Sendmail, 3rd Edition

Name

XDEBUG

Synopsis

In past releases of sendmail, changes in file descriptors and other key variables have sometimes occurred for reasons that remain a mystery to this day. Small “sanity checks” have been included in the code to discover such anomalies, should they happen again. To exclude these checks, redefine XDEBUG to 0:

APPENDDEF(`confENVDEF', `-DXDEBUG=0')

Generally, however, XDEBUG should always remain enabled. It adds only a microscopic amount of overhead to sendmail and helps to certify sendmail’s rational behavior.

If sendmail’s notion of who it is (as defined by the $j defined-macro, $j) gets trashed by losing all its dots, sendmail will log the following at LOG_ALERT if XDEBUG is defined, dump its state (SIGUSR1), and abort(3):

daemon process $j lost dot; see syslog

At startup the value in the $j defined-macro ($j) is added to the class w ($=w). If sendmail is compiled with XDEBUG, it periodically checks to make sure that $j is still listed in class w. If $j should vanish, sendmail will log the following at LOG_ALERT, dump its state (SIGUSR1), and abort(3):

daemon process doesn't have $j in $=w; see syslog

With XDEBUG defined, sendmail periodically checks to see whether its standard I/O file descriptors have gotten clobbered. If so, it logs the following and tries to recover by connecting it to /dev/null:

where: fd  which  not open

Here, where will reflect the internal subroutine name and arguments that led to the check, and which will be the bad file descriptor number.

If ...