Linux ldconfig Command Examples

What is ldconfig?

ldconfig is used to create, udpate and remove symbolic links for the current shared libraries based on the lib directories present in the /etc/ld.so.conf

3 ldconfig Examples

1. Display current libraries from the cache

This displays the list of directories and the libraries that are stored in the current cache. In the following example, it indicates that there are 916 libraries found in the cache file /etc/ld.so.cache, and it lists all of them below.

# ldconfig -p | head -5
916 libs found in cache `/etc/ld.so.cache'
	libzephyr.so.4 (libc6) => /usr/lib/libzephyr.so.4
	libzbar.so.0 (libc6) => /usr/lib/libzbar.so.0
	libz.so.1 (libc6) => /lib/libz.so.1
	libz.so (libc6) => /usr/lib/libz.so

2. Display libraries from every directory

Scans all the directories, and prints the directory name, and all the links that are created under it.

# ldconfig -v | head
/usr/lib/mesa:
	libGL.so.1 -> libGL.so.1.2
/usr/lib/i686-linux-gnu:
	liblouis.so.2 -> liblouis.so.2.2.0
/usr/lib/alsa-lib:
	libasound_module_ctl_oss.so -> libasound_module_ctl_oss.so
	libasound_module_ctl_bluetooth.so -> libasound_module_ctl_bluetooth.so
	libasound_module_pcm_bluetooth.so -> libasound_module_pcm_bluetooth.so
	libasound_module_pcm_vdownmix.so -> libasound_module_pcm_vdownmix.so
	libasound_module_rate_speexrate.so -> libasound_module_rate_speexrate_medium.so

The /etc/ld.so.conf has an include statement, which indicates that all the *.conf file under /etc/ld.so.conf.d directory should be considered.

# cat /etc/ld.so.conf
include /etc/ld.so.conf.d/*.conf

As you see below, there are multiple *.conf file located under this ld.so.conf.d directory. All of these files will be used.

# ls -1 /etc/ld.so.conf.d/
GL.conf
i486-linux-gnu.conf
i686-linux-gnu.conf
libasound2.conf
libc.conf

Sometimes when you do ldconfig -v, you might get the following error. This is because the directory referred by some of the *.conf file located under /etc/ld.so.conf.d is not valid, and contains directory names that doesn’t exist.

/sbin/ldconfig.real: Can't stat /lib/i486-linux-gnu: No such file or directory
/sbin/ldconfig.real: Can't stat /usr/lib/i486-linux-gnu: No such file or directory
/sbin/ldconfig.real: Can't stat /lib/i686-linux-gnu: No such file or directory
/sbin/ldconfig.real: Can't stat /lib64: No such file or directory

Note: You can either ignore these error mesages are remove those *.conf files from the /etc/ld.so.conf.d directory.

3. Inform System about the New Libraries

If you’ve installed a new program by compiling it from source, you might want to inform the system about the new libraries.

For example, let us assume that you’ve installed a program called dummy, which has all it’s libraries under /opt/dummy/lib directory.

The following example will update the links using only the directory /opt/dummy/lib. This doesn’t rebuilt the links by processing the /etc/ld.so.conf file. Please note that this doesn’t rebuild the cache. It just updates the link.

# ldconfig -n /opt/dummy/lib

Instead of the above, you can also add the “/opt/dummy/lib” to /etc/ld.so.conf and do the following.

# vi /etc/ld.so.conf

# ldconfig

Syntax and Options

Syntax:

ldconfig [OPTION...]
Short Option Long Option Option Description
-v –verbose Indicates verbose mode. Prints current version number, name of each directory as it is scanned and links that are created.
-n Process the directories that are specified from the command line. This doesn’t process the regular /usr/lib and lib directories. This also doesn’t process directories specified in the /etc/ld.so.conf. This option implies -N.
-N This doesn’t rebuild the cache. Unless -X is also specified, links are still updated.
-X This doesn’t update the links. Unless -N is also specified, the cache is still rebuilt.
-f Use the specified config file instead of /etc/ld.so.conf.
-C Use the specified cache instead of /etc/ld.so.cache.
-r Change to and use root as the root directory.
-l This is library mode, which manually links individual libraries.
-p –print-cache Print the lists of directories and candidate libraries stored in the current cache.
-c FORMAT –format=FORMAT Uses FORMAT for the cache file. Valid values for FORMAT: old, new and compat. compat is the default value.
-i –ignore-aux-cache Ignore auxiliary cache file.
-? –help, –usage Display help
-V –version Display version number
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