How do I read numeric permissions greater than 777?

Question

I noticed this just now, when using find and stat to get the permissions of all the items in /usr/local/share/locale before I recursively change them. stat shows the permissions in a numeric format that I'm not familiar with—all the directories are 40755 and the files are 100644. I'm guessing that the last three are just normal octal permissions (which I already know about), but what do the 40s and 100s mean?

Answer 1

stat(1) is primarily a wrapper for stat(2), and the man page of stat(2) reveals this:

 The status information word st_mode has the following bits:

 #define S_IFMT   0170000  /* type of file */
 #define S_IFIFO  0010000  /* named pipe (fifo) */
 #define S_IFCHR  0020000  /* character special */
 #define S_IFDIR  0040000  /* directory */
 #define S_IFBLK  0060000  /* block special */
 #define S_IFREG  0100000  /* regular */
 #define S_IFLNK  0120000  /* symbolic link */
 #define S_IFSOCK 0140000  /* socket */
 #define S_IFWHT  0160000  /* whiteout */
 #define S_ISUID  0004000  /* set user id on execution */
 #define S_ISGID  0002000  /* set group id on execution */
 #define S_ISVTX  0001000  /* save swapped text even after use */
 #define S_IRUSR  0000400  /* read permission, owner */
 #define S_IWUSR  0000200  /* write permission, owner */
 #define S_IXUSR  0000100  /* execute/search permission, owner */

So the leading 100 means it's a regular file, and the leading 40 means it's a directory.