Here is an example of an invalid system call: [root@plaguez kernel]# cat no1.c #include #include #include extern void *sys_call_table[]; sc() { // system call number 165 doesn't exist at this time. __asm__( "movl $165,%eax int $0x80"); } main() { errno = -sc(); perror("test of invalid syscall"); } [root@plaguez kernel]# gcc no1.c [root@plaguez kernel]# ./a.out test of invalid syscall: Function not implemented [root@plaguez kernel]# exit