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<p>运用dd命令，将/dev/sdb磁盘中所有的数据全部备份到/dev/sdc磁盘上，需要的命令如下</p><p>dd&nbsp; if=/dev/sdb of=/dev/sdc bs=1024k&nbsp; &nbsp; &nbsp;</p><p>说明，if是需要备份的磁盘&nbsp; of后面是将备份导入的磁盘，bs=1024k这个地方的1024k都不要写错，如果忘了写k默认是1024个字节，容易出很多问题</p><p>备份这两块磁盘的前提是/dev/sdc这块磁盘已经格式化好了<br/></p><p><br style="white-space: normal;"/></p><p>跨服务器数据盘对拷，</p><p>盘大小：500G</p><p>实实际数据不足10G</p><p>dd if=/dev/sda bs=4M|ssh 192.168.1.13 “dd of=/dev/sdc conv=fdatasync”&nbsp;</p><p>居然要21个小时，万兆网卡。怎么能快点加速</p><p><br/></p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;&nbsp;<br/></p><p style="border:0px;line-height:22px;font-size:16px;color:rgb(51,51,51);font-family:&#39;微软雅黑&#39;, Verdana, Arial, Helvetica, sans-serif;">linux系统如果想做备份还原,使用ghost的时候经常出现问题,后来发现可以直接使用dd命令完成硬盘的克隆和还原.当拷贝完硬盘后，就可以拿这个硬盘放到其它设备上跑了。也就是完成了“烧写”了。</p><p style="border:0px;line-height:22px;font-size:16px;color:rgb(51,51,51);font-family:&#39;微软雅黑&#39;, Verdana, Arial, Helvetica, sans-serif;">实际操作中，最好使用另一个系统启动，如另一个硬盘的系统，或者用live cd。当然，拷贝当前运行中的系统也是可以的，但不知当前的这个系统还有哪些不确定东西，所以还是不建议。</p><p style="border:0px;line-height:22px;font-size:16px;color:rgb(51,51,51);font-family:&#39;微软雅黑&#39;, Verdana, Arial, Helvetica, sans-serif;">用fdisk -l查看当前所有分区信息(记得用root，否则执行了啥也看不到)，如：</p><pre style="border:0px;color:rgb(51,51,51);font-size:13px;"><br/></pre><blockquote style="border-width:1px 1px 1px 8px;border-style:solid;border-color:rgb(221,221,221);overflow:auto;">Device Boot &nbsp; &nbsp; &nbsp;Start &nbsp; &nbsp; &nbsp; &nbsp; End &nbsp; &nbsp; &nbsp;Blocks &nbsp; Id &nbsp;System

/dev/sdb1 &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;2048 &nbsp; &nbsp; 1002047 &nbsp; &nbsp; &nbsp;500000 &nbsp; 83 &nbsp;Linux

/dev/sdb2 &nbsp; &nbsp; &nbsp; &nbsp; 1002048 &nbsp; &nbsp;12002047 &nbsp; &nbsp; 5500000 &nbsp; 83 &nbsp;Linux

/dev/sdb3 &nbsp; &nbsp; &nbsp; &nbsp;12002048 &nbsp; &nbsp;13002047 &nbsp; &nbsp; &nbsp;500000 &nbsp; 83 &nbsp;Linux

/dev/sdb4 &nbsp; &nbsp; &nbsp; &nbsp;13002048 &nbsp; &nbsp;15002047 &nbsp; &nbsp; 1000000 &nbsp; 83 &nbsp;Linux</blockquote><p style="border:0px;line-height:22px;font-size:16px;color:rgb(51,51,51);font-family:&#39;微软雅黑&#39;, Verdana, Arial, Helvetica, sans-serif;">上面是我为了方便写文档而做的分区，可以看到Blocks十分工整，那是故意而为之的。</p><p style="border:0px;line-height:22px;font-size:16px;color:rgb(51,51,51);font-family:&#39;微软雅黑&#39;, Verdana, Arial, Helvetica, sans-serif;">全盘拷贝的命令：</p><pre style="border:0px;color:rgb(51,51,51);font-size:13px;"><br/></pre><blockquote style="border-width:1px 1px 1px 8px;border-style:solid;border-color:rgb(221,221,221);overflow:auto;">dd if=/dev/sdb &nbsp;of=/dev/sdc</blockquote><p style="border:0px;line-height:22px;font-size:16px;color:rgb(51,51,51);font-family:&#39;微软雅黑&#39;, Verdana, Arial, Helvetica, sans-serif;">分区拷贝：</p><pre style="border:0px;color:rgb(51,51,51);font-size:13px;"><br/></pre><blockquote style="border-width:1px 1px 1px 8px;border-style:solid;border-color:rgb(221,221,221);overflow:auto;">dd bs=512 count=[fdisk命令中最大的end数+1] if=/dev/sdb of=name.img</blockquote><p style="border:0px;line-height:22px;font-size:16px;color:rgb(51,51,51);font-family:&#39;微软雅黑&#39;, Verdana, Arial, Helvetica, sans-serif;">以上为例：</p><pre style="border:0px;color:rgb(51,51,51);font-size:13px;"><br/></pre><blockquote style="border-width:1px 1px 1px 8px;border-style:solid;border-color:rgb(221,221,221);overflow:auto;">dd bs=512 count=15002048 if=/dev/sdb of=ghost_linux_latelee.img</blockquote><p style="border:0px;line-height:22px;font-size:16px;color:rgb(51,51,51);font-family:&#39;微软雅黑&#39;, Verdana, Arial, Helvetica, sans-serif;">由于ghost_linux_latelee.img会很大，可以在拷贝时将其压缩：</p><pre style="border:0px;color:rgb(51,51,51);font-size:13px;"><br/></pre><blockquote style="border-width:1px 1px 1px 8px;border-style:solid;border-color:rgb(221,221,221);overflow:auto;">dd bs=512 count=15002048 if=/dev/sdb | gzip -9 &gt; ghost_linux_latelee.img.gz</blockquote><p style="border:0px;line-height:22px;font-size:16px;color:rgb(51,51,51);font-family:&#39;微软雅黑&#39;, Verdana, Arial, Helvetica, sans-serif;">上面所做的，就是传说的系统“备份”，或叫“系统克隆”。</p><p style="border:0px;line-height:22px;font-size:16px;color:rgb(51,51,51);font-family:&#39;微软雅黑&#39;, Verdana, Arial, Helvetica, sans-serif;">对应的，有系统恢复的操作。命令如下：</p><pre style="border:0px;color:rgb(51,51,51);font-size:13px;"><br/></pre><blockquote style="border-width:1px 1px 1px 8px;border-style:solid;border-color:rgb(221,221,221);overflow:auto;">dd if=ghost_linux_latelee.img&nbsp;of=/dev/sda</blockquote><p style="border:0px;line-height:22px;font-size:16px;color:rgb(51,51,51);font-family:&#39;微软雅黑&#39;, Verdana, Arial, Helvetica, sans-serif;">如果是压缩包，则命令为：</p><pre style="border:0px;color:rgb(51,51,51);font-size:13px;"><br/></pre><blockquote style="border-width:1px 1px 1px 8px;border-style:solid;border-color:rgb(221,221,221);overflow:auto;">gzip -c -d ghost_linux_latelee.img.gz | dd of=/dev/sda</blockquote><p style="border:0px;line-height:22px;font-size:16px;color:rgb(51,51,51);font-family:&#39;微软雅黑&#39;, Verdana, Arial, Helvetica, sans-serif;">在上面的拷贝过程中，并不知道拷贝了多少，只有最终结束时才显示出时间、拷贝速度。为了查看进度，可以在另一个终端输入(记得用root)：</p><pre style="border:0px;color:rgb(51,51,51);font-size:13px;"><br/></pre><blockquote style="border-width:1px 1px 1px 8px;border-style:solid;border-color:rgb(221,221,221);overflow:auto;">watch -n 5 killall -USR1 dd</blockquote><p style="border:0px;line-height:22px;font-size:16px;color:rgb(51,51,51);font-family:&#39;微软雅黑&#39;, Verdana, Arial, Helvetica, sans-serif;">（注：killall并不是传说中把进程kill掉，而是发送一个指定的信号到指定的进程）</p><p style="border:0px;line-height:22px;font-size:16px;color:rgb(51,51,51);font-family:&#39;微软雅黑&#39;, Verdana, Arial, Helvetica, sans-serif;">之后，就能执行dd的终端看到进度了，如：</p><pre style="border:0px;color:rgb(51,51,51);font-size:13px;"><br/></pre><blockquote style="border-width:1px 1px 1px 8px;border-style:solid;border-color:rgb(221,221,221);overflow:auto;">58299+0 records in
58298+0 records out
29848576 bytes (30 MB) copied, 4.67728 s, 6.4 MB/s
161403+0 records in
161402+0 records out
82637824 bytes (83 MB) copied, 9.69359 s, 8.5 MB/s
238651+0 records in
238650+0 records out
122188800 bytes (122 MB) copied, 14.7105 s, 8.3 MB/s</blockquote><p style="border:0px;line-height:22px;font-size:16px;color:rgb(51,51,51);font-family:&#39;微软雅黑&#39;, Verdana, Arial, Helvetica, sans-serif;">备注：</p><p style="border:0px;line-height:22px;font-size:16px;color:rgb(51,51,51);font-family:&#39;微软雅黑&#39;, Verdana, Arial, Helvetica, sans-serif;">用dd的方式，得到的镜像文件十分庞大——取决于所要做的系统的大小。比如，拷贝4GB的分区，真的就是拷贝4GB，即使是用gzip压缩，也压缩不了多少，文件依然很大。</p><p style="border:0px;line-height:22px;font-size:16px;color:rgb(51,51,51);font-family:&#39;微软雅黑&#39;, Verdana, Arial, Helvetica, sans-serif;">另外dd的方式也消除了我之前的担心，因为现在的Linux发行版的分区使用硬盘uuid作为标识，而不是/dev/sda1这种格式，据说uuid更好。但用dd拷贝，竟然连硬盘的uuid也一一拷贝，毫无变化，这的确让我吃惊。不过，目前看没什么时间研究dd了。</p><p style="border:0px;line-height:22px;font-size:16px;color:rgb(51,51,51);font-family:&#39;微软雅黑&#39;, Verdana, Arial, Helvetica, sans-serif;">PS：使用dd命令，可以读取硬盘的mbr扇区，示例如下：</p><pre style="border:0px;color:rgb(51,51,51);font-size:13px;">dd&nbsp;if=/dev/sdb&nbsp;of=mbr.bin&nbsp;bs=512&nbsp;count=1</pre><p style="border:0px;line-height:22px;font-size:16px;color:rgb(51,51,51);font-family:&#39;微软雅黑&#39;, Verdana, Arial, Helvetica, sans-serif;"><br/></p><p><br/></p><p><br/></p><h3>一：dd命令</h3><p>dd：用指定大小的块拷贝一个文件，并在拷贝的同时进行指定的转换。</p><p>注意：指定数字的地方若以下列字符结尾，则乘以相应的数字：b=512；c=1；k=1024；w=2</p><h4>参数注释：</h4><ol class=" list-paddingleft-2"><li><p>if=文件名：输入文件名，缺省为标准输入。即指定源文件。&lt; if=input file &gt;</p></li><li><p>of=文件名：输出文件名，缺省为标准输出。即指定目的文件。&lt; of=output file &gt;</p></li><li><p>ibs=bytes：一次读入bytes个字节，即指定一个块大小为bytes个字节。<br/>obs=bytes：一次输出bytes个字节，即指定一个块大小为bytes个字节。<br/>bs=bytes：同时设置读入/输出的块大小为bytes个字节。</p></li><li><p>cbs=bytes：一次转换bytes个字节，即指定转换缓冲区大小。</p></li><li><p>skip=blocks：从输入文件开头跳过blocks个块后再开始复制。</p></li><li><p>seek=blocks：从输出文件开头跳过blocks个块后再开始复制。<br/>注意：通常只用当输出文件是磁盘或磁带时才有效，即备份到磁盘或磁带时才有效。</p></li><li><p>count=blocks：仅拷贝blocks个块，块大小等于ibs指定的字节数。</p></li><li><p>conv=conversion：用指定的参数转换文件。</p></li></ol><ul class=" list-paddingleft-2"><ul class=" list-paddingleft-2" style="list-style-type: square;"><li><p>ascii：转换ebcdic为ascii</p></li><li><p>ebcdic：转换ascii为ebcdic</p></li><li><p>ibm：转换ascii为alternate ebcdic</p></li><li><p>block：把每一行转换为长度为cbs，不足部分用空格填充</p></li><li><p>unblock：使每一行的长度都为cbs，不足部分用空格填充</p></li><li><p>lcase：把大写字符转换为小写字符</p></li><li><p>ucase：把小写字符转换为大写字符</p></li><li><p>swab：交换输入的每对字节</p></li><li><p>noerror：出错时不停止</p></li><li><p>notrunc：不截短输出文件</p></li><li><p>sync：将每个输入块填充到ibs个字节，不足部分用空（NUL）字符补齐。</p></li></ul></ul><h3>二、dd应用实例</h3><h4>1.将本地的/dev/hdb整盘备份到/dev/hdd</h4><table border="0" cellpadding="0" cellspacing="0"><tbody><tr class="firstRow"><td class="gutter"><div class="line number1 index0 alt2">1</div></td><td class="code"><div class="line number1 index0 alt2"><code class="bash functions">dd</code> <code class="bash keyword">if</code><code class="bash plain">=</code><code class="bash plain">/dev/hdb</code> <code class="bash plain">of=</code><code class="bash plain">/dev/hdd</code></div></td></tr></tbody></table><h4>2.将/dev/hdb全盘数据备份到指定路径的image文件</h4><table border="0" cellpadding="0" cellspacing="0"><tbody><tr class="firstRow"><td class="gutter"><div class="line number1 index0 alt2">1</div></td><td class="code"><div class="line number1 index0 alt2"><code class="bash functions">dd</code> <code class="bash keyword">if</code><code class="bash plain">=</code><code class="bash plain">/dev/hdb</code> <code class="bash plain">of=</code><code class="bash plain">/root/image</code></div></td></tr></tbody></table><h4>3.将备份文件恢复到指定盘</h4><table border="0" cellpadding="0" cellspacing="0"><tbody><tr class="firstRow"><td class="gutter"><div class="line number1 index0 alt2">1</div></td><td class="code"><div class="line number1 index0 alt2"><code class="bash functions">dd</code> <code class="bash keyword">if</code><code class="bash plain">=</code><code class="bash plain">/root/image</code> <code class="bash plain">of=</code><code class="bash plain">/dev/hdb</code></div></td></tr></tbody></table><h4>4.备份/dev/hdb全盘数据，并利用gzip工具进行压缩，保存到指定路径</h4><table border="0" cellpadding="0" cellspacing="0"><tbody><tr class="firstRow"><td class="gutter"><div class="line number1 index0 alt2">1</div></td><td class="code"><div class="line number1 index0 alt2"><code class="bash functions">dd</code> <code class="bash keyword">if</code><code class="bash plain">=</code><code class="bash plain">/dev/hdb</code> <code class="bash plain">| </code><code class="bash functions">gzip</code> <code class="bash plain">&gt; </code><code class="bash plain">/root/image</code><code class="bash plain">.gz</code></div></td></tr></tbody></table><h4>5.将压缩的备份文件恢复到指定盘</h4><table border="0" cellpadding="0" cellspacing="0"><tbody><tr class="firstRow"><td class="gutter"><div class="line number1 index0 alt2">1</div></td><td class="code"><div class="line number1 index0 alt2"><code class="bash functions">gzip</code> <code class="bash plain">-</code><code class="bash functions">dc</code> <code class="bash plain">/root/image</code><code class="bash plain">.gz | </code><code class="bash functions">dd</code> <code class="bash plain">of=</code><code class="bash plain">/dev/hdb</code></div></td></tr></tbody></table><h4>6.备份与恢复MBR</h4><p>备份磁盘开始的512个字节大小的MBR信息到指定文件：</p><table border="0" cellpadding="0" cellspacing="0"><tbody><tr class="firstRow"><td class="gutter"><div class="line number1 index0 alt2">1</div></td><td class="code"><div class="line number1 index0 alt2"><code class="bash functions">dd</code> <code class="bash keyword">if</code><code class="bash plain">=</code><code class="bash plain">/dev/hda</code> <code class="bash plain">of=</code><code class="bash plain">/root/image</code> <code class="bash plain">count=1 bs=512</code></div></td></tr></tbody></table><p>count=1指仅拷贝一个块；bs=512指块大小为512个字节。</p><p>恢复：</p><table border="0" cellpadding="0" cellspacing="0"><tbody><tr class="firstRow"><td class="gutter"><div class="line number1 index0 alt2">1</div></td><td class="code"><div class="line number1 index0 alt2"><code class="bash functions">dd</code> <code class="bash keyword">if</code><code class="bash plain">=</code><code class="bash plain">/root/image</code> <code class="bash plain">of=</code><code class="bash plain">/dev/had</code></div></td></tr></tbody></table><p>将备份的MBR信息写到磁盘开始部分</p><h4>7.备份软盘</h4><table border="0" cellpadding="0" cellspacing="0"><tbody><tr class="firstRow"><td class="gutter"><div class="line number1 index0 alt2">1</div></td><td class="code"><div class="line number1 index0 alt2"><code class="bash functions">dd</code> <code class="bash keyword">if</code><code class="bash plain">=</code><code class="bash plain">/dev/fd0</code> <code class="bash plain">of=disk.img count=1 bs=1440k (即块大小为1.44M)</code></div></td></tr></tbody></table><h4>8.拷贝内存内容到硬盘</h4><table border="0" cellpadding="0" cellspacing="0"><tbody><tr class="firstRow"><td class="gutter"><div class="line number1 index0 alt2">1</div></td><td class="code"><div class="line number1 index0 alt2"><code class="bash functions">dd</code> <code class="bash keyword">if</code><code class="bash plain">=</code><code class="bash plain">/dev/mem</code> <code class="bash plain">of=</code><code class="bash plain">/root/mem</code><code class="bash plain">.bin bs=1024 (指定块大小为1k)</code></div></td></tr></tbody></table><h4>9.拷贝光盘内容到指定文件夹，并保存为cd.iso文件</h4><table border="0" cellpadding="0" cellspacing="0"><tbody><tr class="firstRow"><td class="gutter"><div class="line number1 index0 alt2">1</div></td><td class="code"><div class="line number1 index0 alt2"><code class="bash functions">dd</code> <code class="bash keyword">if</code><code class="bash plain">=</code><code class="bash plain">/dev/cdrom</code><code class="bash plain">(hdc) of=</code><code class="bash plain">/root/cd</code><code class="bash plain">.iso</code></div></td></tr></tbody></table><h4>10.增加swap分区文件大小</h4><p>第一步：创建一个大小为256M的文件：</p><table border="0" cellpadding="0" cellspacing="0"><tbody><tr class="firstRow"><td class="gutter"><div class="line number1 index0 alt2">1</div></td><td class="code"><div class="line number1 index0 alt2"><code class="bash functions">dd</code> <code class="bash keyword">if</code><code class="bash plain">=</code><code class="bash plain">/dev/zero</code> <code class="bash plain">of=</code><code class="bash plain">/swapfile</code> <code class="bash plain">bs=1024 count=262144</code></div></td></tr></tbody></table><p>第二步：把这个文件变成swap文件：</p><table border="0" cellpadding="0" cellspacing="0"><tbody><tr class="firstRow"><td class="gutter"><div class="line number1 index0 alt2">1</div></td><td class="code"><div class="line number1 index0 alt2"><code class="bash plain">mkswap </code><code class="bash plain">/swapfile</code></div></td></tr></tbody></table><p>第三步：启用这个swap文件：</p><table border="0" cellpadding="0" cellspacing="0"><tbody><tr class="firstRow"><td class="gutter"><div class="line number1 index0 alt2">1</div></td><td class="code"><div class="line number1 index0 alt2"><code class="bash plain">swapon </code><code class="bash plain">/swapfile</code></div></td></tr></tbody></table><p>第四步：编辑/etc/fstab文件，使在每次开机时自动加载swap文件：</p><table border="0" cellpadding="0" cellspacing="0"><tbody><tr class="firstRow"><td class="gutter"><div class="line number1 index0 alt2">1</div></td><td class="code"><div class="line number1 index0 alt2"><code class="bash plain">/swapfile</code> <code class="bash plain">swap swap default 0 0</code></div></td></tr></tbody></table><h4>11.销毁磁盘数据</h4><table border="0" cellpadding="0" cellspacing="0"><tbody><tr class="firstRow"><td class="gutter"><div class="line number1 index0 alt2">1</div></td><td class="code"><div class="line number1 index0 alt2"><code class="bash functions">dd</code> <code class="bash keyword">if</code><code class="bash plain">=</code><code class="bash plain">/dev/urandom</code> <code class="bash plain">of=</code><code class="bash plain">/dev/hda1</code></div></td></tr></tbody></table><p>注意：利用随机的数据填充硬盘，在某些必要的场合可以用来销毁数据。</p><h4>12.测试硬盘的读写速度</h4><table border="0" cellpadding="0" cellspacing="0"><tbody><tr class="firstRow"><td class="gutter"><div class="line number1 index0 alt2">1</div><div class="line number2 index1 alt1">2</div></td><td class="code"><div class="line number1 index0 alt2"><code class="bash functions">dd</code> <code class="bash keyword">if</code><code class="bash plain">=</code><code class="bash plain">/dev/zero</code> <code class="bash plain">bs=1024 count=1000000 of=</code><code class="bash plain">/root/1Gb</code><code class="bash plain">.</code><code class="bash functions">file</code></div><div class="line number2 index1 alt1"><code class="bash functions">dd</code> <code class="bash keyword">if</code><code class="bash plain">=</code><code class="bash plain">/root/1Gb</code><code class="bash plain">.</code><code class="bash functions">file</code> <code class="bash plain">bs=64k | </code><code class="bash functions">dd</code> <code class="bash plain">of=</code><code class="bash plain">/dev/null</code></div></td></tr></tbody></table><p>通过以上两个命令输出的命令执行时间，可以计算出硬盘的读、写速度。</p><h4>13.确定硬盘的最佳块大小：</h4><table border="0" cellpadding="0" cellspacing="0"><tbody><tr class="firstRow"><td class="gutter"><div class="line number1 index0 alt2">1</div><div class="line number2 index1 alt1">2</div><div class="line number3 index2 alt2">3</div><div class="line number4 index3 alt1">4</div><div class="line number5 index4 alt2">5</div><div class="line number6 index5 alt1">6</div><div class="line number7 index6 alt2">7</div></td><td class="code"><div class="line number1 index0 alt2"><code class="bash functions">dd</code> <code class="bash keyword">if</code><code class="bash plain">=</code><code class="bash plain">/dev/zero</code> <code class="bash plain">bs=1024 count=1000000 of=</code><code class="bash plain">/root/1Gb</code><code class="bash plain">.</code><code class="bash functions">file</code></div>&nbsp;<div class="line number3 index2 alt2"><code class="bash functions">dd</code> <code class="bash keyword">if</code><code class="bash plain">=</code><code class="bash plain">/dev/zero</code> <code class="bash plain">bs=2048 count=500000 of=</code><code class="bash plain">/root/1Gb</code><code class="bash plain">.</code><code class="bash functions">file</code></div>&nbsp;<div class="line number5 index4 alt2"><code class="bash functions">dd</code> <code class="bash keyword">if</code><code class="bash plain">=</code><code class="bash plain">/dev/zero</code> <code class="bash plain">bs=4096 count=250000 of=</code><code class="bash plain">/root/1Gb</code><code class="bash plain">.</code><code class="bash functions">file</code></div>&nbsp;<div class="line number7 index6 alt2"><code class="bash functions">dd</code> <code class="bash keyword">if</code><code class="bash plain">=</code><code class="bash plain">/dev/zero</code> <code class="bash plain">bs=8192 count=125000 of=</code><code class="bash plain">/root/1Gb</code><code class="bash plain">.</code><code class="bash functions">file</code></div></td></tr></tbody></table><p>通过比较以上命令输出中所显示的命令执行时间，即可确定系统最佳的块大小。</p><h4>14.修复硬盘：</h4><table border="0" cellpadding="0" cellspacing="0"><tbody><tr class="firstRow"><td class="gutter"><div class="line number1 index0 alt2">1</div></td><td class="code"><div class="line number1 index0 alt2"><code class="bash functions">dd</code> <code class="bash keyword">if</code><code class="bash plain">=</code><code class="bash plain">/dev/sda</code> <code class="bash plain">of=</code><code class="bash plain">/dev/sda</code> <code class="bash plain">或</code><code class="bash functions">dd</code> <code class="bash keyword">if</code><code class="bash plain">=</code><code class="bash plain">/dev/hda</code> <code class="bash plain">of=</code><code class="bash plain">/dev/hda</code></div></td></tr></tbody></table><p>当硬盘较长时间(一年以上)放置不使用后，磁盘上会产生magnetic flux point，当磁头读到这些区域时会遇到困难，并可能导致I/O错误。当这种情况影响到硬盘的第一个扇区时，可能导致硬盘报废。上边的命令有可能使这些数 据起死回生。并且这个过程是安全、高效的。</p><h4>15.利用netcat远程备份</h4><table border="0" cellpadding="0" cellspacing="0"><tbody><tr class="firstRow"><td class="gutter"><div class="line number1 index0 alt2">1</div></td><td class="code"><div class="line number1 index0 alt2"><code class="bash functions">dd</code> <code class="bash keyword">if</code><code class="bash plain">=</code><code class="bash plain">/dev/hda</code> <code class="bash plain">bs=16065b | netcat &lt; targethost-IP &gt; 1234</code></div></td></tr></tbody></table><p>在源主机上执行此命令备份/dev/hda</p><table border="0" cellpadding="0" cellspacing="0"><tbody><tr class="firstRow"><td class="gutter"><div class="line number1 index0 alt2">1</div></td><td class="code"><div class="line number1 index0 alt2"><code class="bash plain">netcat -l -p 1234 | </code><code class="bash functions">dd</code> <code class="bash plain">of=</code><code class="bash plain">/dev/hdc</code> <code class="bash plain">bs=16065b</code></div></td></tr></tbody></table><p>在目的主机上执行此命令来接收数据并写入/dev/hdc</p><table border="0" cellpadding="0" cellspacing="0"><tbody><tr class="firstRow"><td class="gutter"><div class="line number1 index0 alt2">1</div><div class="line number2 index1 alt1">2</div><div class="line number3 index2 alt2">3</div></td><td class="code"><div class="line number1 index0 alt2"><code class="bash plain">netcat -l -p 1234 | </code><code class="bash functions">bzip2</code> <code class="bash plain">&gt; partition.img</code></div>&nbsp;<div class="line number3 index2 alt2"><code class="bash plain">netcat -l -p 1234 | </code><code class="bash functions">gzip</code> <code class="bash plain">&gt; partition.img</code></div></td></tr></tbody></table><p>以上两条指令是目的主机指令的变化分别采用bzip2、gzip对数据进行压缩，并将备份文件保存在当前目录。</p><h4>16.将一个很大的视频文件中的第i个字节的值改成0x41（也就是大写字母A的ASCII值）</h4><table border="0" cellpadding="0" cellspacing="0"><tbody><tr class="firstRow"><td class="gutter"><div class="line number1 index0 alt2">1</div></td><td class="code"><div class="line number1 index0 alt2"><code class="bash functions">echo</code> <code class="bash plain">A | </code><code class="bash functions">dd</code> <code class="bash plain">of=bigfile seek=$i bs=1 count=1 conv=notrunc</code></div></td></tr></tbody></table><h3>三、/dev/null和/dev/zero的区别</h3><p>/dev/null，外号叫无底洞，你可以向它输出任何数据，它通吃，并且不会撑着！</p><p>/dev/zero，是一个输入设备，你可你用它来初始化文件。该设备无穷尽地提供0，可以使用任何你需要的数目——设备提供的要多的多。他可以用于向设备或文件写入字符串0。</p><p>/dev/null——它是空设备，也称为位桶（bit bucket）。任何写入它的输出都会被抛弃。如果不想让消息以标准输出显示或写入文件，那么可以将消息重定向到位桶。</p><table border="0" cellpadding="0" cellspacing="0"><tbody><tr class="firstRow"><td class="gutter"><div class="line number1 index0 alt2">1</div><div class="line number2 index1 alt1">2</div><div class="line number3 index2 alt2">3</div><div class="line number4 index3 alt1">4</div><div class="line number5 index4 alt2">5</div></td><td class="code"><div class="line number1 index0 alt2"><code class="bash plain">heng@me:</code><code class="bash keyword">if</code><code class="bash plain">=</code><code class="bash plain">/dev/zero</code> <code class="bash plain">of=.</code><code class="bash plain">/test</code><code class="bash plain">.txt bs=1k count=1</code></div><div class="line number2 index1 alt1"><code class="bash plain">heng@me:</code><code class="bash functions">ls</code> <code class="bash plain">–l</code></div><div class="line number3 index2 alt2"><code class="bash plain">total 4</code></div><div class="line number4 index3 alt1"><code class="bash plain">-rw-r--r-- 1 oracle dba 1024 Jul 15 16:56 </code><code class="bash functions">test</code><code class="bash plain">.txt</code></div><div class="line number5 index4 alt2"><code class="bash plain">heng@me:</code><code class="bash functions">find</code> <code class="bash plain">/ -name access_log 2&gt;</code><code class="bash plain">/dev/null</code></div></td></tr></tbody></table><h4>使用/dev/nul</h4><p>把/dev/null看作”黑洞”， 它等价于一个只写文件，所有写入它的内容都会永远丢失.，而尝试从它那儿读取内容则什么也读不到。然而， /dev/null对命令行和脚本都非常的有用</p><p>禁止标准输出</p><table border="0" cellpadding="0" cellspacing="0"><tbody><tr class="firstRow"><td class="gutter"><div class="line number1 index0 alt2">1</div></td><td class="code"><div class="line number1 index0 alt2"><code class="bash plain">heng@me:</code><code class="bash functions">cat</code> <code class="bash plain">$filename &gt;</code><code class="bash plain">/dev/null</code> <code class="bash comments">#文件内容丢失，而不会输出到标准输出.</code></div></td></tr></tbody></table><p>禁止标准错误</p><table border="0" cellpadding="0" cellspacing="0"><tbody><tr class="firstRow"><td class="gutter"><div class="line number1 index0 alt2">1</div></td><td class="code"><div class="line number1 index0 alt2"><code class="bash plain">heng@me:</code><code class="bash functions">rm</code> <code class="bash plain">$badname 2&gt;</code><code class="bash plain">/dev/null</code> <code class="bash comments">#这样错误信息[标准错误]就被丢到太平洋去了</code></div></td></tr></tbody></table><p>禁止标准输出和标准错误的输出</p><table border="0" cellpadding="0" cellspacing="0"><tbody><tr class="firstRow"><td class="gutter"><div class="line number1 index0 alt2">1</div></td><td class="code"><div class="line number1 index0 alt2"><code class="bash plain">heng@me:</code><code class="bash functions">cat</code> <code class="bash plain">$filename 2&gt;</code><code class="bash plain">/dev/null</code> <code class="bash plain">&gt;</code><code class="bash plain">/dev/null</code></div></td></tr></tbody></table><p>如果”$filename”不存在，将不会有任何错误信息提示；如果”$filename”存在， 文件的内容不会打印到标准输出。因此，上面的代码根本不会输出任何信息。当只想测试命令的退出码而不想有任何输出时非常有用。</p><h4>使用/dev/zero</h4><p>像/dev/null一样， /dev/zero也是一个伪文件， 但它实际上产生连续不断的null的流（二进制的零流，而不是ASCII型的）。 写入它的输出会丢失不见， 而从/dev/zero读出一连串的null也比较困难， 虽然这也能通过od或一个十六进制编辑器来做到。</p><p>/dev/zero主要的用处是用来创建一个指定长度用于初始化的空文件，就像临时交换文件。</p><p>用/dev/zero创建一个交换临时文件</p><table border="0" cellpadding="0" cellspacing="0"><tbody><tr class="firstRow"><td class="gutter"><div class="line number1 index0 alt2">1</div><div class="line number2 index1 alt1">2</div><div class="line number3 index2 alt2">3</div><div class="line number4 index3 alt1">4</div><div class="line number5 index4 alt2">5</div><div class="line number6 index5 alt1">6</div><div class="line number7 index6 alt2">7</div><div class="line number8 index7 alt1">8</div><div class="line number9 index8 alt2">9</div><div class="line number10 index9 alt1">10</div><div class="line number11 index10 alt2">11</div><div class="line number12 index11 alt1">12</div><div class="line number13 index12 alt2">13</div><div class="line number14 index13 alt1">14</div><div class="line number15 index14 alt2">15</div><div class="line number16 index15 alt1">16</div><div class="line number17 index16 alt2">17</div><div class="line number18 index17 alt1">18</div><div class="line number19 index18 alt2">19</div><div class="line number20 index19 alt1">20</div><div class="line number21 index20 alt2">21</div><div class="line number22 index21 alt1">22</div><div class="line number23 index22 alt2">23</div><div class="line number24 index23 alt1">24</div><div class="line number25 index24 alt2">25</div><div class="line number26 index25 alt1">26</div><div class="line number27 index26 alt2">27</div><div class="line number28 index27 alt1">28</div><div class="line number29 index28 alt2">29</div><div class="line number30 index29 alt1">30</div><div class="line number31 index30 alt2">31</div><div class="line number32 index31 alt1">32</div><div class="line number33 index32 alt2">33</div><div class="line number34 index33 alt1">34</div><div class="line number35 index34 alt2">35</div></td><td class="code"><div class="line number1 index0 alt2"><code class="bash preprocessor bold">#!/bin/bash</code></div><div class="line number2 index1 alt1"><code class="bash comments"># 创建一个交换文件.</code></div><div class="line number3 index2 alt2"><code class="bash plain">ROOT_UID=0 </code><code class="bash comments"># Root 用户的 $UID 是 0.</code></div><div class="line number4 index3 alt1"><code class="bash plain">E_WRONG_USER=65 </code><code class="bash comments"># 不是 root?</code></div><div class="line number5 index4 alt2"><code class="bash plain">FILE=</code><code class="bash plain">/swap</code></div><div class="line number6 index5 alt1"><code class="bash plain">BLOCKSIZE=1024</code></div><div class="line number7 index6 alt2"><code class="bash plain">MINBLOCKS=40</code></div><div class="line number8 index7 alt1"><code class="bash plain">SUCCESS=0</code></div><div class="line number9 index8 alt2"><code class="bash comments"># 这个脚本必须用root来运行.</code></div><div class="line number10 index9 alt1"><code class="bash keyword">if</code> <code class="bash plain">[ </code><code class="bash string">&quot;$UID&quot;</code> <code class="bash plain">-</code><code class="bash keyword">ne</code> <code class="bash string">&quot;$ROOT_UID&quot;</code> <code class="bash plain">]</code></div><div class="line number11 index10 alt2"><code class="bash keyword">then</code></div><div class="line number12 index11 alt1"><code class="bash functions">echo</code><code class="bash plain">; </code><code class="bash functions">echo</code> <code class="bash string">&quot;You must be root to run this script.&quot;</code><code class="bash plain">; </code><code class="bash functions">echo</code></div><div class="line number13 index12 alt2"><code class="bash functions">exit</code> <code class="bash plain">$E_WRONG_USER</code></div><div class="line number14 index13 alt1"><code class="bash keyword">fi</code></div><div class="line number15 index14 alt2"><code class="bash plain">blocks=${1:-$MINBLOCKS} </code><code class="bash comments"># 如果命令行没有指定，</code></div><div class="line number16 index15 alt1"><code class="bash comments">#+ 则设置为默认的40块.</code></div><div class="line number17 index16 alt2"><code class="bash comments"># 上面这句等同如：</code></div><div class="line number18 index17 alt1"><code class="bash comments"># --------------------------------------------------</code></div><div class="line number19 index18 alt2"><code class="bash comments"># if [ -n &quot;$1&quot; ]</code></div><div class="line number20 index19 alt1"><code class="bash comments"># then</code></div><div class="line number21 index20 alt2"><code class="bash comments"># blocks=$1</code></div><div class="line number22 index21 alt1"><code class="bash comments"># else</code></div><div class="line number23 index22 alt2"><code class="bash comments"># blocks=$MINBLOCKS</code></div><div class="line number24 index23 alt1"><code class="bash comments"># fi</code></div><div class="line number25 index24 alt2"><code class="bash comments"># --------------------------------------------------</code></div><div class="line number26 index25 alt1"><code class="bash keyword">if</code> <code class="bash plain">[ </code><code class="bash string">&quot;$blocks&quot;</code> <code class="bash plain">-lt $MINBLOCKS ]</code></div><div class="line number27 index26 alt2"><code class="bash keyword">then</code></div><div class="line number28 index27 alt1"><code class="bash plain">blocks=$MINBLOCKS </code><code class="bash comments"># 最少要有 40 个块长.</code></div><div class="line number29 index28 alt2"><code class="bash keyword">fi</code></div><div class="line number30 index29 alt1"><code class="bash functions">echo</code> <code class="bash string">&quot;Creating swap file of size $blocks blocks (KB).&quot;</code></div><div class="line number31 index30 alt2"><code class="bash functions">dd</code> <code class="bash keyword">if</code><code class="bash plain">=</code><code class="bash plain">/dev/zero</code> <code class="bash plain">of=$FILE bs=$BLOCKSIZE count=$blocks </code><code class="bash comments"># 把零写入文件.</code></div><div class="line number32 index31 alt1"><code class="bash plain">mkswap $FILE $blocks </code><code class="bash comments"># 将此文件建为交换文件（或称交换分区）.</code></div><div class="line number33 index32 alt2"><code class="bash plain">swapon $FILE </code><code class="bash comments"># 激活交换文件.</code></div><div class="line number34 index33 alt1"><code class="bash functions">echo</code> <code class="bash string">&quot;Swap file created and activated.&quot;</code></div><div class="line number35 index34 alt2"><code class="bash functions">exit</code> <code class="bash plain">$SUCCESS</code></div></td></tr></tbody></table><p>关于 /dev/zero 的另一个应用是为特定的目的而用零去填充一个指定大小的文件， 如挂载一个文件系统到环回设备 （loopback device）或&quot;安全地&quot; 删除一个文件。</p><p>例子创建ramdisk</p><table border="0" cellpadding="0" cellspacing="0"><tbody><tr class="firstRow"><td class="gutter"><div class="line number1 index0 alt2">1</div><div class="line number2 index1 alt1">2</div><div class="line number3 index2 alt2">3</div><div class="line number4 index3 alt1">4</div><div class="line number5 index4 alt2">5</div><div class="line number6 index5 alt1">6</div><div class="line number7 index6 alt2">7</div><div class="line number8 index7 alt1">8</div><div class="line number9 index8 alt2">9</div><div class="line number10 index9 alt1">10</div><div class="line number11 index10 alt2">11</div><div class="line number12 index11 alt1">12</div><div class="line number13 index12 alt2">13</div><div class="line number14 index13 alt1">14</div><div class="line number15 index14 alt2">15</div><div class="line number16 index15 alt1">16</div><div class="line number17 index16 alt2">17</div><div class="line number18 index17 alt1">18</div><div class="line number19 index18 alt2">19</div><div class="line number20 index19 alt1">20</div><div class="line number21 index20 alt2">21</div><div class="line number22 index21 alt1">22</div><div class="line number23 index22 alt2">23</div><div class="line number24 index23 alt1">24</div><div class="line number25 index24 alt2">25</div><div class="line number26 index25 alt1">26</div><div class="line number27 index26 alt2">27</div><div class="line number28 index27 alt1">28</div><div class="line number29 index28 alt2">29</div><div class="line number30 index29 alt1">30</div><div class="line number31 index30 alt2">31</div><div class="line number32 index31 alt1">32</div><div class="line number33 index32 alt2">33</div><div class="line number34 index33 alt1">34</div><div class="line number35 index34 alt2">35</div><div class="line number36 index35 alt1">36</div><div class="line number37 index36 alt2">37</div><div class="line number38 index37 alt1">38</div><div class="line number39 index38 alt2">39</div><div class="line number40 index39 alt1">40</div><div class="line number41 index40 alt2">41</div><div class="line number42 index41 alt1">42</div><div class="line number43 index42 alt2">43</div><div class="line number44 index43 alt1">44</div></td><td class="code"><div class="line number1 index0 alt2"><code class="bash preprocessor bold">#!/bin/bash</code></div><div class="line number2 index1 alt1"><code class="bash comments"># ramdisk.sh</code></div><div class="line number3 index2 alt2"><code class="bash comments"># &quot;ramdisk&quot;是系统RAM内存的一段，</code></div><div class="line number4 index3 alt1"><code class="bash comments">#+ 它可以被当成是一个文件系统来操作.</code></div><div class="line number5 index4 alt2"><code class="bash comments"># 它的优点是存取速度非常快 (包括读和写).</code></div><div class="line number6 index5 alt1"><code class="bash comments"># 缺点: 易失性, 当计算机重启或关机时会丢失数据.</code></div><div class="line number7 index6 alt2"><code class="bash comments">#+ 会减少系统可用的RAM.</code></div><div class="line number8 index7 alt1"><code class="bash comments"># 10 # 那么ramdisk有什么作用呢?</code></div><div class="line number9 index8 alt2"><code class="bash comments"># 保存一个较大的数据集在ramdisk, 比如一张表或字典,</code></div><div class="line number10 index9 alt1"><code class="bash comments">#+ 这样可以加速数据查询, 因为在内存里查找比在磁盘里查找快得多.</code></div><div class="line number11 index10 alt2"><code class="bash plain">E_NON_ROOT_USER=70 </code><code class="bash comments"># 必须用root来运行.</code></div><div class="line number12 index11 alt1"><code class="bash plain">ROOTUSER_NAME=root</code></div><div class="line number13 index12 alt2"><code class="bash plain">MOUNTPT=</code><code class="bash plain">/mnt/ramdisk</code></div><div class="line number14 index13 alt1"><code class="bash plain">SIZE=2000 </code><code class="bash comments"># 2K 个块 (可以合适的做修改)</code></div><div class="line number15 index14 alt2"><code class="bash plain">BLOCKSIZE=1024 </code><code class="bash comments"># 每块有1K (1024 byte) 的大小</code></div><div class="line number16 index15 alt1"><code class="bash plain">DEVICE=</code><code class="bash plain">/dev/ram0</code> <code class="bash comments"># 第一个 ram 设备</code></div><div class="line number17 index16 alt2"><code class="bash plain">username=`</code><code class="bash functions">id</code> <code class="bash plain">-nu`</code></div><div class="line number18 index17 alt1"><code class="bash keyword">if</code> <code class="bash plain">[ </code><code class="bash string">&quot;$username&quot;</code> <code class="bash plain">!= </code><code class="bash string">&quot;$ROOTUSER_NAME&quot;</code> <code class="bash plain">]</code></div><div class="line number19 index18 alt2"><code class="bash keyword">then</code></div><div class="line number20 index19 alt1"><code class="bash functions">echo</code> <code class="bash string">&quot;Must be root to run &quot;</code><code class="bash plain">`</code><code class="bash functions">basename</code> <code class="bash plain">$0`</code><code class="bash string">&quot;.&quot;</code></div><div class="line number21 index20 alt2"><code class="bash functions">exit</code> <code class="bash plain">$E_NON_ROOT_USER</code></div><div class="line number22 index21 alt1"><code class="bash keyword">fi</code></div><div class="line number23 index22 alt2"><code class="bash keyword">if</code> <code class="bash plain">[ ! -d </code><code class="bash string">&quot;$MOUNTPT&quot;</code> <code class="bash plain">] </code><code class="bash comments"># 测试挂载点是否已经存在了,</code></div><div class="line number24 index23 alt1"><code class="bash keyword">then</code> <code class="bash comments">#+ 如果这个脚本已经运行了好几次了就不会再建这个目录了</code></div><div class="line number25 index24 alt2"><code class="bash functions">mkdir</code> <code class="bash plain">$MOUNTPT </code><code class="bash comments">#+ 因为前面已经建立了.</code></div><div class="line number26 index25 alt1"><code class="bash keyword">fi</code></div><div class="line number27 index26 alt2"><code class="bash functions">dd</code> <code class="bash keyword">if</code><code class="bash plain">=</code><code class="bash plain">/dev/zero</code> <code class="bash plain">of=$DEVICE count=$SIZE bs=$BLOCKSIZE</code></div>&nbsp;<div class="line number29 index28 alt2"><code class="bash comments"># 把RAM设备的内容用零填充.</code></div><div class="line number30 index29 alt1"><code class="bash comments"># 为何需要这么做?</code></div><div class="line number31 index30 alt2"><code class="bash plain">mke2fs $DEVICE </code><code class="bash comments"># 在RAM设备上创建一个ext2文件系统.</code></div><div class="line number32 index31 alt1"><code class="bash functions">mount</code> <code class="bash plain">$DEVICE $MOUNTPT </code><code class="bash comments"># 挂载设备.</code></div><div class="line number33 index32 alt2"><code class="bash functions">chmod</code> <code class="bash plain">777 $MOUNTPT </code><code class="bash comments"># 使普通用户也可以存取这个ramdisk.</code></div><div class="line number34 index33 alt1"><code class="bash comments"># 但是, 只能由root来缷载它.</code></div><div class="line number35 index34 alt2"><code class="bash functions">echo</code> <code class="bash string">&quot;&quot;</code><code class="bash plain">$MOUNTPT</code><code class="bash string">&quot; now available for use.&quot;</code></div><div class="line number36 index35 alt1"><code class="bash comments"># 现在 ramdisk 即使普通用户也可以用来存取文件了.</code></div><div class="line number37 index36 alt2"><code class="bash comments"># 注意, ramdisk是易失的, 所以当计算机系统重启或关机时ramdisk里的内容会消失.</code></div><div class="line number38 index37 alt1"><code class="bash comments"># 拷贝所有你想保存文件到一个常规的磁盘目录下.</code></div><div class="line number39 index38 alt2"><code class="bash comments"># 重启之后, 运行这个脚本再次建立起一个 ramdisk.</code></div><div class="line number40 index39 alt1"><code class="bash comments"># 仅重新加载 /mnt/ramdisk 而没有其他的步骤将不会正确工作.</code></div><div class="line number41 index40 alt2"><code class="bash comments"># 如果加以改进, 这个脚本可以放在 /etc/rc.d/rc.local,</code></div><div class="line number42 index41 alt1"><code class="bash comments">#+ 以使系统启动时能自动设立一个ramdisk.</code></div><div class="line number43 index42 alt2"><code class="bash comments"># 这样很合适速度要求高的数据库服务器.</code></div><div class="line number44 index43 alt1"><code class="bash functions">exit</code> <code class="bash plain">0</code></div></td></tr></tbody></table><p>via&nbsp;<a class="external" href="http://www.linuxde.net/2013/03/12928.html" rel="external nofollow" target="_blank">http://www.linuxde.net/2013/03/12928.html</a>&nbsp;</p><p><br/></p><p><br/></p><p><br/></p><p><br/></p><p><br/></p><p><br/></p><p><br/></p><p><br/></p><p>dd命令：convert and copy a file</p><p><strong>用法：</strong></p><p>dd if=/PATH/FROM/SRC of=/PATH/TO/DEST</p><p>bs=#：block size, 复制单元大小；</p><p>count=#：复制多少个bs；</p><p><strong>磁盘拷贝：</strong></p><p>dd if=/dev/sda of=/dev/sdb</p><p><strong>备份MBR</strong></p><p>dd if=/dev/sda of=/tmp/mbr.bak bs=512 count=1</p><p><strong>破坏MBR中的bootloader：</strong></p><p>dd if=/dev/zero of=/dev/sda bs=256 count=1</p><p>两个特殊设备：</p><p>/dev/null: 数据黑洞；</p><p>/dev/zero：吐零</p><p><strong>1.做硬盘对拷：</strong></p><p>dd if=/dev/sda of=/dev/sdb bs=1024k &amp;</p><p>注意：</p><p>(1).先改fstab文件，把LABLE换成对应的&nbsp; /dev/sda(不改的话，拷完后重启系统不知道从哪块盘启动了）</p><p>/dev/sda2&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;/&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;ext3&nbsp; &nbsp; defaults&nbsp; &nbsp; &nbsp; &nbsp; 1 1</p><p>/dev/sda5&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;/data&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;ext3&nbsp; &nbsp; defaults&nbsp; &nbsp; &nbsp; &nbsp; 1 2</p><p>/dev/sda1&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;/boot&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;ext3&nbsp; &nbsp; defaults&nbsp; &nbsp; &nbsp; &nbsp; 1 2</p><p>(2).一定要写bs=1024k，一定要加k, 默认是bytes,不加K或M,是以bytes写入，</p><p>&nbsp; &nbsp; 有可能系统要挂了,至于 也有人写bs=4M,没啥区别，最后速度差不多。</p><p>(3).加 &amp; 后台进行,因为要用当前的终端来查看dd进度,如果忘了加 &amp;,可以用Ctrl+z</p><p>把dd进程移到后台，再运行 bg 记其后台运行(为了在当前终端查看进度）。</p><p><strong>2.查看dd完成进度，要不然鬼知道啥时候能dd完成啊</strong></p><p>ps -ef|grep dd&nbsp; &nbsp;//查看 dd 进程id号,其实上边命令加&amp;后，己经显示了。</p><p>kill -USR1&nbsp; id&nbsp; &nbsp;//查看 dd 完成进度</p><p>100118036480 bytes (100 GB) copied, 1346.94 seconds, 74.3 MB/s</p><p>如果想时时查看进度，可以用下面语句:</p><p>watch -n 1 kill -USR1 3730&nbsp; &nbsp;// 每2秒查看一次进度</p><p>while kill -USR1 3730;do sleep 2;done;&nbsp; &nbsp;//每2秒查看一次进度</p><p>这种是通过发送USR1信号的方法，去产生一个标准的IO错误，来达到显示当前COPY进度与COPY速度的目的。</p><p><strong>3.如果sdb原来是一个裸盘没有格式化过，dd可能并不能拷贝superblock信息，所以盘不能mount起来。</strong></p><p>所以只需要进入fdisk界面：</p><p># fdisk /dev/sdb</p><p># w</p><p>“write table to disk and exit”，sdb就可以mount起来了，如果是格过的，可能需要fsck一下就可以了</p><p>注意：建议不要轻易dd，有可能把系统搞坏,在有把握情况下或数据备份过情况下使用dd</p><p><span style="font-size: small;"><strong>本文永久更新链接地址</strong></span>：<a href="../../Linux/2017-03/141749.htm">http://www.linuxidc.com/Linux/2017-03/141749.htm</a></p><p><br/></p><p><br/></p><p><br/></p><p><br/></p><p><span style="font-size:18px;"><strong>只拷贝前120GB：</strong></span></p><p><span style="font-size:18px;">120GB=<span style="line-height:1.5;">128MB</span><span style="line-height:1.5;">&nbsp;*&nbsp;</span><span style="line-height:1.5;">938</span><span style="line-height:1.5;">=64MB*1875</span></span></p><p><span style="font-size:18px;">sudo dd if=/dev/sdb of=/dev/sdc conv=notrunc bs=128MB count=938<br/></span></p><p><span style="font-size:18px;">sudo dd if=/dev/sdb of=/dev/sdc conv=notrunc bs=64MB count=1875</span></p><p><span style="font-size:18px;">count为bs的次数<br/></span></p><p><span style="font-size:18px;"><br/></span></p><p><span style="font-size:18px;"><strong>一个盘到多个盘的拷贝：</strong></span></p><p><span style="font-size:18px;">dd if=image.bin | tee &gt;(dd of=/dev/sdc) | dd of=/dev/sdh<br/></span></p><p><span style="font-size:18px;">进度条dd with progress bar and statistics</span></p><p><span style="font-size:18px;">dd if=/dev/source | pv -s $(pv -s $(blockdev –getsize64 /dev/source) | tee &gt;(dd of=/dev/dest1) | dd of=/dev/dest2</span></p><p><span style="font-size:18px;"><br/></span></p><p><span style="font-size:18px;"><strong>部分拷贝问题修复：</strong></span></p><p><span style="font-size:18px;">对于GPT格式的硬盘，如果只拷贝前面的部分，则会漏掉backup gpt table，出现下面的错误：</span></p><p><span style="font-size:18px;">the backup gpt table is corrupt<br/></span></p><p><span style="font-size:18px;">小盘向大盘拷贝，使用parted命令查看硬盘时，会自动修复gpt备份表。</span></p><p><span style="font-size:18px;">等大小的盘拷贝，parted不会自动修复，需要使用gdisk命令：</span></p><p><span style="line-height:1.5;"><span style="font-size:18px;">sudo gdisk /dev/sda<br/></span></span></p><p><span style="line-height:1.5;"><span style="font-size:18px;">然后分别执行：x（专家模式）&nbsp;e（将gpt备份表写到硬盘尾部） w（写入到磁盘）y(yes)</span></span></p><p><span style="font-size:18px;"><br/></span></p><p><span style="line-height:1.5;"><span style="font-size:18px;"><br/></span></span></p><p><span style="font-size:18px;"><strong>查看UUID：</strong></span></p><p><span style="font-size:18px;">ls -l /dev/disk/by-uuid</span></p><p><span style="font-size:18px;">blkid /dev/sda1</span></p><p><span style="font-size:18px;"><br/></span></p><p><span style="line-height:1.5;"><span style="font-size:18px;"><strong>改变UUID：</strong></span></span></p><p><span style="line-height:1.5;"><span style="font-size:18px;">tune2fs /dev/sdbX -U random<br/></span></span></p><p><span style="line-height:1.5;"><span style="font-size:18px;"><br/></span></span></p><p><span style="line-height:1.5;"><span style="font-size:18px;"><strong>其他相关命令：</strong></span></span></p><p><span style="font-size:18px;"><span style="line-height:1.5;">partprobe&nbsp;通知内核分区表已经改变<br/></span><span style="line-height:1.5;">dcfldd</span><span style="line-height:1.5;">&nbsp;</span><span style="line-height:1.5;">直接支持</span><span style="line-height:1.5;"></span><span style="line-height:1.5;">一个盘到多个盘的拷贝</span></span></p><p><span style="font-size:18px;"><span style="line-height:1.5;"></span></span></p><p><span style="font-size:18px;">guymager&nbsp;是将 dd 与 dcfldd 命令转换为图形化接口</span></p><p><span style="font-size:18px;">PyFlag&nbsp;是一个使用 python 语言编写的硬盘分析工具<br/></span></p><p><span style="font-size:18px;">partimage&nbsp;分区备份压缩</span></p><p><span style="font-size:18px;">rsync&nbsp;数据镜像远程备份工具<br/></span></p><p><span style="font-size:18px;"><span style="font-family:Arial, &#39;Liberation Sans&#39;, &#39;DejaVu Sans&#39;, sans-serif;line-height:18px;">ddrescue, gddrescue</span>硬盘数据恢复工具</span></p><p><br/></p><p><br/></p>