Linux error while loading shared libraries: cannot open shared object file: No such file or directory

Your library is a dynamic library. You need to tell the operating system where it can locate it at runtime.

To do so, we will need to do those easy steps:

1. Find where the library is placed if you don't know it.

sudo find / -name the_name_of_the_file.so

2. Check for the existence of the dynamic library path environment variable(LD_LIBRARY_PATH)

$ echo $LD_LIBRARY_PATH

        if there is nothing to be displayed, add a default path value (or not if you wish to)

$ LD_LIBRARY_PATH=/usr/local/lib

3. We add the desired path, export it and try the application.

Note that the path should be the directory where the path.so.something is. So if path.so.something is in /my_library/path.so.something it should be :

$ LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/my_library/
$ export LD_LIBRARY_PATH
$ ./my_app

Reference to source

Here are a few solutions you can try:

ldconfig

As AbiusX pointed out: If you have just now installed the library, you may simply need to run ldconfig.

sudo ldconfig

ldconfig creates the necessary links and cache to the most recent shared libraries found in the directories specified on the command line, in the file /etc/ld.so.conf, and in the trusted directories (/lib and /usr/lib).

Usually your package manager will take care of this when you install a new library, but not always, and it won't hurt to run ldconfig even if that is not your issue.

Dev package or wrong version

If that doesn't work, I would also check out Paul's suggestion and look for a "-dev" version of the library. Many libraries are split into dev and non-dev packages. You can use this command to look for it:

apt-cache search <libraryname>

This can also help if you simply have the wrong version of the library installed. Some libraries are published in different versions simultaneously, for example, Python.

Library location

If you are sure that the right package is installed, and ldconfig didn't find it, it may just be in a nonstandard directory. By default, ldconfig looks in /lib, /usr/lib, and directories listed in /etc/ld.so.conf and $LD_LIBRARY_PATH. If your library is somewhere else, you can either add the directory on its own line in /etc/ld.so.conf, append the library's path to $LD_LIBRARY_PATH, or move the library into /usr/lib. Then run ldconfig.

To find out where the library is, try this:

sudo find / -iname *libraryname*.so*

(Replace libraryname with the name of your library)

If you go the $LD_LIBRARY_PATH route, you'll want to put that into your ~/.bashrc file so it will run every time you log in:

export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/path/to/library

Update
While what I write below is true as a general answer about shared libraries, I think the most frequent cause of these sorts of message is because you've installed a package, but not installed the -dev version of that package.

Well, it's not lying - there is no libpthread_rt.so.1 in that listing. You probably need to re-configure and re-build it so that it depends on the library you have, or install whatever provides libpthread_rt.so.1.

Generally, the numbers after the .so are version numbers, and you'll often find that they are symlinks to each other, so if you have version 1.1 of libfoo.so, you'll have a real file libfoo.so.1.0, and symlinks foo.so and foo.so.1 pointing to the libfoo.so.1.0. And if you install version 1.1 without removing the other one, you'll have a libfoo.so.1.1, and libfoo.so.1 and libfoo.so will now point to the new one, but any code that requires that exact version can use the libfoo.so.1.0 file. Code that just relies on the version 1 API, but doesn't care if it's 1.0 or 1.1 will specify libfoo.so.1. As orip pointed out in the comments, this is explained well at here.

In your case, you might get away with symlinking libpthread_rt.so.1 to libpthread_rt.so. No guarantees that it won't break your code and eat your TV dinners, though.

You need to ensure that you specify the library path during linking when you compile your .c file:

gcc -I/usr/local/include xxx.c -o xxx -L/usr/local/lib -Wl,-R/usr/local/lib

The -Wl,-R part tells the resulting binary to also look for the library in /usr/local/lib at runtime before trying to use the one in /usr/lib/.

Try adding LD_LIBRARY_PATH, which indicates search paths, to your ~/.bashrc file

LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/path_to_your_library

It works!