yum 查詢多版本，降級軟體包

# yum search --showduplicates salt

...

salt-2015.5.10-2.el6.noarch : A parallel remote execution system

salt-2016.11.3-1.el6.noarch : A parallel remote execution system

# yum downgrade salt

降級指定版本後面寫查詢到的軟體包全名。