In that year, I learned Linux C-undefined reference to 'pthread _ create' step by step to solve the problem.

Undefined reference to 'pthread _ create'
Undefined reference to 'pthread _ join'

Cause:
 The pthread library is not the default library in Linux. You must use the static library libpthread. A for connection. Therefore, you must use pthread_create () to create a thread and call the pthread_atfork () function to create a fork for processing.ProgramYou need to link the library.

Solution:
Add the-lpthread parameter to the compilation.
GCC thread. C-o thread-lpthread

Thread. C is your source file. Do not forget to add the header file # include <pthread. h>