Introduction to ldconfig in Linux

Ldconfig is a dynamic link library management command to share the dynamic link library with the system.

Main uses of ldconfig:

Search for/lilb and/usr/lib by default, and the library files under the directories listed in the configuration file/etc/lD. So. conf.

Search for a shared dynamic link library. The format of the library file is lib ***. so. ** to create a dynamic loader (LD. so) the required connection and cache file.

The default cache file is/etc/lD. So. cache. This file stores the list of Dynamic Linked Library names sorted.

Ldconfig is usually run when the system starts. When you install a new dynamic link library, you need to manually run this command.

Ldconfig command parameters:

1.-V or -- verbose: When this option is used, ldconfig displays the directory being scanned, The searched dynamic link library, and the name of the connection it created.

2.-N: When this option is used, ldconfig only scans the directory specified by the command line and does not scan the default directory (/lib,/usr/lib ), nor scan the configuration file/etc/lD. so. conf directory.

3.-N: This option indicates that ldconfig does not recreate the cache file (/etc/lD. So. cache). If the-x option is not used, ldconfig updates the file connection as usual.

4.-X: This option indicates that ldconfig does not update the file connection. If the-n option is not used, the cached file will be updated normally.

5.-F conf: This option specifies that the configuration file of the dynamic link library is Conf, and the default value is/etc/lD. So. conf.

6.-C cache: This option specifies that the generated cache file is cache. The default value is/etc/lD. so. cache. This file stores the list of dynamically linked libraries that can be shared in the sorted order.

7.-R root: This option changes the root directory of the application to root (implemented by calling the chroot function ). when this option is selected, the system default configuration file/etc/lD. so. conf, which corresponds to root/etc/lD. so. conf. for example, when-r/usr/ZZZ is used, open the configuration file/etc/lD. so. in Conf,/usr/ZZZ/etc/LD is actually enabled. so. CONF file. this option can greatly increase the flexibility of dynamic link library management.

8.-L: Generally, ldconfig automatically establishes a connection to the dynamic link library when searching for a dynamic link library. when this option is selected, the expert mode is enabled. You need to manually set the connection. this option is not required for general users.

9.-P or -- print-Cache: This option indicates that ldconfig prints the names of all the shared libraries saved in the current cache file.

10.-C format or -- format = format: This option is used to specify the format used by the cache file. There are three types: LD (old format), new (new format) and compat (compatible format, which is the default format ).

11.-V: This option prints the version information of ldconfig and then exits.

12.-Or
-- Help or -- Usage:
The three options share the same role, so that ldconfig prints the help information and then exits .,

Ldconfig:

1. add something to/lib and/usr/lib without modifying/etc/lD. so. CONF file, but after adding it, you need to call ldconfig. Otherwise, the added library will not be found.

2. If the added library is not in/lib and/usr/lib, you must modify/etc/lD. so. CONF file, append the path of the Library to the file, and then call the ldconfig command again. For example, when installing MySQL, the library file/usr/local/MySQL/lib needs to be appended to the/etc/lD. So. conf file. The command is as follows:

# Echo "/usr/local/MySQL/lib">/etc/lD. So. conf

# Ldconfig-v | grep MySQL

3. If the added library is not under/lib or/usr/lib, but you do not have the permission to write/etc/lD. so. in the conf file, you need to write a global variable LD_LIBRARY_PATH to the export.