Anders Johansson wrote:
On Monday 07 January 2008 16:54:54 Bill Anderson wrote:
I think you need to get on a Unix box, and check out the actual
structure. Linux has never followed this path, and holds to the old Unix
structure. I have been working with Unix since 1978, and have been
through a number of file structure changes.
The point is that symbolic links are used to for backwards compatibility.
As a side light, a number of the utilities that you mention are now
shell built-ins, which take precedence over the equivalent command. For
example, pwd is a built-in that has the -L and -P options for ksh and
bash. The /usr/bin command does not have these options, and exists for
Bourne shell compatibility. You might also note that under Linux it is
/usr/bin/sh, /usr/bin/ksh, and /bin/bash.
It's worth noting that the filesystem is ruled by the Filesystem Hierarchy
Standard, http://www.pathname.com/fhs/pub/fhs-2.3.pdf
According to it, /bin must be functioning when no partitions other than / are
mounted, and thus can't be a symlink
Also, it mandates /bin/sh, even though it might be a symlink to another shell,
in most cases that is /bin/bash
There is also /usr/bin/sh but that is secondary
The same is true for ksh, it is also /bin/ksh as well as /usr/bin/ksh,
although both are symlinks to /lib/ast/bin/ksh, which is fine since /lib is
also mandatory on the / partition
For some unknown reason /bin/csh may be a symlink to /usr/bin/tcsh, so if
you're on a distribution that keeps tcsh in /usr you should perhaps not use
csh as the root shell, in case you have to do any emergency repairs without
filesystems mounted (in SuSE it is in /bin)
Anders
The FHS document applies to Linux, not to Unix. The symbolic link of
/bin to /usr/bin only exits in current Unix file system hierarchies. I
just checked an AIX 5.3 system and a Solaris 10 system, both have this
symbolic link.
Bill Anderson
WW7BA
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