安装linux系统后调优及安全设置

[root@server1 ~]# cat /etc/redhat-release 
CentOS release 6.9 (Final)
[root@server1 ~]# uname -r
2.6.32-696.el6.x86_64

mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup        <<-备份系统自带yum源
wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-6.repo  <<—国内使用阿里云yum源速度比较快
wget -O /etc/yum.repos.d/epel.repo http://mirrors.aliyun.com/repo/epel-6.repo

注：镜像官方网址http://mirrors.aliyun.com/

如有自建yum仓可以更改成自建yum仓地址信息

永久关闭（需要重启系统）
sed -i ‘s/SELINUX=enforcing/SELINUX=disabled/‘ /etc/selinux/config

临时关闭（无需重启）
setenforce 0  
数字0表示Premissive,即给出警告提示，不会阻止操作，相当于disabled
数字1表示Enfocing，即表示SELinux为开启状态

getenforce      <<-查看selinux当前状态

/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

chkconfig|egrep -v "crond|sshd|network|rsyslog|sysstat"|awk ‘{print "chkconfig",$1,"off"}‘|bash       <<-关闭服务
chkconfig --list|grep 3:on       <<-检查开机启动的服务

cp /etc/sysconfig/i18n /etc/sysconfig/i18n.ori
echo ‘LANG="zh_CN.UTF-8"‘  >/etc/sysconfig/i18n 
source /etc/sysconfig/i18n
echo $LANG

useradd mmod
echo 123456|passwd --stdin mmod
\cp /etc/sudoers /etc/sudoers.ori
echo "mmod  ALL=(ALL) NOPASSWD: ALL " >>/etc/sudoers
tail -1 /etc/sudoers
visudo -c

echo ‘#time sync by mmod 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

注：集群中有时间服务器，更改成时间服务器地址

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 HISTSIZE=5‘ >>/etc/profile
echo ‘export HISTFILESIZE=5‘ >>/etc/profile
tail -3 /etc/profile
./etc/profile

echo ‘*               -       nofile          65535‘ >>/etc/security/limits.conf 
tail -1 /etc/security/limits.conf 

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

yum install lrzsz nmap tree dos2unix nc -y

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"

[root@server1 ~]# > /etc/issue
[root@server1 ~]# >  /etc/issue.net 
[root@server1 ~]# cat /etc/issue.net 
[root@server1 ~]# cat /etc/issue

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

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

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

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

 1 修改默认文件路径
 2 vim /etc/ssh/sshd_config
 3 
 4 修改的参数
 5 port       #端口
 6 PermitEmptyPasswords   #是否允许密码为空的用户远程登录
 7 PermitRootLogin             #是否允许root登录
 8 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。
 9 GSSAPIAuthentication no   #解决linux之间使用SSH远程连接慢的问题
10 ListenAddress    #监听指定的IP地址
11 
12 批量操作：
13 sed -ir ‘13 iPort 55666\nPermitRootLogin  no\nPermitEmptyPasswords  no\nUseDNS no\nGSSAPIAuthentication no‘  /etc/ssh/sshd_config