Distcc

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

If you are planning on using distcc to help you bootstrap a Gentoo installation, make sure you read the section Using Distcc to Bootstrap.

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 a computer is sending away for compilation, enabled with the    flag.

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:

Now, set the  variable and   variable as shown below. A common strategy is to set N as twice the number of total (local + remote) CPUs + 1 and M as number of local CPUs. In case distcc hosts are not available, or the ebuild requires local-only compile (e.g. gcc),  flag this will prevent spawning too many tasks.

For instance, if you're connected to two quad core host PCs running  and your local PC has a dual core, then the   variable could look like this:

While editing your, make sure that you do not have  in your   or. will not distribute work to other machines if  is set to. You may find the appropriate value with. See also Inlining -march=native for distcc blog post.

Specifying Participating Hosts
Use the  command to set the list of hosts. Here is an example of some hosts that might be in your list:

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:

Edit to your needs and be sure to set the   directive to allow only hosts you trust. For added security, you should also use the  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:

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  variable to include  in front of the directory that contains. However, there is a caveat. If you use ccache you have to put distcc after the ccache part:

You can put this in your or equivalent file to have the PATH set every time you log in.

Then, as you would normally type , you would type   (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.

Setting up Distcc to Work With ssh
Setting up distcc via ssh includes some pitfalls. First, generate a ssh key pair without password setup. Be aware that portage compiles programs as user portage. The home folder of the user portage is, which means the keys need to be stored in

Second, create a section for each host in the ssh config file:

Also make sure that each host is available in the file and append your public key to the  file of the hosts. To set up the hosts test1 and test2 run

Please note the '@'-sign, which specifies ssh hosts for.

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.

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:

Step 2: Getting Distcc
Install distcc:

Step 3: Setting Up Distcc
Run  to setup distcc; substitute   with the IP addresses or hostnames of the participating DistCC nodes.

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

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  instead of. 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  or to put it in

-march=native
Starting with GCC 4.3.0, the compiler supports the -march=native option which turns on CPU autodetection and optimizations that are worth being enabled on the processor which GCC is running. This creates a problem when using distcc because it allows the mixing of code optimized for different processors. For example, running distcc with -march=native on a system that has an AMD Athlon processor and doing the same on another that has an Intel Pentium processor will mix code compiled on both processors together. Heed the following warning.

To know the flags that GCC would enable when called with -march=native, execute the following:

Distcc Monitors
Distcc ships with two monitors. The text-based one is always built and is called. 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 enabled through the    flag. This one is GTK+ based, runs in an X environment and it is quite lovely. For Gentoo, the GUI monitor has been called  for less confusion. Elsewhere it may be referred to as.

or run :

To monitor Portage's distcc usage you can use:

Links

 * Inlining -march=native for distcc.

Acknowledgements
We would like to thank the following authors and editors for their contributions to this guide:


 * Lisa Seelye
 * Mike Frysinger
 * Erwin
 * Sven Vermeulen
 * Lars Weiler
 * Tiemo Kieft
 * nightmorph