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Fixing ld Cannot Find Shared Library Error in Linux

Ubuntu 11

When working with Linux, you might encounter an error message that says “ld cannot find shared library”. This error typically occurs when the linker, ld, is unable to locate the shared library it needs to link against. In this article, we will walk you through the steps to resolve this issue.

Quick Answer

To fix the "ld cannot find shared library" error in Linux, you need to identify the missing library by using the -L and -l options with the ld command. Once you know the exact filename, create a symbolic link to it using the ln -s command. After creating the symbolic link, you should be able to link against the shared library without any issues.

Understanding the Error

Before we dive into the solution, it’s important to understand what the error message means. The linker, ld, is a program that combines various object (.o) and archive (.a) files into a single executable file. When linking against a shared library, ld needs to know the exact filename of the library. If it can’t find the library, it will throw the “ld cannot find shared library” error.

Identifying the Missing Library

The first step in resolving this error is to identify what file the linker is expecting to find. You can do this by using the -L and -l options with the ld command. The -L option specifies the path to the directory where the library is located, and the -l option specifies the name of the library.

For example, if you’re trying to link against a library named libcustom_program_options, you would use the following command:

ld -L/usr/local/lib -lcustom_program_options --verbose

The --verbose option will print a list of all considered directories along with the exact expected file name.

Creating a Symbolic Link

Once you’ve identified the exact filename that the linker is looking for, you can create a symbolic link to it. A symbolic link, or symlink, is a type of file that is a reference to another file or directory.

In this case, you’ll want to create a symbolic link from the expected filename to the actual filename of the library. You can do this using the ln -s command. The -s option tells ln to create a symbolic link.

For example, if the linker is looking for a file named libcustom_program_options.so and the actual filename is libcustom_program_options.so.1, you would use the following command:

sudo ln -s /usr/local/lib/libcustom_program_options.so.1 /usr/local/lib/libcustom_program_options.so

This command creates a symbolic link from libcustom_program_options.so to libcustom_program_options.so.1.

Verifying the Solution

After creating the symbolic link, you should be able to link against the shared library without any issues. You can verify this by running the ld command again. If everything is set up correctly, you should not see the “ld cannot find shared library” error.

Conclusion

The “ld cannot find shared library” error can be a bit confusing at first, but it’s actually quite simple to resolve once you understand what’s going on. By identifying the missing library and creating a symbolic link to it, you can get your Linux system back up and running in no time.

Remember, it’s always important to ensure that the shared library file exists in the specified directory before creating the symbolic link. If the library file does not exist, you will need to install it or build it from source.

We hope this article has been helpful in resolving the “ld cannot find shared library” error. If you have any questions or run into any issues, feel free to leave a comment below.

How do I know which shared library is missing?

You can use the ldd command followed by the path to your executable file to list the shared libraries required by the program. Any missing libraries will be marked as "not found".

Can I specify multiple paths using the `-L` option?

Yes, you can specify multiple paths by using multiple -L options. For example, ld -L/path/to/dir1 -L/path/to/dir2 -lcustom_program_options.

Can I use relative paths with the `-L` option?

Yes, you can use relative paths with the -L option. However, it’s important to ensure that the relative path is correct and that the library file exists in the specified directory.

Do I always need to use `sudo` when creating a symbolic link?

No, you only need to use sudo if you don’t have the necessary permissions to create the symbolic link. If you have write access to the directory where the link is created, you can omit sudo.

What should I do if the shared library file does not exist?

If the shared library file does not exist, you will need to either install it or build it from source. Refer to the documentation or the source code of the library for instructions on how to obtain or build the file.

Can I use a different name for the symbolic link?

Yes, you can use a different name for the symbolic link if desired. Just make sure that the name you choose is consistent with the name expected by the linker when linking against the library.

After creating the symbolic link, do I need to restart my system?

No, you do not need to restart your system. The symbolic link will take effect immediately, and you should be able to link against the shared library without any issues.

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