Purpose unclear of unknown file /etc/apache2/apache2.conf.in

[thermoman]

I just upgraded apache2:amd64 2.4.18-2ubuntu3.15 --> 2.4.18-2ubuntu3.17 and now there is a file

  /etc/apache2/apache2.conf.in

with the following difference to apache2.conf:

% diff -u /etc/apache2/apache2.conf /etc/apache2/apache2.conf.in
--- /etc/apache2/apache2.conf 2020-08-13 03:35:57.000000000 +0200
+++ /etc/apache2/apache2.conf.in 2020-07-21 05:13:31.000000000 +0200
@@ -71,7 +71,7 @@
 #
 # The accept serialization lock file MUST BE STORED ON A LOCAL DISK.
 #
-#Mutex file:${APACHE_LOCK_DIR} default
+___MUTEX___Mutex file:${APACHE_LOCK_DIR} default

 #
 # PidFile: The file in which the server should record its process

apache2.conf.in is part of the .deb file, see

  https://packages.ubuntu.com/xenial-updates/amd64/apache2/filelist

apache2.conf.in is not mentioned in any config file in /etc/apache2,
not in the init.d script or systemd service file nor in the changelog.

What's the purpose of that file?

From the diff above it doesn't even look like a valid apache2 config file
because of the "___MUTEX___" prefix.

Is this some kind of leftover from a search/replace operation?

[Sergio Durigan Junior (sergiodj)]

Thanks for your report and for making Ubuntu better.

I can confirm this bug. The .in file was added as of:

apache2 (2.4.18-2ubuntu3.16) xenial; urgency=medium

  * On Linux, use pthread mutexes. On kfreebsd/hurd, continue using
    fctnl because they lack robust pthread mutexes.
    (LP: #1565744)

 -- Bryce Harrington <email address hidden> Thu, 16 Jul 2020 00:20:55 +0000

but you're correct in saying that the changelog entry does not mention the file. You are also correct in your guess: the file is a leftover of a search-and-replace operation; it should have probably been removed after the replace took place.

Even though the .in file is harmless (Apache will not try to load it in any way), it should not have been installed. I am marking this bug as Triaged and will contact Bryce to sync.

Thanks!

[Bryce Harrington (bryce)]

Yeah I remember this, thanks for raising it I'll take a look when I get a chance.