출처:
http://www.linuxdoc.org/LDP/lasg/servers/shell/index.html  <p>For an ISP that wishes to allow customers to change their
password easily, but not allow them access to the system (my ISP
uses Ultrasparcs and refuses to give out user accounts for some
reason, I wonder why).</p>
<p>사용자가 쉽게 암호를 바꿀 수 있도록 하고 싶지만,
시스템에 접근할 수는 없도록 하고 싶은 경우.</p>
 <p>in /etc/shells list:</p>
<p>/etc/shells 목록에 다음을 넣고</p>
 <pre>/usr/bin/passwd</pre>
 <p>and set the users shell to /usr/bin/passwd so you end&nbsp;up
with something like:</p>
<p>사용자 쉘로 /usr/bin/passwd를 지정한다. 다음과 같다.</p>
 <pre>username:x:1000:1000::/home/username:/usr/bin/passwd</pre>
 <p>and voila. The user telnets to the server, is prompted for
their username and password, and is&nbsp;<br>
then prompted to change their password. If they do so
successfully passwd then exits and they are disconnected. If they
are unsuccessful passwd exits and they are disconnected. The
following is a transcript of such a setup when a user telnets in:</p>
<p>사용자가 서버에 텔넷을 걸면, 사용자명과 암호를 묻고서,
암호를 바꾸도록 기다릴 것이다. 암호를 바꾸거나 그냥 나오면
접속이 끝난다. 다음 내용은 예시이다.</p>
 <pre>Trying 1.2.3.4&#133;
Connected to localhost.
Escape character is '^]'.
 Red Hat Linux release 5.2 (Apollo)
Kernel 2.2.5 on an i586
login: tester
Password:&nbsp;
Changing password for tester
(current) UNIX password:&nbsp;
New UNIX password:&nbsp;
Retype new UNIX password:&nbsp;
passwd: all authentication tokens updated successfully
Connection closed by foreign host.</pre>
 <p>---</p>
 <p>글쎄요.. FTP에서 valid shell을 요구할 경우가 어떻게 될런지 모르겠습니
다. 아마 될 듯하지만요.</p>
 <p>메일이나 FTP를 제공하고 싶지만 텔넷은 막고 싶은 경우 이런 것도 좋겠지
요.</p>
 --
from [ke'izi] : where is [r]?