linux-shell

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linux-shell

<link href="/image.php?url=https://csdnimg.cn/release/download_crawler_static/css/base.min.css" rel="stylesheet"/><link href="/image.php?url=https://csdnimg.cn/release/download_crawler_static/css/fancy.min.css" rel="stylesheet"/><link href="/image.php?url=https://csdnimg.cn/release/download_crawler_static/89596528/raw.css" rel="stylesheet"/><div id="sidebar" style="display: none"><div id="outline"></div></div><div class="pf w0 h0" data-page-no="1" id="pf1"><div class="pc pc1 w0 h0"><img alt="" class="bi x0 y0 w1 h1" src="/image.php?url=https://csdnimg.cn/release/download_crawler_static/89596528/bg1.jpg"/><div class="c x1 y1 w2 h2"><div class="t m0 x2 h3 y2 ff1 fs0 fc0 sc0 ls0 ws0">下载</div><div class="t m0 x3 h4 y3 ff2 fs0 fc1 sc0 ls0 ws0">第<span class="ff3">1</span>章<span class="_ _0"> </span>文件安全与权限</div><div class="t m0 x4 h5 y4 ff2 fs1 fc0 sc0 ls1 ws0">为了防止未授权用户访问你的文件，可以在文件和目录上设置权限位。还可以设定文件</div><div class="t m0 x5 h5 y5 ff2 fs1 fc0 sc0 ls2 ws0">在创建时所具有的缺省权限：这些只是整个系统安全问题中的一小部分。在这里我们并不想</div><div class="t m0 x5 h5 y6 ff2 fs1 fc0 sc0 ls3 ws0">对系统安全问题的方方面面进行全面的探讨，只是介绍一下有关文件和目录的安全问题。</div><div class="t m0 x4 h5 y7 ff2 fs1 fc0 sc0 ls4 ws0">本章包含以下内容：</div><div class="t m0 x4 h6 y8 ff3 fs1 fc0 sc0 ls0 ws0">• <span class="_ _1"></span><span class="ff2 ls4">文件和目录的权限。</span></div><div class="t m0 x4 h6 y9 ff3 fs1 fc0 sc0 ls5 ws0">• setuid<span class="ff2 ls0">。</span></div><div class="t m0 x4 h6 ya ff3 fs1 fc0 sc0 ls6 ws0">• chown<span class="ff2 ls0">和<span class="_ _2"></span><span class="ff3 ws1">c h g r p</span>。</span></div><div class="t m0 x4 h6 yb ff3 fs1 fc0 sc0 ls6 ws0">• umask<span class="ff2 ls0">。</span></div><div class="t m0 x4 h6 yc ff3 fs1 fc0 sc0 ls0 ws0">• <span class="_ _1"></span><span class="ff2">符号链接。</span></div><div class="t m0 x4 h6 yd ff2 fs1 fc0 sc0 ls7 ws0">创建文件的用户和他<span class="_ _3"></span><span class="ff3">(</span><span class="ls0">她<span class="_ _2"></span><span class="ff3">)<span class="_ _2"></span></span><span class="ls8">所属于的组拥有该文件。文件的属主可以设定谁具有读、写、执</span></span></div><div class="t m0 x5 h5 ye ff2 fs1 fc0 sc0 ls2 ws0">行该文件的权限。当然，根用户或系统管理员可以改变任何普通用户的设置。一个文件一经</div><div class="t m0 x5 h5 yf ff2 fs1 fc0 sc0 ls9 ws0">创建，就具有三种访问方式：</div><div class="t m0 x4 h6 y10 ff3 fs1 fc0 sc0 ls0 ws0">1) <span class="_ _1"></span><span class="ff2 ls9">读，可以显示该文件的内容。</span></div><div class="t m0 x4 h6 y11 ff3 fs1 fc0 sc0 ls0 ws0">2) <span class="_ _1"></span><span class="ff2 lsa">写，可以编辑或删除它。</span></div><div class="t m0 x4 h6 y12 ff3 fs1 fc0 sc0 ls0 ws0">3) <span class="_ _2"></span><span class="ff2 lsa">执行，如果该文件是一个<span class="_ _4"> </span></span><span class="ws1">s h e l l</span><span class="ff2 lsb">脚本或程序。</span></div><div class="t m0 x4 h5 y13 ff2 fs1 fc0 sc0 lsc ws0">按照所针对的用户，文件的权限可分为三类：</div><div class="t m0 x4 h6 y14 ff3 fs1 fc0 sc0 ls0 ws0">1) <span class="_ _1"></span><span class="ff2 lsd">文件属主，创建该文件的用户。</span></div><div class="t m0 x4 h6 y15 ff3 fs1 fc0 sc0 ls0 ws0">2) <span class="_ _2"></span><span class="ff2 lsc">同组用户，拥有该文件的用户组中的任何用户。</span></div><div class="t m0 x4 h6 y16 ff3 fs1 fc0 sc0 ls0 ws0">3) <span class="_ _1"></span><span class="ff2 lse">其他用户，即不属于拥有该文件的用户组的某一用户。</span></div><div class="t m0 x5 h7 y17 ff4 fs2 fc1 sc0 ls0 ws0">1.1 <span class="ff5">文件</span></div><div class="t m0 x4 h5 y18 ff2 fs1 fc0 sc0 lsf ws0">当你创建一个文件的时候，系统保存了有关该文件的全部信息，包括：</div><div class="t m0 x4 h6 y19 ff3 fs1 fc0 sc0 lsf ws0">•<span class="_ _5"> </span><span class="ff2 ls10">文件的位置。</span></div><div class="t m0 x4 h6 y1a ff3 fs1 fc0 sc0 ls0 ws0">• <span class="_ _1"></span><span class="ff2">文件类型。</span></div><div class="t m0 x4 h6 y1b ff3 fs1 fc0 sc0 ls0 ws0">• <span class="_ _2"></span><span class="ff2">文件长度。</span></div><div class="t m0 x4 h6 y1c ff3 fs1 fc0 sc0 ls0 ws0">• <span class="_ _1"></span><span class="ff2 lsc">哪位用户拥有该文件，哪些用户可以访问该文件。</span></div><div class="t m0 x4 h6 y1d ff3 fs1 fc0 sc0 ls0 ws0">• i<span class="_ _1"></span><span class="ff2">节点。</span></div><div class="t m0 x4 h6 y1e ff3 fs1 fc0 sc0 ls0 ws0">• <span class="_ _2"></span><span class="ff2 ls11">文件的修改时间。</span></div><div class="t m0 x4 h6 y1f ff3 fs1 fc0 sc0 ls0 ws0">• <span class="_ _1"></span><span class="ff2 ls5">文件的权限位。</span></div><div class="t m0 x4 h6 y20 ff2 fs1 fc0 sc0 ls0 ws0">让我们使用<span class="_ _3"></span><span class="ff3">ls -l<span class="_ _6"></span></span><span class="ls12">命令，来看一个典型的文件：</span></div><div class="t m0 x6 h8 y21 ff6 fs3 fc1 sc0 ls13 ws0">第一部分<span class="_ _7"> </span><span class="ff4 ls0 ws2">s h e l l</span></div></div></div><div class="pi" data-data='{"ctm":[1.860465,0.000000,0.000000,1.860465,0.000000,0.000000]}'></div></div><div id="pf2" class="pf w0 h0" data-page-no="2"><div class="pc pc2 w0 h0"><img class="bi x0 y0 w1 h1" alt="" src="/image.php?url=https://csdnimg.cn/release/download_crawler_static/89596528/bg2.jpg"><div class="t m0 x7 h5 y22 ff2 fs1 fc0 sc0 lsf ws0">下面让我们来分析一下该命令所得结果的前面两行，看看都包含了哪些信息：</div><div class="t m0 x7 h6 y23 ff3 fs1 fc0 sc0 ls14 ws0">total 4232<span class="ff2 lsc">：这一行告诉我们该目录中所有文件所占的空间。</span></div><div class="t m0 x7 h6 y24 ff3 fs1 fc0 sc0 ls0 ws3">- r w x r- x r- x<span class="_ _2"></span><span class="ff2 ls15 ws0">：这是该文件的权限位。如果除去最前面的横杠，这里一共是<span class="_ _8"> </span><span class="ff3">9<span class="_ _2"></span></span><span class="ls16">个字符，他们</span></span></div><div class="t m0 x8 h6 y25 ff2 fs1 fc0 sc0 ls17 ws0">分别对应<span class="_ _6"></span><span class="ff3">9</span><span class="ls18">个权限位。通过这些权限位，可以设定用户对文件的访问权限。这<span class="_ _8"> </span><span class="ff3">9</span><span class="ls19">个字符可以分</span></span></div><div class="t m0 x8 h5 y26 ff2 fs1 fc0 sc0 ls0 ws0">为三组：</div><div class="t m0 x7 h6 y27 ff3 fs1 fc0 sc0 ls0 ws1">r w x<span class="_"> </span><span class="ff2 ls5 ws0">：文件属主权限<span class="_ _9"> </span><span class="ls10">这是前面三位</span></span></div><div class="t m0 x7 h6 y28 ff3 fs1 fc0 sc0 ls10 ws0">r<span class="ls0 ws1">- x</span><span class="ff2 ls5">：同组用户权限<span class="_ _a"> </span><span class="ls10">这是中间三位</span></span></div><div class="t m0 x7 h6 y29 ff3 fs1 fc0 sc0 ls10 ws0">r<span class="ls0 ws1">- x<span class="_"> </span></span><span class="ff2 ls5">：其他用户权限<span class="_ _a"> </span><span class="lsb">这是最后三位</span></span></div><div class="t m0 x7 h6 y2a ff2 fs1 fc0 sc0 ls1a ws0">后面我们还将对这些权限位作更详细的介绍。出现在<span class="_ _b"> </span><span class="ff3">r<span class="_ _2"></span></span><span class="ls0">、<span class="_ _2"></span><span class="ff3">w<span class="_ _2"></span></span>、<span class="_ _1"></span><span class="ff3">x<span class="_ _2"></span></span><span class="ls1b">位置上的横杠表示相应的访</span></span></div><div class="t m0 x8 h5 y2b ff2 fs1 fc0 sc0 ls1c ws0">问权限被禁止。</div><div class="t m0 x7 h6 y2c ff3 fs1 fc0 sc0 ls0 ws0">1 <span class="_ _6"></span><span class="ff2 ls1d">该文件硬链接的数目。</span></div><div class="t m0 x7 h6 y2d ff3 fs1 fc0 sc0 ls1e ws0">root <span class="ff2 ls10">文件的属主。</span></div><div class="t m0 x7 h6 y2e ff3 fs1 fc0 sc0 ls5 ws0">root <span class="ff2 ls0">文件的属主<span class="_ _3"></span><span class="ff3 ws1">r o o t<span class="_"> </span></span><span class="ls10">所在的缺省组<span class="_ _6"></span><span class="ff3">(</span></span>也叫做<span class="_ _c"></span><span class="ff3 ws1">r o o t )</span>。</span></div><div class="t m0 x7 h6 y2f ff3 fs1 fc0 sc0 ls5 ws0">3578 <span class="_ _2"></span><span class="ff2 ls1f">用字节来表示的文件长度，记住，不是<span class="_ _d"> </span><span class="ff3">K</span><span class="ls0">字节！</span></span></div><div class="t m0 x7 h6 y30 ff3 fs1 fc0 sc0 ls6 ws0">Oct 14 04:44 <span class="ff2 ls11">文件的更新时间。</span></div><div class="t m0 x7 h6 y31 ff3 fs1 fc0 sc0 ls17 ws0">dmesg <span class="ff2 ls0">文件名。</span></div><div class="t m0 x8 h7 y32 ff4 fs2 fc1 sc0 ls0 ws0">1.2 <span class="ff5">文件类型</span></div><div class="t m0 x7 h5 y33 ff2 fs1 fc0 sc0 ls1 ws0">还记得前面一节所提到的文件权限位前面的那个字符吗？我们现在就解释一下这个横杠</div><div class="t m0 x8 h6 y34 ff2 fs1 fc0 sc0 ls7 ws0">所代表的意思，文件类型有七种，它可以从<span class="_ _e"> </span><span class="ff3 ls20">ls -l</span><span class="ls21">命令所列出的结果的第一位看出，这七种类型</span></div><div class="t m0 x8 h5 y35 ff2 fs1 fc0 sc0 ls0 ws0">是：</div><div class="t m0 x7 h6 y36 ff3 fs1 fc0 sc0 ls0 ws0">d <span class="_ _c"></span><span class="ff2">目录。</span></div><div class="t m0 x7 h6 y37 ff3 fs1 fc0 sc0 ls0 ws0">l <span class="_ _c"></span><span class="ff2">符号链接<span class="_ _6"></span></span>(<span class="_ _2"></span><span class="ff2 ls1c">指向另一个文件<span class="_ _6"></span><span class="ff3">)</span><span class="ls0">。</span></span></div><div class="t m0 x7 h6 y38 ff3 fs1 fc0 sc0 ls0 ws0">s <span class="_ _c"></span><span class="ff2 ls10">套接字文件。</span></div><div class="t m0 x7 h6 y39 ff3 fs1 fc0 sc0 ls0 ws0">b <span class="_ _c"></span><span class="ff2 ls10">块设备文件。</span></div><div class="t m0 x7 h6 y3a ff3 fs1 fc0 sc0 ls0 ws0">c <span class="_ _c"></span><span class="ff2 ls1c">字符设备文件。</span></div><div class="t m0 x7 h6 y3b ff3 fs1 fc0 sc0 ls0 ws0">p <span class="_ _c"></span><span class="ff2 ls1c">命名管道文件。</span></div><div class="t m0 x7 h6 y3c ff3 fs1 fc0 sc0 ls0 ws0">- <span class="_ _2"></span><span class="ff2 lse">普通文件，或者更准确地说，不属于以上几种类型的文件。</span></div><div class="t m0 x8 h7 y3d ff4 fs2 fc1 sc0 ls0 ws0">1.3 <span class="ff5">权限</span></div><div class="t m0 x7 h6 y3e ff2 fs1 fc0 sc0 ls0 ws0">让我们用<span class="_ _c"></span><span class="ff3 ws1">t o u c h<span class="_"> </span></span><span class="ls4">命令创建一个文件：</span></div><div class="t m0 x7 h9 y3f ff7 fs4 fc0 sc0 ls22 ws0">$ touch myfile</div><div class="t m0 x7 h6 y40 ff2 fs1 fc0 sc0 ls11 ws0">现在对该目录使用<span class="_ _6"></span><span class="ff3 ls0">ls -l<span class="_ _6"></span><span class="ff2">命令：</span></span></div><div class="t m0 x9 ha y41 ff8 fs5 fc2 sc0 ls0 ws0">2<span class="_ _f"> </span><span class="ff9 fs1 fc0">第一部分<span class="_ _10"> </span><span class="ffa">shell</span></span></div><div class="c x1 y1 w2 h2"><div class="t m0 xa h3 y2 ff1 fs0 fc0 sc0 ls0 ws0">下载</div></div></div><div class="pi" data-data='{"ctm":[1.860465,0.000000,0.000000,1.860465,0.000000,0.000000]}'></div></div><div id="pf3" class="pf w0 h0" data-page-no="3"><div class="pc pc3 w0 h0"><img class="bi x0 y0 w1 h1" alt="" src="/image.php?url=https://csdnimg.cn/release/download_crawler_static/89596528/bg3.jpg"><div class="t m0 xb h5 y42 ff2 fs1 fc0 sc0 ls1 ws0">我们已经创建了一个空文件，正如我们所希望的那样，第一个横杠告诉我们该文件是一</div><div class="t m0 xc h6 y43 ff2 fs1 fc0 sc0 ls23 ws0">个普通文件。你将会发现所创建的文件绝大多数都是普通文件或符号链接文件<span class="_ _11"> </span><span class="ff3">(</span><span class="ls24">后面将会出现</span></div><div class="t m0 xc h6 y44 ff2 fs1 fc0 sc0 ls4 ws0">更多的符号链接文件<span class="_ _6"></span><span class="ff3">)<span class="_ _2"></span></span><span class="ls0">。</span></div><div class="t m0 xd h5 y45 ff2 fs1 fc0 sc0 lsb ws0">文件属主权限<span class="_ _12"> </span><span class="ls0">组用户权限<span class="_ _13"> </span><span class="ls10">其他用户权限</span></span></div><div class="t m0 xd h6 y46 ff3 fs1 fc0 sc0 ls0 ws1">r w -<span class="_ _14"> </span>r<span class="_"> </span>- -<span class="_ _15"> </span>r<span class="_ _2"></span><span class="ff2 ws0">—</span></div><div class="t m0 xb h5 y47 ff2 fs1 fc0 sc0 ls1 ws0">接下来的三个权限位是文件属主所具有的权限；再接下来的三位是与你同组用户所具有</div><div class="t m0 xc h6 y48 ff2 fs1 fc0 sc0 ls7 ws0">的权限，这里是<span class="_ _3"></span><span class="ff3 ls0 ws4">a d m i n</span><span class="ls25">组；最后三位是其他用户所具有的权限。在该命令的结果中，我所属于</span></div><div class="t m0 xc h5 y49 ff2 fs1 fc0 sc0 ls26 ws0">的缺省组也显示了出来。下面是对该文件权限的精确描述：</div><div class="t m0 xe hb y4a ff5 fs6 fc0 sc0 ls0 ws0">表<span class="_ _2"></span><span class="ff4 ls27">1-1 ls -l<span class="_ _2"></span></span><span class="ls1e">命令输出的含义</span></div><div class="t m0 xf hc y4b ff3 fs7 fc0 sc0 ls1e ws0">(<span class="ff2 ls0">第一个字符<span class="_ _6"></span><span class="ff3 ws5">) -<span class="_ _16"> </span></span>普通文件</span></div><div class="t m0 xf hc y4c ff3 fs7 fc0 sc0 ls0 ws0">(<span class="ff2 ls28">接下来的三个字符<span class="_ _6"></span></span><span class="ws5">) r w -<span class="_ _17"> </span></span><span class="ff2 ls29">文件属主的权限</span></div><div class="t m0 xf hc y4d ff3 fs7 fc0 sc0 ls29 ws0">(<span class="ff2 ls2a">再接下来的三个字符<span class="_ _6"></span></span><span class="ls0 ws5">) r- -<span class="_ _18"> </span></span><span class="ff2 ls1e">同组用户的权限</span></div><div class="t m0 xf hc y4e ff3 fs7 fc0 sc0 ls1e ws0">(<span class="ff2 ls0">最后三个字符<span class="_ _6"> </span><span class="ff3 ws5">) r- -<span class="_ _19"> </span></span><span class="ls1e">其他用户的权限</span></span></div><div class="t m0 xb h6 y4f ff2 fs1 fc0 sc0 ls11 ws0">因此，这三组字符<span class="_ _6"></span><span class="ff3">(</span><span class="ls1c">除了第一个字符<span class="_ _6"></span><span class="ff3">)</span><span class="ls10">分别定义了：</span></span></div><div class="t m0 xb h6 y50 ff3 fs1 fc0 sc0 ls0 ws0">1) <span class="_ _2"></span><span class="ff2 lsa">文件属主所拥有的权限。</span></div><div class="t m0 xb h6 y51 ff3 fs1 fc0 sc0 ls0 ws0">2) <span class="_ _1"></span><span class="ff2 ls1c">文件属主缺省组<span class="_ _6"></span><span class="ff3">(<span class="_ _2"></span></span><span class="ls9">一个用户可以属于很多的组<span class="_ _4"> </span><span class="ff3">)</span></span>所拥有的权限。</span></div><div class="t m0 xb h6 y52 ff3 fs1 fc0 sc0 ls0 ws0">3) <span class="_ _1"></span><span class="ff2 ls27">系统中其他用户的权限。</span></div><div class="t m0 xb h5 y53 ff2 fs1 fc0 sc0 ls2b ws0">在每一组字符中含有三个权限位：</div><div class="t m0 xb h6 y54 ff3 fs1 fc0 sc0 ls0 ws0">r <span class="_ _c"></span><span class="ff2">读权限</span></div><div class="t m0 xb h6 y55 ff3 fs1 fc0 sc0 ls0 ws0">w <span class="_ _c"></span><span class="ff2">写<span class="_ _2"></span></span>/<span class="_ _2"></span><span class="ff2">更改权限</span></div><div class="t m0 xb h6 y56 ff3 fs1 fc0 sc0 ls0 ws0">x <span class="_ _c"></span><span class="ff2 ls27">执行该脚本或程序的权限</span></div><div class="t m0 xb h6 y57 ff2 fs1 fc0 sc0 lsc ws0">这里我们采用另外一种方式来表示刚才所列出<span class="_ _e"> </span><span class="ff3 ls0 ws1">m y f i l e</span><span class="ls10">的文件权限：</span></div><div class="t m0 x10 h6 y58 ff3 fs1 fc0 sc0 ls10 ws0">-<span class="_ _1a"> </span><span class="ls0 ws1">r w -<span class="_ _1b"> </span>r<span class="_"> </span>- -<span class="_ _1c"> </span><span class="ws0">r-- </span></span></div><div class="t m0 x10 h5 y59 ff2 fs1 fc0 sc0 ls2c ws0">文件类型为普通文件<span class="_ _1d"> </span>文件属主可以读、写<span class="_ _1e"> </span><span class="ls5">同组用户可以读<span class="_ _1f"> </span>其他用户可以读</span></div><div class="t m0 xb h6 y5a ff2 fs1 fc0 sc0 ls1d ws0">你可能已经注意到了，<span class="_ _20"></span><span class="ff3 ls0 ws1">m y f i l e<span class="ff2 ls2d ws0">在创建的时候并未给属主赋予执行权限，在用户创建文件时，</span></span></div><div class="t m0 xc h5 y5b ff2 fs1 fc0 sc0 ls2e ws0">系统不会自动地设置执行权限位。这是出于加强系统安全的考虑。必须手工修改这一权限位：</div><div class="t m0 xc h6 y5c ff2 fs1 fc0 sc0 ls0 ws0">后面讲到<span class="_ _6"></span><span class="ff3 ws6">u m a s k</span><span class="ls2f">命令时，你就会明白为什么没有获得执行权限。然而，你可以针对目录设置执</span></div><div class="t m0 xc h5 y5d ff2 fs1 fc0 sc0 ls30 ws0">行权限位，但这与文件执行权限位的意义有所不同，这一点我们将在后面讨论。</div><div class="t m0 xb h6 y5e ff2 fs1 fc0 sc0 lsf ws0">上面这段关于权限位的内容可能不太好理解，让我们来看几个例子<span class="_ _b"> </span><span class="ff3">(<span class="_ _2"></span></span><span class="ls0">见表<span class="_ _2"></span><span class="ff3 ws1">1 - 2 )<span class="_"> </span></span>。</span></div><div class="t m0 xb h5 y5f ff2 fs1 fc0 sc0 ls1 ws0">更令人迷惑的是，对于文件属主来说，在只有读权限位被置位的情况下，仍然可以通过</div><div class="t m0 xc h5 y60 ff2 fs1 fc0 sc0 ls2 ws0">文件重定向的方法向该文件写入。过一会儿我们就会看到，能否删除一个文件还依赖于该文</div><div class="t m0 xc h5 y61 ff2 fs1 fc0 sc0 ls31 ws0">件所在目录权限位的设置。</div><div class="t m0 x11 hb y62 ff5 fs6 fc0 sc0 ls0 ws0">表<span class="_ _2"></span><span class="ff4 lsb">1-2 </span><span class="ls1e">文件权限及含义</span></div><div class="t m0 x12 hd y63 ff2 fs7 fc0 sc0 ls0 ws0">权<span class="_ _21"> </span>限<span class="_ _22"> </span>所代表的含义</div><div class="t m0 x12 hc y64 ff3 fs7 fc0 sc0 ls32 ws0">r-- --- ---<span class="_ _23"> </span><span class="ff2 fc3 ls0">文<span class="_ _2"></span><span class="fc0 ls29">文件属主可读，但不能写或执行</span></span></div><div class="t m0 x12 hc y65 ff3 fs7 fc0 sc0 ls33 ws0">r-- r-- ---<span class="_ _24"> </span><span class="ff2 fc3 ls0">文<span class="_ _2"></span><span class="fc0 ls2a">文件属主和同组用户<span class="_ _c"></span><span class="ff3">(<span class="_ _1"></span></span><span class="ls34">一般来说，是文件属主所在的缺省组<span class="_ _4"> </span><span class="ff3">)</span><span class="ls0">可读</span></span></span></span></div><div class="t m0 x12 hc y66 ff3 fs7 fc0 sc0 ls35 ws0">r-- r-- r<span class="ls0 ws5">- -<span class="_ _24"> </span><span class="ff2 fc3 ws0">文<span class="_ _2"></span><span class="fc0 ls36">任何用户都可读，但不能写或执行</span></span></span></div><div class="t m0 x12 hc y67 ff3 fs7 fc0 sc0 ls37 ws0">rwx r-- r<span class="ls0 ws5">- -<span class="_ _25"> </span><span class="ff2 fc3 ws0">文<span class="_ _2"></span><span class="fc0 ls17">文件属主可读、写、执行，同组用户和其他用户只可读</span></span></span></div><div class="t m0 x12 hc y68 ff3 fs7 fc0 sc0 ls32 ws0">rwx r-x ---<span class="_ _26"> </span><span class="ff2 fc3 ls0">文<span class="_ _2"></span><span class="fc0 ls38">文件属主可读、写、执行，同组用户可读、执行</span></span></div><div class="t m0 x13 ha y41 ff9 fs1 fc0 sc0 ls0 ws0">第<span class="ffa">1</span>章<span class="_ _10"> </span>文件安全与权限<span class="_ _f"> </span><span class="ff8 fs5 fc2">3</span></div><div class="c x1 y1 w2 h2"><div class="t m0 x2 h3 y2 ff1 fs0 fc0 sc0 ls0 ws0">下载</div></div></div><div class="pi" data-data='{"ctm":[1.860465,0.000000,0.000000,1.860465,0.000000,0.000000]}'></div></div><div id="pf4" class="pf w0 h0" data-page-no="4"><div class="pc pc4 w0 h0"><img class="bi x0 y0 w1 h1" alt="" src="/image.php?url=https://csdnimg.cn/release/download_crawler_static/89596528/bg4.jpg"><div class="t m0 x14 hb y69 ff2 fs6 fc0 sc0 ls0 ws0">(续)</div><div class="t m0 x15 hd y6a ff2 fs7 fc0 sc0 ls0 ws0">权<span class="_ _21"> </span>限<span class="_ _27"> </span>所代表的含义</div><div class="t m0 x15 hc y6b ff3 fs7 fc0 sc0 ls35 ws0">rwx r-x r<span class="_ _2"></span><span class="ls0 ws5">- x<span class="_ _28"> </span><span class="ff2 fc3 ws0">文<span class="_ _2"></span><span class="fc0 ls39">文件属主可读、写、执行，同组用户和其他用户可读、执行</span></span></span></div><div class="t m0 x15 hc y45 ff3 fs7 fc0 sc0 ls32 ws0">rw- rw- ---<span class="_ _26"> </span><span class="ff2 fc3 ls0">文<span class="fc0 ls39">文件属主和同组用户可读、写</span></span></div><div class="t m0 x15 hc y6c ff3 fs7 fc0 sc0 ls37 ws0">rw- rw- r<span class="ls0 ws5">- -<span class="_ _29"> </span><span class="ff2 fc3 ws0">文<span class="_ _2"></span><span class="fc0 ls34">文件属主和同组用户可读、写，其他用户可读</span></span></span></div><div class="t m0 x15 hc y6d ff3 fs7 fc0 sc0 ls32 ws0">rw- rw- ---<span class="_ _29"> </span><span class="ff2 fc3 ls0">文<span class="fc0 ls37">文件属主和同组用户及其他用户读可以读、写，慎用这种权限</span></span></div><div class="t m0 x16 hd y6e ff2 fs7 fc0 sc0 ls39 ws0">设置，因为任何用户都可以写入该文件</div><div class="t m0 x8 h7 y6f ff4 fs2 fc1 sc0 ls0 ws0">1.4 <span class="ff5">改变权限位</span></div><div class="t m0 x7 h5 y70 ff2 fs1 fc0 sc0 ls1 ws0">对于属于你的文件，可以按照自己的需要改变其权限位的设置。在改变文件权限位设置</div><div class="t m0 x8 h6 y71 ff2 fs1 fc0 sc0 ls3a ws0">之前，要仔细地想一想有哪些用户需要访问你的文件<span class="_ _2a"> </span><span class="ff3">(</span><span class="ls3b">包括你的目录<span class="_ _6"></span><span class="ff3">)</span><span class="ls7">。可以使用<span class="_ _6"></span><span class="ff3 ls0 ws7">c h m o d<span class="_"> </span></span><span class="ls0">命令来</span></span></span></div><div class="t m0 x8 h5 y72 ff2 fs1 fc0 sc0 ls2 ws0">改变文件权限位的设置。这一命令有比较短的绝对模式和长一些的符号模式。我们先来看一</div><div class="t m0 x8 h5 y73 ff2 fs1 fc0 sc0 ls10 ws0">看符号模式。</div><div class="t m0 x8 h5 y74 ff4 fs1 fc1 sc0 ls0 ws0">1.4.1 <span class="ff5">符号模式</span></div><div class="t m0 x7 h6 y75 ff3 fs1 fc0 sc0 ls0 ws1">c h m o d<span class="_"> </span><span class="ff2 ls4 ws0">命令的一般格式为：</span></div><div class="t m0 x7 h9 y76 ff7 fs4 fc0 sc0 ls3c ws0">chmod [who] operator [permission] filename</div><div class="t m0 x7 h6 y77 ff3 fs1 fc0 sc0 ls0 ws1">w h o<span class="_"> </span><span class="ff2 ws0">的含义是：</span></div><div class="t m0 x7 h6 y78 ff3 fs1 fc0 sc0 ls0 ws0">u <span class="_ _c"></span><span class="ff2 ls1c">文件属主权限。</span></div><div class="t m0 x7 h6 y79 ff3 fs1 fc0 sc0 ls0 ws0">g <span class="_ _c"></span><span class="ff2 ls1c">同组用户权限。</span></div><div class="t m0 x7 h6 y7a ff3 fs1 fc0 sc0 ls0 ws0">o <span class="_ _c"></span><span class="ff2 ls1c">其他用户权限。</span></div><div class="t m0 x7 h6 y7b ff3 fs1 fc0 sc0 ls0 ws0">a <span class="_ _c"></span><span class="ff2">所有用户<span class="_ _6"></span></span>(<span class="_ _2"></span><span class="ff2 lsd">文件属主、同组用户及其他用户<span class="_ _4"> </span><span class="ff3">)<span class="_ _2"></span></span><span class="ls0">。</span></span></div><div class="t m0 x7 h6 y7c ff3 fs1 fc0 sc0 ls0 ws1">o p e r a t o r<span class="ff2 ws0">的含义：</span></div><div class="t m0 x7 h6 y7d ff3 fs1 fc0 sc0 ls0 ws0">+ <span class="_ _c"></span><span class="ff2">增加权限。</span></div><div class="t m0 x7 h6 y7e ff3 fs1 fc0 sc0 ls0 ws0">- <span class="_ _c"></span><span class="ff2">取消权限。</span></div><div class="t m0 x7 h6 y7f ff3 fs1 fc0 sc0 ls0 ws0">= <span class="_ _1"></span><span class="ff2">设定权限。</span></div><div class="t m0 x7 h6 y80 ff3 fs1 fc0 sc0 ls0 ws1">p e r m i s s i o n<span class="ff2 ws0">的含义：</span></div><div class="t m0 x7 h6 y81 ff3 fs1 fc0 sc0 ls0 ws0">r <span class="_ _c"></span><span class="ff2">读权限。</span></div><div class="t m0 x7 h6 y82 ff3 fs1 fc0 sc0 ls0 ws0">w <span class="_ _c"></span><span class="ff2">写权限。</span></div><div class="t m0 x7 h6 y83 ff3 fs1 fc0 sc0 ls0 ws0">x <span class="_ _c"></span><span class="ff2">执行权限。</span></div><div class="t m0 x7 h6 y84 ff3 fs1 fc0 sc0 ls0 ws0">s <span class="_ _c"></span><span class="ff2 ls10">文件属主和组<span class="_ _6"></span></span><span class="ws1">s e t - I D</span><span class="ff2">。</span></div><div class="t m0 x7 h6 y85 ff3 fs1 fc0 sc0 ls0 ws0">t <span class="_ _c"></span><span class="ff2">粘性位<span class="_ _c"></span></span>*<span class="_ _2"></span><span class="ff2">。</span></div><div class="t m0 x7 h6 y86 ff3 fs1 fc0 sc0 ls0 ws0">l <span class="_ _1"></span><span class="ff2 ls2b">给文件加锁，使其他用户无法访问。</span></div><div class="t m0 x7 h6 y87 ff3 fs1 fc0 sc0 ls13 ws0">u,g,o <span class="ff2 lsc">针对文件属主、同组用户及其他用户的操作。</span></div><div class="t m0 x7 h6 y88 ff3 fs1 fc0 sc0 lsc ws0">*<span class="_ _2"></span><span class="ff2 ls3d">在列文件或目录时，有时会遇到“<span class="_ _2b"> </span><span class="ff3">t</span><span class="ls3e">”位。<span class="_ _2c"></span><span class="ls0">“<span class="_ _1"></span><span class="ff3">t<span class="_ _1"></span></span><span class="ls3f">”代表了粘性位。如果在一个目录上出现</span></span></span></span></div><div class="t m0 x17 h6 y89 ff2 fs1 fc0 sc0 ls0 ws0">“<span class="_ _2"></span><span class="ff3">t<span class="_ _1"></span></span><span class="ls40">”位，这就意味着该目录中的文件只有其属主才可以删除，即使某个同组用户具有和属主</span></div><div class="t m0 x8 h5 y8a ff2 fs1 fc0 sc0 ls26 ws0">同等的权限。不过有的系统在这一规则上并不十分严格。</div><div class="t m0 x7 h6 y8b ff2 fs1 fc0 sc0 ls41 ws0">如果在文件列表时看到“<span class="_ _d"> </span><span class="ff3">t<span class="_ _2"></span></span><span class="ls0">”<span class="_ _2c"></span><span class="ls42">，那么这就意味着该脚本或程序在执行时会被放在交换区<span class="_ _5"> </span><span class="ff3">(</span><span class="ls0">虚</span></span></span></div><div class="t m0 x8 h6 y8c ff2 fs1 fc0 sc0 ls0 ws0">存<span class="_ _2"></span><span class="ff3">)</span><span class="lse">。不过由于当今的内存价格如此之低，大可不必理会文件的“<span class="_ _b"> </span><span class="ff3">t<span class="_ _2"></span></span></span>”的使用。</div><div class="t m0 x9 ha y41 ff8 fs5 fc2 sc0 ls0 ws0">4<span class="_ _f"> </span><span class="ff9 fs1 fc0">第一部分<span class="_ _10"> </span><span class="ffa">shell</span></span></div><div class="c x1 y1 w2 h2"><div class="t m0 xa h3 y2 ff1 fs0 fc0 sc0 ls0 ws0">下载</div></div></div><div class="pi" data-data='{"ctm":[1.860465,0.000000,0.000000,1.860465,0.000000,0.000000]}'></div></div><div id="pf5" class="pf w0 h0" data-page-no="5"><div class="pc pc5 w0 h0"><img class="bi x0 y0 w1 h1" alt="" src="/image.php?url=https://csdnimg.cn/release/download_crawler_static/89596528/bg5.jpg"><div class="t m0 xc h5 y42 ff4 fs1 fc1 sc0 ls0 ws0">1.4.2 chmod<span class="_ _2"></span><span class="ff5">命令举例</span></div><div class="t m0 xb h6 y8d ff2 fs1 fc0 sc0 ls41 ws0">现在让我们来看一些使用<span class="_ _d"> </span><span class="ff3 ls0 ws8">c h m o d<span class="_"> </span></span><span class="ls17">命令的例子。假定<span class="_ _d"> </span><span class="ff3 ls0 ws8">m y f i l e</span><span class="ls43">文件最初具有这样的权限：<span class="_ _2d"> </span><span class="ff3 ls0 ws8">r w x</span></span></span></div><div class="t m0 xc h6 y8e ff3 fs1 fc0 sc0 ls13 ws0">rwx rwx <span class="_ _2"></span><span class="ff2 ls0">：</span></div><div class="t m0 x18 hd y8f ff5 fs7 fc0 sc0 ls0 ws0">命<span class="_"> </span>令<span class="_ _2e"> </span>结<span class="_ _10"> </span>果<span class="_ _2f"> </span>含<span class="_ _10"> </span>义</div><div class="t m0 x19 hc y90 ff3 fs7 fc0 sc0 ls44 ws0">chmod a-x myfile<span class="_ _30"> </span><span class="ls32">rw- rw- rw-<span class="_ _31"> </span><span class="ff2 ls45">收回所有用户的执行权限</span></span></div><div class="t m0 x19 hc y91 ff3 fs7 fc0 sc0 ls46 ws0">chmod og-w myfile<span class="_ _32"> </span><span class="ls2d">rw- r-- r<span class="ls0 ws5">- -<span class="_ _33"> </span></span><span class="ff2 ls36">收回同组用户和其他用户的写权限</span></span></div><div class="t m0 x19 hc y92 ff3 fs7 fc0 sc0 ls44 ws0">chmod g+w myfile<span class="_ _34"> </span><span class="ls2d">rw- rw- r<span class="_ _2"></span><span class="ls0 ws5">- -<span class="_ _24"> </span></span><span class="ff2 ls2a">赋予同组用户写权限</span></span></div><div class="t m0 x19 hc y93 ff3 fs7 fc0 sc0 ls17 ws0">chmod u+x myfile<span class="_ _35"> </span><span class="ls37">rwx rw- r<span class="ls0 ws5">- -<span class="_ _36"> </span></span><span class="ff2 ls47">赋予文件属主执行权限</span></span></div><div class="t m0 x19 hc y94 ff3 fs7 fc0 sc0 ls48 ws0">chmod go+x myfile<span class="_ _37"> </span><span class="ls37">rwx rwx r<span class="ls0 ws5">- x<span class="_ _38"> </span></span><span class="ff2 ls49">赋予同组用户和其他用户执行权限</span></span></div><div class="t m0 xb h6 y95 ff2 fs1 fc0 sc0 ls0 ws0">当创建<span class="_ _1"></span><span class="ff3 ws1">m y f i l e</span><span class="ls12">文件时，它具有这样的权限：</span></div><div class="t m0 xb h6 y96 ff2 fs1 fc0 sc0 ls5 ws0">如果这是我写的一个脚本，我希望能够具有执行权限，并取消其他用户<span class="_ _39"> </span><span class="ff3">(<span class="_ _2"></span></span><span class="ls17">所有其他用户<span class="_ _4"> </span><span class="ff3">)</span></span></div><div class="t m0 xc h5 y97 ff2 fs1 fc0 sc0 ls4 ws0">的写权限，可以用：</div><div class="t m0 xb h9 y98 ff7 fs4 fc0 sc0 ls4a ws0">$ chmod u+x o-w myfile</div><div class="t m0 xb h5 y99 ff2 fs1 fc0 sc0 ls31 ws0">这样，该文件的权限变为：</div><div class="t m0 xb h6 y9a ff2 fs1 fc0 sc0 ls47 ws0">现在已经使文件属主对<span class="_ _d"> </span><span class="ff3 ls0 ws9">m y f i l e</span><span class="ls1e">文件具有读、写执行的权限，而<span class="_ _2d"> </span><span class="ff3 ls0 ws9">a d m i n<span class="_"> </span></span><span class="ls19">组的用户对该文件具</span></span></div><div class="t m0 xc h5 y9b ff2 fs1 fc0 sc0 ls0 ws0">有读权限。</div><div class="t m0 xb h5 y9c ff2 fs1 fc0 sc0 ls1 ws0">如果希望某个脚本文件对你自己来说可执行，而且你对该文件的缺省权限很放心，那么</div><div class="t m0 xc h5 y9d ff2 fs1 fc0 sc0 ls1f ws0">只要使它对你来说具有执行权限即可。</div><div class="t m0 xb h9 y9e ff7 fs4 fc0 sc0 ls4b ws0">$ chmod u+x dt</div><div class="t m0 xc h5 y9f ff4 fs1 fc1 sc0 ls0 ws0">1.4.3 <span class="ff5">绝对模式</span></div><div class="t m0 xb h6 ya0 ff3 fs1 fc0 sc0 ls0 ws1">c h m o d<span class="ff2 ls9 ws0">命令绝对模式的一般形式为：</span></div><div class="t m0 xb h9 y13 ff7 fs4 fc0 sc0 ls4c ws0">chmod [mode] file</div><div class="t m0 xb h6 ya1 ff2 fs1 fc0 sc0 ls0 ws0">其中<span class="_ _2"></span><span class="ff3 ws1">m o d e<span class="_"> </span></span><span class="ls13">是一个八进制数。</span></div><div class="t m0 xb h5 ya2 ff2 fs1 fc0 sc0 ls4d ws0">在绝对模式中，权限部分有着不同的含义。每一个权限位用一个八进制数来代表，如表</div><div class="t m0 xc h6 ya3 ff3 fs1 fc0 sc0 ls0 ws1">1 - 3<span class="_ _2"></span><span class="ff2 ws0">所示。</span></div><div class="t m0 x1a hb ya4 ff5 fs6 fc0 sc0 ls0 ws0">表<span class="_ _2"></span><span class="ff4 lsb">1-3 </span>八进制目录<span class="_ _6"></span><span class="ff4">/<span class="_ _2"></span></span><span class="lsb">文件权限表示</span></div><div class="t m0 x1b hd ya5 ff2 fs7 fc0 sc0 ls0 ws0">八<span class="_ _2b"> </span>进<span class="_ _2a"> </span>制<span class="_ _2b"> </span>数<span class="_ _3a"> </span>含<span class="_ _21"> </span>义<span class="_ _3b"> </span>八<span class="_ _2b"> </span>进<span class="_ _2a"> </span>制<span class="_ _2b"> </span>数<span class="_ _3c"> </span>含<span class="_ _21"> </span>义</div><div class="t m0 x1c hc ya6 ff3 fs7 fc0 sc0 ls0 ws5">0 4 0 0<span class="_ _35"> </span><span class="ff2 ws0">文件属主可读<span class="_ _3d"> </span></span>0 0 1 0<span class="_ _12"> </span><span class="ff2 ls29 ws0">同组用户可执行</span></div><div class="t m0 x1c hc ya7 ff3 fs7 fc0 sc0 ls0 ws5">0 2 0 0<span class="_ _35"> </span><span class="ff2 ws0">文件属主可写<span class="_ _3d"> </span></span>0 0 0 4<span class="_ _12"> </span><span class="ff2 ws0">其他用户可读</span></div><div class="t m0 x1c hc y1a ff3 fs7 fc0 sc0 ls0 ws5">0 1 0 0<span class="_ _3e"> </span><span class="ff2 ls29 ws0">文件属主可执行<span class="_ _3f"> </span></span>0 0 0 2<span class="_ _40"> </span><span class="ff2 ws0">其他用户可写</span></div><div class="t m0 x1c hc ya8 ff3 fs7 fc0 sc0 ls0 ws5">0 0 4 0<span class="_ _3e"> </span><span class="ff2 ws0">同组用户可读<span class="_ _3d"> </span></span>0 0 0 1<span class="_ _40"> </span><span class="ff2 ls1e ws0">其他用户可执行</span></div><div class="t m0 x19 hc ya9 ff3 fs7 fc0 sc0 ls0 ws5">0 0 2 0<span class="_ _3e"> </span><span class="ff2 ws0">同组用户可写</span></div><div class="t m0 xb h6 yaa ff2 fs1 fc0 sc0 ls4e ws0">在设定权限的时候，只需按照表<span class="_ _e"> </span><span class="ff3 ls0 wsa">1 - 3<span class="_"> </span></span><span class="ls4f">查出与文件属主、同组用户和其他用户所具有的权限</span></div><div class="t m0 xc h5 yab ff2 fs1 fc0 sc0 ls26 ws0">相对应的数字，并把它们加起来，就是相应的权限表示。</div><div class="t m0 xb h6 yac ff2 fs1 fc0 sc0 ls0 ws0">从表<span class="ff3 wsb">1 - 3</span><span class="ls50">中可以看出，文件属主、同组用户和其他用户分别所能够具有的最大权限值就是<span class="_ _c"></span><span class="ff3">7</span></span>。</div><div class="t m0 x13 ha y41 ff9 fs1 fc0 sc0 ls0 ws0">第<span class="ffa">1</span>章<span class="_ _10"> </span>文件安全与权限<span class="_ _f"> </span><span class="ff8 fs5 fc2">5</span></div><div class="c x1 y1 w2 h2"><div class="t m0 x2 h3 y2 ff1 fs0 fc0 sc0 ls0 ws0">下载</div></div></div><div class="pi" data-data='{"ctm":[1.860465,0.000000,0.000000,1.860465,0.000000,0.000000]}'></div></div>

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