mode meaning group has execute permission (stat s_ixgrpgroup has write permission (stat s_iwgrpgroup has read permission (stat s_irgrpgroup has read/write/exec permission (stat s_irwxgothers have execute permission (stat s_ixothothers have write permission (stat s_iwothothers have read permission (stat s_irothothers have read/write/exec permission (stat s_irwxoset uid mode (stat s_isuidset gid mode (stat s_isgidset the sticky bit (stat s_isvtx the default mode of file is ( ~umask)where the umask setting is used to remove selected permissions for examplea umask of removes the write permission for groups and others the umask can be changed using the os umask(function the umask setting has no effect on windows openpty(opens psuedo-terminal and returns pair of file descriptors (master,slavefor the pty and tty available on some versions of unix pipe(creates pipe that can be used to establish unidirectional communication with another process returns pair of file descriptors (rwusable for reading and writingrespectively this function is usually called prior to executing fork(function after the fork()the sending process closes the read end of the pipe and the receiving process closes the write end of the pipe at this pointthe pipe is activated and data can be sent from one process to another using read(and write(functions (unixread(fdnreads at most bytes from file descriptor fd returns byte string containing the bytes read tcgetpgrp(fdreturns the process group associated with the control terminal given by fd (unixtcsetpgrp(fdpgsets the process group associated with the control terminal given by fd (unixttyname(fdreturns string that specifies the terminal device associated with file descriptor fd if fd is not associated with terminal devicean oserror exception is raised (unixwrite(fdstrwrites the byte string str to file descriptor fd returns the number of bytes actually written lib fl ff