A symbolic link is a connection between one file name in a file system and another (the 'target'; which does not necessarily need to exist at the time the symbolic link is created), such that references to the first name wind up at the second.
They differ from hard links in that if the target file is deleted, and replaced with a different file, references to the symbolic link will go to the new file.
- ITS Reference Manual 1.5 from 1969 mentions links. 1.4 from 1968 doesn't.
- The Multics paper "A General-Purpose File System For Secondary Storage" from 1965 describes symbolic links.
- CTSS supposedly had links.
- Charles Frankston wrote in 1984: "Until recently symbolic file system links seemed to be an MIT secret, being found only in Multics and two homegrown MIT systems: ITS for the PDP-10 and MagicSix for Interdata/Perkin-Elmer 32 bit machines. However, symbolic links have been added to release 4.2 of Berkeley Unix."