The
-b switch tells sendmail in
what mode to operate. For example, sendmail can
"become" a daemon listening for
incoming SMTP connections, or it can run in a mode that tells it to
simply print the contents of the queue and exit. The form of the
-b switch is:
-bmode
If mode is more than a single letter, all
but the first letter is silently ignored. If the
mode is missing or not one of those
allowed, sendmail prints the following error
message and exits:
Invalid operation mode bad letter here
If the -b command-line switch is omitted
altogether, the default mode becomes -bm (deliver
mail and exit).
Beginning with V8.7 sendmail, the letter that
selected the operating mode is assigned at startup to the
${opMode} sendmail macro
(${opMode}).
