# sudo pacman -Syu
...
error: key "5F702428F70E0903" could not be looked up remotely
error: required key missing from keyring
error: failed to commit transaction (unexpected error)
Errors occurred, no packages were upgraded.
...
#sudo pacman -S archlinux-keyring && sudo pacman -Syu
R: https://bbs.archlinux.org/viewtopic.php?id=191279
R: http://tieba.baidu.com/p/3575951619
R: https://bbs.archlinux.org/viewtopic.php?id=193382
pacman -Syu : key could not be looked up remotely.
原文：http://www.cnblogs.com/zhangshaojian/p/4779960.html