CentOS端口的开放及关闭
问题：打开一些常用程度对Centos连接的时候配置没有问题，但是连接不上。
原因：端口不放行的原因主要就是来自于防火墙的阻挡，所以直接关闭防火墙就能解决端口不通的问题，但是这样的解决方案明显是非常不好的。
以下是对/etc/init.d/iptables的操作(iptables可以等同成/etc/init.d/iptables)
①防火墙的关闭
sudo service iptables stop
②防火墙状态查询
sudo service iptables status
③重启防火墙
sudo service iptables restart
④启动防火墙
sudo service iptables start
⑤保存修改
sudo service iptables save
操作和修改的文件为/etc/sysconfig/iptables
保存操作的结果(保存的是下面iptables第一个放行的mysql端口)：
*filter
:INPUT ACCEPT [19:8897]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [19:937]
-A INPUT -p tcp -m tcp --dport 3306 -j ACCEPT
COMMIT
# Completed on Sun May 5 16:25:49 2013
以下是对/sbin/iptables的操作(iptables 命令可以等同成/sbin/iptables)
①具体打开某个端口（以Mysql的端口为例）
sudo iptables -I INPUT -p tcp --dport 3306 -j ACCEPT
②查看已经被放行的端口
sudo iptables --list
关于Iptables命令的--HELP：
Usage: iptables -[AD] chain rule-specification [options]
iptables -I chain [rulenum] rule-specification [options]
iptables -R chain rulenum rule-specification [options]
iptables -D chain rulenum [options]
iptables -[LS] [chain [rulenum]] [options]
iptables -[FZ] [chain] [options]
iptables -[NX] chain
iptables -E old-chain-name new-chain-name
iptables -P chain target [options]
iptables -h (print this help information)Commands:
Either long or short options are allowed.
--append -A chain Append to chain
--delete -D chain Delete matching rule from chain
--delete -D chain rulenum
Delete rule rulenum (1 = first) from chain
--insert -I chain [rulenum]
Insert in chain as rulenum (default 1=first)
--replace -R chain rulenum
Replace rule rulenum (1 = first) in chain
--list -L [chain [rulenum]]
List the rules in a chain or all chains
--list-rules -S [chain [rulenum]]
Print the rules in a chain or all chains
--flush -F [chain] Delete all rules in chain or all chains
--zero -Z [chain [rulenum]]
Zero counters in chain or all chains
--new -N chain Create a new user-defined chain
--delete-chain
-X [chain] Delete a user-defined chain
--policy -P chain target
Change policy on chain to target
--rename-chain
-E old-chain new-chain
Change chain name, (moving any references)Options:
[!] --proto -p proto protocol: by number or name, eg. `tcp'
[!] --source -s address[/mask][...]
source specification
[!] --destination -d address[/mask][...]
destination specification
[!] --in-interface -i input name[+]
network interface name ([+] for wildcard)
--jump -j target
target for rule (may load target extension)
--goto -g chain
jump to chain with no return
--match -m match
extended match (may load extension)
--numeric -n numeric output of addresses and ports
[!] --out-interface -o output name[+]
network interface name ([+] for wildcard)
--table -t table table to manipulate (default: `filter')
--verbose -v verbose mode
--line-numbers print line numbers when listing
--exact -x expand numbers (display exact values)
[!] --fragment -f match second or further fragments only
--modprobe=<command> try to insert modules using this command
--set-counters PKTS BYTES set the counter during insert/append
[!] --version -V print package version.