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[/tmp/]$ cd sb # `pwd' says we are now in /tmp/ # let's change to /tmp/a/b/ [/tmp/sb/]$ cd ../ # Now we are in /tmp/a/b/ # But what is /tmp/a/b/'s parent dir? [/tmp/]$ # See? We didn't come back to /tmp/a/ BUT /tmp/ 

It means that the current parent dir is the second from the right printed by pwd.

Let's add a symlink into dir /tmp/a/b/:

/tmp/ |__a/ | |__b/ | |__sa=../ -> /tmp/a/ # [/tmp/a/b/]$ ln -s ../ sa | |__sb=./a/b/ -> /tmp/a/b/ 

This time, we will come back to the actual parent dir of /tmp/a/b/.

[/tmp/]$ cd sb # change to /tmp/a/b/ [/tmp/sb/]$ cd sa # sa=../ # /tmp/sb/=/tmp/a/b/ # ^ or ^ [/tmp/sb/sa/]$ ls --classify b/ # ??? # We are now in /tmp/a/ because there is a b/ here! 

So Why this time it chooses to refer to the absolute path to determine the parent dir?

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[/tmp/]$ cd sb # `pwd' says we are now in /tmp/ # let's change to /tmp/a/b/ [/tmp/sb/]$ cd ../ # Now we are in /tmp/a/b/ # But what is /tmp/a/b/'s parent dir? [/tmp/]$ # See? We didn't come back to /tmp/a/ BUT /tmp/ 

It means that the current parent dir is the second from the right printed by pwd.

Let's add a symlink into dir /tmp/a/b/:

/tmp/ |__a/ | |__b/ | |__sa=../ -> /tmp/a/ # [/tmp/a/b/]$ ln -s ../ sa | |__sb=./a/b/ -> /tmp/a/b/ 

This time, we will come back to the actual parent dir of /tmp/a/b/:

[/tmp/]$ cd sb # change to /tmp/a/b/ [/tmp/sb/]$ cd sa # sa=../ # /tmp/sb/=/tmp/a/b/ # ^ or ^ [/tmp/sb/sa/]$ ls --classify b/ # ??? # We are now in /tmp/a/ because there is a b/ here! 

So Why this time it chooses to refer to the absolute path to determine the parent dir?