FILES and DIRECTORIES
FILE *fopen(char *name, char *access);
typedef struct { int _cnt, _bufsiz, _flag, _file;
                 char *ptr, *base; } FILE;
void fclose(FILE *file);
void fflush(FILE *file);
int fseek(FILE *file, long int pos, int from);
  /* from= SEEK_SET, SEEK_CUR, or SEEK_END */
char *gets(char *string);
char *fgets(char *string, int max, FILE *file);
int getchar(void);
int fgetc(FILE *file);
int scanf(char *format, ...);
int fscanf(FILE *file, char *format, ...);
int sscanf(char *string, char *format, ...);
int putchar(int c);
int fputc(int c, FILE *f);
int puts(char *string);
int fputs(char *string, FILE *file);
int printf(char *format, ...);
int fprintf(FILE *file, char *format, ...);
int sprintf(char *string, char *format, ...);
int rename(char *oldname, char *newname);
int unlink(char *filename);
int open(char *name, int mode, [int permissions] );
  /* mode= O_RDWR, O_RDONLY, O_WRONLY, O_CREAT, O_APPEND */
int dup(int oldfd);
int dup2(int oldfd, int newfd);
void pipe(int fdpair[]);
int close(int fd);
int read(int fd, char *buffer, int number);
int write(int fd, char *buffer, int number);
long int lseek(int fd, long int pos, int from);
  /* from= L_SET, L_CUR, C_END */
int stat(char *name, struct stat *info);
struct stat { int st_ino, st_mode, st_nlink, st_uid, st_size;
              time_t st_atime, st_mtime, st_ctime; };
DIR *opendir(char *name);
void closedir(DIR *dir);
struct direct *readdir(DIR *dir);
struct direct { char *d_name;  int d_ino; };

TIME and DATE
typedef long int time_t;
struct tm { int tm_year, tm_mon, tm_mday, tm_wday;
            int tm_yday, tm_hour, tm_min, tm_sec, tm_isdst;
            char *tm_zone; };
time_t time(time_t *ptr);  /* ptr should be NULL */
char *ctime(time_t *ptr);
struct tm *localtime(time_t *ptr);
char *asctime(struct tm *ptr);
time_t mktime(struct tm *ptr);
void gettimeofday(struct timeval *tv, struct timezone *tz);
struct timeval { long int tv_sec, tv_usec; };
struct timezone { int tz_minuteswest; };
void ftime(struct timeb *ptr);
struct timeb { time_t time; long int millitm; };

PROCESSES
int fork(void);
void exit(int exitstatus);
char *getenv(char *var);
void setenv(char *var, char *value, int overwr);
void unsetenv(char *var);
int execl(char *path, char *arg0, char *arg1, ...);
int execlp(char *prog, char *arg0, char *arg1, ...);
int execv(char *path, char *args[]);
int execvp(char *prog, char *args[]);
int wait(int *exitstatus);
void sleep(int seconds);
void pause(void);
int alarm(int seconds);
int getpid(void);
int kill(int pid, int code);
void (*signal(int code, void (*handler)(void)))();
  /* codes: SIGHUP, SIGINT, SIGQUIT, SIGKILL, SIGALRM, SIGTERM,
            SIGSTOP, SIGTSTP, SIGCONT, SIGCHLD, SIGUSR1, SIGUSR2,
            SIGSEGV, SIGBUS, SIGSYS, SIGILL, SIGFPE, SIGPIPE */
  /* special handlers: SIG_IGN, SIG_DFL */

SOCKETS
int socket(int family, int type, int protocol);
  /* families: AF_INET, AF_UNIX */
  /* types: SOCK_STREAM, SOCK_DGRAM, SOCK_RAW */
  /* protocols: 0 */
int connect(int socket, struct sockaddr *ia, int ialen);
int bind(int socket, struct sockaddr *ia, int ialen);
int listen(int socket, int maxqueuelen);
int accept(int newsock, struct sockaddr *ia, int *ialen);

the NETWORK
void gethostname(char *string);
struct hostent *gethostbyname(char *hostname);
struct hostent { long int h_name; /* IP address */ };
struct sockaddr_in { int sin_family;
                     in_addr sin_addr;
                     short int sin_port; };
short int htons(short int port);
long int htonl(long int addr);
char *inet_ntoa(long int ipaddr);

PEOPLE
int getuid(void);
struct passwd *getpwuid(int uid);
struct passwd *getpwnam(char *username);
struct passwd { char *pw_name, *pw_passwd, *pw_dir, *pw_shell;
                int pw_uid; };

OTHER
int rand(void);
void srand(int seed);
void perror(char *message);