why httpd reports less active modules than apachectl?

Question

I am trying to enable mod-nss module in Apache2. So after doing what is necessary, I am trying to validate that indeed the module is loaded.

Asking apachectl

# apachectl -M | grep nss
 nss_module (shared)

Asking the daemon itself:

/usr/sbin/httpd-prefork -M | grep nss
-> No output

So, I get two different outputs:

apachectl claims that the mod_nss module is loaded.
httpd claims that the mod_nss module is not loaded.

After this, I decided to list the modules for both (instead of just grep-ing for a specific one), sort the output and then compare them.

# diff -Nur httpd_sorted_modules apachectl_sorted_modules 
--- httpd_sorted_modules        2016-09-01 13:59:16.297139860 +0200
+++ apachectl_sorted_modules    2016-09-01 13:59:26.680985223 +0200
@@ -15,11 +15,15 @@
  expires_module (shared)
  http_module (static)
  include_module (shared)
+ info_module (shared)
  log_config_module (shared)
  mime_module (shared)
  mpm_prefork_module (static)
  negotiation_module (shared)
+ nss_module (shared)
+ php5_module (shared)
  reqtimeout_module (shared)
+ rewrite_module (shared)
  setenvif_module (shared)
  so_module (static)
  socache_shmcb_module (shared)

As you can see, apachectl shows 4 extra modules in contrast to httpd. Why is that happening? And which one should I put my trust on?

I tried to see what's the difference between those, but I failed. Here's some of my findings:

apachectl seems to be a standalone binary

# ls -l `which apachectl`
-rwxr-xr-x 1 root root 3548 Aug 23 13:11 /usr/sbin/apachectl

that comes from apache pkg:

# rpm -qf `which apachectl`
apache2-2.4.16-12.1.x86_64

which is actually used to ease the control around httpd. Apparently, there is difference in using it with SystemD or SySVinit. Here's a quote from the man apachectl page:

When acting in pass-through mode, apachectl can take all the arguments available for the httpd binary.
   apachectl [ httpd-argument ]
When acting in SysV init mode, apachectl takes simple, one-word commands, defined below.
   apachectl command

So, if I request for the -h help option:

 # apachectl -h
Usage: /usr/sbin/httpd-prefork [-D name] [-d directory] [-f file]
                               [-C "directive"] [-c "directive"]
                               [-k start|restart|graceful|graceful-stop|stop]
                               [-v] [-V] [-h] [-l] [-L] [-t] [-T] [-S] [-X]
Options:
  -D name            : define a name for use in <IfDefine name> directives
  -d directory       : specify an alternate initial ServerRoot
  -f file            : specify an alternate ServerConfigFile
  -C "directive"     : process directive before reading config files
  -c "directive"     : process directive after reading config files
  -e level           : show startup errors of level (see LogLevel)
  -E file            : log startup errors to file
  -v                 : show version number
  -V                 : show compile settings
  -h                 : list available command line options (this page)
  -l                 : list compiled in modules
  -L                 : list available configuration directives
  -t -D DUMP_VHOSTS  : show parsed vhost settings
  -t -D DUMP_RUN_CFG : show parsed run settings
  -S                 : a synonym for -t -D DUMP_VHOSTS -D DUMP_RUN_CFG
  -t -D DUMP_MODULES : show all loaded modules 
  -M                 : a synonym for -t -D DUMP_MODULES
  -t                 : run syntax check for config files
  -T                 : start without DocumentRoot(s) check
  -X                 : debug mode (only one worker, do not detach)

So it seems that it's using the /usr/sbin/httpd-prefork or at least that what it says.

But let's try to see what 'httpd' is using in the background:

# which httpd
/usr/sbin/httpd

which seems to be a symlink:

# ls -l `which httpd`
lrwxrwxrwx 1 root root 23 Aug 25 13:28 /usr/sbin/httpd -> /usr/sbin/httpd-prefork

so it uses the /usr/sbin/httpd-prefork which is the same one with what apachectl seems to use. For example if I request for -h help, I get:

# /usr/sbin/httpd-prefork -h
Usage: /usr/sbin/httpd-prefork [-D name] [-d directory] [-f file]
                               [-C "directive"] [-c "directive"]
                               [-k start|restart|graceful|graceful-stop|stop]
                               [-v] [-V] [-h] [-l] [-L] [-t] [-T] [-S] [-X]
Options:
  -D name            : define a name for use in <IfDefine name> directives
  -d directory       : specify an alternate initial ServerRoot
  -f file            : specify an alternate ServerConfigFile
  -C "directive"     : process directive before reading config files
  -c "directive"     : process directive after reading config files
  -e level           : show startup errors of level (see LogLevel)
  -E file            : log startup errors to file
  -v                 : show version number
  -V                 : show compile settings
  -h                 : list available command line options (this page)
  -l                 : list compiled in modules
  -L                 : list available configuration directives
  -t -D DUMP_VHOSTS  : show parsed vhost settings
  -t -D DUMP_RUN_CFG : show parsed run settings
  -S                 : a synonym for -t -D DUMP_VHOSTS -D DUMP_RUN_CFG
  -t -D DUMP_MODULES : show all loaded modules 
  -M                 : a synonym for -t -D DUMP_MODULES
  -t                 : run syntax check for config files
  -T                 : start without DocumentRoot(s) check
  -X                 : debug mode (only one worker, do not detach)

which is identical to what I get with apachectl -h.

However, this one comes from another package:

# rpm -qf /usr/sbin/httpd-prefork
apache2-prefork-2.4.16-12.1.x86_64

Apart from that, I cannot think of a reason why I get different output when I query for the loaded modules :/

For those who would like to know, I am using OpenSUSE Leap 42.1 as my Linux distribution, and I run Apache with Prefork MPM.

score 0 · Answer 1 · answered Sep 02 '16 at 21:39

Given your listing:

# ls -l `which apachectl`
-rwxr-xr-x 1 root root 3548 Aug 23 13:11 /usr/sbin/apachectl

it is unlikely that your apachectl is a "standalone binary" (it is far too small: a plausible binary would be 10-20 times larger). In fact, it is a shell script. When you execute

apachectl -M

the shell script first obtains additional parameters from its configuration files, and puts those before the -M when executing the httpd binary.

For the purpose of discussion, I'll refer to the git mirror of Apache, and the template script apachectl.in. Different releases of Apache differ of course, but one thing common to the variations of apachectl is that the script checks for configuration settings which can include the location of your server's modules. In the current version of the template, that's just below a comment

# pick up any necessary environment variables

If you run httpd-prefork directly without setting those variables, it will not work properly. That explains why it reported that the module was not loaded. You might get a more informative report if you did not grep the output, e.g., there might be no listing at all.

why httpd reports less active modules than apachectl?

1 Answers1