43:39 250 GAA01255 Message acce prog.ammers.com 06:55:08 No status available fbi.dc.gov 03:28:53 Connection refused
Here, the previous connections to there.ufoa.edu and books.ora.com were successful. The status for books.ora.com is currently being updated, hence the asterisk showing it is locked. The host prog.ammers.com shows no status because connection to it could not be made. The last example show that the connection to fbi.dc.gov was refused by that host.
Note that the results are limited to 27 characters unless the
command-line flag is also used. In that case, results are limited
to 79 characters, thus providing more complete information.
The name mailq (a synonym for the
-bp command-line switch)
causes sendmail to print the contents of the
mail queue and then exit (see Section 23.4, "Printing the Queue").
Note that the location of the queue is set with the
Q) option (see Section 34.8.48, QueueDirectory (Q)).
That location can be overridden from the command line, but if it is,
sendmail may give up its root privilege (unless it was
run by root).
The name newaliases (a synonym for the
-bi command-line switch)
causes sendmail to rebuild the
aliases database files, print summary information, and then
immediately exit (see Section 24.5.1, "Rebuild the Alias Database").
In this mode the
-v command-line switch
(see Section 36.7.41, -v)
is automatically implied, and sendmail runs in verbose mode.
The location of the aliases file is given in the configuration
file with the
A) option (see Section 34.8.1, AliasFile (A)).
That location can be overridden
from the command line, but if it is,
sendmail gives up its root privilege (unless
it was run by root).
The name purgestat is a synonym for the V8.8 and above
command-line switch (see Section 36.7.6, -bH).
It causes sendmail to clear (purge) all the host-status information
that was being saved under the
HostStatusDirectory option's directory
(see Section 34.8.31).
Clearing is done by removing all the directories under the
Note that the
HostStatusDirectory directory is not itself removed.
The name smtpd is a synonym for the
switch (see Section 36.7.5, -bd). It causes sendmail to run in the background
as a daemon, listening for incoming SMTP mail (see Section 4.1.1, "Daemon Mode (-bd)").
This mode of operating
is usually combined with the
-q command-line switch
(see Section 23.6.1, "Periodically with -q"), which causes
sendmail to periodically process the queue.