vm86old, vm86 - enter virtual 8086 mode


#include <sys/vm86.h>

int vm86old(struct vm86_struct *info);

int vm86(unsigned long fn, struct vm86plus_struct *v86);


The system call vm86() was introduced in Linux 0.97p2. In Linux 2.1.15 and 2.0.28 it was renamed to vm86old(), and a new vm86() was introduced. The definition of struct vm86_struct was changed in 1.1.8 and 1.1.9.

These calls cause the process to enter VM86 mode (virtual-8086 in Intel literature), and are used by dosemu.

VM86 mode is an emulation of real mode within a protected mode task.


On success, zero is returned. On error, -1 is returned, and errno is set appropriately.


EFAULT This return value is specific to i386 and indicates a problem with getting userspace data.
ENOSYS This return value indicates the call is not implemented on the present architecture.
EPERM Saved kernel stack exists. (This is a kernel sanity check; the saved stack should only exist within vm86 mode itself.)


This call is specific to Linux on 32-bit Intel processors, and should not be used in programs intended to be portable.


This page is part of release 3.23 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at

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