1. Linux emulation
    1. Emulation setup
      1. Configuring the kernel
      2. Installing the Linux libraries
      3. Installing Acrobat Reader
      4. Note
    2. Directory structure
    3. Emulating /proc
    4. Using Linux browser plugins
    5. Further reading

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 compat_linux(8) 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 EXEC_ELF32

or the following options if you are going to use 64-bit ELF binaries:

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:

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 directory.

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


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:

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 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

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 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/

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: