The bug is assigned to F17, but your versions above indicate EL6.

Which do you have?

Additionally, you should have a newer version available regardless.

% bodhi -L munin
dist-6E-epel-testing-candidate  munin-2.0.9-4.el6
      dist-6E-epel-testing  munin-2.0.10-1.el6
              dist-6E-epel  munin-2.0.9-3.el6

     f17-updates-candidate  munin-2.0.9-4.fc17
       f17-updates-testing  munin-2.0.10-1.fc17
               f17-updates  munin-2.0.10-1.fc17

% rpm -q --changelog munin | head
* Wed Jan 09 2013 D. Johnson <fenris02> - 2.0.10-1
- Update to 2.0.10
- BZ# 891940,892377 Only stop/restart services provided by sub-package, not deps.
- BZ# 881689 Fix config file so that it no longer references the build host
- BZ# 877116 Patch using '&' in the URLs instead of '&amp;' in HTMLConfig

* Fri Dec 21 2012 D. Johnson <fenris02> - 2.0.9-4
- Use Makefile.config-dist instead of sed.
- BZ# 890246,890247 "su" directive is not used in epel5/6 logrotate

Update it with:
# su -c 'yum update --enablerepo=updates-testing munin-2.0.10-1.fc17'
as soon as you are able to.

If you have EL6, use "epel-testing" instead of "updates-testing" above.

Sorry, I am running CentOS 6.3 64 bit. The bug is in a package from the EPEL repository. If this is the wrong place to report this bug, could you point me in the right direction? If this is the correct place to report an EPEL package bug, what version should I select in the bug header?

# uname -a
Linux server.example.com 2.6.32-279.19.1.el6.x86_64 #1 SMP Wed Dec 19 07:05:20 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux

# tail /etc/*release*
==> /etc/centos-release <==
CentOS release 6.3 (Final)
==> /etc/redhat-release <==
CentOS release 6.3 (Final)
==> /etc/system-release <==
CentOS release 6.3 (Final)
==> /etc/system-release-cpe <==
cpe:/o:centos:linux:6:GA

For your second question: Oof, I completely forgot to try the packages in epel-testing. As can be seen below, I tried the newer version, and have the same errors.

# yum reinstall --enablerepo=epel-testing munin-node munin-cgi

# rpm -qa | grep munin
munin-common-2.0.10-1.el6.noarch
munin-node-2.0.10-1.el6.noarch
munin-cgi-2.0.10-1.el6.noarch
munin-2.0.10-1.el6.noarch

# yum remove munin-cgi munin-node
Downloading Packages:
Running rpm_check_debug
Running Transaction Test
Transaction Test Succeeded
Running Transaction
Error in PREUN scriptlet in rpm package munin-node
Error in PREUN scriptlet in rpm package munin-cgi
munin-cgi-2.0.10-1.el6.noarch was supposed to be removed but is not!
  Verifying  : munin-cgi-2.0.10-1.el6.noarch   1/2 
munin-node-2.0.10-1.el6.noarch was supposed to be removed but is not!
  Verifying  : munin-node-2.0.10-1.el6.noarch   2/2 
Failed:
  munin-cgi.noarch 0:2.0.10-1.el6   munin-node.noarch 0:2.0.10-1.el6                                                                                     

# rpm --erase munin-cgi munin-node
error reading information on service munin-asyncd: No such file or directory
error reading information on service munin-fcgi-html: No such file or directory
error reading information on service munin-fcgi-graph: No such file or directory
error: %preun(munin-node-2.0.10-1.el6.noarch) scriptlet failed, exit status 1
error reading information on service munin-fcgi-html: No such file or directory
error reading information on service munin-fcgi-graph: No such file or directory
error: %preun(munin-cgi-2.0.10-1.el6.noarch) scriptlet failed, exit status 1

You said:
A workaround is to use "rpm --erase --nopreun munin-cgi munin-node", but I don't know how safe that is.

That will work, as would --noscripts.

Then you can easily install 2.0.10 and it should remove safely and cleanly.  The two bugs that prevent it from removing cleanly are BZ# 891940, and BZ# 892377 (one is fedora, other is epel).  This issue should be resolved in .10

(Corrected EPEL-6 assignment to match)

I tried uninstalling with --nopreun, which succeeded, then installing from epel-testing, then uninstalling normally, but the problem still occurred.
I then tried running a live CD, and installed the 2.0.10 version from epel-testing (first time installing Munin on the live boot), but the problem still occurred during uninstall. I do not think the bug has been fixed in 2.0.10.

On the live CD:

[root@livecd ~]# yum install --enablerepo=epel-testing munin-node munin-cgi
...
Installing:
 munin-cgi   noarch   2.0.10-1.el6   epel-testing   25 k
 munin-node   noarch   2.0.10-1.el6   epel-testing   401 k
...

[root@livecd ~]# rpm -qa | grep munin
munin-cgi-2.0.10-1.el6.noarch
munin-node-2.0.10-1.el6.noarch
munin-2.0.10-1.el6.noarch
munin-common-2.0.10-1.el6.noarch

[root@livecd ~]# yum remove munin-cgi munin-node
Loaded plugins: fastestmirror, refresh-packagekit, security
Setting up Remove Process
Resolving Dependencies
--> Running transaction check
---> Package munin-cgi.noarch 0:2.0.10-1.el6 will be erased
---> Package munin-node.noarch 0:2.0.10-1.el6 will be erased
--> Processing Dependency: perl(Munin::Node::Config) for package: munin-2.0.10-1.el6.noarch
--> Processing Dependency: perl(Munin::Node::ProxySpooler) for package: munin-2.0.10-1.el6.noarch
--> Running transaction check
---> Package munin.noarch 0:2.0.10-1.el6 will be erased
--> Finished Dependency Resolution

Dependencies Resolved

============================================================
 Package   Arch   Version   Repository   Size
============================================================
Removing:
 munin-cgi   noarch   2.0.10-1.el6   @epel-testing   20 k
 munin-node   noarch   2.0.10-1.el6   @epel-testing   1.3 M
Removing for dependencies:
 munin   noarch   2.0.10-1.el6   @epel-testing   515 k

Transaction Summary
============================================================
Remove        3 Package(s)

Installed size: 1.8 M
Is this ok [y/N]: y
Downloading Packages:
Running rpm_check_debug
Running Transaction Test
Transaction Test Succeeded
Running Transaction
Error in PREUN scriptlet in rpm package munin-cgi
  Erasing    : munin-2.0.10-1.el6.noarch1/3 
error reading information on service munin-fcgi-html: No such file or directory
error reading information on service munin-fcgi-graph: No such file or directory
error: %preun(munin-cgi-2.0.10-1.el6.noarch) scriptlet failed, exit status 1
Error in PREUN scriptlet in rpm package munin-node
munin-cgi-2.0.10-1.el6.noarch was supposed to be removed but is not!
  Verifying  : munin-cgi-2.0.10-1.el6.noarch   1/3 
munin-node-2.0.10-1.el6.noarch was supposed to be removed but is not!
  Verifying  : munin-node-2.0.10-1.el6.noarch   2/3 
  Verifying  : munin-2.0.10-1.el6.noarch   3/3 

Dependency Removed:
  munin.noarch 0:2.0.10-1.el6

Failed:
  munin-cgi.noarch 0:2.0.10-1.el6   munin-node.noarch 0:2.0.10-1.el6

Complete!

[root@livecd ~]# rpm --erase munin-cgi munin-node
error reading information on service munin-asyncd: No such file or directory
error reading information on service munin-fcgi-html: No such file or directory
error reading information on service munin-fcgi-graph: No such file or directory
error: %preun(munin-node-2.0.10-1.el6.noarch) scriptlet failed, exit status 1
error reading information on service munin-fcgi-html: No such file or directory
error reading information on service munin-fcgi-graph: No such file or directory
error: %preun(munin-cgi-2.0.10-1.el6.noarch) scriptlet failed, exit status 1

Created attachment 730945 [details]
fix %preun cgi for el6

This seems to be partially fixed in http://pkgs.fedoraproject.org/cgit/munin.git/commit/munin.spec?id=3b63d51e1af1f740db656b7eaa2b7be07cf83905 (2.0.12-2)

However, munin-cgi is still buggy.

[root@test1 ~]# rpm -vve munin-cgi
(snip)
D:     erase: %preun(munin-cgi-2.0.12-2.el6.noarch) scriptlet start
D:     erase: %preun(munin-cgi-2.0.12-2.el6.noarch)	execv(/bin/sh) pid 27124
+ '[' 0 = 0 ']'
+ for svc in fcgi-html fcgi-graph
+ service munin-fcgi-html stop
+ :
+ /sbin/chkconfig --del munin-fcgi-html
error reading information on service munin-fcgi-html: No such file or directory
+ for svc in fcgi-html fcgi-graph
+ service munin-fcgi-graph stop
+ :
+ /sbin/chkconfig --del munin-fcgi-graph
error reading information on service munin-fcgi-graph: No such file or directory
D:     erase: waitpid(27124) rc 27124 status 100 secs 0.057
error: %preun(munin-cgi-2.0.12-2.el6.noarch) scriptlet failed, exit status 1
(snip)

However, no such services are installed (or are necessary, apache autocreates the fcgi munin-cgi-html and munin-cgi-graph processes).

Suggested patch attached.

Good call out, but epel5/6 should likely have initscripts for those to so that it matches newer releases.

The others have:

ExecStart=/usr/bin/spawn-fcgi -s /run/munin/fcgi-graph.sock -U apache -u munin -g munin /var/www/cgi-bin/munin-cgi-graph -P /run/munin/fcgi-graph.pid

ExecStart=/usr/bin/spawn-fcgi -s /run/munin/fcgi-html.sock -U apache -u munin -g munin /var/www/cgi-bin/munin-cgi-html -P /run/munin/fcgi-html.pid

which match the two services in question.

(In reply to comment #6)
> Good call out, but epel5/6 should likely have initscripts for those to so
> that it matches newer releases.
> 
> The others have:
> 
> ExecStart=/usr/bin/spawn-fcgi -s /run/munin/fcgi-graph.sock -U apache -u
> munin -g munin /var/www/cgi-bin/munin-cgi-graph -P /run/munin/fcgi-graph.pid
> 
> ExecStart=/usr/bin/spawn-fcgi -s /run/munin/fcgi-html.sock -U apache -u
> munin -g munin /var/www/cgi-bin/munin-cgi-html -P /run/munin/fcgi-html.pid
> 
> which match the two services in question.

Hmm.

Those services are not needed or used with apache. And since the munin-cgi package seems to deal with apache (package httpd) only, and especially mod_fcgid which only uses dynamic fcgi servers (review the documentation at http://httpd.apache.org/mod_fcgid/mod/mod_fcgid.html), I don't really see the point of them. I would suggest to get rid of them and the spawn-fcgi require. I can make a patch later.

If the package is supposed to support lighttpd and nginx too, then it should not require apache (via mod_fcgid) and maybe at least have documentation on how to get munin working with those servers, and preferably working out-of-the-box configuration - like it is with apache.

Thinking further, the best solution would probably be multiple "cgi" packages, the current for apache (with the above change) and separate cgi packages for lighttpd (which also can use dynamic fcgi processes) and nginx (which requires external processes with spawn-fcgi).

I can provide a patch for a separate lighttpd munin-cgi package later.

Anyway, perhaps these separate packages should be discussed in another bug, and just leave this bug for the immediate preun scriptlet problems?

You realize you do not need munin-cgi just to have zooming graphics right?

Munin-cgi subpackage is purely for running under fcgi. The config file I'm providing does use apache.

(In reply to comment #8)
> You realize you do not need munin-cgi just to have zooming graphics right?

Sure.
 
> Munin-cgi subpackage is purely for running under fcgi. The config file I'm
> providing does use apache.

Please read my previous comment #7 more carefully. Apache does not use the external fcgi processes spawned with spawn-fcgi, they are unnecessary, and should be removed.

Created attachment 731280 [details]
remove unnecessary and unused fcgi service processes from spec file

Here's the patch to remove the fcgi services from the spec file.

Obviously it also fixes the preun scriptlet fails...

Created attachment 738273 [details]
Separate cgi package for nginx

Here's a suggestion for a separate cgi package for nginx, even though it's not really related to this bug (oh and I can still create a separate cgi package for lighttpd if there is interest...). I've tested this on Fedora 18 and el6. 

Obviously this also fixes the uninstall issues.

The patch was included in 2.0.12-4, and munin-nginx 2.0.19-1 should resolve this.