October 2007
Intermediate to advanced
1308 pages
161h 13m
English
Content preview from sendmail, 4th EditionBecome an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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Pitfalls
Each release of sendmail offers more and better ways to handle queue problems. They are mostly implemented as options. Table 24-7 on page 966 lists all options that affect the queue. Whenever you upgrade to a new sendmail release, be sure to read the RELEASE_NOTES for information about new ways to solve queueing problems.
The queue directory should never be shared among machines. Such sharing can make detection of orphaned locks impossible. Bugs in network-locking daemons can lead to race conditions in which neither of two machines can generate a queue identifier.
Homespun programs and shell scripts for delivery of local mail can fail and lose mail by exiting with the wrong value. In the case of a recoverable error (a full disk, for example), they should exit with EX_OSERR or EX_TEMPFAIL. Both of these exit values are defined in <sysexits.h> and cause the message to be re-queued.
Because sendmail does a chdir(2) into its queue directory, you should avoid removing and re-creating that directory while the sendmail daemon is running. When processing the queue, sendmail tries to read the queue directory by doing an opendir(3) of the current directory. When the queue directory is removed, sendmail fails that open and syslog(3)s the following warning:
orderq: cannot open "/usr/spool/mqueue" as ".": No such file or directory
Some very old versions of sendmail had a bug in handling the queue that could cause a message to be lost when that message was the last in a queue run to be processed. ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.