centos系统组件优化

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CentOS Linux在公司服务器上广泛被使用，本文总结了一些常见的加固方法。

基本原则：

最小的权限+最小的服务=最大的安全
操作之前先备份；
为避免配置错误无法登录主机，请始终保持有一个终端已用root登录并不退出，在另一个终端中做配置修改。这样即使改错，也不至于因系统无法登录导致永远无法登录或恢复配置。

操作项：

一、注释掉系统不需要的用户和用户组

注意：不建议直接删除，当你需要某个用户时，自己重新添加会很麻烦。
cp  /etc/passwd  /etc/passwdbak #修改之前先备份
vi /etc/passwd  #编辑用户，在前面加上#注释掉此行
#adm:x:3:4:adm:/var/adm:/sbin/nologin
#lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin
#sync:x:5:0:sync:/sbin:/bin/sync
#shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
#halt:x:7:0:halt:/sbin:/sbin/halt
#uucp:x:10:14:uucp:/var/spool/uucp:/sbin/nologin
#operator:x:11:0perator:/root:/sbin/nologin
#games:x:12:100:games:/usr/games:/sbin/nologin
#gopher:x:13:30:gopher:/var/gopher:/sbin/nologin
#ftp:x:14:50:FTP User:/var/ftp:/sbin/nologin #注释掉ftp匿名账号
  cp /etc/group /etc/groupbak #修改之前先备份
  vi /etc/group  #编辑用户组，在前面加上#注释掉此行
  #adm:x:4:root,adm,daemon
  #lp:x:7:daemon,lp
  #uucp:x:14:uucp
  #games:x:20:
  #dip:x:40:

二、关闭系统不需要的服务

使用命令 chkconfig|grep on 检查开机自启动的服务；

abrt-ccpp 0:off 1:off 2:off 3:on 4:off 5:on 6:off
abrtd 0:off 1:off 2:off 3:off 4:off 5:on 6:off
acpid 0:off 1:off 2:on 3:on 4:on 5:on 6:off
auditd 0:off 1:off 2:on 3:on 4:on 5:on 6:off
autofs 0:off 1:off 2:off 3:on 4:on 5:on 6:off
blk-availability 0:off 1:on 2:on 3:on 4:on 5:on 6:off
certmonger 0:off 1:off 2:off 3:on 4:on 5:on 6:off
cgconfig 0:off 1:off 2:off 3:off 4:off 5:off 6:off
cpuspeed 0:off 1:on 2:on 3:on 4:on 5:on 6:off
crond 0:off 1:off 2:on 3:on 4:on 5:on 6:off
cups 0:off 1:off 2:on 3:on 4:on 5:on 6:off
haldaemon 0:off 1:off 2:off 3:on 4:on 5:on 6:off
ip6tables 0:off 1:off 2:on 3:off 4:on 5:on 6:off
iptables 0:off 1:off 2:on 3:on 4:on 5:on 6:off
irqbalance 0:off 1:off 2:off 3:on 4:on 5:on 6:off
kdump 0:off 1:off 2:off 3:off 4:on 5:on 6:off
lvm2-monitor 0:off 1:on 2:on 3:off 4:on 5:on 6:off
mcelogd 0:off 1:off 2:off 3:on 4:off 5:on 6:off
mdmonitor 0:off 1:off 2:on 3:on 4:on 5:on 6:off
messagebus 0:off 1:off 2:on 3:on 4:on 5:on 6:off
netconsole 0:off 1:off 2:off 3:off 4:off 5:off 6:off
netfs 0:off 1:off 2:off 3:on 4:on 5:on 6:off
network 0:off 1:off 2:on 3:on 4:on 5:on 6:off
nfslock 0:off 1:off 2:off 3:on 4:on 5:on 6:off
portreserve 0:off 1:off 2:on 3:on 4:on 5:on 6:off
postfix 0:off 1:off 2:on 3:on 4:on 5:on 6:off
restorecond 0:off 1:off 2:off 3:off 4:off 5:off 6:off
rpcbind 0:off 1:off 2:on 3:on 4:on 5:on 6:off
rpcgssd 0:off 1:off 2:off 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
udev-post 0:off 1:on 2:on 3:on 4:on 5:on 6:off

服务说明：

auditd	The audit package contains the user space utilities for storing and searching the audit records generate by the audit subsystem in the Linux 2.6 kernel.
blk-availability	Controls availability of LVM2 block devices.
cgconfig	Start cgconfigparser.
cgred	This is a daemon for automatically classifying processes into cgroups based on UID/GID.
cpuspeed	This program monitors the system's idle percentage and reduces or raises the CPUs' clock speeds and voltages accordingly to minimize power consumption when idle and maximize perfor-mance when needed.
crond	The daemon to execute scheduled commands.
ip6tables	It's IPv6 packet filter administration.
iptables	It's administration tool for IPv4 packet filtering and NAT.
lvm2-monitor	Monitor LVM2 with using dmeventd.
netconsole	It sends printk message from kernel on UDP.
netfs	NFS clinet.
network	Network system.
postfix	SMTP service daemon.
rdisc	Detect routers in local subnets.
restorecond	It's the daemon that watches for file creation and then sets the default SELinux file context.
rsyslog	It reads and/or clears kernel message ring buffer; set console_loglevel.
saslauthd	saslauthd is a daemon process that handles plaintext authentication requests on behalf of the SASL library.
sshd	OpenSSH sshd daemon.
udev-post	Moves the generated persistent udev rules to /etc/udev/rules.d.

（见http://www.server-world.info/en/note?os=CentOS_6&p=initial_conf&f=4）

关闭不必要的服务

service acpid stop;chkconfig acpid off #电源进阶设定，常用在 Laptop 上
  service cpuspeed stop;chkconfig  cpuspeed  off #停用控制CPU速度主要用来省电
  service cups stop;chkconfig cups off #停用 Common UNIX Printing System 使系统支援印表机
  service ip6tables stop;chkconfig ip6tables off #禁止IPv6

三、禁止非root用户执行/etc/rc.d/init.d/下的系统命令
chmod -R 700 /etc/rc.d/init.d/* (chmod -R 755 /etc/rc.d/init.d/* #恢复默认设置)

四、修改history命令记录

cp /etc/profile /etc/profilebak
vi /etc/profile
找到 HISTSIZE=1000 改为 HISTSIZE=50

五、调整文件描述符大小

echo "ulimit -SHn 65535" >> /etc/rc.local

/etc/security/limits.conf

* soft nofile 65535

* hard nofile 65535
* soft stack unlimited
* hard stack unlimited

六、同步系统时间

cp /usr/share/zoneinfo/Asia/Shanghai /etc/localtime

crontab -e
0-59/10 * * * * /usr/sbin/ntpdate us.pool.ntp.org | logger -t NTP

chkconfig --list | grep ntp #看下服务情况

chkconifg ntpd on

service ntpd start

七、内核参数优化

vi /etc/sysctl.conf #末尾添加如下参数 (备注：内核参数优化根据不同服务器不同业务进行调整)

net.ipv4.tcp_max_tw_buckets = 6144
net.ipv4.tcp_sack = 1
net.ipv4.tcp_window_scaling = 1
net.ipv4.tcp_rmem = 4096 87380 4194304
net.ipv4.tcp_wmem = 4096 16384 4194304

net.core.wmem_default = 8388608
net.core.rmem_default = 8388608
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.ipv4.tcp_timestamps = 1
net.ipv4.tcp_synack_retries = 1
net.ipv4.tcp_syn_retries = 1
net.ipv4.tcp_tw_recycle = 1
net.ipv4.tcp_tw_reuse = 1
net.ipv4.tcp_mem = 94500000 915000000 927000000
net.ipv4.tcp_fin_timeout = 10
net.ipv4.tcp_keepalive_time = 600
net.ipv4.ip_local_port_range = 1024 65000

vm.swappiness = 5
vm.zone_reclaim_mode = 0
net.ipv4.tcp_max_syn_backlog = 5000
vm.dirty_ratio = 60
vm.dirty_background_ratio = 5

八、CentOS 系统优化
cp  /etc/profile  /etc/profilebak2
   vi /etc/profile    #在文件末尾添加以下内容
   ulimit -c unlimited
   ulimit -s unlimited
   ulimit -SHn 65535
   source  /etc/profile #使配置立即生效
   ulimit -a #显示当前的各种用户进程限制

九、去除系统相关信息

事先备份到安全的地方哈：）

echo "Welcome to Server" >/etc/issue

echo "Welcome to Server" >/etc/issue.net

echo "Welcome to Server" >/etc/redhat-release

十、SSH服务安全配置

vi /etc/ssh/sshd_config

1. 禁用root远程登录

PermitRootLoginno

PermitEmptyPasswords no #禁止空密码登录

2.不要支持闲置会话，并配置 Idle Log Out Timeout 间隔：
ClientAliveInterval 600 # (Set to 600 seconds = 10 minutes)
ClientAliveCountMax 0

3.禁用用户的 .rhosts 文件：

IgnoreRhosts yes

4.PasswordAuthentication no

6.ssh安全技巧之更改 SSH 端口
建议改成 10000 以上，以降低扫描到端口的机率。

Port 36000

7.使用iptables允许特定的主机连接
作为TCP wrappers的一个代替品，你可以使用iptables来限制SSH访问（但可以同时使用这个两个的），这里有一个简单的例子，指出了如何允许一个特定的主机连接到你的SSH服务：
iptables -A INPUT -p tcp -m state --state NEW --source 193.180.177.13 --dport 22 -j ACCEPT

保存后重启ssh服务。

十一、添加普通用户并进行sudo授权管理

useradd -d /home/goal user (指定home目录与用户名不同)
passwd user #设置密码
vi /etc/sudoers #或visudo打开，添加user用户所有权限
root ALL=(ALL) ALL
user ALL=(ALL) ALL

十二、安装安全补丁（经常更新为好）

yum install yum-security

检查安全更新
yum –security check-update
只安装安全更新
yum update –security
检查特定软件有无安全更新
yum list-security software_name
列出更新的详细信息
yum info-security software_name

十三、将 SSH 程序包和需要的库保持为最新：
yum update openssh-server openssh openssh-clients -y

十四、清空防火墙并设置规则 配置防火墙以接受仅来自已知网段的 SSH 连接：

iptables -t filter -P INPUT ACCEPT

iptables -t filter -F INPUT

iptables -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT

iptables -A INPUT -i lo -j ACCEPT