====== Library Paths ======

**General Information**

Configuring and viewing OS library paths. 

**Checklist**
  * Distro(s): Enterprise Linux 6/7

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====== Library Config Files ======

**Main Config File**: /etc/ld.so.conf includes a directory
<code bash>
include ld.so.conf.d/*.conf
</code>

\\
**Directory of drop in paths**: /etc/ld.so.conf.d/
\\
Example: /etc/ld.so.conf.d/mylibraries.conf
<code bash>
/data/lib/application1/
/data/lib/application2/
</code>

\\
Apply Changes: If any changes are made to the above config files, run ldconfig to reload the library cache
<code bash>
ldconfig -v
</code>
  * -v => verbose

\\
Print the Cache Contents: To see what is currently in the library cache<code bash>ldconfig --print-cache</code>

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====== Library Search Order ======

Shared libraries needed by programs are searched for in this order:
  * Environment variable "LD_LIBRARY_PATH" => This environmental variable can be set like any other environment variable. (shell, .bashrc, .profile)
  * (ELF binaries only) => Directories specified within the binary. (DT_RUNPATH)
  * From cache file (/etc/ld.so.cache) => created via ldconfig
  * In default system library paths (/lib, /lib64, /usr/lib)

====== Override Search Order ======

To get a path specified in front of another, define the environmental variable "LD_LIBRARY_PATH" in a configuration file (per user or system wide).

\\
Example: Ensure that /usr/lib64 is ahead of /usr/local/lib for user "robert"
<code bash>
vim /home/robert/.bashrc

LD_LIBRARY_PATH=/usr/lib64:${LD_LIBRARY_PATH}
</code>
  * Including the "${LD_LIBRARY_PATH}" as a second entry ensures that nothing is completely over written if the variable has been set elsewhere

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