Distcc

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Distcc 是一个被设计用来将编译任务发布到网络上特定主机的程序。 它由一个服务器 distccd和一个客户端 distcc>程序组成. Distcc 可以很好的与ccache, Portage协同工作,对Automake只需少量的配置。

如果打算使用distcc 来安装Gentoo系统,确保先阅读Using distcc to bootstrap.

安装

在配置distcc之前,让我们先看看在所有主机上安装的sys-devel/distcc软件包。

所有主机的要求

为了使用distcc,网络上的所有计算机都必须具有相同版本的GCC。例如,可以混合使用3.3.x(其中x有所不同),但是将3.3.x与3.2.x混合可能会导致编译错误或运行时错误。

验证所有系统都使用相同版本的binutils(eselect binutils list),否则许多软件包将由于诸如文本重定位之类的各种错误而链接失败。

USE 标记

USE flags for sys-devel/distcc Distribute compilation of C code across several machines on a network

gssapi Enable support for net-libs/libgssglue
gtk Add support for x11-libs/gtk+ (The GIMP Toolkit)
hardened Activate default security enhancements for toolchain (gcc, glibc, binutils)
ipv6 Add support for IP version 6
selinux !!internal use only!! Security Enhanced Linux support, this must be set by the selinux profile or breakage will occur
xinetd Add support for the xinetd super-server
zeroconf Support for DNS Service Discovery (DNS-SD)

安装(Emerge)

Distcc附带了一个图形监视器,用于监视计算机发送出的编译任务。当设置了gtk USE标志时,将启用此监视器。

配置USE设置后,安装sys-devel/distcc软件包:

root #emerge --ask sys-devel/distcc
重要
记得在所有参与的计算机上安装sys-devel/distcc

配置

服务

为了使distccd自动启动,请遵循以下说明。

OpenRC

编辑/etc/conf.d/distccd并确保将--allow指令设置为仅允许受信任的客户端。为了提高安全性,请使用--listen指令来告知distccd守护程序要侦听的IP(对于多宿主系统)。有关distcc安全性的更多信息,请参见Distcc安全说明

警告
可以连接到distcc服务器端口的任何人都可以作为distccd用户在该计算机上运行任意命令。

以下示例允许运行在192.168.0.4192.168.0.5的distcc客户端连接到本地运行的distccd服务器:

FILE /etc/conf.d/distccd 允许特定客户端连接到distccd
DISTCCD_OPTS="--port 3632 --log-level notice --log-file /var/log/distccd.log -N 15 --allow 192.168.0.4 --allow 192.168.0.5"

When logging to a file in /var/log, create the log and give appropriate permissions:

root #touch /var/log/distccd.log
root #chown distcc:root /var/log/distccd.log
重要
使用--allow--listen很重要。请阅读distccd手册页或以上安全性文档以获取更多信息。

现在,在所有参与的计算机上启动distccd守护程序:

root #rc-update add distccd default
root #rc-service distccd start

systemd

编辑/etc/systemd/system/distccd.service.d/00gentoo.conf文件,以CIDR格式添加允许的客户端。如示例将添加192.168.1.xxx范围内的所有IP地址:

FILE /etc/systemd/system/distccd.service.d/00gentoo.conf配置 ALLOWED_SERVERS
Environment="ALLOWED_SERVERS=192.168.1.0/24"

Or an example with multiple clients and a manually specified log-level

FILE /etc/systemd/system/distccd.service.d/00gentoo.confSetting ALLOWED_SERVERS
Environment="ALLOWED_SERVERS=127.0.0.1 --allow 192.168.1.0/24 --allow 10.1.1.1/24 --log-level error"
附注
这里的名称“ALLOWED_SERVERS”相当混乱,因为它指的是允许连接到本地distccd服务器的客户端。不过,此变量在distccd服务中用作--allow option选项的值 – 有关更多信息,请参见/usr/lib/systemd/system/distccd.service文件。
Important
In contrast to OpenRC, environment variables put in /etc/env.d/* will not take effect for systemd users even after running env-update and restarting the distccd service. This is because /etc/environment.d generated by env-update is only sourced by systemd user instance. Whereas, distccd is spawned by systemd system instance.

To set the proper environment variables for distccd, place them into /etc/systemd/system/distccd.service.d/00gentoo.conf. For example,

FILE /etc/systemd/system/distccd.service.d/00gentoo.conf
[Service]
Environment="ALLOWED_SERVERS=192.168.121.0/24"
Environment="DISTCC_VERBOSE=1"
Environment="DISTCC_SAVE_TEMPS=1"
Environment="CCACHE_DIR=/var/cache/ccache"
Warning
The Environment= directive in /etc/systemd/system/distccd.service.d/00gentoo.conf file does not support variable expansion. Environment="PATH=/usr/lib/ccache/bin:$PATH" will be treated as is, therefore will not work as intended.

For workaround, you need to edit distccd.service by running the following command.

root #systemctl edit --full distccd.service

This will open up an editor. Change the line with ExecStart= directive to

CODE Workaround for appending to PATH
ExecStart=/bin/bash -c "PATH=/usr/lib/ccache/bin:$PATH exec /usr/bin/distccd --no-detach --daemon --port 3632 -N 15 --allow $ALLOWED_SERVERS --log-level debug"

Alternatively, you could also write a shell script wrapper for /usr/bin/distccd.

进行此类更改后,重新加载单元文件:

root #systemctl daemon-reload

配置distccd自动启动,然后启动服务:

root #systemctl enable distccd
root #systemctl start distccd

指定参与主机

使用distcc-config命令设置主机列表。

以下是主机定义的示例列表。在大多数情况下,参考第1行和第2行就足够了。第2行使用/limit语法向distcc通知要在此节点上启动的最大作业数。有关第3行和第4行中使用的语法的更多信息,请参见distcc手册页

CODE 主机定义示例
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

还有其他几种设置主机的方法。有关更多详细信息,请参见distcc手册页(man distcc)。

如果还应该在本地计算机上进行编译,则将localhost放在主机列表中。相反,如果不使用本地计算机进行编译,请从主机列表中将其忽略。在使用本地主机的慢速计算机上,实际上可能会使速度降低。确保测试性能设置。

让我们将distcc配置为使用示例第一行中提到的主机:

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

Distcc还通过调用pump命令支持pump模式。当并行编译多个文件时,这可能会大大减少构建时间。它在服务器端缓存了经过预处理的标头,因此避免了重复重复上传和预处理这些标头文件。

要将主机配置为pump模式,请在主机定义中添加,cpp,lzo后缀。Pump模式需要cpp lzo标志(无论文件是C还是C++)。

root #/usr/bin/distcc-config --set-hosts "192.168.0.1,cpp,lzo 192.168.0.2,cpp,lzo 192.168.0.3,cpp,lzo"

Hosts also need to be in:

FILE /etc/distcc/hostsShould match --set-hosts
192.168.0.1
192.168.0.2
192.168.0.3

Optionally, to set the maximum number of threads used by a host, add a forward slash "/" after each host:

FILE /etc/distcc/hostsSpecify max number of threads
192.168.0.1/8
192.168.0.2/4
192.168.0.3/16

The same applies to the distcc-config command. If the maximum threads number is not specified, it will default to 4.

使用

With Portage

设置 Portage 来使用 distcc 很容易。这是启用 distcc 功能并为同时构建作业的数量设置合适值的问题(因为 distcc 会增加构建资源的数量)。

设置 MAKEOPTS 变量和 FEATURES 变量如下。

一个常见的策略是

  • N 的值设置为 “所有”(本地 + 远程)CPU 内核数的“两倍”+ 1,以及
  • M 的值设置为“本地”CPU 内核数

The use of -lM in the MAKEOPTS variable will prevent spawning too many tasks when some of the distcc cluster hosts are unavailable (increasing the amount of simultaneous jobs on the other systems) or when an ebuild is configured to disallow remote builds (such as with gcc). This is accomplished by refusing to start additional jobs when the system load is at or above the value of M.

FILE /etc/portage/make.conf设置 MAKEOPTS 和 FEATURES
# Replace N and M with the right value as calculated previously
MAKEOPTS="-jN -lM"
FEATURES="distcc"

例如,当有两台运行 distccd 的四核主机 PC 并且本地 PC 具有双核 CPU 时,MAKEOPTS 变量可能如下所示:

FILE /etc/portage/make.conf2 个四核(远程)和一个双核(本地)PC 的 MAKEOPTS 示例
# 2 remote hosts with 4 cores each = 8 cores remote
# 1 local host with 2 cores = 2 cores local
# total number of cores is 10, so N = 2*10+1 and M=2
MAKEOPTS="-j21 -l2"

CFLAGS 和 CXXFLAGS

在编辑 make.conf 文件时,确保它在 CFLAGSCXXFLAGS 中没有 -march=native 变量。如果 march 设置为 nativedistccd 不会将工作分发到其他机器。可以通过运行以下命令获得一组近似的 -march= 和机器标志:

FILE /etc/portage/make.confinlined *FLAGS
# Minimal list of flags is generated with:
#   $ diff -U0 <(LANG=C gcc -Q -O2 -march=sandybridge --help=target) <(LANG=C gcc -Q -O2 -march=native --help=target)
COMMON_FLAGS="-march=sandybridge -mtune=sandybridge -maes" # don't use -march=native!
CFLAGS="${COMMON_FLAGS}"
CXXFLAGS="${COMMON_FLAGS}"

See Inlining -march=native for distcc for more information.

With automake

This is, in some cases, easier than the Portage setup. All that is needed is to update the PATH variable to include /usr/lib/distcc/bin/ in front of the directory that contains gcc (/usr/bin/). However, there is a caveat. If ccache is used, then put the distcc location after the ccache one:

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

Put this in the user's ~/.bashrc or equivalent file to have the PATH set every time the user logs in, or set it globally through an /etc/env.d/ file.

Instead of calling make alone, add in -jN (where N is an integer). The value of N depends on the network and the types of computers that are used to compile. A heuristic approach to the right value is given earlier in this article.

With ccache

To make Ccache work with distcc, some prerequisites must be fulfilled:

  • Ccache is successfully set up locally
  • Distcc is successfully set up on the desired hosts

The following setup will work as follows:

CODE Flow diagram
[client]                                                      [remote]
ccache <miss?> → compile it and save cache files,
<hit?>           also distribute other source code → distccccache <miss?> → compile it, save cache files, return cache file to client
  ↓                                                           <hit?>
use the local cache file                                        ↓
                                                 return local cache file to client
Warning
The following configuration must be done on all desired hosts!

Configure distccd

In order to let the daemon distccd use ccache, it must masquerade the path /usr/bin with /usr/lib/ccache/bin. Furthermore, when it uses ccache, ccache should use the prefix distcc:

FILE /etc/conf.d/distccd
PATH="/usr/lib/ccache/bin:${PATH}"
CCACHE_PREFIX="distcc"

Additionally distccd must be aware of the environment variables DISTCC_DIR and CCACHE_DIR:

Warning
These variables must be set somewhere in /etc/env.d/, otherwise ccache tries to put cache files in ${HOME}/.ccache/, which might result in a COMPILE_ERROR, due to insufficient permissions. To pinpoint this, use the testing example mentioned below and export DISTCC_SAVE_TEMPS="1" as mentioned here. This will provide error logs from the remote site in /tmp/ by default. The logs will look like this: distcc_server_stderr_*.txt. Be aware, that these environment variables cannot be set in /etc/conf.d/distccd, since they will not be read from distccd for some reason.
FILE /etc/env.d/03distcc_ccache
CCACHE_DIR="/var/cache/ccache"
DISTCC_DIR="/var/tmp/portage/.distcc"

Next, update the environment variables:

root #env-update
>>> Regenerating /etc/ld.so.cache...

Finally, restart the daemon distccd to adapt all changes:

root #rc-service distccd restart

Configure ccache

Warning
When using distcc with ccache, it is necessary to prepare the cache directories manually, since the daemon distccd only works with the user distcc for some reason and it cannot create directories within /var/cache/ccache/. It is not sufficient to add this user to the group portage. Also be aware, that the variable cache_dir_levels, defined in ccache.conf, specifies how many subdirectories have to be created. The following example uses the default, which is 2.

First, prepare the cache directories:

root #cd "/var/cache/ccache/"
root #mkdir {a..z} {0..9} tmp
root #for first_level_directory in $(find . -maxdepth 1 -type d -not -name "." -and -not -name "tmp"); do pushd "${first_level_directory}" >/dev/null; mkdir {a..z} {0..9}; popd >/dev/null; done

The second command (mkdir) will create the first level directories from a to z, 0 to 9 and tmp. The following for loop will then look for the first level directories (find . -maxdepth 1 -type d), excluding the current directory . and tmp (-not -name "." -and -not -name "tmp"). It then descends into each of them (pushd), creates the second level directories from a to z and 0 to 9 (mkdir) and goes back to the previous directory (popd), which is /var/cache/ccache/.

Important
The current directory . must be excluded with -not -name ".", otherwise the first pushd command will go to the current directory . and then goes back to whatever directory is currently on the stack via popd. It will navigate through the entire stack until it is empty, creating directories, where each pushd command fails. If this happens, one can search for them using find / -type d -name "0" and remove them with rm --recursive [a-z] [0-9]. It is advised to this manually!

When the preparation is done, every directory - including the directory ccache itself - must be owned by the user distcc:

root #find /var/cache/ccache -type d -exec chown distcc:portage "{}" +

Configure portage

To use emerge with distcc and ccache, make sure, that both features are enabled and that CCACHE_DIR is set in /etc/portage/make.conf:

FILE /etc/portage/make.conf
[...]
FEATURES="distcc ccache"
CCACHE_DIR="/var/cache/ccache"

It might be redundant to set CCACHE_DIR here, since it is already defined in /etc/env.d/03distcc_ccache, mentioned here. But to make absolutely sure, configure it like that.

Testing distcc with ccache manually

Remote

First enable verbose logging by setting --log-level to debug in /etc/conf.d/distccd:

FILE /etc/conf.d/distccd
[...]
DISTCCD_OPTS="${DISTCCD_OPTS} --log-level debug"
[...]

After that, restart the daemon to adapt the changes:

root #rc-service distccd restart

Also check, if there are directories in /var/cache/ccache - including the directory ccache itself - which are not owned by the user distcc and correct their owner permissions:

root #chown -R distcc:portage /var/cache/ccache
Client

Make sure, that the following environment variables are present in the current shell:

root #export PATH="/usr/lib/ccache/bin:${PATH}"
root #export CCACHE_DIR="/var/cache/ccache"
root #export DISTCC_DIR="/var/tmp/portage/.distcc"
root #export DISTCC_SAVE_TEMPS="1"
root #export DISTCC_VERBOSE="1"

After that, navigate to a temporary directory within /tmp/ and compile the example mentioned below:

root #cd $(mktemp --directory)
root #distcc gcc -c main.c -o main.o

This will provide a verbose output, while also keeping temporary files receiving from the remote site in /tmp/ by default:

CODE
[...]
distcc[29466] (dcc_cleanup_tempfiles_inner) skip cleanup of /tmp/distcc_9c42f0a6.i
distcc[29466] (dcc_cleanup_tempfiles_inner) skip cleanup of /tmp/distcc_server_stderr_9cc0f0a6.txt
[...]

Any occuring error from the remote site are saved in /tmp/distcc_server_stderr_*.txt.

If the compilation was successful, the following line will be shown.

CODE
[...]
distcc[29466] compile main.c on 192.168.0.4 completed ok
[...]

On the remote site, it will look like this:

CODE
[...]
distccd[13296] (dcc_check_compiler_masq) /usr/lib/ccache/bin/gcc is a safe symlink to /usr/bin/ccache
[...]
distccd[13296] (dcc_job_summary) client: 192.168.0.4:33880 COMPILE_OK exit:0 sig:0 core:0 ret:0 time:20ms gcc main.c

The important part here, is, that any symlink of /usr/lib/ccache/bin/ is a save symlink to /usr/bin/ccache.

Also, on the remote site, there should be the cached file 2beaa22dc2a2873d6869d69411840c-17229.o in /var/cache/ccache/c/0/, assuming, the example with its filename was copied from this wiki article. Generally, one can monitor the ccache size using watch "ccache --show-stats", while compiling.

Testing distcc with ccache using emerge

Check, if necessary environment variables are present for the current shell, see here and that /etc/portage/make.conf was configured properly, see here.

To produce some cached files on the remote site, one can compile small packages like htop and bzip2 on the client:

root #emerge --ask htop bzip2

Future usage

Make sure, that the following environment variables are always set in the desired shell:

CODE
PATH="/usr/lib/ccache/bin:${PATH}"
CCACHE_DIR="/var/cache/ccache"
DISTCC_DIR="/var/tmp/portage/.distcc"

To bootstrap

Using distcc to bootstrap (i.e. build a working toolchain before installing the remainder of the system) requires some additional steps to take.

Step 1: Configure Portage

Boot the new box with a Gentoo Linux LiveCD and follow the installation instructions, while keeping track of the instructions in the Gentoo FAQ for information about bootstrapping. Then configure Portage to use distcc:

FILE /etc/portage/make.confConfigure Portage to use distcc
FEATURES="distcc"
MAKEOPTS="-jN"

Update the PATH variable in the installation session as well:

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

Step 2: Getting distcc

Install sys-devel/distcc:

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

Step 3: Setting up distcc

Run distcc-config to setup distcc; substitute the host# in the example with the IP addresses or hostnames of the participating nodes.

root #/usr/bin/distcc-config --set-hosts "localhost host1 host2 host3 ..."

Distcc is now set up to bootstrap! Continue with the proper installation instructions and do not forget to run emerge distcc after running emerge @system. This is to make sure that all of the necessary dependencies are installed.

Note
During bootstrap and emerge @system distcc may not appear to be used. This is expected as some ebuilds do not work well with distcc, so they intentionally disable it.

Extras

The distcc application has additional features and applications to support working in a distcc environment.

Monitoring utilities

Distcc ships with two monitoring utilities. The text-based monitoring utility 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 the program is run with no parameter it will run just once. However, if it is passed a number it will update every N seconds, where N is the argument that was passed.

user $distccmon-text 10

The other monitoring utility is only enabled when the gtk USE flag is set. This one is GTK based, runs in an X environment, and it is quite lovely. For Gentoo, the GUI monitor has been renamed to distccmon-gui to make it less confusing (it is originally called distccmon-gnome).

user $distccmon-gui

To monitor Portage's distcc usage:

root #DISTCC_DIR="/var/tmp/portage/.distcc/" distccmon-text 10
root #DISTCC_DIR="/var/tmp/portage/.distcc/" distccmon-gui
Important
If the distcc directory is elsewhere, change the DISTCC_DIR variable accordingly.

A trick is to set DISTCC_DIR in environment variables:

root #echo 'DISTCC_DIR="/var/tmp/portage/.distcc/"' >> /etc/env.d/03distcc_custom
Important
Be aware that DISTCC_DIR must be set somewhere else than /etc/env.d/02distcc, as it gets overwritten everytime, when using distcc-config!. distcc-config --set-env DISTCC_DIR <some_path> does not work.

Now update the environment:

root #env-update
root #source /etc/profile

Finally, start the GUI application:

root #distccmon-gui

SSH for communication

Setting up distcc via SSH includes some pitfalls. First, generate an SSH key pair without password setup. Be aware that portage compiles programs as the Portage user (or as root if FEATURES="userpriv" is not set). The home folder of the Portage user is /var/tmp/portage/, which means the keys need to be stored in /var/tmp/portage/.ssh/

Warning
Home folder of the Portage user changed in recent versions to /var/lib/portage/home, but this folder cannot be used for distcc via SSH because it is out of the accessible path during compilation. You should then update it:
root #usermod -d /var/tmp/portage portage
root #ssh-keygen -b 2048 -t rsa -f /var/tmp/portage/.ssh/id_rsa

Second, create a section for each host in the SSH configuration file:

FILE /var/tmp/portage/.ssh/configAdd per-host sections
Host test1
    HostName 123.456.789.1
    Port 1234
    User UserName
 
Host test2
    HostName 123.456.789.2
    Port 1234
    User UserName

Send the public key to each compilation node:

root #ssh-copy-id -i /var/tmp/portage/.ssh/id_rsa.pub UserName@CompilationNode

Also make sure that each host is available in the known_hosts file:

root #ssh-keyscan -t rsa <compilation-node-1> <compilation-node-2> [...] > /var/tmp/portage/.ssh/known_hosts

Fix the file ownership as follows:

root #chown -R portage:portage /var/tmp/portage/.ssh/

To set up the hosts test1 and test2, run:

root #/usr/bin/distcc-config --set-hosts "@test1 @test2"

Please note the @ (@ sign), which specifies ssh hosts for distcc.

Finally, tell distcc which SSH binary to use:

FILE /etc/portage/make.conf
DISTCC_SSH="ssh"

It is not necessary to run the distccd initscript on the hosts when distcc communicates via SSH.

Reverse SSH

As an alternative to distcc's built-in SSH solution, a compiling server can connect to the distcc client via SSH, redirecting the client's distcc TCP port to the compiling server. There is no need for password-less SSH keys on the client.

user $ssh -R3632:127.0.0.1:3632 root@distcc-client

Note that distcc uses localhost as a literal keyword for special purpose so that 127.0.0.1 has to be used instead. For multiple compiling servers each needs its own port redirection on the client (e.g. 127.0.0.1:4000, 127.0.0.1:4001 etc). Assert that IP addresses and ports are listed in /etc/distcc/hosts on the client.

Testing

To test distcc, write a simple Hello distcc program and run distcc in verbose mode to see if it communicates properly.

FILE main.c
#include <stdio.h>
 
int main() {
    printf("Hello distcc!\n");
    return 0;
}

Next, turn on verbose mode, compile the program using distcc and link the generated object file into an executable:

user $export DISTCC_VERBOSE=1
user $distcc gcc -c main.c -o main.o # or 'pump distcc <...>'
user $gcc main.o -o main
Note
Replace distcc command with pump distcc for use pump mode.

There should be a bunch of output about distcc finding its configuration, selecting the host to connect to, starting to connect to it, and ultimately compile main.c. If the output does not list the desired distcc hosts, check the configuration.

Finally, ensure the compiled program works properly. To test each host, enumerate each compile host in the hosts file.

user $./main
Hello distcc!

Troubleshooting

If a problem occurs while using distcc, then this section might help in resolving the problem.

ERROR: failed to open /var/log/distccd.log

As of January 22nd, 2015 emerging fails to create the proper distccd.log file in /var/log/. This apparently only effects version 3.1-r8 of distcc. This bug is in the process of being corrected (see bug #477630). It is possible to work around this by manually creating the log file, giving it proper ownership, and restarting the distccd daemon:

root #mkdir -p /var/log/distcc
root #touch /var/log/distcc/distccd.log
root #chown distcc:daemon /var/log/distcc/distccd.log

Next update the /var/log path of the distccd configuration file in /etc/conf.d/distccd to the distcc directory created in the step before:

FILE /etc/conf.d/distccdUpdating log path
DISTCCD_OPTS="--port 3632 --log-level notice --log-file /var/log/distcc/distccd.log -N 15

Finally, restart the distccd service:

root #/etc/init.d/distccd restart

Some packages do not use distcc

As various packages are installed, users will notice that some of them aren't being distributed (and aren't being built in parallel). This may happen because the package' 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, please report it.

Rust package is known to cause excessive IO utilization as --local-load is ignored and --jobs is usually too high for local build resources. A package.env needs to be provisioned with non-distcc MAKEOPTS values to workaround this behaviour.

Mixed GCC versions

If the environment hosts different GCC versions, 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 (minus gcc) instead of gcc. This means that if i686 machines are mixed with other types (i386, i586) then the builds will run into troubles. A workaround for this may be to run:

root #export CC='gcc' CXX='c++'

It is also possible to set the CC and CXX variables in /etc/portage/make.conf to the values list in the command above.

Important
Doing this explicitly redefines some behavior of Portage and may have some weird results in the future. Only do this if mixing CHOSTs is unavoidable.
Note
Having the right version of gcc as a slot on a server isn’t enough. Portage uses distcc as a replacement for the compiler referenced by the CHOST variable (i.e. x86_64-pc-linux-gnu) and distccd invokes it by exactly same name. The right version of gcc should be a default system’s compiler on all involved compilation hosts.

-march=native

Starting with GCC 4.3.0, the compiler supports the -march=native option which turns on CPU auto-detection and optimizations that are worth being enabled on the processor on 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 system that has an Intel Pentium processor will mix code compiled on both processors together.

Heed the following warning:

Warning
Do not use -march=native or -mtune=native in the CFLAGS or CXXFLAGS variables of make.conf when compiling with distcc.

See the CFLAGS and CXXFLAGS section and Inlining -march=native for distcc for more information.

Network is unreachable

Note
When using SSH connection, you may also face the error: ssh: Could not resolve hostname: Temporary failure in name resolution.

Due to network restrictions introduced by the feature network-sandbox, you may run into this issue. Since distcc contradicts with this security feature, you have to disable it:

FILE /etc/portage/make.confDisabling network-sandbox feature
FEATURES="${FEATURES} -network-sandbox"

Get more output from emerge logs

It is possible to obtain more logging by enabling verbose mode. This is accomplished by adding DISTCC_VERBOSE to /etc/portage/bashrc:

FILE /etc/portage/bashrcEnabling verbose logging
export DISTCC_VERBOSE=1

The verbose logging can then be found in /var/tmp/portage/$CATEGORY/$PF/temp/build.log.

Keep in mind that the first distcc invocation visible in build.log isn’t necessary the first distcc call during a build process. For example a build server can get a one-minute backoff period during the configuration stage when some checks are performed using a compiler (distcc sets a backoff period when compilation on a remote server failed, it doesn’t matter whether it failed on local machine or not).

Dig into the /var/tmp/portage/$CATEGORY/$PF/work/ directory to investigate such situations. Find other logs, or call make explicitly from within the working directory.

Another interesting variable to use is DISTCC_SAVE_TEMPS. When set, it saves the standard output/error from a remote compiler which, for Portage builds, results in files in the /var/tmp/portage/$CATEGORY/$PF/temp/ directory.

FILE /etc/portage/bashrcSaving temporary output
export DISTCC_SAVE_TEMPS=1

Failed to create directory /dev/null/.cache/ccache/tmp: Not a directory

This error can be discovered from the standard error output file in the server if you set DISTCC_SAVE_TEMPS. It only occurs when using distccd with ccache.

Likely, it is because CCACHE_DIR is not properly set, or not passed correctly to distccd. ccache will then default to $HOME/.cache/ccache as its cache folder. However, ccache is run by distccd under user distcc, which is a non-login account. See systemd section and With ccache section for setting CCACHE_DIR.

Portage build failing with errors that are apparently not connected with distcc at all

When builds are failing with errors that do not seem to be connected to distcc, but the build works with FEATURES="-distcc", it has been reported that builds sometimes fail because of DISTCC_VERBOSE=1. Try the build with DISTCC_VERBOSE=0.

See also

External resources


This page is based on a document formerly found on our main website gentoo.org.
The following people contributed to the original document: Lisa Seelye, Mike Gilbert (floppym) , Erwin, Sven Vermeulen (SwifT) , Lars Weiler, Tiemo Kieft, and
They are listed here because wiki history does not allow for any external attribution. If you edit the wiki article, please do not add yourself here; your contributions are recorded on each article's associated history page.