Editing GNU Hurd (section)

=== Unix extensions ===
{{Unreferenced section|date=March 2007}}

A number of traditional Unix concepts are replaced or extended in the Hurd.

Under Unix, every running program has an associated [[user id]], which normally corresponds to the user that started the [[process (computing)|process]]. This id largely dictates the actions permitted to the program. No outside process can change the user id of a running program. A Hurd process, on the other hand, runs under a ''set'' of user ids, which can contain multiple ids, one, or none. A sufficiently privileged process can add and remove ids to another process. For example, there is a password server that will hand out ids in return for a correct login password.

Regarding the [[file system]], a suitable program can be designated as a ''translator'' for a single file or a whole directory hierarchy. Every access to the translated file, or files below a hierarchy in the second case, is in fact handled by the program. For example, a file translator may simply redirect read and write operations to another file, like a Unix [[symbolic link]]. The effect of Unix ''[[mount (computing)|mounting]]'' is achieved by setting up a filesystem translator (using the "settrans" command). Translators can also be used to provide services to the user. For example, the [[ftpfs]] translator allows a user to encapsulate remote FTP sites within a directory. Then, standard tools such as [[ls]], [[cp (Unix)|cp]], and [[rm (Unix)|rm]] can be used to manipulate files on the remote system. Even more powerful translators are ones such as [[UnionFS]], which allows a user to unify multiple directories into one; thus listing the unified directory reveals the contents of all the directories.

The Hurd requires a [[Multiboot Specification|multiboot]]-compliant [[booting|boot loader]], such as [[GNU GRUB|GRUB]].