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GNU cfengine

4.6.2 Unique filesystem mountpoints

The first step towards treating NFS filesystems as network resources is to invent a naming scheme so that every filesystem has a unique name on which it can be mounted. If we don't sort this out now, we could find two or more hosts with a filesystem called /usr/local, both of which we might like to mount since they contain different software.

A simple but extremely useful naming scheme is the following. (2) If you don't like this scheme you can invent your own, but the remainder of the text will encourage you to use this one. If you follow this scheme, exactly as described here, you will never have any problems with mount points. We shall describe the scheme in detail below. Here are some points to digest:

• When mounting a remote filesystem on your local system, the local and remote directories should always have exactly the same name.

• The name of every filesystem mountpoint should be unique and tell you something meaningful about where it is located and what its function is.

• You can always make links from special unique names to more general names like `/usr/local'. If you this involves compiled software and you do this on one host, you should do it on others which are of the same type.

• It doesn't matter whether software compiles in the path names of special directories into software as long as you follow the points above.

Each filesystem is given a directory name composed of three parts:

/site/host/contents

The first directory (which only exists to create a suitable mountpoint) is the name of your local site. If you are a physics department at a university (with a separate setup) you could call this `physics'. It could be your company name or whatever. The second piece is the name of the host to which the disk space is physically attached. The final piece is the name of the filesystem. Here are some typical examples:

/physics/einstein/local # /usr/local for einstein@physics /physics/newton/u1 # user partition 1 for newton@physics

On the machines which are home to the `local' partition, it is better to make a link to /usr/local than call the filesystem /usr/local directly. This is because it makes the procedure of organizing the entire network much clearer.

It is worth noting that, when you ask cfagent to mount such a resource, it will automatically make the mount directory and can easily be asked to make a link to /usr/local, so this small amount of extra work is really no work at all.

The whole naming convention is compactly summarized by defining a mount point variable, mountpattern. With the present scheme, this can be defined as

mountpattern = ( /$(site)/$(host) )

so that it evaluates to the name of the host executing the file regardless of who that may be. This variable is used together with the homepattern pattern variable, which is used to distinguish between home directories and binary resources. (See homepattern in the reference section). You can think of this as being part of the naming convention. In this text, we use the convention u1 u2 u3... for home disks. You could equally well use home1 home2... etc. As long as the name is unique, it doesn't matter.

The full list of named resources should now be listed in the mountables list, which is simply a list of all the resources available for mounting on the network.