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GNU Info (am-utils.info)Union FilesystemUnion Filesystem (`union') ========================== The "union" (`type:=union') filesystem type allows the contents of several directories to be merged and made visible in a single directory. This can be used to overcome one of the major limitations of the Unix mount mechanism which only allows complete directories to be mounted. For example, supposing `/tmp' and `/var/tmp' were to be merged into a new directory called `/mtmp', with files in `/var/tmp' taking precedence. The following command could be used to achieve this effect: amd ... /mtmp union:/tmp:/var/tmp -type:=union Currently, the unioned directories must _not_ be automounted. That would cause a deadlock. This seriously limits the current usefulness of this filesystem type and the problem will be addressed in a future release of Amd. Files created in the union directory are actually created in the last named directory. This is done by creating a wildcard entry which points to the correct directory. The wildcard entry is visible if the union directory is listed, so allowing you to see which directory has priority. The files visible in the union directory are computed at the time Amd is started, and are not kept up-to-date with respect to the underlying directories. Similarly, if a link is removed, for example with the `rm' command, it will be lost forever. automatically generated by info2www version 1.2.2.9 |