Gentoo Distcc Documentation

1.  Introduction

What is distcc?

Distcc is a program designed to distribute compiling tasks across a network to participating hosts. It is comprised of a server, distccd, and a client program, distcc. Distcc can work transparently with ccache, Portage, and Automake with a little setup.

Using distcc to bootstrap

If you are planning on using distcc to help you bootstrap a Gentoo installation, make sure you read the section Using distcc to Bootstrap, which is situated further down in this document.

2.  Setup

Dependencies

In order to use Distcc, all of the computers on your network need to have the same GCC versions. For example, mixing 3.3.x (where the x varies) is okay, but mixing 3.3.x with 3.2.x may result in compilation errors or runtime errors.

Installing Distcc

There are a couple of options you should be aware of before you start installing distcc.

Distcc ships with a graphical monitor to monitor tasks that your computer is sending away for compilation. If you use Gnome then put 'gnome' in your USE flags. However, if you don't use Gnome and would still like to have the monitor then you should put 'gtk' in your USE flags.

# emerge distcc

Setting up Portage to use Distcc

Setting up Portage to use distcc is easy. Execute the following steps on each system that should participate in the distributed compiling:

# emerge distcc
# nano -w /etc/make.conf
(Set N to a suitable number for your particular setup)
(A common strategy is setting N as twice the number of total CPUs + 1 available)
MAKEOPTS="-jN"
(Add distcc to your FEATURES)
FEATURES="distcc"

Specifying Participating Hosts

Use the distcc-config command to set the list of hosts. Here is an example of some hosts that might be in your list:

192.168.0.1          192.168.0.2                       192.168.0.3
192.168.0.1/2        192.168.0.2                       192.168.0.3/10
192.168.0.1:4000/2   192.168.0.2/1                     192.168.0.3:3632/4
@192.168.0.1         @192.168.0.2:/usr/bin/distccd     192.168.0.3
(There are also several other methods of setting up hosts.  See the 
distcc manpage for more details.)
If you wish to compile on the local machine you should put 'localhost'
in the hosts list.  Conversely if you do not wish to use the local machine to
compile (which is often the case) omit it from the hosts list.  On a slow
machine using localhost may actually slow things down. Make sure to test your
settings for performance.

It may all look complicated, but in most cases a variant of line 1 or 2 will work.

Since most people won't be using lines 3 or 4, I'll refer to the distcc docs (man distcc) for more information, which includes being able to run distcc over an SSH connection.

For instance, to set the first line in the previous example:

# /usr/bin/distcc-config --set-hosts "192.168.0.1 192.168.0.2 192.168.0.3"

Edit /etc/conf.d/distccd to your needs and be sure to set the --allow directive to allow only hosts you trust. For added security, you should also use the --listen directive to tell the distcc daemon what IP to listen on (for multi-homed systems). More information on distcc security can be found at Distcc Security Design.

Now start the distcc daemon on all the participating computers:

(Add distccd to the default runlevel)
# rc-update add distccd default
(Start the distcc daemon)
# /etc/init.d/distccd start

Setting up Distcc to Work With Automake

This is, in some cases, easier than the Portage setup. What you have to do is update your PATH variable to include /usr/lib/distcc/bin in front of the directory that contains gcc (/usr/bin). However, there is a caveat. If you use ccache you have to put distcc after the ccache part:

# export PATH="/usr/lib/ccache/bin:/usr/lib/distcc/bin:${PATH}"
(You can put this in your ~/.bashrc or equivalent file to have the PATH
set every time you log in)

Then, as you would normally type make, you would type make -jN (where N is an integer). The value of N depends on your network and the types of computers you are using to compile. Test your own settings to find the number that yields the best performance.

3.  Cross-Compiling

Cross-compiling is using one architecture to build programs for another architecture. This can be as simple as using an Athlon (i686) to build a program for a K6-2 (i586), or using a Sparc to build a program for a ppc. This is documented in our DistCC Cross-compiling Guide.

4.  Using Distcc to Bootstrap

Step 1: Configure Portage

Boot your new box with a Gentoo Linux LiveCD and follow the installation instructions up until the bootstrapping part. (See the Gentoo FAQ for more information about bootstrapping.) Then configure Portage to use distcc:

# nano -w /etc/make.conf
(Add distcc to the FEATURES
FEATURES="distcc"
(Modify MAKEOPTS to include -jN, where N is twice the number of CPUs
+1 available)
MAKEOPTS="-jN"

# export PATH="/usr/lib/ccache/bin:/usr/lib/distcc/bin:${PATH}"

Step 2: Getting Distcc

Install distcc:

# USE='-*' emerge --nodeps sys-devel/distcc

Step 3: Setting Up Distcc

Run distcc-config --install to setup distcc:

(Substitute host1, host2, ... with the IP number(s) of the
participating hosts)
# /usr/bin/distcc-config --set-hosts "localhost host1 host2 host3 ..."
An example: /usr/bin/distcc-config --set-hosts "localhost
192.168.0.4 192.168.0.6"

Distcc is now set up to bootstrap! Continue with the official installation instructions and do not forget to re-emerge distcc after emerge system. This is to make sure that all of the dependencies you want are installed as well.

5.  Troubleshooting

Some Packages Don't Use Distcc

As you emerge various packages, you'll notice that some of them aren't being distributed (and aren't being built in parallel). This may happen because the package's Makefile doesn't support parallel operations or the maintainer of the ebuild has explicitly disabled parallel operations due to a known problem.

Sometimes distcc might cause a package to fail to compile. If this happens for you, please report it to us.

Mixed GCC Versions

If you have different GCC versions on your hosts, there will likely be very weird problems. The solution is to make certain all hosts have the same GCC version.

Recent Portage updates have made Portage use ${CHOST}-gcc instead of gcc. This means that if you're mixing i686 machines with other types (i386, i586) you will run into problems. A workaround for this may be to export CC='gcc' CXX='c++' or to put it in /etc/make.conf.

-march=native

Starting with GCC 4.3.0, the compiler supports the -march=native switch which turns on CPU autodetection and optimizations that are worth being enabled on the processor the GCC is running at. This is a problem with distcc as it allows mixing of code optimized for different processors (like AMD Athlon and Intel Pentium). Don't use -march=native or -mtune=native in your CFLAGS or CXXFLAGS when compiling with distcc.

6.  Distcc Extras

Distcc Monitors

Distcc ships with two monitors. The text-based one is always built and is called distccmon-text. Running it for the first time can be a bit confusing, but it is really quite easy to use. If you run the program with no parameter it will run once. However, if you pass it a number it will update every N seconds, where N is the argument you passed.

The other monitor is only turned on if you enabled gtk or gnome in your USE flags. This one is GTK+ based, runs in an X environment and it is quite lovely. For Gentoo the GUI monitor has been called distccmon-gui for less confusion. Elsewhere it may be referred to as distccmon-gnome.

# distccmon-text N
(Or)
# distccmon-gui
To monitor Portage's distcc usage you can use:
# DISTCC_DIR="/var/tmp/portage/.distcc/" distccmon-text N
(Or)
# DISTCC_DIR="/var/tmp/portage/.distcc/" distccmon-gui

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