Analysis of Linux LD_LIBRARY_PATH

(I) Historical Background

Nowadays, most software comes with shared libraries, or for security or business considerations.

For example:

Oracle: $ ORACLE_HOME/lib

MySQL: $ HOME/mysql/lib

The following is the configuration of LD_LIBRARY_PATH in. bash_profile under the oracle user.

Export LD_LIBRARY_PATH = $ ORACLE_HOME/lib
Export LD_LIBRARY_PATH = $ LD_LIBRARY_PATH:/usr/lib:/usr/X11R6/lib
Export LD_LIBRARY_PATH = $ LD_LIBRARY_PATH: $ ORACLE_HOME/jdk/jre/lib/i386
Export LD_LIBRARY_PATH = $ LD_LIBRARY_PATH: $ ORACLE_HOME/jdk/jre/lib/i386/server
Export LD_LIBRARY_PATH = $ LD_LIBRARY_PATH: $ ORACLE_HOME/rdbms/lib

(Ii) Concepts

① Below are some similar things

Shared Library, dynamic link library,. so file

② Ld. so is also called the shared library loader.

(3) meaning of existence

Used to tell ld. so where to find someone's shared library

(Iv) Let's Talk About

The. so file is managed and loaded by ld. so, which searches for the. so file required by the APP in the standard path/lib or/usr/lib,

But for non-standard paths:

In Linux, add the private path to/etc/ld. so. conf, run ldconfig to generate ld. so. cache, and ld. so.

For UNIX, LD_LIBRARY_PATH is used to process. so files in non-standard paths.

The Search priority is as follows (Linux ):

① LD_LIBRARY_PATH environment variable specifies the Directory

②/Etc/ld. so. conf specifies the Directory

③ Standard path first/usr/lib and then/lib

(V) Common Errors

Error while loading shared libraries: ooxx. so.0: cannot open shared object file: No such file or directory

How is ooxx named? If you are interested, click here to open the link.

(Vi) General Solutions

① Place the built-in library cp to/usr/lib or/lib, and then ldconfig has a case: Click to open the link

②/Etc/ld. so. conf, and then ldconfig

③ LD_LIBRARY_PATH (this variable has been criticized)

Supplement:

You can view the shared libraries that a program depends on as follows:

[Root @ b7-~] # Ldd/home/mysql/bin/mysqldump
Libpthread. so.0 =>/lib64/libpthread. so.0 (0x000000337d200000)
Libz. so.1 =>/usr/lib64/libz. so.1 (0x000000337e600000)
Librt. so.1 =>/lib64/librt. so.1 (0x000000337d600000)
Libdl. so.2 =>/lib64/libdl. so.2 (0x000000337c600000)
Libstdc ++. so.6 =>/usr/lib64/libstdc ++. so.6 (0x00000031ebe00000)
Libm. so.6 =>/lib64/libm. so.6 (0x000000337da00000)
Libgcc_s.so.1 =>/lib64/libgcc_s.so.1 (0x00000031e9e00000)
Libc. so.6 =>/lib64/libc. so.6 (0x000000337c200000)
/Lib64/ld-linux-x86-64.so.2 (0x000000337be000)

The output can be divided into three columns:

Column 1: Library on which the program depends

Column 2: Corresponding libraries provided by the system and required libraries of the program

Column 3: Start address of Library Loading

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