Version 3.* writes warnings and error messages using the syslog(3) facility. Depending on your system the syslog-daemon writes these messages to files and/or sends them to another host. On most GNU/Linux distributions the place to look at is either /var/log/syslog or /var/log/messages.
Version 4.0 and later comes with the logfile and syslog plugins which can be used to write status messages to a file or send it to the syslog daemon.

Yes, that's a known bug. You probably have one or more white spaces at the end of the lines being ignored.
This is a bug in the library used by collectd 3.* to parse the configfile. Versions 4.0 and later use a different library and don't have this problem.

Yes, since version 3.9.0 this can be set at compiletime. Keep in mind, though, that this will change the layout of the generated RRD-files. Also, clients and servers should have the same setting here to avoid interesting results.
Version 4.0 allows this setting to be adjusted in the configfile.

In order to generate ICMP packets one needs to open a so called "RAW socket". On most UNIX systems only the superuser (root) may open such sockets.
In addition, some virtualization environments, such as VServer and Solaris Zones have been reported to cause some trouble.

I don't know. That entirely depends on your network setup. By default collectd uses "site local" addresses, that should not be routed to outside your AS. If that's really the case is up to you.

Is means that the mode "Local" is not available. Most likely the "librrd" library wasn't found. If you want to write to RRD-files install "librrd" or, if you already did that, use the --with-rrdtool option of the ./configure-script to point to the right direction.

If you installed libraries in a non-standard (or non-system) path you need to specify them when running the configure script. Otherwise it will not find them and build the binaries without linking against the library.
You need to set the PATH as given to the --prefix option when compiling the library. The script actually looks for the two subdirectories PATH/include and PATH/lib, so check for their existence if things don't work. If, for example, you installed RRDTool in /opt/rrdtool-x.y.z you need to run configure like this:

The response received was too big and didn't fit into the buffer. Check the URL-option in the configfile. Especially check that the URL ends in "?auto": collectd requires the machine readable output generated by the Apache-plugin mod_status and will not work with anything else.

The version numbers consist of three numbers: The major- and minor-number and the patchlevel.

• Versions with different major-numbers are basically not compatible. This means that the definitions of RRD-files or config-options have been changed or, in general, that the user has to do something in addition to install the new version. This is not nice and avoided when possible, but sometimes necessary to prevent old mistakes to become ancient mistakes. We try to provide migration scripts, though, to make a switch as easy as possible. See the v3 to v4 migration guide for details.
• Versions with differing minor-numbers are backwards compatible, i. e. you can replace the lower version with the higher one and everything should still work. This means that features are added, but not removed or changed and that the default behavior does not change.
• Versions with different patchlevels are both, forward- and backwards-compatible, because no new features have been introduced. The only difference between the two versions is one or more bugfixes, so you should generally install the higher version of the two.

Since version 4.0.0 a server process doesn't need to load the plugins from which data should be received - in contrast to versions 3.*. This means, that plugins with unmet dependencies no longer have any purpose. So, we moved dependency checking into the configure script, starting with version 4.1.0. I. e. the configure script now automatically disables all plugins with unmet dependencies and enables all plugins whose dependencies are met.
So, if a plugin is displayed as disabled, it's dependencies are not met. The normal way to get a plugin compiled is to install the missing dependencies and re-run the configure script.
You can force it to be build using --enable-foo, but you need to know exactly what you are doing. If you do this you're out in the dark, cold woods and totally on your own!

Many plugins have to be linked against libraries. A few of them (currently iptables, netlink and nut are known to be affected) link against libraries that are only available as "static libraries" in many distributions. Most distributions (e. g. Debian and SuSE GNU/Linux) do not compile static libraries with the "-fPIC" option. Thus they cannot be linked with shared objects compiled with "-fPIC". Some architectures (among them i386) do not seem to care about that and handle it in some (probably magic) way. However, other architectures (mostly 64bit like amd64 or hppa) cannot handle that and thus the compiler aborts with the error message mentioned above.
To fix this issue, you need a version of the static library compiled with "-fPIC" (or a shared library). Ask your distributor to provide a suitable version of the library or compile it yourself.
For more detailed information please refer to:

• the gentoo documentation,
• Debian Bug #358637
• Debian Bug #419684
• Debian Bug #430933

There are two known issues with Solaris, but both can be fixed relatively easy:
If you build a 32bit binary, the configure script will (try to) enable LFS. This will result in an error which looks somehow like this: Also, the swap-plugin has some problems of it's own with this: The solution is to build a 64bit binary! If you build a 64bit binary LFS is not needed and the swap plugin works as intended. To do this, pass the -m64 flag to the compiler (assuming you're using the Sun C compiler.
Another problem is that by default Sun defines a version of getgrnam_r that isn't POSIX-compatible. To enable POSIX-compatibility pass the _POSIX_PTHREAD_SEMANTICS define to the compiler.
Putting all together you need to pass the following flags to the configure-script: Please note that we only test the Sun C compiler ourselves, but GCC may work, too. When using the GCC you need to substitute the -mt flag with the -pthreads flag. So if you use GCC the above invokation of ./configure becomes: Thanks to Christophe Kalt for sharing his insights :)

The short answer is: That is because otherwise backwards compatibility would be impossible and you would have to re-create your files from scratch regularly. And, "no".
The long answer and explanation of the short answer is: collectd runs on a variety of operating systems. Each operating system has it's own method for accounting CPU states, memory consumption, swap usage, and so on. If all these data sources where in one data set, every new supported operating system or any addition to an already supported operating system would mean that we need to modify the data set. This cannot be done without breaking backwards compatibility.
To give you a few examples: Sometime in mid-2.6 the Linux kernel added some Xen-patches which provided a new CPU state: "steal time". When adding support for BSD systems we had to add "wired" memory. NFSv4 added some new procedures that NFSv3 didn't have, etc pp.
That interface traffic has two data sources is different, because every operating system will account received and transmitted bytes. Likewise for the system load: The 1, 5, and 15 minute averages have been like that for ages and it's very unlikely that any weird UNIX does this different.
Changing the layout of the data is not just a matter of changing the types.db file. That file describes the layout of the data submitted by plugins. The plugins don't need it - they know what data they submit. It's needed by the daemon and writing plugin to know how to store the data. If you mess with the file without knowing what you do, you will most likely end up with the data not being collected at all anymore.