yum安装不了软件

小弟想要使用yum安装软件但总是不能安装，不知道怎么回事？
[CentOs]
name=Red Hat Enterprise Linux $releasever - $basearch - Debug
baseurl=http://ftp.twaren.net/Linux/CentOS/5/os/i386/
enabled=1
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-redhat-release

[root@localhost yum.repos.d]# yum install grub
Loaded plugins: rhnplugin, security
This system is not registered with RHN.
RHN support will be disabled.
CentOs | 2.1 kB 00:00
Setting up Install Process
Resolving Dependencies
--> Running transaction check
---> Package grub.i386 0:0.97-13.5 set to be updated
--> Finished Dependency Resolution

Dependencies Resolved

================================================================================
Package Arch Version Repository Size
================================================================================
Installing:
grub i386 0.97-13.5 CentOs 486 k

Transaction Summary
================================================================================
Install 1 Package(s)
Update 0 Package(s)
Remove 0 Package(s)

Total size: 486 k
Is this ok [y/N]: y
Downloading Packages:
警告：rpmts_HdrFromFdno: 表? V3 DSA ?名：NOKEY, key ID e8562897
CentOs/gpgkey | 1.1 kB 00:00


Public key for grub-0.97-13.5.i386.rpm is not installed

不明白
警告：rpmts_HdrFromFdno: 表? V3 DSA ?名：NOKEY, key ID e8562897 这个，怎么解决，谢谢