如果一个程序运行时需要链接库，它如何找到那个库文件？

碧月修光

就像系统自带程序运行时在$PAH中搜索一样，搜索库也是有个指定的路径吗？

asert

那是当然的咯，系统默认会在/usr/lib下找库文件，如果是其他地方那么就需要在/etc/ld.so.conf文件里添加路径告诉操作系统，不要忘记在更新了/etc/ld.so.conf后要执行命令ldconfig

remote fish

除了 2 楼所说的方法外, 也可以通过环境变量或给 /lib/ld-linux.so.2 传参数来在运行时临时改变查找路径. 看下面几个命令

1. 
   
2. [yun@localhost ~]$ echo "hello" # 这是默认查找路径下的结果, 一切正常
   
3. hello
   
4. 
   
5. 
   
6. [yun@localhost ~]$ /lib/ld-linux.so.2 # 对, 就是要直接运行
   
7. Usage: ld.so [OPTION]... EXECUTABLE-FILE [ARGS-FOR-PROGRAM...]
   
8. You have invoked `ld.so', the helper program for shared library executables.
   
9. This program usually lives in the file `/lib/ld.so', and special directives
   
10. in executable files using ELF shared libraries tell the system's program
    
11. loader to load the helper program from this file.  This helper program loads
    
12. the shared libraries needed by the program executable, prepares the program
    
13. to run, and runs it.  You may invoke this helper program directly from the
    
14. command line to load and run an ELF executable file; this is like executing
    
15. that file itself, but always uses this helper program from the file you
    
16. specified, instead of the helper program file specified in the executable
    
17. file you run.  This is mostly of use for maintainers to test new versions
    
18. of this helper program; chances are you did not intend to run this program.
    
19. 
    
20.   --list                list all dependencies and how they are resolved
    
21.   --verify              verify that given object really is a dynamically linked
    
22.                         object we can handle
    
23.   --library-path PATH   use given PATH instead of content of the environment
    
24.                         variable LD_LIBRARY_PATH
    
25.   --inhibit-rpath LIST  ignore RUNPATH and RPATH information in object names
    
26.                         in LIST
    
27. [yun@localhost ~]$ /lib/ld-linux.so.2 --library-path / echo "hello" # 指定查找路径 (只) 为 "/", 因此会找不到库而无法运行
    
28. echo: error while loading shared libraries: echo: cannot open shared object file

复制代码

更具体的请参见 man ld.so

timepie

编译的时候告诉  库 在哪里可以吗？

khc

$LD_LIBRARY_PATH