Shared memory is used by sendmail to store the
amount of available disk space of the queue disks and the total
number of messages queued across all queues (Section 11.6.2). For sendmail to do
these two tasks, the binary must have been compiled with shared
memory support (SM_CONF_SHM), and this
SharedMemoryKey option must be declared.
You declare the
SharedMemoryKey option like this:
O SharedMemoryKey=key ← configuration file (V8.12 and later) -OSharedMemoryKey=key ← command line (V8.12 and later) define(`confSHARED_MEMORY_KEY',key)← mc configuration (V8.12 and later)
key is of type
numeric and can be positive, negative, or zero.
A nonnumeric key evaluates to zero. A
of zero causes use of shared memory to be disabled. Otherwise, the
value specified becomes the key used by
If you specify the
SharedMemoryKey option, and
shared memory support was not included in
sendmail, the following error is printed and
Option: SharedMemoryKey requires shared memory support (-DSM_CONF_SHM)
If shared memory is used, only the initial daemon will create and destroy it. If you run multiple initial daemons, you must be careful not to specify the same key for each. For example, two lines in a boot-time rc file might look like this:
/usr/sbin/sendmail -OSharedMemoryKey=1001 -C /etc/mail/fast.cf -q10m /usr/sbin/sendmail -OSharedMemoryKey=1002 -C /etc/mail/slow.cf -q1h
SharedMemoryKey option is not safe. If specified from the command line, it can ...