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今天 LZ 在运行一个程序的时候，出现找不到 so 库的情况：
>$ ./core ./core: error while loading shared libraries: libudev.so.0: cannot open shared object file: No such file or directory >$
可以看出来， core 这个程序依赖了一个叫做 libudev.so 的库，但是再系统中找不到这个库，那么就需要安装一下。
可是如果通过 apt-get 的方式安装的话，需要知道 libudev.so 在哪个软件包中才行。
那么问题来了，怎样查找一个 so 库在哪个软件包中呢？
通过 apt-file 命令就可以查找了。
首先 apt-file 命令不像 apt-get 命令一样，它在系统中是没有预装的，需要我们手动安装一下：
>$ sudo apt-get install apt-file Reading package lists... Done Building dependency tree Reading state information... Done The following extra packages will be installed: curl libconfig-file-perl libregexp-assemble-perl The following NEW packages will be installed: apt-file curl libconfig-file-perl libregexp-assemble-perl 0 upgraded, 4 newly installed, 0 to remove and 2 not upgraded. Need to get 242 kB of archives. After this operation, 743 kB of additional disk space will be used. Do you want to continue? [Y/n] y Get:1 http://cn.archive.ubuntu.com/ubuntu/ trusty-updates/main curl amd64 7.35.0-1ubuntu2.6 [123 kB] Get:2 http://cn.archive.ubuntu.com/ubuntu/ trusty/universe libconfig-file-perl all 1.50-2 [10.1 kB] Get:3 http://cn.archive.ubuntu.com/ubuntu/ trusty/universe libregexp-assemble-perl all 0.35-8 [81.2 kB] Get:4 http://cn.archive.ubuntu.com/ubuntu/ trusty/universe apt-file all 2.5.2ubuntu1 [27.1 kB] Fetched 242 kB in 10s (22.2 kB/s) Selecting previously unselected package curl. (Reading database ... 204801 files and directories currently installed.) Preparing to unpack .../curl_7.35.0-1ubuntu2.6_amd64.deb ... Unpacking curl (7.35.0-1ubuntu2.6) ... Selecting previously unselected package libconfig-file-perl. Preparing to unpack .../libconfig-file-perl_1.50-2_all.deb ... Unpacking libconfig-file-perl (1.50-2) ... Selecting previously unselected package libregexp-assemble-perl. Preparing to unpack .../libregexp-assemble-perl_0.35-8_all.deb ... Unpacking libregexp-assemble-perl (0.35-8) ... Selecting previously unselected package apt-file. Preparing to unpack .../apt-file_2.5.2ubuntu1_all.deb ... Unpacking apt-file (2.5.2ubuntu1) ... Processing triggers for man-db (2.6.7.1-1ubuntu1) ... Setting up curl (7.35.0-1ubuntu2.6) ... Setting up libconfig-file-perl (1.50-2) ... Setting up libregexp-assemble-perl (0.35-8) ... Setting up apt-file (2.5.2ubuntu1) ... The system-wide cache is empty. You may want to run 'apt-file update' as root to update the cache. You can also run 'apt-file update' as normal user to use a cache in the user's home directory. >$
安装好 apt-file 工具之后还不能马上进行查找，得先更新它的索引文件才行。
从上面的提示可以看出来，更新索引文件必须使用 root 身份，所以别忘了用 sudo 命令。
>$ sudo apt-file update Downloading complete file http://cn.archive.ubuntu.com/ubuntu/dists/trusty/Contents-amd64.gz % Total % Received % Xferd Average Speed Time Time Time Current Dload Upload Total Spent Left Speed 100 28.0M 100 28.0M 0 0 84554 0 0:05:47 0:05:47 --:--:-- 99773 Downloading complete file http://cn.archive.ubuntu.com/ubuntu/dists/trusty-updates/Contents-amd64.gz % Total % Received % Xferd Average Speed Time Time Time Current Dload Upload Total Spent Left Speed 100 25.5M 100 25.5M 0 0 65803 0 0:06:47 0:06:47 --:--:-- 63514 Downloading Index http://cn.archive.ubuntu.com/ubuntu/dists/trusty/Contents-amd64.diff/Index: No Index available. Downloading complete file http://cn.archive.ubuntu.com/ubuntu/dists/trusty/Contents-amd64.gz % Total % Received % Xferd Average Speed Time Time Time Current Dload Upload Total Spent Left Speed 0 28.0M 0 0 0 0 0 0 --:--:-- --:--:-- --:--:-- 0 File is up-to-date. Downloading Index http://cn.archive.ubuntu.com/ubuntu/dists/trusty-updates/Contents-amd64.diff/Index: No Index available. Downloading complete file http://cn.archive.ubuntu.com/ubuntu/dists/trusty-updates/Contents-amd64.gz % Total % Received % Xferd Average Speed Time Time Time Current Dload Upload Total Spent Left Speed 0 25.5M 0 0 0 0 0 0 --:--:-- --:--:-- --:--:-- 0 File is up-to-date. Downloading Index http://cn.archive.ubuntu.com/ubuntu/dists/trusty/Contents-amd64.diff/Index: No Index available. Downloading complete file http://cn.archive.ubuntu.com/ubuntu/dists/trusty/Contents-amd64.gz % Total % Received % Xferd Average Speed Time Time Time Current Dload Upload Total Spent Left Speed 0 28.0M 0 0 0 0 0 0 --:--:-- --:--:-- --:--:-- 0 File is up-to-date. Downloading Index http://cn.archive.ubuntu.com/ubuntu/dists/trusty-updates/Contents-amd64.diff/Index: No Index available. Downloading complete file http://cn.archive.ubuntu.com/ubuntu/dists/trusty-updates/Contents-amd64.gz % Total % Received % Xferd Average Speed Time Time Time Current Dload Upload Total Spent Left Speed 0 25.5M 0 0 0 0 0 0 --:--:-- 0:00:05 --:--:-- 0 File is up-to-date. Downloading complete file http://cn.archive.ubuntu.com/ubuntu/dists/trusty-backports/Contents-amd64.gz % Total % Received % Xferd Average Speed Time Time Time Current Dload Upload Total Spent Left Speed 100 285k 100 285k 0 0 60524 0 0:00:04 0:00:04 --:--:-- 59904 Downloading complete file http://security.ubuntu.com/ubuntu/dists/trusty-security/Contents-amd64.gz % Total % Received % Xferd Average Speed Time Time Time Current Dload Upload Total Spent Left Speed 100 22.6M 100 22.6M 0 0 55478 0 0:07:07 0:07:07 --:--:-- 100k Downloading Index http://security.ubuntu.com/ubuntu/dists/trusty-security/Contents-amd64.diff/Index: No Index available. Downloading complete file http://security.ubuntu.com/ubuntu/dists/trusty-security/Contents-amd64.gz % Total % Received % Xferd Average Speed Time Time Time Current Dload Upload Total Spent Left Speed 0 0 0 0 0 0 0 0 --:--:-- --:--:-- --:--:-- 0 File is up-to-date. Downloading Index http://security.ubuntu.com/ubuntu/dists/trusty-security/Contents-amd64.diff/Index: No Index available. Downloading complete file http://security.ubuntu.com/ubuntu/dists/trusty-security/Contents-amd64.gz % Total % Received % Xferd Average Speed Time Time Time Current Dload Upload Total Spent Left Speed 0 0 0 0 0 0 0 0 --:--:-- --:--:-- --:--:-- 0 File is up-to-date. Ignoring source without Contents File: http://extras.ubuntu.com/ubuntu/dists/trusty/Contents-amd64.gz >$
耐心等待这些包更新完，然后就可以查找我们要的库了。好在这些索引文件不是很大，用不了多久就更新完毕了。
接下来使用 apt-file 命令查找我们的 so 在哪个 package 中。
>$ sudo apt-file search libudev.so libudev-dev: /usr/lib/x86_64-linux-gnu/libudev.so libudev1: /lib/x86_64-linux-gnu/libudev.so.1 libudev1: /lib/x86_64-linux-gnu/libudev.so.1.3.5 >$
本来 LZ 搜索的是 libudev.so.0，但是没有搜索到，所以就只好把末尾的 .0 去掉来搜索更大的范围。
在搜索的结果中，左侧的是 package，右侧就是 so 的路径，所以在查到 package 后通过 apt-get 命令安装它就可以了。
>$ sudo apt-get install libudev1 Reading package lists... Done Building dependency tree Reading state information... Done libudev1 is already the newest version. 0 upgraded, 0 newly installed, 0 to remove and 2 not upgraded. >$
======================分割线====================
LZ 的运气总是不好，用 libudev.so.0 这个库来举栗子不够典型，因为这个库多少有些特殊，通过上面的安装结果可以看出来， libudev1 这个库并没有安装成功，因为它早已被安装好了。
既然我们运行的 ./core 程序中提示找不到 libudev.so.0，而我们的系统中只有一个 libudev.so.1，那么直接做一个符号链接就可以了。
>$ sudo ln -s /lib/x86_64-linux-gnu/libudev.so.1 /lib/x86_64-linux-gnu/libudev.so.0 >$
在绝大多数情况下，通过 apt-file 命令根据 so 反查归属的 package，然后再通过 apt-get 命令安装这个 package 就可以了。
在少数情况下，比如 LZ 遇到的这种情况下，就需要通过一些变通的手段了。