title: /etc/passwd vs /usr/bin/passwd
body: <p>In my CentOS 7 system (and other Linux flavors), I have noticed that there are two passwd files, /etc/passwd and /usr/bin/passwd. The former contains plaintext information about the users, groups, default shells, etc., whereas the latter is a binary (?) file that the "passwd" command invokes (as suggested by "which passwd").</p>
  
  <p>These may be basic questions, but I have tried my luck with manuals and explanations on forums, albeit not fully clarifying my mental picture:</p>
  
  <p>1) What is the purpose of each file, and why do we have both?
  2) Are the two files related -- is the /usr/bin/passwd a binary version of the /etc/passwd that is constantly updated, for efficiency purposes?
  3) What are the appropriate permissions on these files (I am getting a "passwd: Authentication token manipulation error" if I try to change the login password of a non-sudoer user from that user's account, which is what prompted this line of questioning to begin with). </p>
  
  <p>Thanks for reading and I am looking forward to your thoughts!</p>