发现了lsyncd这个程序，比较好用，于是就寻思这用这个来替代。
A若要实现免密码登录B，那么需要在A上面生成密钥，然后将密钥传给B，这样A就可以实现免秘钥登录B了。

ssh-keygen -t rsa
ssh-copy-id username@host

编译要求：
Lua >= 5.2
Lsyncd depends on Lua 5.2 or greater; that is 5.2 or 5.3. For most distributions you need to install the liblua??, the liblua??-dev and the lua?? package, with ?? being the respective Lua version.

cmake >= 2.8
To configure Lsyncd to your system, cmake >= 2.8 is required

rsync >= 3.1
During runtime Lsyncd needs rsync > 3.1 installed both on source and target systems

yum -y install lua-devel cmake rsync

从github同步源码并编译安装

$ git clone https://github.com/LoveyCat/lsyncd.git
$ cd lsyncd && mkdir build && cd build && cmake .. -DCMAKE_INSTALL_PREFIX=/opt/lsyncd && make
$ sudo make install

创建配置文件

$ sudo vim /etc/lsyncd.conf
settings {
logfile = "/var/lsyncd.log",
statusFile = "/var/lsyncd.status",
inotifyMode = "CloseWrite",
}
sync {
default.rsync,
source = "/home/Data",
target = "root@172.16.0.1:/mnt/sdb1",
rsync = {
binary= "/usr/bin/rsync",
archive = true,
-- compress = true,
}
}

简单说下logfile是日志文件，statusFile是运行状态文件，这个可有可无，source就是你要监视并同步的目录，target就是你要同步的目标，比如本次主机B就是我的目标，这种属于远程同步，想要了解更多，请参阅官方文档。

保存后，直接用命令启动就可以了

$ sudo /opt/lsyncd/bin/lsyncd /etc/lsyncd.conf

这样可以直接加载配置文件运行lsyncd，如果不用配置文件，最简单的命令就是官方提供的部分例子了：
Although for standard use or quick testing it can be cursorily configured by command line options. The following will keep a local source and destination directory in sync using rsync:

lsyncd -rsync /home/USER/src /home/USER/dst

The target can here be anything that Rsync recognizes.

lsyncd -rsync /home/USER/src remotehost:dst

Two (or more) targets are configured by calling -rsync twice (or several times).

lsyncd -rsync /home/USER/src remotehost1:dst -rsync /home/USER/src remotehost2:dst

写出了自启动脚本，更新下：

[Unit]
Description=lsyncd service
After=network.target

[Service]
Type=simple
ExecStart=/opt/lsyncd/bin/lsyncd -nodaemon /etc/lsyncd.conf
ExecReload=
ExecStop=/bin/kill -WINCH ${MAINPID}

[Install]
WantedBy=multi-user.target

参考的文章还是要说下的：http://seanlook.com/2015/05/06/lsyncd-synchronize-realtime/

至于更多的用法，请自己参阅官方文档吧：https://axkibe.github.io/lsyncd/manual/invoking/