ROS 踩坑录（一）

输入sudo apt-get update
之后
出现了

W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://packages.ros.org/ros/ubuntu trusty InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY F42ED6FBAB17C654
W: Failed to fetch http://packages.ros.org/ros/ubuntu/dists/trusty/InRelease  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY F42ED6FBAB17C654
W: Some index files failed to download. They have been ignored, or old ones used instead.

百度后查询
输入`

     sudo apt-get clean
     cd /var/lib/apt 
     sudo apt-get update

`然后问题出现了

W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://packages.ros.org/ros/ubuntu trusty InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY F42ED6FBAB17C654
W: Failed to fetch http://packages.ros.org/ros/ubuntu/dists/trusty/InRelease  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY F42ED6FBAB17C654
W: Some index files failed to download. They have been ignored, or old ones used instead.

查询百度后
继续输入
sudo apt-get clean
cd /var/lib/apt
sudo mv lists lists.old
sudo mkdir -p lists/partial
sudo apt-get clean
sudo apt-get update`
问题继续

W: GPG error: http://packages.ros.org/ros/ubuntu trusty InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY F42ED6FBAB17C654
W: The repository 'http://packages.ros.org/ros/ubuntu trusty InRelease' is not signed.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.

继续查询百度输入

sudo apt-key adv --keyserver ha.pool.sks-keyservers.net --recv-keys F42ED6FBAB17C654
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys F42ED6FBAB17C654
sudo add-apt-repository ppa:webupd8team/y-ppa-manager 
sudo apt-get update

这次更新成功