关于/usr/bin/ld: cannot find -lcrypto的问题

make[1]: Entering directory `/usr/zhengsheng/ceph-0.20.2/src'
g++ -I. -fPIC -shared -g -o libcls_crypto.so -lcrypto cls_crypto.cc
/usr/bin/ld: cannot find -lcrypto
collect2: ld returned 1 exit status
make[1]: *** [libcls_crypto.so] Error 1


该问题的解决方法：
  /usr/lib# ln -s libcrypto.so.0.9.8 libcrypto.so
在/usr/lib下建立软连接

参考文献：
“http://www.yolinux.com/TUTORIALS/LibraryArchives-StaticAndDynamic.html”

Dynamically Linked "Shared Object" Libraries: (.so)

How to generate a shared object: (Dynamically linked object library file.) Note that this is a two step process.

1. Create object code
2. Create library
3. Optional: create default version using a symbolic link.

Library creation example:

    gcc -Wall -fPIC -c *.c
    gcc -shared -Wl,-soname,libctest.so.1 -o libctest.so.1.0   *.o
    mv libctest.so.1.0 /opt/lib
    ln -sf /opt/lib/libctest.so.1.0 /opt/lib/libctest.so
    ln -sf /opt/lib/libctest.so.1.0 /opt/lib/libctest.so.1
          

This creates the library libctest.so.1.0 and symbolic links to it.

Compiler options:

• -Wall: include warnings. See man page for warnings specified.
• -fPIC: Compiler directive to output position independent code, a characteristic required by shared libraries. Also see "-fpic".
• -shared: Produce a shared object which can then be linked with other objects to form an executable.
• -W1: Pass options to linker.
  In this example the options to be passed on to the linker are: "-soname libctest.so.1". The name passed with the "-o" option is passed to gcc.
• Option -o: Output of operation. In this case the name of the shared object to be output will be "libctest.so.1.0"

Library Links:

• The link to /opt/lib/libctest.so allows the naming convention for the compile flag -lctest to work.
• The link to /opt/lib/libctest.so.1 allows the run time binding to work. See dependency below.

Compile main program and link with shared object library:

Compiling for runtime linking with a dynamically linked libctest.so.1.0:

    gcc -Wall -I/path/to/include-files -L/path/to/libraries prog.c -lctest -o prog
Use:
    gcc -Wall -L/opt/lib prog.c -lctest -o prog
      

Where the name of the library is libctest.so. (This is why you must create the symbolic links or you will get the error "/usr/bin/ld: cannot find -lctest".)
The libraries will NOT be included in the executable but will be dynamically linked during runtime execution.

List Dependencies:

The shared library dependencies of the executable can be listed with the command: ldd name-of-executable

Example: ldd prog

        libctest.so.1 => /opt/lib/libctest.so.1 (0x00002aaaaaaac000)
        libc.so.6 => /lib64/tls/libc.so.6 (0x0000003aa4e00000)
        /lib64/ld-linux-x86-64.so.2 (0x0000003aa4c00000)