Int 21H, AH=43H, AL=01H

2 and higher

“CHMOD” - SET FILE ATTRIBUTES

      AX = 4301h
      CX = new file attributes (see #01420)
      DS:DX -> ASCIZ filename

CF clear if successful

          AX destroyed
      CF set on error
          AX = error code (01h,02h,03h,05h) (see #01680 at AH=59h)

will not change volume label or directory attribute bits, but will change the other attribute bits of a directory (the directory bit must be cleared to successfully change the other attributes of a directory, but the directory will not be changed to a normal file as a result)

MS-DOS 4.01 reportedly closes the file if it is currently open

for security reasons, the Novell NetWare execute-only bit can never be cleared; the file must be deleted and recreated

under the FlashTek X-32 DOS extender, the filename pointer is in DS:EDX

DOS 5.0 SHARE will close the file if it is currently open in sharing-compatibility mode, otherwise a sharing violation critical error is generated if the file is currently open

DR DOS 3.41/5.0 will silently ignore attempts to change the 'directory' attribute bit

Bitfields for file attributes:

AX=4300h,AX=7143h,INT 2F/AX=110Eh

Text based on Ralf Brown Interrupt List Release 61