Name
${load_avg}
Synopsis
The ${load_avg}
macro contains as its value the
current one-minute load average of the machine on which
sendmail is running. That value is a rounded
integer representation of a possible floating-point value.
One use
for this ${load_avg}
sendmail
macro might be to reject SMTP ETRN commands when the load average it
too high:
LOCAL_CONFIG D{OurETRNlimit}5 Karith math LOCAL_RULESETS Scheck_etrn R $* $: $(math l $@ $&{load_avg} $@ ${OurETRNlimit} $) R FALSE $# error $@ 4.7.1 $: "450 The load average is currently too high."
Here, we add two new sections to our mc
configuration file. The first, under LOCAL_CONFIG, defines a
sendmail macro,
${OurETRNlimit}
, that will hold as its value the
limit we have set to reject ERTN commands. In this
mc section we also defined a database map of
type arith
(arith).
In the second section, following the LOCAL_RULESETS, we declare the
check_etrn
rule set (check_etrn). That rule set is called from inside
sendmail (just after an SMTP ETRN command is
received, but before the reply to that command is sent) and can
determine if the SMTP ETRN command should be allowed. If the rule set
returns the $#error
delivery agent, the SMTP ETRN
command is denied. Otherwise, it is allowed.
The first rule matches anything in the LHS, then ignores that value
in the RHS. The RHS looks up the current ($&
)
value of the ${load_avg}
macro, then uses the
math
database map to compare that value to the
limit set in our ${OurETRNlimit}
macro. If the load average ...
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