#include <sys/types.h>
#include <sys/stat.h>
mode_t umask(mode_t mask);
在进程创建一个新的文件或目录时，如调用open函数创建一个新文件，新文件的实际存取权限是mode与umask按照 mode&~umask运算以后的结果。umask函数用来修改进程的
umask。参数mask可以直接取数值也可以为open系统调用第三个参数mode的11个宏或他们的组合。
The following symbolic constants are provided for mode:
S_IRWXU 00700 user (file owner) has read, write and execute permission
S_IRUSR 00400 user has read permission
S_IWUSR 00200 user has write permission
S_IXUSR 00100 user has execute permission
S_IRWXG 00070 group has read, write and execute permission
S_IRGRP 00040 group has read permission
S_IWGRP 00020 group has write permission
S_IXGRP 00010 group has execute permission
S_IRWXO 00007 others have read, write and execute permission
S_IROTH 00004 others have read permission
S_IWOTH 00002 others have write permission
S_IXOTH 00001 others have execute permission
int main(int argc, char* argv[])
{
umask(0);//不屏蔽任何权限
creat("t1", S_IRWXU|S_IRWXG|S_IRWXO);
umask(S_IRWXO);//屏蔽其他用户的所有权限
creat("t2", S_IRWXU|S_IRWXG|S_IRWXO);
return 0;
}
-rwxrwxrwx 1 root root 0 Jan 22 10:26 t1
-rwxrwx--- 1 root root 0 Jan 22 10:26 t2