centos7系统安装后的基础优化

涉及内容：
1.DNS
2.网络yum源
3.epel源
4.同步时间
5.安装vim
6.设置最大打开文件描述符数
7.禁用selinux
8.关闭防火墙
9.优化ssh连接速度
10.内核参数优化
11.设置vim退格键删除最后一个字符类型
12.更新内核
脚本如下：

#!/bin/bash
#author yundd by
#this script is only for CentOS 7.x
#check the OS

platform=`uname -i`
if [ $platform != "x86_64" ];then
echo "this script is only for 64bit Operating System !"
exit 1
fi
echo "the platform is ok"
cat << EOF
your system is CentOS 7 x86_64
EOF
#添加公网DNS地址
cat >> /etc/resolv.conf << EOF
nameserver 114.114.114.114
EOF
#Yum源更换为国内阿里源
yum install wget telnet -y
mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup
wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo
#添加阿里的epel源
#add the epel
wget -O /etc/yum.repos.d/epel.repo http://mirrors.aliyun.com/repo/epel-7.repo
# rpm -ivh http://dl.Fedoraproject.org/pub/epel/7/x86_64/e/epel-release-7-8.noarch.rpm
#yum重新建立缓存
yum clean all
yum makecache
#同步时间
ln -sf /usr/share/zoneinfo/Asia/Shanghai /etc/localtime
yum -y install ntp
/usr/sbin/ntpdate cn.pool.ntp.org
echo "* 4 * * * /usr/sbin/ntpdate cn.pool.ntp.org > /dev/null 2>&1" >> /var/spool/cron/root
systemctl restart crond.service
#安装vim
yum -y install vim
ln -sf /usr/share/zoneinfo/Asia/Shanghai /etc/localtime
#安装lrzsz实现win与linux之间的文件互相下载上传
yum -y install lrzsz
#设置最大打开文件描述符数
echo "ulimit -SHn 102400" >> /etc/rc.local
cat >> /etc/security/limits.conf << EOF
* soft nofile 655350
* hard nofile 655350
EOF

#禁用selinux
sed -i 's/SELINUX=enforcing/SELINUX=disabled/' /etc/selinux/config
setenforce 0
#关闭防火墙
systemctl disable firewalld.service
systemctl stop firewalld.service
#set ssh
sed -i 's/^GSSAPIAuthentication yes$/GSSAPIAuthentication no/' /etc/ssh/sshd_config
sed -i 's/#UseDNS yes/UseDNS no/' /etc/ssh/sshd_config
systemctl restart sshd.service

#内核参数优化
cat >> /etc/sysctl.conf << EOF
vm.overcommit_memory = 1
net.ipv4.ip_local_port_range = 1024 65536
net.ipv4.tcp_fin_timeout = 1
net.ipv4.tcp_keepalive_time = 1200
net.ipv4.tcp_mem = 94500000 915000000 927000000
net.ipv4.tcp_syncookies=1
net.ipv4.tcp_tw_reuse = 1
net.ipv4.tcp_tw_recycle = 1
net.ipv4.tcp_fin_timeout=120
net.ipv4.tcp_keepalive_time = 2400
net.ipv4.tcp_max_syn_backlog = 8192
net.ipv4.tcp_max_tw_buckets = 5000
net.ipv4.tcp_timestamps = 0
net.ipv4.tcp_synack_retries = 1
net.ipv4.tcp_syn_retries = 1
net.ipv4.tcp_abort_on_overflow = 0
net.core.rmem_max = 16777216
net.core.wmem_max = 16777216
net.core.netdev_max_backlog = 262144
net.core.somaxconn = 262144
net.ipv4.tcp_max_orphans = 3276800
net.ipv4.tcp_max_syn_backlog = 262144
net.core.wmem_default = 8388608
net.core.rmem_default = 8388608
net.ipv4.netfilter.ip_conntrack_max = 2097152
net.nf_conntrack_max = 655360
net.netfilter.nf_conntrack_tcp_timeout_established = 1200
EOF
/sbin/sysctl -p
#vim定义退格键可删除最后一个字符类型
echo 'alias vi=vim' >> /etc/profile
echo 'stty erase ^H' >> /etc/profile
cat >> /root/.vimrc << EOF
set tabstop=4
set shiftwidth=4
set expandtab
syntax on
"set number
EOF
# update soft
# yum -y update