A fifodir is a rendez-vous point between the notifier of certain events and its listeners. It is implemented via a directory in the filesystem. No data is stored; it is appropriate to create fifodirs in a RAM filesystem.

Manipulating fifodirs


For the notifier

For a listener

Unix API

For the notifier

For a listener

Internals and Unix permissions

Note that in the s6 implementation of fifodirs, there are a few additional details: for instance, the named pipes created in a fifodir by a listener follow a strict naming convention, for efficiency and safety reasons. If you are using fifodirs, it is recommended that you use the provided C library functions or the s6-ftrig-* command line utilities instead of directly hacking into the fifodir internals.

Fifodirs are created by their notifier, so they always originally inherit its uid and gid. A notifier must be able to make his fifodir either publicly accessible (anyone can subscribe) or restricted (only a given group can subscribe).

A publicly accessible fifodir must have rights 1733:

A restricted fifodir must have the gid g of the group of allowed listeners and have rights 3730. Unless the notifier is root, it must be in the group of allowed listeners to be able to create such a fifodir.

A named pipe in a fifodir must always belong to its listener and have rights 0622:

The libftrig interface takes care of all the subtleties.