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# Linux emulation

The NetBSD port for i386, amd64, 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.

## Emulation setup

The installation of the Linux emulation is described in the
man page; using the package system, only two steps are needed.

 1. Configuring the kernel.
 2. Installing the Linux libraries.
 3. Installing Linux applications like Acrobat Reader

### Configuring the kernel

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.

### Installing the Linux libraries

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/`, it will first be
   searched in `/emul/linux/etc/`, and if not found there, in

 * 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 `suse121_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/suse121` directory and then run `make` and
`make install` after going to the `/usr/pkgsrc/emulators/suse121_base`

With the same method install `suse121_compat` and `suse121_x11`. The final
configuration is:

    # pkg_info -a | grep suse
	suse_base-12.1nb3   Linux compatibility package
	suse_compat-12.1    Linux compatibility package with old shared libraries
	suse_x11-12.1       Linux compatibility package for X11

*Note*: Of course you can also install the packages binary. To do this, you
would either set the proper `PKG_PATH` and then

    # pkg_add rpm
    # pkg_add suse_base
    # pkg_add suse_compat
    # pkg_add suse_x11

Or, using `pkgin`:

    # pkgin install rpm suse_base suse_compat suse_x11

*Note*: You can also skip this step when you are installing a package from
pkgsrc which requires Linux emulation! A good example for this is the package
`www/opera`, which will automatically install the packages needed for emulating
the Linux version of the Opera browser.

### Installing Acrobat Reader

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

### Note

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`.

## Directory structure

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/`

*Note*: 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

## Emulating /proc

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

    # 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

    procfs /emul/linux/proc procfs ro,linux

## Using Linux browser plugins

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

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

    # 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/

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.

## Further reading

The following articles may be of interest for further understanding Linux (and other) emulation:

 * *[Implementing Linux emulation on NetBSD](*. Peter Seebach. May 2004.
 * *[Linux compatibility on BSD for the PPC platform, part 1](*. Emmanuel Dreyfus. May 2001.
 * *[Linux compatibility on BSD for the PPC platform, part 2](*. Emmanuel Dreyfus. May 2001.
 * *[Linux compatibility on BSD for the PPC platform, part 3](*. Emmanuel Dreyfus. Jun 2001.
 * *[Linux compatibility on BSD for the PPC platform, part 4](*. Emmanuel Dreyfus. Jun 2001.
 * *[Linux compatibility on BSD for the PPC platform, part 5](*. Emmanuel Dreyfus. Aug 2002.
 * *[Irix binary compatibility, part 1](*. Emmanuel Dreyfus. Aug 2002.
 * *[Irix binary compatibility, part 2](*. Emmanuel Dreyfus. Aug 2002.
 * *[Irix binary compatibility, part 3](*. Emmanuel Dreyfus. Sep 2002.
 * *[Irix binary compatibility, part 4](*. Emmanuel Dreyfus. Oct 2002.
 * *[Irix binary compatibility, part 5](*. Emmanuel Dreyfus. Dec 2002.
 * *[Irix binary compatibility, part 6](*. Emmanuel Dreyfus. Apr 2003.

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