Incorrect Configuration

Although misidentification can be a serious problem, one that's just as common is incorrect configuration. Many configuration files have sensitive formats—for some, a misplaced space or comma can spell the difference between a working configuration and one that doesn't work. As a general rule, computer programs are good at getting such details right, but this isn't always the case. Furthermore, some configurations rely on very specific information for particular hardware or software. For instance, you may need to pass particular options to a kernel module to get it to work, but other kernel modules may require different options. Therefore, automatic configuration tools often use databases of configuration options, and if these databases are flawed, the tool may fail.

As an example, consider Samba, which handles the Server Message Block/Common Internet File System (SMB/CIFS) file- and printer-sharing protocol that's common on Windows-dominated networks. Several GUI Samba configuration tools exist, the most flexible of which is the web-based Samba Web Administration Tool (SWAT). SWAT handles most configurations correctly, but it corrupts a specific type of configuration. Samba supports splitting configuration files into parts. The main file then uses an include directive to tell Samba to load referenced files. Unfortunately, SWAT doesn't know what to do with the include directive. Early versions of SWAT ignored that directive. Using such versions of SWAT, if you create a Samba configuration that relies on include and then try to modify that configuration using SWAT, you'll lose all the include references, which may cause subtle or not-so-subtle problems. Later versions of SWAT merge the included file into the main file but leave the include directive intact, which is likely to result in a working configuration; however, if you fail to notice the change, you might make subsequent changes by hand that won't be implemented.

Some incorrect configurations are fairly small. These can be easy to fix—if you know where to look and how to fix the problem. Other tools tend to make a real mess of things, and such problems can be tedious to correct.

Tip Once your system is working fairly well, back up the entire /etc directory tree, ideally to a removable disk. If an automatic configuration tool mangles a configuration file, you should then be able to restore the original relatively easily.

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