cannot stat /proc/sys/net/bridge/bridge-nf-call-iptables: No such file or directory

问题：
在执行命令sysctl -p时报错

 sysctl: cannot stat /proc/sys/net/bridge/bridge-nf-call-iptables: No such file or directory

解决：

[root@k8s-master1 net]# modprobe br_netfilter
[root@k8s-master1 net]# ls /proc/sys/net/bridge/
bridge-nf-call-arptables  bridge-nf-call-iptables        bridge-nf-filter-vlan-tagged
bridge-nf-call-ip6tables  bridge-nf-filter-pppoe-tagged  bridge-nf-pass-vlan-input-dev
[root@k8s-master1 net]# sysctl -p

-bash: netstart: command not found

问题：
在执行netstat -tunlp | grep haproxy时报错

-bash: netstart: command not found

解决：
原因是因为没有netstat这个命令，需要安装。

yum install -y net-tools

再次执行就可以了

Could not resolve host: ftp.cc.uoc.gr; Unknown error

问题：
执行yum install ntpdate -y时报错：

[root@k8s-worker1 ~]# yum install ntpdate -y
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
 * base: ftp.sjtu.edu.cn
 * elrepo: dfw.mirror.rackspace.com
 * extras: ftp.sjtu.edu.cn
 * updates: ftp.sjtu.edu.cn
http://mirrors.tuna.tsinghua.edu.cn/centos/7.9.2009/os/x86_64/repodata/repomd.xml: [Errno 14] curl#6 - "Could not resolve host: mirrors.tuna.tsinghua.edu.cn; Unknown error"
Trying other mirror.
http://mirrors.bupt.edu.cn/centos/7.9.2009/os/x86_64/repodata/repomd.xml: [Errno 14] curl#6 - "Could not resolve host: mirrors.bupt.edu.cn; Unknown error"
Trying other mirror.
http://ftp.sjtu.edu.cn/centos/7.9.2009/os/x86_64/repodata/repomd.xml: [Errno 14] curl#6 - "Could not resolve host: ftp.sjtu.edu.cn; Unknown error"
Trying other mirror.
http://mirror.lzu.edu.cn/centos/7.9.2009/os/x86_64/repodata/repomd.xml: [Errno 14] curl#6 - "Could not resolve host: mirror.lzu.edu.cn; Unknown error"
Trying other mirror.
http://mirror01.idc.hinet.net/centos/7.9.2009/os/x86_64/repodata/repomd.xml: [Errno 14] curl#6 - "Could not resolve host: mirror01.idc.hinet.net; Unknown error"
Trying other mirror.
http://mirrors.bfsu.edu.cn/centos/7.9.2009/os/x86_64/repodata/repomd.xml: [Errno 14] curl#6 - "Could not resolve host: mirrors.bfsu.edu.cn; Unknown error"
Trying other mirror.
http://mirrors.cqu.edu.cn/CentOS/7.9.2009/os/x86_64/repodata/repomd.xml: [Errno 14] curl#6 - "Could not resolve host: mirrors.cqu.edu.cn; Unknown error"
Trying other mirror.
^Chttp://mirrors.nju.edu.cn/centos/7.9.2009/os/x86_64/repodata/repomd.xml: [Errno -1] Error importing repomd.xml for base: Damaged repomd.xml file
Trying other mirror.
http://mirrors.qlu.edu.cn/centos/7.9.2009/os/x86_64/repodata/repomd.xml: [Errno 14] curl#6 - "Could not resolve host: mirrors.qlu.edu.cn; Unknown error"
Trying other mirror.
http://mirrors.ustc.edu.cn/centos/7.9.2009/os/x86_64/repodata/repomd.xml: [Errno 14] curl#6 - "Could not resolve host: mirrors.ustc.edu.cn; Unknown error"
Trying other mirror.
https://mirrors.tuna.tsinghua.edu.cn/elrepo/elrepo/el7/x86_64/repodata/repomd.xml: [Errno 14] curl#6 - "Could not resolve host: mirrors.tuna.tsinghua.edu.cn; Unknown error"
Trying other mirror.
http://dfw.mirror.rackspace.com/elrepo/elrepo/el7/x86_64/repodata/repomd.xml: [Errno 14] curl#6 - "Could not resolve host: dfw.mirror.rackspace.com; Unknown error"
Trying other mirror.
http://elrepo.mirror.angkasa.id/elrepo/elrepo/el7/x86_64/repodata/repomd.xml: [Errno 14] curl#6 - "Could not resolve host: elrepo.mirror.angkasa.id; Unknown error"
Trying other mirror.
http://elrepo.mirrors.arminco.com/elrepo/el7/x86_64/repodata/repomd.xml: [Errno 14] curl#6 - "Could not resolve host: elrepo.mirrors.arminco.com; Unknown error"
Trying other mirror.
http://elrepo.org/linux/elrepo/el7/x86_64/repodata/repomd.xml: [Errno 14] curl#6 - "Could not resolve host: elrepo.org; Unknown error"
Trying other mirror.
http://fedora.is/elrepo/elrepo/el7/x86_64/repodata/repomd.xml: [Errno 14] curl#6 - "Could not resolve host: fedora.is; Unknown error"
Trying other mirror.
http://ftp.cc.uoc.gr/mirrors/elrepo/elrepo/el7/x86_64/repodata/repomd.xml: [Errno 14] curl#6 - "Could not resolve host: ftp.cc.uoc.gr; Unknown error"
Trying other mirror.
http://ftp.icm.edu.pl/pub/Linux/distributions/elrepo/elrepo/el7/x86_64/repodata/repomd.xml: [Errno 14] curl#6 - "Could not resolve host: ftp.icm.edu.pl; Unknown error"
Trying other mirror.

解决：
配置文件不全，修改如下

# vi /etc/resolv.conf
# Generated by NetworkManager
nameserver 8.8.8.8
nameserver fe80::1%ens33