Pthrread programming on linux

Bonjour à tous!
Voici un problème qui me rend dingue.
Je dois utiliser des threads dans mon programme, mais au premier essai de l'utilisation de thread, un fiasco. ça ne compile même pas.
Voici mon code:
#include <pthread.h>
#include "errors.h"

typedef struct alarm_tag {
int seconds;
char message[64];
} alarm_t;

void *alarm_thread (void *arg)
{
alarm_t *alarm = (alarm_t*)arg;
int status;

status = pthread_detach (pthread_self ());
if (status != 0)
err_abort (status, "Detach thread");
sleep (alarm->seconds);
printf ("(%d) %s\n", alarm->seconds, alarm->message);
free (alarm);
return NULL;
}
int main (int argc, char *argv[])
{
int status;
char line[128];
alarm_t *alarm;
pthread_t thread;

while (1) {
printf ("Alarm> ");
if (fgets (line, sizeof (line), stdin) == NULL) exit (0);
if (strlen (line) <= 1) continue;
alarm = (alarm_t*)malloc (sizeof (alarm_t));
if (alarm == NULL)
errno_abort ("Allocate alarm");

/*
* Parse input line into seconds (%d) and a message
* (%64[^\n]), consisting of up to 64 characters
* separated from the seconds by whitespace.
*/
if (sscanf (line, "%d %64[^\n]",
&alarm->seconds, alarm->message) < 2) {
fprintf (stderr, "Bad command\n");
free (alarm);
} else {
status = pthread_create (
&thread, NULL, alarm_thread, alarm);
if (status != 0)
err_abort (status, "Create alarm thread");
}
}
}

N.B: sur linux, le compilateur gcc
et error.h est un fichier pr la gestion des erreurs
l'erreur est: "undefined reference to 'pthread_detach'
"undefined reference to 'pthread_create'

Take care of You!