The Cfg plugin provides a repository to describe configuration file contents for clients. In its simplest form, the Cfg repository is just a directory tree modeled off of the directory tree on your client machines.

The Cfg Repository

The Cfg plugin is enabled by including Cfg on the plugins line of the [server] section of your Bcfg2 server config file. The repository itself lives in /var/lib/bcfg2/Cfg, assuming you are using the default repository location of /var/lib/bcfg2. The contents of this directory are a series of directories corresponding to the real-life locations of the files on your clients, starting at the root level. For example:

lueningh@tg-prez:~/bcfg2/repository> ls Cfg
bin/  boot/  etc/  opt/  root/  usr/  var/

Specific config files go in like-named directories in this heirarchy. For example the password file, /etc/passwd, goes in Cfg/etc/passwd/passwd, while the ssh pam module config file, /etc/pam.d/sshd, goes in Cfg/etc/pam.d/sshd/sshd. The reason for the like-name directory is to allow multiple versions of each file to exist, as described below. Note that these files are exact copies of what will appear on the client machine - no templates, XML wrappers, etc.

Group-Specific Files

It is often that you want one version of a config file for all of your machines except those in a particular group. For example, /etc/fstab should look alike on all of your desktop machines, but should be different on your file servers. Bcfg2 can handle this case through use of group-specific files.

As mentioned above, all Cfg entries live in like-named directories at the end of their directory tree. In the case of fstab, the file at Cfg/etc/fstab/fstab will be handed out by default to any client that asks for a copy of /etc/fstab. Group-specific files are located in the same directory and are named with the syntax:


in which NN is a priority number where 00 is lowest and 99 is highest, and groupname is the name of a group defined in Metadata/groups.xml. Back to our fstab example, we might have a Cfg/etc/fstab/ directory that looks like:


By default, clients will receive the plain fstab file when they request /etc/fstab. Any machine that is in the server group, however, will instead receive the fstab.G50_server file. Finally, any machine that is in the fileserver group will receive the fstab.G99_fileserver file, even if they are also in the server group.

Host-Specific Files

Similar to the case with group-specific files, there are cases where a specific machine should have a different version of a file than all others. This can be accomplished with host-specific files. The format of a host-specific file name is:


Host-specific files have a higher priority than group specific files. Again, the fstab example:


In this case, will always get the host-specific version, even if it is part of the server or fileserver (or both) classes.


If you have the ability to choose between using a group-specific and a host-specific file, it is almost always best to use a group-specific one. That way if a hostname changes or an extra copy of a particular client is built, it will get the same changes as the original.


Bcfg2 has finer grained control over how to deliver configuration files to a host. Let’s say we have a Group named file-server. Members of this group need the exact same /etc/motd as all other hosts except they need one line added. We could copy motd to motd.G01_file-server, add the one line to the Group specific version and be done with it, but we’re duplicating data in both files. What happens if we need to update the motd? We’ll need to remember to update both files then. Here’s where deltas come in. A delta is a small change to the base file. There are two types of deltas: cats and diffs. The cat delta simply adds or removes lines from the base file. The diff delta is more powerful since it can take a unified diff and apply it to the base configuration file to create the specialized file. Diff deltas should be used very sparingly.

Cat Files

Continuing our example for cat files, we would first create a file named The .cat suffix designates that the file is a diff. We would then edit that file and add the following line:

+This is a file server

The + at the begining of the file tells Bcfg2 that the line should be appended to end of the file. You can also start a line with - to tell Bcfg2 to remove that exact line wherever it might be in the file. How do we know what base file Bcfg2 will choose to use to apply a delta? The same rules apply as before: Bcfg2 will choose the highest priority, most specific file as the base and then apply deltas in the order of most specific and then increasing in priority. What does this mean in real life. Let’s say our machine is a web server, mail server, and file server and we have the following configuration files:


If our machine isn’t then here’s what would happen:

Bcfg2 would choose motd.G01_web-server as the base file. It is the most specific base file for this host. Bcfg2 would apply the delta to the motd.G01_web-server base file. It is the least specific delta. Bcfg2 would then apply the delta to the result of the delta before it. If our machine is then here’s what would happen:

Bcfg2 would choose motd.G01_web-server as the base file. It is the most specific base file for this host. Bcfg2 would apply the delta to the motd.G01_web-server base file. The reason the other deltas aren’t applied to is because a .H_ delta is more specific than a .G##_ delta. Bcfg2 applies all the deltas at the most specific level.

File permissions

File permissions for entries handled by Cfg are controlled via the use of Info files. Note that you cannot use both a Permissions entry and a Path entry to handle the same file.

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