Project with shared lib and test application using that lib - linux

Question

I've built a shared lib and a test application with CMake (2.8)
Now, after make install, I get a tree like this:
root/
lib/
mylib.so
samples/
test1
test2
...
Now when I run my test app, it can't find the shared library file to run:
error while loading shared libraries: mylib.so: cannot open shared object file: No such file or directory
How can I solve this?
EDIT
Here is the relevant part of my CMakeLists.txt
For the mylib
add_library(mylib SHARED ${LIB_SOURCES})
target_link_libraries(mylib ${VTK_LIBRARIES} ${OpenCV_LIBS})
install(TARGETS mylib DESTINATION lib)
install(FILES include/mylib.h DESTINATION include)
install(DIRECTORY models DESTINATION .)
add_subdirectory(samples)
For the executables folder:
file(GLOB APP_SOURCES RELATIVE ${CMAKE_CURRENT_SOURCE_DIR} *.cpp)
foreach( samplesourcefile ${APP_SOURCES} )
string( REPLACE ".cpp" "" samplename ${samplesourcefile} )
add_executable( ${samplename} ${samplesourcefile} )
target_link_libraries( ${samplename} mylib )
install(TARGETS ${samplename} DESTINATION samples)
endforeach( samplesourcefile )

Answer 1

This may be caused because your library was installed in a non default directory in your Linux operating system.
File /etc/ld.so.conf contains the directories used by the dynamic loader for searching shared libs in Linux, see ldconfig manpage.
You can always check if all shared dependencies of a dynamic linked executable like your test application are found with command ldd.
So a solution to your missing library problem would be to install your library under a directory that your system uses as a search path for finding shared libraries.
A proper place to install development shared libraries in Linux distros is /usr/local/lib; this is almost certainly included as a search path for shared libraries by default in all Linuxes. Likewise, development binaries like your test app would be better placed under /usr/local/bin (however having it elsewhere is not the cause of the missing lib problem).
For the record, here follows an excerpt about /usr/local as documented by The Linux Documentation Project:
[...] It copies the structure of '/usr'. These days, '/usr/local' is
widely regarded as a good place in which to keep
self-compiled or third-party programs. The /usr/local hierarchy is for
use by the system administrator when installing software locally. It
needs to be safe from being overwritten when the system software is
updated. It may be used for programs and data that are shareable
amongst a group of hosts, but not found in /usr. Locally installed
software must be placed within /usr/local rather than /usr unless it
is being installed to replace or upgrade software in /usr.