Why do I have to define LD LIBRARY PATH with an export every time I run my application

Question

I have some code that uses some shared libraries  c code on gcc   When compiling I have to explicitly define the include and library directories using -I and -L  since they aren t in the standard places  When I try to run the code  I get the following error     sync test    sync test  error while loading shared libraries  libsync so  cannot open shared object file  No such file or directory   However  do the following  everything works just fine   export LD LIBRARY PATH   path to library     sync test   Now  the strange part is  this only works once  If I try and run sync test again I get the same error unless I run the export command first  I tried adding the following to my  bashrc  but it made no difference   LD LIBRARY PATH   path to library

User · Answer

What you also can do  if it s something you installed on your system  is to add the directory that contains the shared libraries to your  etc ld so conf file  or make a new file in  etc ld so conf d    I ve both checked RHEL5 and Ubuntu distribution so I think it s generic for linux   The ldconfig program will make sure they are system-wide included   See the following link for more information  www dwheeler com secure-programs Secure-Programs-HOWTO dlls html

User · Answer

Use  export LD LIBRARY PATH   path to library     in your  bashrc otherwise  it ll only be available to bash and not any programs you start   Try -R path to library  flag when you re linking  it ll make the program look in that directory and you won t need to set any environment variables   EDIT  Looks like -R is Solaris only  and you re on Linux   An alternate way would be to add the path to  etc ld so conf and run ldconfig  Note that this is a global change that will apply to all dynamically linked binaries

User · Answer

Instead of overriding the library search path at runtime with LD LIBRARY PATH  you could instead bake it into the binary itself with rpath  If you link with GCC adding -Wl -rpath  lt libdir gt  should do the trick  if you link with ld it s just -rpath  lt libdir gt

User · Answer

You should avoid setting LD LIBRARY PATH in your  bashrc   See  Why LD LIBRARY PATH is bad  for more information   Use the linker option -rpath while linking so that the dynamic linker knows where to find libsync so during runtime   gcc     -Wl -rpath  path to library -L path to library -lsync -o sync test   EDIT   Another way would be to use a wrapper like this     bin bash  LD LIBRARY PATH  path to library sync test        If sync test starts any other programs  they might end up using the libs in  path to library which may or may not be intended

User · Answer

You can just put this all on one line   LD LIBRARY PATH   LD LIBRARY PATH  path to library    sync test   Should make things a little easier  even if it doesn t change anything fundamental

User · Answer

Did you  export  in your  bashrc   export LD LIBRARY PATH  LD LIBRARY PATH   path to library

User · Answer

You could add in your code a call system with the new definition   sprintf newdef  export LD LIBRARY PATH  LD LIBRARY PATH  s  s  ld1 ld2   system newdef     But  I don t know it that is the rigth solution but it works   Regards

[c] Why do I have to define LD_LIBRARY_PATH with an export every time I run my application?

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