How to use hook functions in Linux?

In Linux, hook functions can be used to intercept and modify the behavior of system calls. Here are some steps for using hook functions:

1. Include the necessary header files.
2. Include the necessary libraries: unistd, printf, dlfcn, and sys/types.
3. Create a function to replace the original system call.
4. The write_hook function intercepts and logs the behavior of the write system call. It then calls the original write system call function.
5. Use the dlsym function to obtain the address of the original system call.
6. Compile as a shared library.
7. Compile the file “hook.c” to a shared library called “hook.so” using the GNU Compiler Collection (gcc) with the options for shared library and position-independent code (-shared -fPIC), and linking against the dynamic linker library (-ldl).
8. Load the hook shared library using the LD_PRELOAD environment variable.
9. Run your_program using the hook.so library preloaded.

By following the steps above, you can intercept and modify system call behaviors in Linux using hook functions. Please be aware that using hook functions may require root permissions and could potentially impact the stability of the system, so use with caution.