ERROR: Missing prebuilt package

When you are installing packages (with conan install or conan test_package) it is possible that you get an error like the following one:

WARN: Can't find a 'libzmq/4.2.0@memsharded/testing' package for the specified options and settings:
- Settings: arch=x86_64, build_type=Release, compiler=gcc, compiler.libcxx=libstdc++, compiler.version=4.9, os=Windows
- Options: shared=False

ERROR: Missing prebuilt package for 'libzmq/4.2.0@memsharded/testing'
Try to build it from sources with "--build libzmq" or read ""

This means that the package recipe libzmq/4.2.0@memsharded/testing exists, but for some reason there is no precompiled package for your current settings. Maybe the package creator didn’t build and shared pre-built packages at all and only uploaded the package recipe, or maybe they are only providing packages for some platforms or compilers. E.g. the package creator built packages from the recipe for gcc 4.8 and 4.9, but you are using gcc 5.4.

By default, conan doesn’t build packages from sources. There are several possibilities:

  • You can try to build the package for your settings from sources, indicating some build policy as argument, like --build libzmq or --build missing. If the package recipe and the source code work for your settings you will have your binaries built locally and ready for use.
  • If building from sources fail, you might want to fork the original recipe, improve it until it supports your configuration, and then use it. Most likely contributing back to the original package creator is the way to go. But you can also upload your modified recipe and pre-built binaries under your own username too.

ERROR: Invalid setting

It might happen sometimes, when you specify a setting not present in the defaults that you receive a message like this:

$ conan install -s compiler.version=4.19 ...

ERROR: Invalid setting '4.19' is not a valid 'settings.compiler.version' value.
Possible values are ['4.4', '4.5', '4.6', '4.7', '4.8', '4.9', '5.1', '5.2', '5.3', '5.4', '6.1', '6.2']
Read ""

This doesn’t mean that such architecture is not supported by conan, it is just that it is not present in the actual defaults settings. You can find in your user home folder ~/.conan/settings.yml a settings file that you can modify, edit, add any setting or any value, with any nesting if necessary.

As long as your team or users have the same settings (you can share with them the file), everything will work. The settings.yml file is just a mechanism so users agree on a common spelling for typically settings. Also, if you think that some settings would be useful for many other conan users, please submit it as an issue or a pull request, so it is included in future releases.

It is possible that some build helper, like CMake will not understand the new added settings, don’t use them or even fail. Such helpers as CMake are simple utilities to translate from conan settings to the respective build system syntax and command line arguments, so they can be extended or replaced with your own one that would handle your own private settings.

ERROR: Failed to create process

When conan is installed via pip/PyPI, and python is installed in a path with spaces (like many times in Windows “C:/Program Files...”), conan can fail to launch. This is a known python issue, and can’t be fixed from conan. The current workarounds would be:

  • Install python in a path without spaces
  • Use virtualenvs. Short guide:
$ pip install virtualenvwrapper-win # virtualenvwrapper if not Windows
$ mkvirtualenv conan
(conan) $ pip install conan
(conan) $ conan --help

Then, when you will be using conan, for example in a new shell, you have to activate the virtualenv:

$ workon conan
(conan) $ conan --help

Virtualenvs are very convenient, not only for this workaround, but to keep your system clean and to avoid unwanted interaction between different tools and python projects.

ERROR: Failed to remove folder (Windows)

It is possible that operating conan, some random exceptions (some with complete tracebacks) are produced, related to the impossibility to remove one folder. Two things can happen:

  • The user has some file or folder open (in a file editor, in the terminal), so it cannot be removed, and the process fails. Make sure to close files, specially if you are opening or inspecting the local conan cache.
  • In Windows, the Search Indexer might be opening and locking the files, producing random, difficult to reproduce and annoying errors. Please disable the Windows Search Indexer for the conan local storage folder