As reported by Chris:i The manual entry for KDGETMODE specifies "argp points to a long which is set to one of the above values." At least on x86_64-bit Fedora24, the text should probably specify argp is an int (32-bit), rather than a long (64-bit). [To verify:] Open a file descriptor to the local console, and execute some code like the following: long arg = -1; if (-1 == ioctl(fd, KDGETMODE, &arg)) { return -1; } printf("KDGETMODE: 0x%lx\n", arg); Now try this version: int arg = -1; if (-1 == ioctl(fd, KDGETMODE, &arg)) { return -1; } printf("KDGETMODE: 0x%x\n", arg); Result: The first version gives this result: KDGETMODE: 0xffffffff00000001 The second version gives this result: KDGETMODE: 0x1 Reading the kernel source confirms this point. Reported-by: Chris Gassib <position0x45@hotmail.com> Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>