#include <stdio.h> #include <string.h> #include <errno.h> #include <sys/param.h> #include <netinet/in.h> #include <netdb.h> #include <fcntl.h> #include <unistd.h> #define HOSTID "/etc/hostid" int sethostid(long int new_id) { int fd; int ret; if (geteuid() || getuid()) return errno=EPERM; if ((fd=open(HOSTID,O_CREAT|O_WRONLY,0644))<0) return -1; ret = write(fd,(void *)&new_id,sizeof(new_id)) == sizeof(new_id) ? 0 : -1; close (fd); return ret; } long int gethostid(void) { char host[MAXHOSTNAMELEN + 1]; int fd, id; /* If hostid was already set the we can return that value. * It is not an error if we cannot read this file. It is not even an * error if we cannot read all the bytes, we just carry on trying... */ if ((fd=open(HOSTID,O_RDONLY))>=0 && read(fd,(void *)&id,sizeof(id))) { close (fd); return id; } if (fd >= 0) close (fd); /* Try some methods of returning a unique 32 bit id. Clearly IP * numbers, if on the internet, will have a unique address. If they * are not on the internet then we can return 0 which means they should * really set this number via a sethostid() call. If their hostname * returns the loopback number (i.e. if they have put their hostname * in the /etc/hosts file with 127.0.0.1) then all such hosts will * have a non-unique hostid, but it doesn't matter anyway and * gethostid() will return a non zero number without the need for * setting one anyway. * Mitch */ if (gethostname(host,MAXHOSTNAMELEN)>=0 && *host) { struct hostent *hp; struct in_addr in; if ((hp = gethostbyname(host)) == (struct hostent *)NULL) /* This is not a error if we get here, as all it means is that * this host is not on a network and/or they have not * configured their network properly. So we return the unset * hostid which should be 0, meaning that they should set it !! */ return 0; else { memcpy((char *) &in, (char *) hp->h_addr, hp->h_length); /* Just so it doesn't look exactly like the IP addr */ return(in.s_addr<<16|in.s_addr>>16); } } else return 0; }