C language extensions library function

Reference: "Embedded Linux, C-language programming practice" 

1. File I / O operations functions 

   * open function: open file 
          int open (const char * pathname, int flags) 

   * close function: close file 

   * read function: read the file 
          ssize_t read (int_fd, void * buf, size_t count) 
            transfer bytes of count number into point buf
         

   * write function: write file 
          ssize_t write (int fd, const void * buf, size_t count) 
          write bytes of count number into file(fd) with beginning of point buf in the memory 

   * lseek Function: File Positioning 
          off_t lseek (int fildes, off_t offset, int whence); 
          retuen the current position of reading and writing 

   * flock function: lock file 
          int flock (int fd, int operation) 

   * mmap function and munmap functions: memory-mapped 
          int munmap (void * start, size_t length) 
         map the contents of a file into memory, to write or read this memory region is the direct access to to the content of the document. 

   * create a function: to create a new file 
          int create (const char * pathname, mode_t mode) 

   * fcntl function: to change the file attributes which has been opened 

          int fcntl (int fields, int cmd, int arg) 
          If success,return the implementation of the new descriptor, otherwise returns -1 

2. the function of related file permissions

   * access functions: to determine whether access to the file permissions 
          int access (const char * pathname, int mode) 
          if (0 == access (argv [1], W_OK)) R_OK X_OK F_OK 

   * chown function and fchown function: to change the file owner of the 
          int fchown (int fd, uid_t owner, gid_t group) 

   * chmod function and fchmod function: to change the permissions 
         int fchmod (int fildes, mode_t mode) 

   * unlink function: delete the file 

3. User group manipulation functions 

   * getegid function and setegid function: get / set the effective group ID 
         gid_t gete (gid_t egid) 

   * geteuid function and seteuid function: get / set the real user ID 

         uid_t getuid (void) 

  4. Signaling Function 

    * kill function: to send a signal to the specified process

         int kill (pid_t pid, int sig) 

    * rais function: signaling 

         int raise (int sig) 

    * alarm function: Set the timer 

         unsigned int alarm (unsigned int seconds) 

    * signal function: Signal Installation Function 
         sighandler_t signal (int signum, sighandler_t handler) 

5. The process of dealing with the function 

    * getpid function and getppid function: to obtain the process ID and the parent process ID 
         pid_t getpid (void) 
         pid_t getppid (void) 

    * fork function: the establishment of child process 
         pid_t fork (void) 
         The parent process has been the return value is the child process ID, while the child process returns 0 

    * sleep function: Let the process was suspended for a period of time 
         unsigned int sleep (unsigned int seconds) 

    * exec function: find the executable file 

    * _exit function: the end of the process of implementation of the