aout(4) [freebsd man page]

AOUT(4) 						   BSD Kernel Interfaces Manual 						   AOUT(4)

NAME

     aout -- kernel support for executing binary files in legacy a.out format

SYNOPSIS

	   kldload a.out

DESCRIPTION

     The a.out(5) executable format was used before the release of FreeBSD 3.0.  Since i386 was the only supported architecture at that time,
     a.out(5) executables can only be activated on platforms that support execution of i386 code, such as i386 and amd64.

     To add kernel support for old syscalls and old syscall invocation methods, place the following options in the kernel configuration file:

	   options COMPAT_43
	   options COMPAT_FREEBSD32

     The COMPAT_FREEBSD32 option is only required on 64-bit CPU architectures.

     The aout.ko module needs to be loaded with the kldload(8) utility in order to support the a.out(5) image activator:

	   kldload aout

     Alternatively, to load the module at boot time, place the following line in loader.conf(5):

	   aout_load="YES"

     The a.out(5) format was mainstream quite a long time ago.	Reasonable default settings and security requirements of modern operating systems
     today contradict the default environment of that time and require adjustments of the system to mimic natural environment for old binaries.

     The following sysctl(8) tunables are useful for this:

	   security.bsd.map_at_zero   Set to 1 to allow mapping of process pages at address 0.	Some very old ZMAGIC executable images require
				      text mapping at address 0.

	   kern.pid_max 	      Old versions of FreeBSD used signed 16-bit type for pid_t.  Current kernels use 32-bit type for pid_t, and
				      allow process id's up to 99999.  Such values cannot be represented by old pid_t, mostly causing issues for
				      processes using wait(2) syscalls, for example shells.  Set the sysctl to 30000 to work around the problem.

	   kern.elf32.read_exec       Set to 1 to force any accessible memory mapping performed by 32-bit process to allow execution, see mmap(2).
				      Old i386 CPUs did not have a bit in PTE which disallowed execution from the page, so many old programs did
				      not specify PROT_EXEC even for mapping of executable code.  The sysctl forces PROT_EXEC if mapping has any
				      access allowed at all.  The setting is only needed if the host architecture allows non-executable mappings.

SEE ALSO

     execve(2), a.out(5), elf(5), sysctl(8)

HISTORY

     The a.out(5) executable format was used on ancient AT&T UNIX and served as the main executable format for FreeBSD from the beginning up to
     FreeBSD 2.2.9.  In FreeBSD 3.0 it was superseded by elf(5).

AUTHORS

     The aout manual page was written by Konstantin Belousov <kib@FreeBSD.org>.

BUGS

     On 64bit architectures, not all wrappers for older syscalls are implemented.

BSD
								  August 14, 2012							       BSD

LINUX(4)                                                   BSD Kernel Interfaces Manual                                                   LINUX(4)

NAME

     linux -- Linux ABI support

SYNOPSIS

     To compile support for this ABI into an i386 kernel place the following line in your kernel configuration file:

           options COMPAT_LINUX

     for an amd64 kernel use:

           options COMPAT_LINUX32

     Alternatively, to load the ABI as a module at boot time, place the following line in loader.conf(5):

           linux_load="YES"

DESCRIPTION

     The linux module provides limited Linux ABI (application binary interface) compatibility for userland applications.  The module provides the
     following significant facilities:

     o   An image activator for correctly branded elf(5) executable images

     o   Special signal handling for activated images

     o   Linux to native system call translation

     It is important to note that the Linux ABI support it not provided through an emulator.  Rather, a true (albeit limited) ABI implementation
     is provided.

     The following sysctl(8) tunable variables are available:

     compat.linux.osname       Linux kernel operating system name.

     compat.linux.osrelease    Linux kernel operating system release.  Changing this to something else is discouraged on non-development systems,
                               because it may change the way Linux programs work.  Recent versions of GNU libc are known to use different syscalls
                               depending on the value of this sysctl.

     compat.linux.oss_version  Linux Open Sound System version.

     The linux module can be linked into the kernel statically with the COMPAT_LINUX kernel configuration option or loaded as required.  The fol-
     lowing command will load the module if it is neither linked into the kernel nor already loaded as a module:

           if ! kldstat -v | grep -E 'linux(aout|elf)' > /dev/null; then
                   kldload linux > /dev/null 2>&1
           fi

     Note that dynamically linked Linux executables will require a suitable environment in /compat/linux.  Specifically, the Linux run-time
     linker's hints files should be correctly initialized.  For this reason, it is common to execute the following commands to prepare the system
     to correctly run Linux executables:

           if [ -x /compat/linux/sbin/ldconfig ]; then
                   /compat/linux/sbin/ldconfig -r /compat/linux
           fi

     For information on loading the linux kernel loadable module automatically on system startup, see rc.conf(5).  This information applies
     regardless of whether the linux module is statically linked into the kernel or loaded as a module.

FILES

     /compat/linux       minimal Linux run-time environment
     /compat/linux/proc  limited Linux process file system
     /compat/linux/sys   limited Linux system file system

SEE ALSO

     brandelf(1), elf(5), linprocfs(5), linsysfs(5)

HISTORY

     Linux ABI support first appeared in FreeBSD 2.1.

BSD                                                              February 8, 2010                                                              BSD