My server's some processes are getting killed automatically

[root@localhost ~]# yum install repo Loaded plugins: fastestmirror, protectbase, replace, security Loading mirror speeds from cached hostfile Killed [root@localhost ~]# yum upgrade Loaded plugins: fastestmirror, protectbase, replace, security Loading mirror speeds from cached hostfile Killed [root@localhost ~]#

Please find some solution , I am running Centos 5. Even i unable to run iftop.