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Richard Nunziata
Asked: 2019-01-31 08:30:09 +0800 CST

Question about instructions for Point Cloud Library (pcl) install on Ubuntu 16.04

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In following instructions for pcl install:

How to install Point Cloud Library v1.8 (pcl-1.8.0) on Ubuntu 16.04.2 [LTS] for C++?

why after:

sudo apt-mark hold libeigen3-dev

is there not

sudo apt-mark unhold libeigen3-dev
software-installation pcloud

1 Answers

  1. Best Answer

    From man apt-mark

    PREVENT CHANGES FOR A PACKAGE

    hold

     hold is used to mark a package as held back, which will prevent the
 package from being automatically installed, upgraded or removed.

    unhold

     unhold is used to cancel a previously set hold on a package to
 allow all actions again.

    So, the pcl v1.8 app you are trying to install probably needs a specific version 3.2.5-4 of the libeigen3-dev. This is called dependency. However, Ubuntu 16.04 probably uses a different version of the same file which probably does not work for pcl.

    The hold tells Ubuntu not to update the libeigen3-dev you have installed specifically for pcl v1.8. After you run the command:

    sudo apt-mark hold libeigen3-dev

    Ubuntu will remember not to update this specific file.

    If you use the unhold option then the special version of libeigen3-dev that works with pcl v1.8 will be replaced by the version that does not work with pcl v.1.8.

    Note, as the installation guide implies, this issue is resolved in newer version pcl v1.8.1 and Ubnutu 17.10, as there is no apt-mark hold command needed for these versions.

    It is possible that the libeigen3-dev (version 3.3.4-4) in the current version of Ubuntu 16.04 also does not suffer from this problem. If so, you may use the apt-mark unhold to let Ubuntu update this file.

    If pcl breaks, then repeat the 4 lines of instructions including the apt-mark hold:

    cd ~/Downloads
wget http://launchpadlibrarian.net/209530212/libeigen3-dev_3.2.5-4_all.deb
sudo dpkg -i libeigen3-dev_3.2.5-4_all.deb
sudo apt-mark hold libeigen3-dev

    This will download the pcl compatible version of libeigen3-dev again and install it.

    Hope this helps

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