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Chapter 10. Linux emulation

Table of Contents

10.1. Emulation setup
10.1.1. Configuring the kernel
10.1.2. Installing the Linux libraries
10.1.3. Installing Acrobat Reader
10.2. Directory structure
10.3. Emulating /proc

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 4 program.

10.1. 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

10.1.1. 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

when you have compiled a kernel with the previous options you can start installing the necessary software.

10.1.2. 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/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/acroread and give the make depends command, you get the following message:

    ===>  acroread-4.0 requires Linux glibc2 libraries - see compat_linux(8).

Both operations will be handled automatically by the package system, without the need of manual intervention from the user (I 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 suse_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/suse directory and then run make and make install after going to the /usr/pkgsrc/emulators/suse_base directory.

With the same method install suse_compat and suse_x11. The final configuration is:

# pkg_info -a | grep suse
suse_base-7.3nb5    Linux compatibility package
suse_x11-7.3nb2     Linux compatibility package for X11 binaries
suse_compat-7.3     Linux compatibility package with old shared libraries 

10.1.3. Installing Acrobat Reader

Now everything is ready for the installation of the Acrobat Reader program (or other Linux programs). Change to /usr/pkgsrc/print/acroread 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.

10.2. 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/
boot/
cdrom/
dev/
etc/
floppy/
home/
lib/
mnt/
opt/
proc/
root/
sbin/
usr/

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 my system I get the following figure:

# cd /usr/pkg/emul
# du -k linux
...
214049   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 

10.3. 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