1、更改阿里云yum源
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-6.repo
wget -O /etc/yum.repos.d/epel.repo http://mirrors.aliyun.com/repo/epel-6.repo
2、常用软件下载
yum install -y vim wget lrzsz telnet tools ntpdate sysstat tree dos2unix nc nmap
3、关闭selinux
永久关闭（需要重启系统）
sed -i 's#SELINUX=enforcing#SELINUX=disabled#g' /etc/selinux/config
临时关闭（无需重启）
setenforce 0
4、关闭iptables
/etc/init.d/iptables stop <<-关闭iptables服务
/etc/init.d/iptables status <<-查看iptables状态
chkconfig iptables off <<—开机启动关闭
5、 精简开机启动
for oldboy in `chkconfig --list |grep "3:on"|awk '{print $1}'|grep -vE "crond|sshd|network|rsyslog|sysstat"`;do chkconfig $oldboy off ;done <<-关闭服务
[root@oldboy-39 ~]# chkconfig --list|grep 3:on <<-检查开机启动的服务
crond 0:off 1:off 2:on 3:on 4:on 5:on 6:off
network 0:off 1:off 2:on 3:on 4:on 5:on 6:off
rsyslog 0:off 1:off 2:on 3:on 4:on 5:on 6:off
sshd 0:off 1:off 2:on 3:on 4:on 5:on 6:off
sysstat 0:off 1:on 2:on 3:on 4:on 5:on 6:off
6、更改字符集（选做）
cp /etc/sysconfig/i18n /etc/sysconfig/i18n.ori
echo LANG="zh_CN.UTF-8" >/etc/sysconfig/i18n
source /etc/sysconfig/i18n
7、普通用户提权
useradd oldboy
echo 123456|passwd --stdin oldboy
\cp /etc/sudoers /etc/sudoers.ori
echo "oldboy ALL=(ALL) NOPASSWD: ALL " >>/etc/sudoers
tail -1 /etc/sudoers
visudo -c
8、时间同步
echo '#time sync by oldboy at 2015-2-1' >>/var/spool/cron/root
echo '*/5 * * * * /usr/sbin/ntpdate time.nist.gov >/dev/null 2>&1' >>/var/spool/cron/root
crontab -l
9、 命令行安全（选配）
设置闲置账号超时时间
echo 'export TMOUT=300' >>/etc/profile
命令行历史记录数
echo 'export HISTFILESIZE=500' >>/etc/profile
tail -3 /etc/profile
. /etc/profile
10、加大文件描述
echo '* - nofile 65535' >>/etc/security/limits.conf
tail -1 /etc/security/limits.conf
11、内核优化
cat >>/etc/sysctl.conf<<EOF
net.ipv4.tcp_fin_timeout = 2
net.ipv4.tcp_tw_reuse = 1
net.ipv4.tcp_tw_recycle = 1
net.ipv4.tcp_syncookies = 1
net.ipv4.tcp_keepalive_time = 600
net.ipv4.ip_local_port_range = 4000 65000
net.ipv4.tcp_max_syn_backlog = 16384
net.ipv4.tcp_max_tw_buckets = 36000
net.ipv4.route.gc_timeout = 100
net.ipv4.tcp_syn_retries = 1
net.ipv4.tcp_synack_retries = 1
net.core.somaxconn = 16384
net.core.netdev_max_backlog = 16384
net.ipv4.tcp_max_orphans = 16384
#以下参数是对iptables防火墙的优化，防火墙不开会提示，可以忽略不理。
net.nf_conntrack_max = 25000000
net.netfilter.nf_conntrack_max = 25000000
net.netfilter.nf_conntrack_tcp_timeout_established = 180
net.netfilter.nf_conntrack_tcp_timeout_time_wait = 120
net.netfilter.nf_conntrack_tcp_timeout_close_wait = 60
net.netfilter.nf_conntrack_tcp_timeout_fin_wait = 120
EOF
sysctl –p <<-配置完成后查看
12、定时清理邮件服务临时目录垃圾文件
centos 5版本
find /var/spool/clientmqueue/ -type f | xargs rm -f
centos 6.x版本
find /var/spool/postfix/maildrop/ -type f | xargs rm -f
写成脚本，做定时任务
mkdir -p /server/scripts/
echo "find /var/spool/postfix/maildrop/ -type f | xargs rm -f " > /server/scripts/del_mailfile.sh
echo "00 00 * * * /bin/bash /server/scripts/del_mailfile.sh > /dev/null 2>&1"
13、隐藏linux版本信息显示
[root@server1 ~]# > /etc/issue
[root@server1 ~]# > /etc/issue.net
[root@server1 ~]# cat /etc/issue.net
[root@server1 ~]# cat /etc/issue
14、 锁定关键系统文件，防止被提权篡改
chattr +i /etc/passwd /etc/shadow /etc/group /etc/gshadow /etc/inittab
使用lsattr 进行查看，chattr -i进行解锁
15、 为grub菜单加密
先利用/sbin/grub-md5-crypt 产生一个MD5密钥串，命令如下：
[root@m01 ~]# /sbin/grub-md5-crypt
Password:
Retype password:
$1$SQxvZ/$AXRHUbkNy9EkDHtmoEoQS0
修改grub.conf文件，命令如下：
[root@m01 ~]# vim /etc/grub.conf
# grub.conf generated by anaconda
#
# Note that you do not have to rerun grub after making changes to this file
# NOTICE: You have a /boot partition. This means that
# all kernel and initrd paths are relative to /boot/, eg.
# root (hd0,0)
# kernel /vmlinuz-version ro root=/dev/sda3
# initrd /initrd-[generic-]version.img
#boot=/dev/sda
default=0
timeout=5
splashimage=(hd0,0)/grub/splash.xpm.gz
hiddenmenu
passwd --md5 $1$SQxvZ/$AXRHUbkNy9EkDHtmoEoQS0
#注意:password要加在splashimage和title之间，否则无法生效
title CentOS 6 (2.6.32-696.el6.x86_64)
root (hd0,0)
kernel /vmlinuz-2.6.32-696.el6.x86_64 ro root=UUID=33ec961c-16e1-4234-bdbf-644bfdabf1eb rd_NO_LUKS KEYBOARDTYPE=pc KEYTABLE=us rd_NO_MD crashkernel=auto LANG=zh_CN.UTF-8 rd_NO_LV
16、禁止linux系统被ping(选配)
echo "net.ipv4.icmp_echo_ignore_all=1" >> /etc/sysctl.conf
sysctl -p
拓展：设置特定ip可以ping
iptables -t filter -I INPUT -p icmp --icmp-type 8 -i eth0 -s 10.0.0.0/24 -j ACCEPT
17、升级具有典型漏洞
查看相关软件的版本号，命令如下：
[root@m01 ~]# rpm -qa openssl openssh bash
openssl-1.0.1e-57.el6.x86_64
bash-4.1.2-48.el6.x86_64
openssh-5.3p1-122.el6.x86_64
升级已知漏洞的软件版本到最新，命令如下：
yum install openssl openssh bash -y
18、更改ssh服务端远程登录的配置
修改默认文件路径
vim /etc/ssh/sshd_config
修改的参数
port #端口
PermitEmptyPasswords #是否允许密码为空的用户远程登录
PermitRootLogin #是否允许root登录
UseDNS #指定sshd是否应该对远程主机名进行反向解析，以检查主机名是否与其IP地址真实对应。默认yes.建议改成no ，否则可能会导致SSH连接很慢。
GSSAPIAuthentication no #解决linux之间使用SSH远程连接慢的问题
ListenAddress #监听指定的IP地址
批量操作：
sed -ir '13 iPort 55666\nPermitRootLogin no\nPermitEmptyPasswords no\nUseDNS no\nGSSAPIAuthentication no' /etc/ssh/sshd_config