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<TITLE>Developer.com - Online Reference Library - 0672311623:SAMS TEACH YOURSELF LINUX IN 24 HOURS:Basic System Administration</TITLE>

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<!-- ISBN=0672311623 //-->

<!-- TITLE=SAMS TEACH YOURSELF LINUX IN 24 HOURS //-->

<!-- AUTHOR=BILL BALL, STEPHEN SMOOGEN //-->

<!-- PUBLISHER=MACMILLAN //-->

<!-- IMPRINT=SAMS //-->

<!-- PUBLICATION DATE=1998 //-->

<!-- CHAPTER=20 //-->

<!-- PAGES=0291-0312 //-->

<!-- UNASSIGNED1 //-->

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<P><CENTER>

<a href="0305-0307.html">Previous</A> | <a href="../ewtoc.html">Table of Contents</A> | <a href="0311-0312.html">Next</A>

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<A NAME="PAGENUM-308"><P>Page 308</P></A>





<P>

management using the su command. There are several ways to create new users in

Linux, but this section shows you the easy way, using a trio of commands:

adduser, passwd, and chfn.

</P>



<P>The first step in creating a new user is to use the

adduser command, found under the /usr/sbin directory. You must be the root operator to run this program:

</P>



<!-- CODE SNIP //-->

<PRE>

# adduser

Only root may add users to the system.

</PRE>

<!-- END CODE SNIP //-->



<P>The adduser program also requires you to specify a user name on the command line,

for example:

</P>

<!-- CODE //-->

<PRE>

# adduser cloobie



Looking for first available UID... 502

Looking for first available GID... 502



Adding login: cloobie...done.

Creating home directory: /home/cloobie...done.

Creating mailbox: /var/spool/mail/cloobie...done.



Don't forget to set the password.

</PRE>

<!-- END CODE //-->



<P>The command will create an account, assign a user identification (UID), a

group identification (GID), and then create a directory called

cloobie under the /home directory. As a reminder, the

adduser program tells you to set a password for your new user.

</P>



<H4><A NAME="ch20_ 21">

Changing Passwords in /etc/passwd with the passwd Command

</A></H4>



<P>After creating your new user, you must assign a password with the

passwd command. This command will create an entry in the

passwd text database in the /etc directory. To show

you how this works, the following example shows you the

passwd file, creates a password for your new user, and then shows you the password file so you can see the new entry.

</P>



<!-- CODE //-->

<PRE>

# cat /etc/passwd

root:syvolaPd3M4QE:0:0:root:/root:/bin/bash

bin:*:1:1:bin:/bin:

daemon:*:2:2:daemon:/sbin:

adm:*:3:4:adm:/var/adm:

lp:*:4:7:lp:/var/spool/lpd:

sync:*:5:0:sync:/sbin:/bin/sync

shutdown:*:6:0:shutdown:/sbin:/sbin/shutdown

halt:*:7:0:halt:/sbin:/sbin/halt

mail:*:8:12:mail:/var/spool/mail:

news:*:9:13:news:/var/spool/news:

uucp:*:10:14:uucp:/var/spool/uucp:

operator:*:11:0:operator:/root:

games:*:12:100:games:/usr/games:

gopher:*:13:30:gopher:/usr/lib/gopher-data:

ftp:*:14:50:FTP User:/home/ftp:

nobody:*:99:99:Nobody:/:

bball:ODyJ5x09iRgNQ:500:500:Billy Ball,,,,:/home/bball:/bin/bash

</PRE>

<!-- END CODE //-->



<A NAME="PAGENUM-309"><P>Page 309</P></A>





<!-- CODE SNIP //-->

<PRE>

cloobie:*:502:502:RHS Linux User:/home/cloobie:/bin/bash

</PRE>

<!-- END CODE SNIP //-->



<P>You can see that although an account has been created, and contains a

username, UID, PID, name, directory, and default shell, there's no password. To add a password, type

the command, along with the new user's name:

</P>

<!-- CODE SNIP //-->

<PRE>

# passwd cloobie

New UNIX password:

Retype new UNIX password:

passwd: all authentication tokens updated successfully

</PRE>

<!-- END CODE SNIP //-->



<P>You'll be asked for a password, and then asked to retype it to verify. If all goes well,

the password will be recorded in /etc/passwd, for example:

</P>

<!-- CODE SNIP //-->

<PRE>

cloobie:9Qa4.uFMhmInA:502:502:RHS Linux User:/home/cloobie:/bin/bash

</PRE>

<!-- END CODE SNIP //-->



<P>Later on, users can change their own password by using the

passwd command, and you should encourage frequent password changes.

</P>

<P>



<CENTER>

<TABLE BGCOLOR="#FFFF99">

<TR><TD><B>

CAUTION

</B></TD></TR>

<TR><TD>

<BLOCKQUOTE>

As the sysadmin, you can change anyone's password if they forget it.

Don't forget yours!

</BLOCKQUOTE></TD></TR>

</TABLE></CENTER>

</P>

<P>Finally, you'll also want to use the chfn command to enter formal information about

users, or have your users enter this information. The

chfn command will ask

</P>

<!-- CODE //-->

<PRE>

# chfn cloobie

Changing finger information for cloobie.

Name [RHS Linux User]: Mr. Cloobie Doo

Office []: 400 Pennsylvania Ave.

Office Phone []: 202-555-1212

Home Phone []: 202-555-4000



Finger information changed.

</PRE>

<!-- END CODE //-->



<P>If you now examine the /etc/passwd entry, you'll see

</P>

<!-- CODE SNIP //-->

<PRE>

cloobie:9Qa4.uFMhmInA:502:502:Mr. Cloobie Doo,400 Pennsylvania Ave.,

202-555-1212,202-555-4000,:/home/cloobie:/bin/bash

</PRE>

<!-- END CODE SNIP //-->



<P>This information is used by the finger command. The formal name may also

be used along with the user name in mail messages, for example:

</P>

<!-- CODE //-->

<PRE>

#  finger cloobie

Login: cloobie                          Name: Mr. Cloobie Doo

Directory: /home/cloobie                Shell: /bin/bash

Office: 400 Pennsylvania Ave.           Office Phone: 202-555-1212

Home Phone: 202-555-4000

Never logged in.

No mail.<BR>

</PRE>

<!-- END CODE //-->





<A NAME="PAGENUM-310"><P>Page 310</P></A>





<!-- CODE SNIP //-->

<PRE>

No Plan.

</PRE>

<!-- END CODE SNIP //-->



<P>The finger command will extract the user's information from the

/etc/passwd file and print it in a nice format. One of the other things you should note in a user's

/etc/passwd entry is the name of a shell at the end. This can be a unique way to not only specify the type of

shell used (your Linux system is set up to assign the bash shell by default), but to restrict the

user to a particular program.

</P>



<H4><A NAME="ch20_ 22">

Restricting Logins

</A></H4>



<P>Your users normally can change the shell used after login through the

chsh command. You can list the currently available shells by using the

chsh command's -l (list shells) option, for example:

</P>

<!-- CODE //-->

<PRE>

# chsh -l

/bin/ash

/bin/bsh

/bin/bash

/bin/sh

/bin/csh

/bin/ksh

/bin/tcsh

</PRE>

<!-- END CODE //-->



<P>The chsh command looks in a file called shells under the

/etc directory, and prints a list. This does not mean that these shells are available, just &quot;acceptable.&quot; You can edit this file,

adding or removing shells that can be specified by your users. You should make sure that the

shells listed in this file are available on your system. To change shells, you can type

</P>

<!-- CODE SNIP //-->

<PRE>

# chsh -s /bin/ksh

Changing shell for root.

Shell changed.

</PRE>

<!-- END CODE SNIP //-->



<P>You can also use the chsh command to specify a program, other than a

shell, to use as the program run when the user logs in, for example:

</P>



<!-- CODE SNIP //-->

<PRE>

# chsh -s /usr/bin/pico cloobie

Changing shell for cloobie.

Warning: &quot;/usr/bin/pico&quot; is not listed as a valid shell.

Shell changed.

</PRE>

<!-- END CODE SNIP //-->



<P>The chsh program will complain if the program is not listed as a shell in the

/etc/shells file. Then check to see if the change was made:

</P>

<!-- CODE //-->

<PRE>

# cat /etc/passwd

...

cloobie:9Qa4.uFMhmInA:502:502:Mr. Cloobie Doo,400 Pennsylvania Ave.,

202-555-1212,202-555-4000,:/home/cloobie:/usr/bin/pico

</PRE>

<!-- END CODE //-->



<P>The preceding example specified the text editor

pico, which would allow a user to do word processing, printing, or spell-checking of documents, but that's all! As soon as the user

logs into Linux, the user is right in the text editor. After quitting the text editor, the user is

logged out. This is a handy technique you can use to restrict users, especially children, if you

only

</P>



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