mkfifo makes a FIFO special file with name pathname. mode specifies the FIFO's permissions. It is modified by the process's umask in the usual way: the permissions of the created file are (mode .
A FIFO special file is similar to a pipe, except that it is created in a different way. Instead of being an anonymous communications channel, a FIFO special file is entered into the file system by calling mkfifo.
One of the directories in pathname did not allow search (execute) permission.
pathname already exists.
Either the total length of pathname is greater than PATH_MAX, or an individual file name component has a length greater than NAME_MAX. In the GNU system, there is no imposed limit on overall file name length, but some file systems may place limits on the length of a component.
A directory component in pathname does not exist or is a dangling symbolic link.
The directory or filesystem has no room for the new file.
A component used as a directory in pathname is not, in fact, a directory.