what's usage of LD_LIBRARY_PATH?

hongxing · 10-20-2005, 03:04 AM

can anyone explain in detail?

MensaWater · 10-20-2005, 07:02 AM

It is used as a shell variable so that ld (see "man ld") will know what directories to search for shared libraries.

To set it you type:
LD_LIBRARY_PATH=/1stpath/to/libraries:/2ndpath/to/libraries (:...)

Example for Oracle (truncated here) on one of my servers I have:
LD_LIBRARY_PATH=/opt/oracle/product/10.1.0/db_1/lib:/lib:/usr/lib:/opt/oracle/product/10.1.0/db_1/jdk/jre/lib/i386

The above would tell it to first search for a given library in /opt/oracle/product/10.1.0/db_1/lib. If not found there it would
then search in /lib. If not found there it would then search in /usr/lib and so on.

Of course you have to export it like any variable to make it available:

export LD_LIBRARY_PATH

hongxing · 10-20-2005, 06:57 PM

do you mean is it used to specify the lib path to link when programming?

when running my app, how to specify the lib path?

thanks!

MensaWater · 10-21-2005, 07:47 AM

The same way. Some programs (Oracle again as an example) use the variable for runtime as well as linking.

sundialsvcs · 10-21-2005, 02:35 PM

When Linux searches for a library file, it looks at various locations in a certain order. This information is spelled out by man ld.so and, for your convenience, is reproduced here:

Code:

The necessary shared libraries needed by the program are  searched  for
in the following order:

o Using  the  DT_RPATH  dynamic section attribute of the binary if
  present and DT_RUNPATH attribute does not exist.

o Using the environment variable LD_LIBRARY_PATH.  Except if  the
  executable  is  a  setuid/setgid  binary,  in  which  case it is
  ignored.

o Using the DT_RUNPATH dynamic section attribute of the binary  if
  present.

o From  the  cache file /etc/ld.so.cache which contains a compiled
  list of candidate libraries previously found  in  the  augmented
  library  path.  If, however, the binary was linked with -z node-
  flib linker option, libraries in the default library  paths  are
  skipped.  (Note: the ldconfig program builds this cache.)

o In  the default path /lib, and then /usr/lib.  If the binary was
  linked with -z nodeflib linker option, this step is skipped.