Information Technology Reference
In-Depth Information
The
ifdef()
macro provides a conditional control statement. If
condition
is
true, the
define_if_true
expression is in effect. If not, the
define_if_false
expression is in effect.
The only relevant
condition
for the
/etc/syslog.conf
file is the
LOGHOST
keyword. This keyword is used to determine whether the local system has an
alias of
loghost
in the
/etc/hosts
file. This alias indicates that the associat-
ed host is configured to store local syslog messages and possibly syslog mes-
sages from remote hosts. The following
/etc/hosts
entry shows the
solaris8
system as being identified as
loghost
:
192.168.99.9 solaris9 loghost
The following listing shows a typical example of using an
m4 ifdef
macro in
the action column of the
/etc/syslog.conf
file:
auth.notice ifdef(`LOGHOST', /var/log/authlog, @loghost)
This specifies that for
auth.notice
messages, if the local system is identified
in the
/etc/hosts
file as
loghost
, add the message to the
/var/log/authlog
file. Or if the local system is not identified as the
loghost
, forward it to the
system identified as the
loghost
.
The following listing uses an
m4 ifdef
macro to optionally define entire
/etc/syslog.conf
file entries based on the local system
not
being the
loghost
:
ifdef(`LOGHOST', ,
user.err /dev/sysmsg
user.err /var/adm/messages
user.alert `root, operator'
user.emerg *
)
This specifies that if the local system is defined as
loghost
, do nothing (the
define_if_true
expression is blank). If the local system is not
loghost
,
process the
user.err
(and
user.crit
),
user.alert
, and
user.emerg
messages
locally. Keep in mind that messages at the specified severity level,
as well as
all higher severity levels,
are processed by the
/etc/syslog.conf
entries.
The /etc/syslog.conf File
Entries in the
/etc/syslog.conf
file determine the handling of syslog mes-
sages. The
syslogd
daemon reads the
/etc/syslog.conf
file whenever it is
started, or when it is sent the
SIGHUP(1)
signal. Table 13.4 summarizes the
default syslog message handling (
/etc/syslog.conf
contents) for systems
that log messages locally. The previously described
m4
macro for
user
mes-
sages is also included.
