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<HTML><!--Distributed by F --><HEAD><TITLE>[Chapter 22] 22.13 Groups and Group Ownership </TITLE><METANAME="DC.title"CONTENT="UNIX Power Tools"><METANAME="DC.creator"CONTENT="Jerry Peek, Tim O'Reilly & Mike Loukides"><METANAME="DC.publisher"CONTENT="O'Reilly & Associates, Inc."><METANAME="DC.date"CONTENT="1998-08-04T21:40:34Z"><METANAME="DC.type"CONTENT="Text.Monograph"><METANAME="DC.format"CONTENT="text/html"SCHEME="MIME"><METANAME="DC.source"CONTENT="1-56592-260-3"SCHEME="ISBN"><METANAME="DC.language"CONTENT="en-US"><METANAME="generator"CONTENT="Jade 1.1/O'Reilly DocBook 3.0 to HTML 4.0"><LINKREV="made"HREF="mailto:online-books@oreilly.com"TITLE="Online Books Comments"><LINKREL="up"HREF="ch22_01.htm"TITLE="22. File Security, Ownership, and Sharing"><LINKREL="prev"HREF="ch22_12.htm"TITLE="22.12 A Directory that People Can Access but Can't List "><LINKREL="next"HREF="ch22_14.htm"TITLE="22.14 Add Users to a Group to Deny Permission "></HEAD><BODYBGCOLOR="#FFFFFF"TEXT="#000000"><DIVCLASS="htmlnav"><H1><IMGSRC="gifs/smbanner.gif"ALT="UNIX Power Tools"USEMAP="#srchmap"BORDER="0"></H1><MAPNAME="srchmap"><AREASHAPE="RECT"COORDS="0,0,466,58"HREF="index.htm"ALT="UNIX Power Tools"><AREASHAPE="RECT"COORDS="467,0,514,18"HREF="jobjects/fsearch.htm"ALT="Search this book"></MAP><TABLEWIDTH="515"BORDER="0"CELLSPACING="0"CELLPADDING="0"><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch22_12.htm"TITLE="22.12 A Directory that People Can Access but Can't List "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 22.12 A Directory that People Can Access but Can't List "BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="171"><B><FONTFACE="ARIEL,HELVETICA,HELV,SANSERIF"SIZE="-1">Chapter 22<BR>File Security, Ownership, and Sharing</FONT></B></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch22_14.htm"TITLE="22.14 Add Users to a Group to Deny Permission "><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 22.14 Add Users to a Group to Deny Permission "BORDER="0"></A></TD></TR></TABLE> <HRALIGN="LEFT"WIDTH="515"TITLE="footer"></DIV><DIVCLASS="SECT1"><H2CLASS="sect1"><ACLASS="title"NAME="UPT-ART-3030">22.13 Groups and Group Ownership </A></H2><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-24479"></A><ACLASS="indexterm"NAME="AUTOID-24481"></A>Group membership is an important part of UNIX security. All users aremembers of one or more groups, as determined by your entry in<SPANCLASS="link"><EMCLASS="emphasis">/etc/passwd</EM> (<ACLASS="linkend"HREF="ch36_03.htm"TITLE="Changing the Field Delimiter ">36.3</A>)</SPAN>and the <EMCLASS="emphasis">/etc/group</EM> file.</P><PCLASS="para">To find out what groups you belong to, "<SPANCLASS="link"><EMCLASS="emphasis">grep</EM> (<ACLASS="linkend"HREF="ch27_01.htm#UPT-ART-7420"TITLE="Different Versions of grep ">27.1</A>)</SPAN>for" your entry in<EMCLASS="emphasis">/etc/passwd</EM>:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">% <CODECLASS="userinput"><B>grep mikel /etc/passwd</B></CODE>mikel:sflghjraloweor:50:100:Mike Loukides:/home/mikel:/bin/csh</PRE></BLOCKQUOTE></P><PCLASS="para">[If that didn't work, try a command like <CODECLASS="literal">ypcat passwd | grepmike1</CODE>. -<EMCLASS="emphasis">JP</EM> ] The fourth field (the second number) is your <EMCLASS="emphasis">primarygroup ID</EM>. Look up this number in the <EMCLASS="emphasis">/etc/group</EM> file:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">% <CODECLASS="userinput"><B>grep 100 /etc/group</B></CODE>staff:*:100:root</PRE></BLOCKQUOTE></P><PCLASS="para">Or use <CODECLASS="literal">ypcat group | grep 100</CODE>. -<EMCLASS="emphasis">JP</EM> ] My primary group is <EMCLASS="emphasis">staff</EM>. Therefore, when I log in, my group ID isset to 100.<ACLASS="indexterm"NAME="AUTOID-24507"></A>To see what other groups you belong to, use the <EMCLASS="emphasis">groups</EM> commandif your UNIX version has it.Otherwise, look for your namein <EMCLASS="emphasis">/etc/group</EM>:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">% <CODECLASS="userinput"><B>grep mikel /etc/group</B></CODE>power:*:55:mikel,jerry,timweakness:*:60:mikel,harry,susan</PRE></BLOCKQUOTE></P><PCLASS="para">[Or <CODECLASS="literal">ypcat group | grep mike1</CODE>. -<EMCLASS="emphasis">JP</EM> ] I'm also a member of the groups <EMCLASS="emphasis">power</EM> and <EMCLASS="emphasis">weakness</EM>, with groupIDs 55 and 60.</P><PCLASS="para">With BSD UNIX, you're always a member of all your groups. Thismeans that I can access files that are owned by the <EMCLASS="emphasis">staff</EM>, <EMCLASS="emphasis">power</EM>, and<EMCLASS="emphasis">weakness</EM> groups, without doing anything in particular. Under System VUNIX, you can only be "in" one group at a time, even though you can bea member of several. (I suppose this is like social clubs; you canbelong to the Elks and the Odd Fellows, but you can only wear onesilly hat at a time.) If you need to access files that are owned byanother group, use the <EMCLASS="emphasis">newgrp</EM> command:<ACLASS="indexterm"NAME="AUTOID-24524"></A><ACLASS="indexterm"NAME="AUTOID-24526"></A></P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">% <CODECLASS="userinput"><B>newgrp </B></CODE><CODECLASS="replaceable"><I>groupname</I></CODE></PRE></BLOCKQUOTE></P><PCLASS="para">(System V even lets you change to groups that you don't belong to. Inthis case, you have to give a <EMCLASS="emphasis">group password</EM>. Group passwords arerarely used - usually, the password field is filled with a <CODECLASS="literal">*</CODE>, whicheffectively says that there are no valid passwords for this group.)</P><PCLASS="para">On most systems, there are groups for major projects or departments,groups for system administration, and maybe one or two groups forvisitors. Some BSD-based systems have a <EMCLASS="emphasis">wheel</EM> group; to become<SPANCLASS="link">root (<ACLASS="linkend"HREF="ch01_24.htm"TITLE="The Superuser (Root) ">1.24</A>)</SPAN>,you must belong to <EMCLASS="emphasis">wheel</EM>.Many systems make terminals writable only by the owner and a specialgroup named <EMCLASS="emphasis">tty</EM>; this prevents other users from sendingcharacters to your terminal without using an approved<SPANCLASS="link"><EMCLASS="emphasis">setgid</EM> (<ACLASS="linkend"HREF="ch01_23.htm"TITLE="File Access Permissions ">1.23</A>)</SPAN>program like<SPANCLASS="link"><EMCLASS="emphasis">write</EM> (<ACLASS="linkend"HREF="ch01_33.htm"TITLE="UNIX Networking and Communications ">1.33</A>)</SPAN>.</P><DIVCLASS="sect1info"><PCLASS="SECT1INFO">- <SPANCLASS="authorinitials">ML</SPAN></P></DIV></DIV><DIVCLASS="htmlnav"><P></P><HRALIGN="LEFT"WIDTH="515"TITLE="footer"><TABLEWIDTH="515"BORDER="0"CELLSPACING="0"CELLPADDING="0"><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch22_12.htm"TITLE="22.12 A Directory that People Can Access but Can't List "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 22.12 A Directory that People Can Access but Can't List "BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="171"><ACLASS="book"HREF="index.htm"TITLE="UNIX Power Tools"><IMGSRC="gifs/txthome.gif"SRC="gifs/txthome.gif"ALT="UNIX Power Tools"BORDER="0"></A></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch22_14.htm"TITLE="22.14 Add Users to a Group to Deny Permission "><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 22.14 Add Users to a Group to Deny Permission "BORDER="0"></A></TD></TR><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="172">22.12 A Directory that People Can Access but Can't List </TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="171"><ACLASS="index"HREF="index/idx_0.htm"TITLE="Book Index"><IMGSRC="gifs/index.gif"SRC="gifs/index.gif"ALT="Book Index"BORDER="0"></A></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="172">22.14 Add Users to a Group to Deny Permission </TD></TR></TABLE><HRALIGN="LEFT"WIDTH="515"TITLE="footer"><IMGSRC="gifs/smnavbar.gif"SRC="gifs/smnavbar.gif"USEMAP="#map"BORDER="0"ALT="The UNIX CD Bookshelf Navigation"><MAPNAME="map"><AREASHAPE="RECT"COORDS="0,0,73,21"HREF="../index.htm"ALT="The UNIX CD Bookshelf"><AREASHAPE="RECT"COORDS="74,0,163,21"HREF="index.htm"ALT="UNIX Power Tools"><AREASHAPE="RECT"COORDS="164,0,257,21"HREF="../unixnut/index.htm"ALT="UNIX in a Nutshell"><AREASHAPE="RECT"COORDS="258,0,321,21"HREF="../vi/index.htm"ALT="Learning the vi Editor"><AREASHAPE="RECT"COORDS="322,0,378,21"HREF="../sedawk/index.htm"ALT="sed & awk"><AREASHAPE="RECT"COORDS="379,0,438,21"HREF="../ksh/index.htm"ALT="Learning the Korn Shell"><AREASHAPE="RECT"COORDS="439,0,514,21"HREF="../lrnunix/index.htm"ALT="Learning the UNIX Operating System"></MAP></DIV></BODY></HTML>⌨️ 快捷键说明
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