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docs/Install-Guide/install-guide-2.2.2/node171.html
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<!DOCTYPE HTML PUBLIC "-//W3O//DTD W3 HTML 2.0//EN">
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<!Converted with LaTeX2HTML 95.1 (Fri Jan 20 1995) by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds >
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<HEAD>
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<TITLE>4.4.5 Groups</TITLE>
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</HEAD>
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<BODY>
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<meta name="description" value="4.4.5 Groups">
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<meta name="keywords" value="gs">
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<meta name="resource-type" value="document">
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<meta name="distribution" value="global">
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<P>
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<BR> <HR><A NAME=tex2html3947 HREF="node172.html"><IMG ALIGN=BOTTOM ALT="next" SRC="next_motif.gif"></A> <A NAME=tex2html3945 HREF="node166.html"><IMG ALIGN=BOTTOM ALT="up" SRC="up_motif.gif"></A> <A NAME=tex2html3941 HREF="node170.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="previous_motif.gif"></A> <A NAME=tex2html3949 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="contents_motif.gif"></A> <A NAME=tex2html3950 HREF="node250.html"><IMG ALIGN=BOTTOM ALT="index" SRC="index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html3948 HREF="node172.html">4.5 Archiving and Compressing </A>
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<B>Up:</B> <A NAME=tex2html3946 HREF="node166.html">4.4 Managing Users</A>
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<B> Previous:</B> <A NAME=tex2html3942 HREF="node170.html">4.4.4 Setting user attributes</A>
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<BR> <HR> <P>
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<H2><A NAME=SECTION00645000000000000000>4.4.5 Groups</A></H2>
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<A NAME=secmanagegroups> </A>
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<A NAME=4454> </A>
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<A NAME=4455> </A>
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<A NAME=4456> </A>
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As we have mentioned, each user belongs to one or more groups. The
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only real importance of group relationships pertains to file permissions,
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as you'll recall from Section <A HREF="node124.html#secperms">3.9</A>, each file has a ``group
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ownership'' and a set of group permissions which defines how users in that
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group may access the file.
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<P>
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There are several system-defined groups such as <tt>bin</tt>, <tt>mail</tt>,
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and <tt>sys</tt>. Users should not belong to any of these groups; they
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are used for system file permissions. Instead, users should belong to
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an individual group such as <tt>users</tt>. If you want to be cute, you
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can maintain several groups of users such as <tt>student</tt>,
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<tt>staff</tt>, and <tt>faculty</tt>.
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<P>
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<A NAME=4516> </A>
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The file <tt>/etc/group</tt> contains information about groups.
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The format of each line is
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<P><TT> group name:password:GID:other members
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<P></TT>
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Some example groups might be:
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<P><TT> root:*:0: <BR>
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users:*:100:mdw,larry <BR>
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guest:*:200: <BR>
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other:*:250:kiwi
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<P></TT>
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<A NAME=4471> </A>
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<A NAME=4517> </A>
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The first group, <tt>root</tt>, is a special system group reserved for
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the <tt>root</tt> account. The next group, <tt>users</tt>, is for regular
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users. It has a GID of 100. The users <tt>mdw</tt> and <tt>larry</tt>
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are given access to this group. Remember that in <tt>/etc/passwd</tt>
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each user was given a default GID. However, users may belong to
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more than one group, by adding their usernames to other group lines
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in <tt>/etc/group</tt>. The <tt>groups</tt> command lists what groups you
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are given access to.
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<P>
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The third group, <tt>guest</tt>, is for guest users, and <tt>other</tt>
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is for ``other'' users. The user <tt>kiwi</tt> is given access to this
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group as well.
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<P>
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As you can see, the ``password'' field of <tt>/etc/group</tt>
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is rarely used. It is sometimes used to set a password on group
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access. This is seldom necessary. To protect users from changing into
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priveleged groups (with the <tt>newgroup</tt> command), set the password
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field to ``<tt>*</tt>''.
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<P>
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<A NAME=4518> </A>
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<A NAME=4519> </A>
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<A NAME=4489> </A>
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<A NAME=4490> </A>
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The commands <tt>addgroup</tt> or <tt>groupadd</tt> may be used to
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add groups to your system. Usually, it's easier just to add
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entries in <tt>/etc/group</tt> yourself, as no other configuration
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needs to be done to add a group. To delete a group, simply delete
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its entry in <tt>/etc/group</tt>.
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<P>
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<BR> <HR><A NAME=tex2html3947 HREF="node172.html"><IMG ALIGN=BOTTOM ALT="next" SRC="next_motif.gif"></A> <A NAME=tex2html3945 HREF="node166.html"><IMG ALIGN=BOTTOM ALT="up" SRC="up_motif.gif"></A> <A NAME=tex2html3941 HREF="node170.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="previous_motif.gif"></A> <A NAME=tex2html3949 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="contents_motif.gif"></A> <A NAME=tex2html3950 HREF="node250.html"><IMG ALIGN=BOTTOM ALT="index" SRC="index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html3948 HREF="node172.html">4.5 Archiving and Compressing </A>
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<B>Up:</B> <A NAME=tex2html3946 HREF="node166.html">4.4 Managing Users</A>
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<B> Previous:</B> <A NAME=tex2html3942 HREF="node170.html">4.4.4 Setting user attributes</A>
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<BR> <HR> <P>
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<BR> <HR>
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<P><ADDRESS>
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<I>Matt Welsh <BR>
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mdw@sunsite.unc.edu</I>
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</ADDRESS>
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</BODY>
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