Path to Linux-unable to download software

If you want to install a gftp in the afternoon, you will find that you cannot install or download the software. Whether you download the software on the terminal "sudo apt-Get install gftp" or in the Software Center, an error is prompted.

Baidu once circled it and couldn't find the reason. I suddenly remembered that I changed the software source once yesterday. Is that the reason?

Baidu gave another comment:

GPG -- keyserver keyserver.ubuntu.com --Recv 40976eaf437d05b5gpg-- Export -- armor 40976eaf437d05b5 | sudo apt-key add-

Run the command in sequence!

Continue Baidu... This error is reported because the signature of the update source is incorrect (it seems that it is related to my replacement of the software source)

For more information, see the three pages:

Http://forum.ubuntu.org.cn/viewtopic.php? T = 378189

Http://ar.newsmth.net/thread-a419ff81c5d501.html

Http://blog.sina.com.cn/s/blog_7121ea680100x4es.html