Shared libraries are the most common way to manage dependencies on Linux systems. These shared resources are loaded into memory before the application starts, and when several processes require the same library, it will be loaded only once on the system. This feature saves on memory usage by the application.
Static Libraries are linked into a compiled executable (or another library). After the compilation, the new artifact contains the static library’s content. Shared Libraries are loaded by the executable (or other shared library) at runtime.
How does Linux load libraries?
Linux supports two classes of libraries, namely:
- Static libraries – are bound to a program statically at compile time.
- Dynamic or shared libraries – are loaded when a program is launched and loaded into memory and binding occurs at run time.
If the program is already running, we can also get the list of loaded shared libraries by reading the file /proc/<PID>/maps. In this file, each row describes a region of contiguous virtual memory in a process or thread. If the process has loaded a shared library, the library will show up in this file.
According to the FHS, most libraries should be installed in /usr/lib, but libraries required for startup should be in /lib and libraries that are not part of the system should be in /usr/local/lib.
Shared Libraries are the libraries that can be linked to any program at run-time. They provide a means to use code that can be loaded anywhere in the memory. Once loaded, the shared library code can be used by any number of programs.
An alternative is for the program to selectively call functions with the library in a process called dynamic loading. With dynamic loading, a program can load a specific library (unless already loaded), and then call a particular function within that library. (Figure 2 shows these two methods.)
Steps to find shared library dependency in Linux:
- Launch your preferred terminal application.
- Get absolute path of the program you want to check. …
- Print shared object dependencies using ldd. …
- Find dynamic library required by program using readelf. …
- Read library requirement of running processes from /proc/<process-id>/maps.
Shared Object: A library that is automatically linked into a program when the program starts, and exists as a standalone file. The library is included in the linking list at compile time (ie: LDOPTS+=-lmylib for a library file named mylib.so ).
Look under Shared Libraries on the left to see if the Shared Library appears. If it does, you can click on it, and then click the star in the top right to follow it. If it does not appear, click More libraries, and then Go to SharePoint Home. If the Shared Library appears there, click the star beside it to follow it.
- Just create a one line script in the same directory: ./my_program. and set Allow executing file as program in Nautilus. (Or add +x via chmod .)
- Open this directory in Terminal and run there. ( or drag and drop the file from Nautilus to Terminal)
How do I know if my library is 32 bit or 64 bit Linux?
In LINUX determine if a . a library/archive 32-bit or 64-bit?
- extract a .o member and ask the “file” command (e.g., ELF 32-bit etc)
- start including a dummy member coded to indicate, e.g. 32bit.o/64bit.o and use “ar -t” to check.
Privileged users can install a shared library in one of the standard library directories:
- /usr/lib – directory in which most standard libraries are installed.
- /lib – directory containing libraries required during system startup.
- /usr/local/lib – non-standard or experimental libraries should be installed here;
How do I get 32 bit Linux libraries?
To install 32-bit libraries on Ubuntu 13.04 (64-bit) or later, open Terminal and type: sudo apt-get install lib32z1 (you will need to enter your password). Then just for good measure, let’s make sure your Ubuntu is up to date. Type sudo apt-get update and lastly, restart your computer.
There are four steps:
- Compile C++ library code to object file (using g++)
- Create shared library file (. SO) using gcc –shared.
- Compile the C++ code using the header library file using the shared library (using g++)
- Set LD_LIBRARY_PATH.
- Run the executable (using a. out)
- Step 1: Compile C code to object file.