Use POSIX unknown semaphores in Linux

In Linux, use POSIX unknown semaphores-Linux general technology-Linux programming and kernel information. The following is a detailed description. The functions of POSIX's unknown semaphores include the following:
# Include
Int sem_init (sem_t * sem, int pshared, unsigned int value );
Int sem_destroy (sem_t * sem );
Int sem_wait (sem_t * sem );
Int sem_trywait (sem_t * sem );
Int sem_post (sem_t * sem );
Int sem_getvalue (sem_t * sem );

In linux, when gcc is used for compilation, the following error occurs: undefined reference to 'sem _ init'

You can use the-pthread or-lpthread parameter.