CentOS中使用yum命令产生报错_centos gpgkey

之前想使用yum命令进行一个网络扫描命令nmap的安装，发现系统进行相关报错。输入yum -y install nmap后发现
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Loaded plugins: fastestmirror, security
Loading mirror speeds from cached hostfile
Could not retrieve mirrorlist http://mirrorlist.centos.org/?release=6&arch=i386&repo=os error was
14: PYCURL ERROR 6 - "Couldn't resolve host 'mirrorlist.centos.org'"
Error: Cannot find a valid baseurl for repo: base
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然后想进行网络yum源的配置文件的检查，查看问题所在。键入vi /etc/yum.repos.d/CentOS-Base.repo
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# vi /etc/yum.repos.d/CentOS-Base.repo 
# CentOS-Base.repo
#
# The mirror system uses the connecting IP address of the client and the
# update status of each mirror to pick mirrors that are updated to and
# geographically close to the client.  You should use this for CentOS updates
# unless you are manually picking other mirrors.
#
# If the mirrorlist= does not work for you, as a fall back you can try the
# remarked out baseurl= line instead.
#
#

[base]
name=CentOS-$releasever - Base
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=os
#baseurl=http://mirror.centos.org/centos/$releasever/os/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6

#released updates
[updates]
name=CentOS-$releasever - Updates
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=updates
#baseurl=http://mirror.centos.org/centos/$releasever/updates/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6

#additional packages that may be useful
[extras]
name=CentOS-$releasever - Extras
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=extras
#baseurl=http://mirror.centos.org/centos/$releasever/extras/$basearch/
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发现网络yum源配置文件没有问题，这里对于配置文件中的一些参数进行简要解释：
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• [base] 容器名称
• name 容器说明，可以自己随便写
• mirrorlist 镜像站点，这个可以注释掉
• baseurl yum源服务器的地址
• enabled 此容器是否生效，如果不写或者写成enable=1都是生效，写成enable=0就是不生效
• gpgcheck 如果是1是指RPM的数字证书生效，如果是0则不生效

• gpgkey 数字证书的公钥文件保存位置，不用修改

  检查网络yum源配置没有问题之后，查看光盘yum源是否挂载
  mount /dev/cdrom /mnt/cdrom

# mount /dev/cdrom /mnt/cdrom
mount: block device /dev/sr0 is write-protected, mounting read-only
mount: /dev/sr0 already mounted or /mnt/cdrom busy
mount: according to mtab, /dev/sr0 is already mounted on /mnt/cdrom
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如若挂载正常，常理光盘yum源是可以使用的，此时出现报错，检查yum源文件目录
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[root@localhost ~]# cd /etc/yum.repos.d/
[root@localhost yum.repos.d]# ls
CentOS-Base.repo  CentOS-Debuginfo.repo  CentOS-Media.repo  CentOS-Vault.repo
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发现目录中的网络yum源文件与光盘yum源都是调用格式，产生冲突，导致无法使用yum命令，此时选择将网络yum源文件失效，保留CentOS-Media.repo文件名不变
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[root@localhost yum.repos.d]# mv CentOS-Base.repo CentOS-Base.repo.bak
[root@localhost yum.repos.d]# mv CentOS-Debuginfo.repo CentOS-Debuginfo.repo.bak
[root@localhost yum.repos.d]# mv CentOS-Vault.repo CentOS-Vault.repo.bak
[root@localhost yum.repos.d]# ls
CentOS-Base.repo.bak  CentOS-Debuginfo.repo.bak  CentOS-Media.repo  CentOS-Vault.repo.bak
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名称修改后即可将网络yum源文件失效，接着进行光盘yum源文件的修改，注意将地址改为自己的光盘挂载地址，注释掉两个不存在的地址以及将文件中的enabled=0改为enabled=1，让这个yum源配置文件生效
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[root@localhost yum.repos.d]# vim CentOS-Media.repo 
# CentOS-Media.repo
#
# This repo is used to mount the default locations for a CDROM / DVD on
#  CentOS-6.  You can use this repo and yum to install items directly off the
#  DVD ISO that we release.
#
# To use this repo, put in your DVD and use it with the other repos too:
#  yum --enablerepo=c6-media [command]
#
# or for ONLY the media repo, do this:
#
#  yum --disablerepo=\* --enablerepo=c6-media [command]

[c6-media]
name=CentOS-$releasever - Media
baseurl=file:///mnt/cdrom
#file:///media/CentOS/
#        file:///media/cdrom/
#       file:///media/cdrecorder/
gpgcheck=1
enabled=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6
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上述操作完成后，重新试一下yum命令是否可用，输入 yum -y install nmap
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[root@localhost ~]# yum install nmap
Loaded plugins: fastestmirror, security
Loading mirror speeds from cached hostfile
c6-media                                                                                                                     | 4.0 kB     00:00 ... 
Setting up Install Process
Package 2:nmap-5.51-2.el6.i686 already installed and latest version
Nothing to do
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提示nmap命令已经下载且为最新版本，没有产生报错，则yum命令此时正确可用。
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