How to trigger SIGUSR1 and SIGUSR2?
They are user-defined signals, so they aren't triggered by any particular action. You can explicitly send them programmatically:
#include <signal.h>kill(pid, SIGUSR1);where pid is the process id of the receiving process. At the receiving end, you can register a signal handler for them:
#include <signal.h>void my_handler(int signum){ if (signum == SIGUSR1) { printf("Received SIGUSR1!\n"); }}signal(SIGUSR1, my_handler);
They are signals that application developers use. The kernel shouldn't ever send these to a process. You can send them using kill(2) or using the utility kill(1).
If you intend to use signals for synchronization you might want to check real-time signals (there's more of them, they are queued, their delivery order is guaranteed etc).