: ./producer: símbolo indefinido: sem_post, versão GLIBC_2.2.5

Question

Funcionou aqui

void* Produce(void* param)
{
    Item* itemP =  (Item*) param;

    sem_wait(empty);
    sem_wait(lock);
    Item item;
    snprintf(item.msg, 100, "%lu_msg_%i", pthread_self(), 
    item.msgIndex);
    shared.buffer[shared.firstEmpty] = item;
    shared.firstEmpty = (shared.firstEmpty+1)%BUFFER_SIZE;  
    printf("Producer %i produced %s on buffer %i\n", itemP-
    >threadIndex, item.msg, shared.firstEmpty); 
    memcpy(sharedMem, &shared, sizeof(Shared) + BUFFER_SIZE);
    sem_post(lock);
    sem_post(full);
    sleep(.5);
    return NULL;
}

Mas, de repente, quebrou! Estou recebendo este erro no linuxlite:

virtual-machine:~/Desktop/projects/project1_new$ gcc -o producer 
producer.c -pthread -lrt
virtual-machine:~/Desktop/projects/project1_new$ ./producer
Arguments given:
argv[0] = ./producer
Producer 1 produced 140377718953728_msg_0 on buffer 1
./producer: symbol lookup error: ./producer: undefined symbol: 
sem_post, version GLIBC_2.2.5