Question regarding FLOCK or POSIX with Sendmail 8.13.x and MailScanner.

Scott Silva ssilva at
Wed Nov 1 22:25:53 GMT 2006

Duncan, Brian M. spake the following on 11/1/2006 11:40 AM:
> I never was aware of people have some issues back in August with flock
> and posix with sendmail 8.13.x and MailScanner.
> I have looked through the archives regarding this issue, after seeing
> mention of it in a recent posting.  I have found people telling others
> to change it to Posix for fixing problem X. I have found at least 1 post
> where a person says we have no issues, but is told turn it to Posix or
> you will.
> We run Linux, we use Sendmail 8.13.x on 3 servers and MailScanner +
> SpamAssasin etc..  We dot NOT have anything specified in the
> Mailscanner.conf file regarding lock type.
> Based on the comments in the Mailscanner.conf it says it will default to
> using POSIX on Sendmail. (but says to change it to Posix if running
> 8.13.x  Does that mean it ONLY auto detects and works properly with
> Sendmail 8.12.x and below?  Because mine is defaulting to supposedly
> using flock.
> When I look in the maillog logs, it says it is using flock.
> When I run the command: sendmail -d0.1 -d0.4 -bt </dev/null
> I DO NOT see flock in the compiled with field on ANY of my servers.
> I have not had any issues that I am aware of with any of my servers.  We
> have been using 8.13.x for awhile now, I would guess that
> My primary server has probably passed close to 200 million messages with
> flock on.  The other 2 servers 5-10% percent of that.
> So I am hesitant to switch my settings to POSIX. 
> Are there any risks to Switching to Posix if I am not having any issues
> with FLOCK?
> Thanks for any info.

Posix is a "safer" method of locking, so you shouldn't have problems
switching. There are risks of NOT switching to posix. There have been symptoms
as benign as mail delivered more than once, to unmatched qf/df files being
left behind. You have been lucky what you have not had any problem with flock,
and you should not depend on MailScanner detecting the proper setting.  In the
current versions of MailScanner.conf you have the following comment;

# How to lock spool files.
# Don't set this unless you *know* you need to.
# For sendmail, it defaults to "posix".
# For sendmail 8.12 and older, you will probably need to change it to flock,
# particularly on Linux systems.
# For Exim, it defaults to "posix".
# No other type is implemented.
Lock Type =

It does not mention any type of auto detection, I believe because Julian had
too many problems with its function. Change it to posix with sendmail 8.13.
MailScanner --lint will tell you what is currently running.


MailScanner is like deodorant...
You hope everybody uses it, and
you notice quickly if they don't!!!!

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