OpenBSD-4.6/share/man/man8/compat_aout.8

.\"	$OpenBSD: compat_aout.8,v 1.4 2007/05/31 19:19:58 jmc Exp $
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.Dd $Mdocdate: May 31 2007 $
.Dt COMPAT_AOUT 8
.Os
.Sh NAME
.Nm compat_aout
.Nd setup for running a.out OpenBSD binaries on ELF systems
.Sh DESCRIPTION
.Ox
supports running legacy a.out binaries.
This only applies to i386 systems for now.
Most programs should work.
.Pp
The a.out compatibility feature is active
for kernels compiled with the
.Nm COMPAT_AOUT
option and kern.emul.aout
.Xr sysctl 8
enabled.
.Pp
A lot of programs are dynamically linked.
This means that the shared libraries that the programs depend on
and the runtime linker are also needed.
A "shadow root" directory for these files
on the
.Ox
system will have to be created.
This directory is named
.Pa /emul/a.out .
Selected file operations done by legacy a.out programs run under
.Ox
will look in this directory first.
.Ss Setting up shared libraries
Up until
.Ox 3.3 ,
programs were using the a.out file format.
When migrating to a current ELF system,
some old binaries may still be used.
Before installing a current system, all the necessary shared libraries
in the
.Pa /usr/lib ,
.Pa /usr/X11R6/lib ,
.Pa /usr/local/lib
and the a.out dynamic linker system, namely
.Pa /usr/libexec/ld.so ,
.Pa /usr/bin/ldd ,
and
.Pa /sbin/ldconfig
should be copied to the corresponding location in the shadow tree.
(e.g., copy
.Pa /sbin/ldconfig
into
.Pa /emul/a.out/sbin/ldconfig ) .
The directory
.Pa /emul/a.out/var/run
should also be created.
.Pp
Before running a.out binaries, the
.Nm ld.so
cache must be prepared, by running
.Pa /emul/a.out/sbin/ldconfig .
.Pp
Once everything is set up properly, a.out programs will look for shared
libraries under
.Pa /emul/a.out
and ELF programs will not see the a.out shared libraries.