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.
Syntax and Options
|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|