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The NetBSD port for i386, alpha, mac68k, macppc, and many others can execute a great number of native Linux programs, using the Linux emulation layer. Generally, when you think about emulation you imagine something slow and inefficient because, often, emulations must reproduce hardware instructions and even architectures (usually from old machines) in software. In the case of the Linux emulation this is radically different: it is only a thin software layer, mostly for system calls which are already very similar between the two systems. The application code itself is processed at the full speed of your CPU, so you don't get a degraded performance with the Linux emulation and the feeling is exactly the same as for native NetBSD applications.
This chapter explains how to configure the Linux emulation with an example: the installation of the well known Acrobat Reader version 7 program.
The installation of the Linux emulation is described in the compat_linux(8) man page; using the package system only two steps are needed.
Configuring the kernel.
Installing the Linux libraries.
Installing Linux applications like Acrobat Reader
If you use a GENERIC kernel you don't need to do anything because Linux compatibility is already enabled.
If you use a customized kernel, check that the following options are enabled:
option COMPAT_LINUX option EXEC_ELF32
or the following options if you are going to use 64-bit ELF binaries:
option COMPAT_LINUX option EXEC_ELF64
when you have compiled a kernel with the previous options you can start installing the necessary software.
Usually, applications are linked against shared libraries, and for Linux applications, Linux shared libraries are needed. You can get the shared libraries from any Linux distribution, provided it's not too old, but the suggested method is to use the package system and install the libraries automatically (which uses SUSE libraries). When you install the libraries, the following happens:
A secondary root directory is created
which will be used for Linux programs.
This directory is /emul/linux.
The Linux programs in emulation mode will use this directory
as their root directory and use files there. If a required
file is not found, it will be searched with
/ as root directory.
For example, if a Linux application opens
/etc/ld.so.conf, it will first be
searched in
/emul/linux/etc/ld.so.conf, and if
not found there in /etc/ld.so.conf.
The shared libraries for Linux are installed.
Most applications are linked dynamically and expect to find
the necessary libraries on the system.
For example, for Acrobat Reader,
if you go to the
/usr/pkgsrc/print/acroread7 and give the
make depends command, pkgsrc will fetch
and install all dependencies for Acrobat
Reader.
Both operations will be handled automatically by the package system, without the need of manual intervention from the user (we suppose that, by now, you have already begun to love the package system...). Note that this section describes manual installation of the Linux libraries.
To install the libraries, a program must be installed that
handles the RPM format: it is
rpm, which will be used to extract the
SUSE libraries. Execute make and
make install in the
/usr/pkgsrc/misc/rpm/ directory to
build and install rpm.
Next the suse100_base package must be
installed.
The SUSE RPM files can be downloaded by the package system or, if
you have a SUSE CD, you can copy them in the
/usr/pkgsrc/distfiles/suse100 directory and
then run make and make install
after going to the
/usr/pkgsrc/emulators/suse100_base
directory.
With the same method install suse100_compat
and suse100_x11.
The final configuration is:
#pkg_info -a | grep susesuse_base-10.0nb3 Linux compatibility package suse_compat-10.0nb1 Linux compatibility package with old shared libraries suse_x11-10.0nb2 Linux compatibility package for X11 binaries
Now everything is ready for the installation of the
Acrobat Reader program (or other Linux
programs).
Change to
/usr/pkgsrc/print/acroread7 and give the
usual commands.
#make#make install
To download and install Acrobat Reader you need to add the line
“ACCEPTABLE_LICENSES+=adobe-acrobat-license” to
/etc/mk.conf to accept the Acrobat Reader
license, simply follow the instructions given after
make.
If we examine the outcome of the installation of the Linux
libraries and programs we find that
/emul/linux is a symbolic link pointing to
/usr/pkg/emul/linux, where the following
directories have been created:
bin/
dev/
etc/
lib/
opt/
proc/
root/
sbin/
usr/
var/
Please always refer to /emul/linux and not
to /usr/pkg/emul/linux.
The latter is an implementation detail and may change in the
future.
How much space is required for the Linux emulation software? On one system we got the following figure:
#cd /usr/pkg/emul#du -k /emul/linux/... 127804 /emul/linux/
Acrobat Reader, the program, has been
installed in the usual directory for package binaries:
/usr/pkg/bin. It can be run just as any
other program:
$acroread netbsd.pdf
Some Linux programs rely on a Linux-like /proc
filesystem. The NetBSD procfs filesystem can emulate a
/proc filesystem that contains Linux-specific
pseudo-files. To accomplish this you can mount the procfs with
the “linux”-option:
#mount_procfs -o linux procfs /emul/linux/proc
In this example a Linux-like proc filesystem will be mounted to
the /emul/linux/proc directory. You can also
let NetBSD mount it automatically during the booting process of
NetBSD, by adding the following line to /etc/fstab:
procfs /emul/linux/proc procfs ro,linux
Linux plugins for Mozilla-based browsers can be used on native NetBSD Firefox builds through nspluginwrapper, a wrapper that translates between the native browser and a foreign plugin. At the moment, nspluginwrapper only works reliably on Mozilla-based browsers that link against GTK2+ (GTK1+ is not supported). nspluginwrapper can be installed through pkgsrc:
#cd /usr/pkgsrc/www/nspluginwrapper#make install
Plugins can then be installed in two steps: first, the plugin has to be installed on the system (e.g. through pkgsrc). After that the plugin should be registered with the nspluginwrapper by the users who want to use that plugin.
In this short example we will have a look at installing the Macromedia Flash plugin. We can fullfill the first step by installing the Flash plugin through pkgsrc:
#cd /usr/pkgsrc/multimedia/ns-flash#make install
After that an unprivileged user can register the Flash plugin:
$ nspluginwrapper -i /usr/pkg/lib/netscape/plugins/libflashplayer.so
The plugin should then be registered correctly. You can check this
by using the -l option of
nspluginwrapper
(nspluginwrapper -l). If the plugin is listed,
you can restart Firefox, and verify that the plugin was installed
by entering about:plugins in the location
bar.
The following articles may be of interest for further understanding Linux (and other) emulation:
Implementing Linux emulation on NetBSD . May 2004.
Irix binary compatibility, part 1 . Aug 2002.
Irix binary compatibility, part 2 . Aug 2002.
Irix binary compatibility, part 3 . Sep 2002.
Irix binary compatibility, part 4 . Oct 2002.
Irix binary compatibility, part 5 . Dec 2002.
Irix binary compatibility, part 6 . Apr 2003.