树莓派的内网穿透

家里的宽带没有公网IP，从外面没有办法SSH到树莓派上。如果有公网IP的话，现在一般的路由器都支持端口转发功能，在路由器的管理界面添加一条转发规则即可。

不过有一天，我突然想到了SSH的端口转发功能，其实很简单的一条命令：

ssh -N -f -R 8022:localhost:22 xxx@remote-host.com

1	ssh -N -f -R 8022:localhost:22 xxx@remote-host.com

简单解释一下，-N表示了不要执行任何命令，-f表示在后台执行，-R 8022:localhost:22表示remote-host.com上将会监听8022端口，并将所有的流量转发到localhost:22端口上来。就是这么简单。

当然了，前提是你要有一台有公网IP的主机，这个就自己想办法搞定吧，比如阿里云什么的。

但是，这个办法有个缺点，树莓派重启了就失效了，可以参考[这个][autosshd]，在树莓派上略加修改就能用了，把autosshd脚本放到/etc/init.d下，再执行

update-rd.d autosshd defaults

1	update-rd.d autosshd defaults

把autosshd加到自启动项里去。其实这个脚本就是利用了autossh这个工具。

不过我对上面的那个脚本做了些修改，供大家参考：

#!/bin/bash

### BEGIN INIT INFO
# Provides: autossh
# Required-Start: $network $local_fs
# Required-Stop: $network $local_fs
# Default-Start: 2 3 4 5
# Default-Stop: 0 1 6
# Short-Description: This script starts and stops the autossh daemon
### END INIT INFO

# Source function library.
#. /etc/rc.d/init.d/functions

# Source networking configuration.
#. /etc/sysconfig/network

# Check that networking is up.
#[ ${NETWORKING} = "no" ] &amp;&amp; exit 0

TUNNEL_SSHCONFIG="/home/pi/.ssh/config"
TUNNEL_IDENTITY="/home/pi/.ssh/id_rsa"
TUNNEL_HOST="xxx@remote-host.com"
TUNNEL_REDIRECT="8022:localhost:22"

export AUTOSSH_PIDFILE="/var/run/autossh.pid"

# By default it's all good.
RETVAL=0

# Start function.
start() {
 local name=$1
 echo -n $"Starting ${name}: "
 if [ -e "/var/lock/subsys/${name}" ]; then
 if [ -e "/var/run/${name}.pid" ] &amp;&amp; [ -e /proc/`cat /var/run/${name}.pid` ]; then
 echo -n $"already exists.";
 failure $"already exists.";
 echo
 return 1
 fi
 fi
 #daemon /usr/bin/autossh -M 0 -f -nNT -F ${TUNNEL_SSHCONFIG} -i ${TUNNEL_IDENTITY} ${TUNNEL_HOST}
 /usr/bin/autossh -f -M 0 -CNnqT -F ${TUNNEL_SSHCONFIG} -i ${TUNNEL_IDENTITY} -R ${TUNNEL_REDIRECT} ${TUNNEL_HOST} -o ServerAliveInterval=30 -o ServerAliveCountMax=5
 RETVAL=$?
 [ $RETVAL -eq 0 ] &amp;&amp; touch "/var/lock/subsys/${name}"
 echo
 return $RETVAL
}

# Stop function.
stop() {
 local name=$1
 echo -n $"Stopping ${name}: "
 #killproc -p "/var/run/${name}.pid" ${name}
 kill `cat /var/run/${name}.pid`
 RETVAL=$?
 echo
 [ $RETVAL -eq 0 ] &amp;&amp; rm -f "/var/lock/subsys/${name}"
 return $RETVAL
}

# See how we were called.
case "$1" in
 start)
 start "autossh"
 ;;
 stop)
 stop "autossh"
 ;;
 restart)
 $0 stop
 sleep 3
 $0 start
 ;;
 status)
 status "autossh"
 RETVAL=$?
 ;;
 *)
 echo $"Usage: $0 {start|stop|restart|status}"
 exit 1
 ;;
esac

exit $RETVAL

#!/bin/bash

### BEGIN INIT INFO

# Provides: autossh

# Required-Start: $network $local_fs

# Required-Stop: $network $local_fs

# Default-Start: 2 3 4 5

# Default-Stop: 0 1 6

# Short-Description: This script starts and stops the autossh daemon

### END INIT INFO

# Source function library.

#. /etc/rc.d/init.d/functions

# Source networking configuration.

#. /etc/sysconfig/network

# Check that networking is up.

#[ ${NETWORKING} = "no" ] && exit 0

TUNNEL_SSHCONFIG="/home/pi/.ssh/config"

TUNNEL_IDENTITY="/home/pi/.ssh/id_rsa"

TUNNEL_HOST="xxx@remote-host.com"

TUNNEL_REDIRECT="8022:localhost:22"

export AUTOSSH_PIDFILE="/var/run/autossh.pid"

# By default it's all good.

RETVAL=0

# Start function.

start() {

local name=$1

echo -n $"Starting ${name}: "

if [ -e "/var/lock/subsys/${name}" ]; then

if [ -e "/var/run/${name}.pid" ] && [ -e /proc/`cat /var/run/${name}.pid` ]; then

echo -n $"already exists.";

failure $"already exists.";

echo

return 1

#daemon /usr/bin/autossh -M 0 -f -nNT -F ${TUNNEL_SSHCONFIG} -i ${TUNNEL_IDENTITY} ${TUNNEL_HOST}

/usr/bin/autossh -f -M 0 -CNnqT -F ${TUNNEL_SSHCONFIG} -i ${TUNNEL_IDENTITY} -R ${TUNNEL_REDIRECT} ${TUNNEL_HOST} -o ServerAliveInterval=30 -o ServerAliveCountMax=5

RETVAL=$?

[ $RETVAL -eq 0 ] && touch "/var/lock/subsys/${name}"

echo

return $RETVAL

}

# Stop function.

stop() {

local name=$1

echo -n $"Stopping ${name}: "

#killproc -p "/var/run/${name}.pid" ${name}

kill `cat /var/run/${name}.pid`

RETVAL=$?

echo

[ $RETVAL -eq 0 ] && rm -f "/var/lock/subsys/${name}"

return $RETVAL

}

# See how we were called.

case "$1" in

start)

start "autossh"

;;

stop)

stop "autossh"

;;

restart)

$0 stop

sleep 3

$0 start

;;

status)

status "autossh"

RETVAL=$?

;;

echo $"Usage: $0 {start|stop|restart|status}"

exit 1

;;

esac

exit $RETVAL

做了几点改进：

修改了一下在树莓派上可以跑，但是很多地方还有待改进
修改了ssh的启动参数，添加了-Cq，可以man ssh自己看
添加了-o ServerAliveInterval=30 -o ServerAliveCountMax=5，可以自动检测SSH连接可用性

至此。

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