Just what it says. Do they have a name besides "those dot thingies"?
2 Answers
They're called directory abbreviations.
. = current directory
.. = parent directory
See this question for a bit more information. Section 2.13 (CTRL-F for 2.13) on this page also covers them.
They're normally called 'dot' and 'dot-dot' in my experience. I don't know that they have a collective name - they're just the entries that hold the hierarchical file system together, and they aren't shown by 'ls(1)
' by default because they're always there (and other names beginning with dot are also not shown).
As John T says, they're meanings are fixed - dot is a name for the current directory, and dot-dot is a name for the parent directory.
If you look at a Unix 7th Edition manual, you'd find that there wasn't a mkdir(2)
system call, but the super-user could use the link(2)
system call to make the dot and dot-dot entries in a directory (and mknod(2)
to make the directory), and the mkdir(1)
program was, consequently, a setuid root program that did the job properly. If misused, you could end up with an incorrectly hierarchical file system - and one of the jobs of the fsck(8)
program was to check for, and if necessary fix, mis-assembled directory hierarchies.