mjhjmtu

I am learning linux file system from Centos and noticed that:

[root@iz2ze9wve43n2nyuvmsfx5z ~]# ls /
bin dev home lib64 media opt root sbin sys usr
boot etc lib lost+found mnt proc run srv tmp var

and the /usr

[root@iz2ze9wve43n2nyuvmsfx5z ~]# ls /usr
bin etc games include lib lib64 libexec local sbin share src tmp

only one of them is a linked

[root@iz2ze9wve43n2nyuvmsfx5z ~]# ls -l /usr
total 120
dr-xr-xr-x. 2 root root 32768 Sep 18 22:44 bin
drwxr-xr-x. 2 root root 4096 Apr 11 2018 etc
drwxr-xr-x. 2 root root 4096 Apr 11 2018 games
drwxr-xr-x. 51 root root 4096 Jul 4 11:27 include
dr-xr-xr-x. 30 root root 4096 Apr 11 2018 lib
dr-xr-xr-x. 43 root root 36864 Aug 10 16:31 lib64
drwxr-xr-x. 24 root root 4096 Aug 10 13:53 libexec
drwxr-xr-x. 15 root root 4096 Aug 19 02:38 local
dr-xr-xr-x. 2 root root 12288 Sep 6 12:28 sbin
drwxr-xr-x. 96 root root 4096 Aug 10 16:33 share
drwxr-xr-x. 4 root root 4096 Apr 11 2018 src
lrwxrwxrwx 1 root root 10 Jun 15 22:08 tmp -> ../var/tmp

Why they are identical to one another? Is it the rare case on Centos?

On a CentOS 7 system, /bin, /lib, /lib64, and /sbin are normally symbolic links to their corresponding directories in /usr. You can see this by looking at the output of ls -l /.

The /etc and /usr/etc directories are distinctly separate. In my experience, most programs check /etc for their configurations but likely can be configured to use /usr/etc if you really wanted to.