/* 错误处理 */
#include
void assert(int exp);
void perror(char* str);
char* strerror(int errno);

/* 进程控制 */
#include
void abort(void);
int exit(int ret);
int _exit(int ret);
int atexit(void(*exitfun)(void));

#include
int execl(char *pathname,char *arg0,char *arg1,…,char *argn,NULL);
int execle(char *pathname,char *arg0,char *arg1,…, char *argn,NULL,char *envp[]) ;
int execlp(char *pathname,char *arg0,char *arg1,…,NULL);
int execlpe(char *pathname,char *arg0,char *arg1,…,NULL,char *envp[]);
int execv(char *pathname,char *argv[]);
int execve(char *pathname,char *argv[],char *envp[]);
int execvp(char *pathname,char *argv[]);
int execvpe(char *pathname,char *argv[],char *envp[]);

int spawnl(int mode,char *pathname,char *arg0,char *arg1,…, char *argn,NULL);
int spawnle(int mode,char *pathname,char *arg0,char *arg1,…, char *argn,NULL,char *envp[]);
int spawnlp(int mode,char *pathname,char *arg0,char *arg1,…, char *argn,NULL);
int spawnlpe(int mode,char *pathname,char *arg0,char *arg1,…, char *argn,NULL,char *envp[]);
int spawnv(int mode,char *pathname,char *argv[]);
int spawnve(int mode,char *pathname,char *argv[],char *envp[]);
int spawnvp(int mode,char *pathname,char *argv[]);
int spawnvpe(int mode,char *pathname,char *argv[],char *envp[]);

/* 内存相关 */
void* calloc(unsigned n, unsigned size);
void* malloc(unsigned int size);
void free(void* ptr);

对于不清楚的函数，强烈建议看AUPE(Unix环境高级编程)。
就工作的帮助价值来说，这本书在我心目中排第一。