23.1.1. Installing Linux Mode in 3.0-RELEASE and later

It is no longer necessary to specify options LINUX or options COMPAT_LINUX. Linux binary compatibility is done with an KLD object (``Kernel LoaDable object'') so it can be installed on the fly without having to reboot. You will need the following things in your startup files, however:

1. In /etc/rc.conf, you need the following line:

   
       linux_enable=YES
   
   

2. This, in turn, triggers the following action in /etc/rc.i386:

   
       # Start the Linux binary compatibility if requested.
   
       if [ "X${linux_enable}" = X"YES" ]; then echo -n '
   
               linux';               linux > /dev/null 2>&1
   
       fi
   
   

If you want to verify that the KLD is loaded, kldstat will do that:

    % kldstat

    Id Refs Address    Size     Name

     1    2 0xc0100000 16bdb8   kernel

     7    1 0xc24db000 d000     linux.ko

If for some reason you do not want to or cannot load the Linux KLD, then statically link the binary compatibility in the kernel by adding

    options  LINUX

23.1.2. Installing Linux Mode in 2.2.2-RELEASE and later 2.2.x versions

It is no longer necessary to specify options LINUX or options COMPAT_LINUX. Linux binary compatibility is done with an LKM (``Loadable Kernel Module'') so it can be installed on the fly without having to reboot. You will need the following things in your startup files, however:

1. In /etc/rc.conf, you need the following line:

   
       linux_enable=YES
   
   

2. This, in turn, triggers the following action in /etc/rc.i386:

   
       # Start the Linux binary emulation if requested.
   
       if [ "X${linux_enable}" = X"YES" ]; then echo -n '
   
               linux';               linux > /dev/null 2>&1
   
       fi
   
   

If you want to verify that the LKM is running, modstat will do that:

    % modstat

    Type     Id Off Loadaddr Size Info     Rev Module Name

    EXEC      0   4 f09e6000 001c f09ec010   1 linux_mod

However, there have been reports that this fails on some 2.2-RELEASE and later systems. If for some reason you cannot load the Linux LKM, then statically link the Linux compatibility in the kernel by adding

    options  LINUX

23.1.3. Installing Linux Mode in 2.1-STABLE

The GENERIC kernel in 2.1-STABLE is not configured for Linux compatibility so you must reconfigure your kernel for it. There are two ways to do this: 1. linking the binary compatibility statically in the kernel itself and 2. configuring your kernel to dynamically load the Linux loadable kernel module (LKM).

To enable Linux binary compatibility, add the following to your configuration file (c.f. /sys/i386/conf/LINT):

    options COMPAT_LINUX

If you want to run doom or other applications that need shared memory, also add the following.

    options SYSVSHM

The Linux system calls require 4.3BSD system call compatibility. So make sure you have the following.

    options "COMPAT_43"

If you prefer to statically link the binary compatibility in the kernel rather than use the loadable kernel module (LKM), then add

    options  LINUX

Then run config and install the new kernel as described in the kernel configuration section.

If you decide to use the LKM you must also install the loadable module. A mismatch of versions between the kernel and loadable module can cause the kernel to crash, so the safest thing to do is to reinstall the LKM when you install the kernel.

    # cd /usr/src/lkm/linux

    # make all install

Once you have installed the kernel and the LKM, you can invoke linux as root to load the LKM.

    # linux

    Linux emulator installed

    Module loaded as ID 0

To see whether the LKM is loaded, run modstat.

    % modstat

    Type     Id Off Loadaddr Size Info     Rev

    Module Name EXEC      0   3 f0baf000 0018 f0bb4000   1 linux_emulator

You can cause the LKM to be loaded when the system boots in either of two ways. In FreeBSD 2.2.1-RELEASE and 2.1-STABLE enable it in /etc/sysconfig

    linux=YES

    linux

23.1.4. Installing Linux Runtime Libraries

    # cd /usr/ports/emulators/linux_base

    # make all install

    % ldd linuxxdoom

    libXt.so.3 (DLL Jump 3.1) => /usr/X11/lib/libXt.so.3.1.0

    libX11.so.3 (DLL Jump 3.1) => /usr/X11/lib/libX11.so.3.1.0

    libc.so.4 (DLL Jump 4.5pl26) => /lib/libc.so.4.6.29

    /compat/linux/usr/X11/lib/libXt.so.3.1.0

    /compat/linux/usr/X11/lib/libXt.so.3 -> libXt.so.3.1.0

    /compat/linux/usr/X11/lib/libX11.so.3.1.0

    /compat/linux/usr/X11/lib/libX11.so.3 -> libX11.so.3.1.0

    /compat/linux/lib/libc.so.4.6.29 /compat/linux/lib/libc.so.4 -> libc.so.4.6.29

    /compat/linux/lib/ld.so

    /compat/linux/etc/ld.so.config

    /sbin/ldconfig

    /usr/bin/ldd

    /lib/libc.so.x.y.z

    /lib/ld.so

    /usr/X11/lib

    /usr/local/lib

    # cd /compat/linux/lib

    # /compat/linux/sbin/ldconfig

    # ldd-linux `which ldd-linux`

    libc.so.4 (DLL Jump 4.5pl26) => /lib/libc.so.4.6.29

23.1.5. Installing Linux ELF binaries

ELF binaries sometimes require an extra step of ``branding''. If you attempt to run an unbranded ELF binary, you will get an error message like the following;

    % ./my-linux-elf-binary

    ELF binary type not known

    Abort

To help the FreeBSD kernel distinguish between a FreeBSD ELF binary from a Linux binary, use the brandelf(1) utility.

    % brandelf -t Linux my-linux-elf-binary

The GNU toolchain now places the appropriate branding information into ELF binaries automatically, so you should be needing to do this step increasingly rarely in future.

23.1.6. Configuring the host name resolver

If DNS does not work or you get the messages

    resolv+: "bind" is an invalid keyword resolv+:

    "hosts" is an invalid keyword

    order hosts, bind

    multi on

Lastly, those who run 2.1-STABLE need to set an the RESOLV_HOST_CONF environment variable so that applications will know how to search the host tables. If you run FreeBSD 2.2-RELEASE or later, you can skip this. For the /bin/csh shell use:

    % setenv RESOLV_HOST_CONF /compat/linux/etc/host.conf

For /bin/sh use:

    % RESOLV_HOST_CONF=/compat/linux/etc/host.conf; export RESOLV_HOST_CONF

23.1.7. Finding the necessary files

Linux is distributed by several groups that make their own set of binaries that they distribute. Each distribution has its own name, like ``Slackware'' or ``Yggdrasil''. The distributions are available on a lot of ftp sites. Sometimes the files are unpacked, and you can get the individual files you need, but mostly they are stored in distribution sets, usually consisting of subdirectories with gzipped tar files in them. The primary ftp sites for the distributions are:

1. sunsite.unc.edu:/pub/Linux/distributions

2. tsx-11.mit.edu:/pub/linux/distributions

Some European mirrors:

1. ftp.luth.se:/pub/linux/distributions

2. ftp.demon.co.uk:/pub/unix/linux

3. src.doc.ic.ac.uk:/packages/linux/distributions

For simplicity, let us concentrate on Slackware here. This distribution consists of a number of subdirectories, containing separate packages. Normally, they are controlled by an install program, but you can retrieve files ``by hand'' too. First of all, you will need to look in the contents subdirectory of the distribution. You will find a lot of small text files here describing the contents of the separate packages. The fastest way to look something up is to retrieve all the files in the contents subdirectory, and grep through them for the file you need. Here is an example of a list of files that you might need, and in which contents-file you will find it by grepping through them:

So, in this case, you will need the packages ldso, shlibs, xf_lib and oldlibs. In each of the contents-files for these packages, look for a line saying PACKAGE LOCATION, it will tell you on which ``disk'' the package is, in our case it will tell us in which subdirectory we need to look. For our example, we would find the following locations:

The locations called ``diskXX'' refer to the slakware/XX subdirectories of the distribution, others may be found in the contrib subdirectory. In this case, we could now retrieve the packages we need by retrieving the following files (relative to the root of the Slackware distribution tree):

• slakware/a2/ldso.tgz

• slakware/a2/shlibs.tgz

• slakware/x6/oldlibs.tgz

• slakware/x9/xf_lib.tgz

Extract the files from these gzipped tarfiles in your /compat/linux directory (possibly omitting or afterwards removing files you do not need), and you are done.

See also: ftp://ftp.FreeBSD.org/pub/FreeBSD/2.0.5-RELEASE/xperimnt/linux-emu/README and /usr/src/sys/i386/ibcs2/README.iBCS2