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In Ubuntu, /bin/sh is a symbolic link that points to /bin/dash.

Has there been a Unix or Unix-like operating system where /bin/sh was an actual shell and not a symbolic link that points to a shell?

In Ubuntu, it was not always a symlink to dash. This occurred with the release of Ubuntu 6.10. An extensive document explaining the rationale for the change can be found here.

From that document:

The major reason to switch the default shell was efficiency. bash is
an excellent full-featured shell appropriate for interactive use;
indeed, it is still the default login shell. However, it is rather
large and slow to start up and operate by comparison with dash. A
large number of shell instances are started as part of the Ubuntu boot
process. Rather than change each of them individually to run
explicitly under /bin/dash, a change which would require significant
ongoing maintenance and which would be liable to regress if not paid
close attention, the Ubuntu core development team felt that it was
best simply to change the default shell. The boot speed improvements
in Ubuntu 6.10 were often incorrectly attributed to Upstart, which is
a fine platform for future development of the init system but in
Ubuntu 6.10 was primarily running in System V compatibility mode with
only small behavioural changes. These improvements were in fact
largely due to the changed /bin/sh.

sh cannot have always been a symbolic link, as symbolic links were only introduced in 4.2 BSD (1977) and the older Sixth Edition of Unix has

$ tar tvzf v6root.tar.gz | grep 5888
-rwxrwxr-x 0 3 3 5888 May 13 1975 ./bin/sh
$ 

You can see BSDs today that do not have /bin/sh as a symbolic link. For examples:

• On OpenBSD it is a hard link to the Korn shell (OpenBSD's variant of pdksh):
  

  $ ls -il /bin/,k,rksh
  26004 -r-xr-xr-x 3 root bin 469976 Feb 26 2016 /bin/ksh
  26004 -r-xr-xr-x 3 root bin 469976 Feb 26 2016 /bin/rksh
  26004 -r-xr-xr-x 3 root bin 469976 Feb 26 2016 /bin/sh
  $

  
  


• On FreeBSD it is a descendant of the Almquist shell:
  

  % ls -il /bin/sh
  561595 -r-xr-xr-x 1 root wheel 143432 Jan 7 2017 /bin/sh
  %