Hi, I was trying to generate a simple broadcasting message in sel4. I have used a c code I found in the internet. #include #include #include #include #include #include void DieWithError(char *errorMessage) { perror(errorMessage); exit(1); } int main(int argc, char *argv[]) { int sock; struct sockaddr_in broadcastAddr; char *broadcastIP; unsigned short broadcastPort; char *sendString; int broadcastPermission; unsigned int sendStringLen; broadcastIP = "0.0.0.0"; broadcastPort = 6741; sendString = "Hello World!"; printf("start\n"); printf("Socket is about to be created!\n"); if ( (sock = socket(AF_INET, SOCK_DGRAM, 0)) < 0 ) { perror("socket creation failed"); exit(EXIT_FAILURE); } printf("Socket is created! \n"); broadcastPermission = 1; if (setsockopt(sock, SOL_SOCKET, SO_BROADCAST, (void *) &broadcastPermission, sizeof(broadcastPermission)) < 0) DieWithError("setsockopt() failed"); memset(&broadcastAddr, 0, sizeof(broadcastAddr)); broadcastAddr.sin_family = AF_INET; broadcastAddr.sin_addr.s_addr = inet_addr(broadcastIP); broadcastAddr.sin_port = htons(broadcastPort); sendStringLen = strlen(sendString); for (;;) { if (sendto(sock, sendString, sendStringLen, 0, (struct sockaddr *) &broadcastAddr, sizeof(broadcastAddr)) != sendStringLen) DieWithError("sendto() sent a different number of bytes than expected"); sleep(3); } return 0; } However, I get the error in syscall 41. What I understood is that for some reason the socket is not created successfully and can't find an endpoint. What can be the reason for that? libsel4muslcsys: Error attempting syscall 41 Caught cap fault in send phase at address (nil) while trying to handle: vm fault on data at address 0x28 with status 0x4 in thread 0xffffff801fe09400 "rootserver" at address 0x40e3af With stack: 0x41ce28: 0x40c0fe 0x41ce30: 0x418720 0x41ce38: 0x0 0x41ce40: 0x41ceb0 0x41ce48: 0x0 0x41ce50: 0x0 0x41ce58: 0x4011bd 0x41ce60: 0x41cf10 0x41ce68: 0x200402323 0x41ce70: 0x3 0x41ce78: 0x3 0x41ce80: 0x41ceb0 0x41ce88: 0x401ce2 0x41ce90: 0xffffffff00000000 0x41ce98: 0x412008 0x41cea0: 0x1a5500000041cf20 Thanks! -- Regards' Shahnewaz Karim Sakib