My understanding of UIDs is that is a unique positive integer assigned by a Unix-like operating system to each user. Each user is identified to the system by its UID, and user names are generally used only as an interface for humans.

How can two users have the same UID, isn't this a conflict for my system and packages?

root@kdc:~# id test12

uid=1005(test10) gid=1000(server) groups=1005(test10)

root@kdc:~# id test13

uid=1005(test10) gid=1000(server) groups=1005(test10)

root@kdc:~#

I've added two users with same UID and GID: test12 and test13

The output of /etc/passwd:

client@kdc:~$ cat /etc/passwd | grep test12

test12:x:1005:1000::/home/test12:/bin/sh

client@kdc:~$ cat /etc/passwd | grep test13

test13:x:1005:1000::/home/test13:/bin/sh

I added the users by useradd -ou 1005 -g1000 username.

I got confused what is the purpose of this, and can it affect permissions and user logs etc. So now if a user is added with uid=0 and gid=0 will has privileges like a root account?