keepalived 安装：
cd <keepalived_sourcecode_path> ./configure --prefix=/usr/local/keepalived make && make install mkdir /etc/keepalived mkdir /etc/keepalived/scripts cp /usr/local/keepalived/etc/keepalived/keepalived.conf /etc/keepalived/ cp /root/keepalived-2.0.6/keepalived/etc/init.d/keepalived /etc/init.d/ cp /usr/local/keepalived/sbin/keepalived /sbin/keepalived cp /usr/local/keepalived/etc/sysconfig/keepalived /etc/sysconfig/ chmod +x /etc/init.d/keepalived
由于在默认状态下keepalived的日志会写入到/var/log/message中，我们需要将此剥离出来。
在centos 6下可以：
（1）首先修改/etc/sysconfig/keepalived文件，注释掉如下，添加如下：
#KEEPALIVED_OPTIONS="-D" KEEPALIVED_OPTIONS="-D -d -S 0"
（2）其次修改 /etc/rsyslog.conf 文件，添加如下：
local0.* /var/log/keepalived.log
在centos 7 下，还需要修改/lib/systemd/system/keepalived.service 文件：
centos 7使用。因为centos 7使用systemctl，通过systemctl调用service，所以需要修改/lib/systemd/system/keepalived.service文件。
将里面的：
EnvironmentFile=-/usr/local/keepalived/etc/sysconfig/keepalived ExecStart=/usr/local/keepalived/sbin/keepalived $KEEPALIVED_OPTIONS
修改成：
EnvironmentFile=/etc/sysconfig/keepalived ExecStart=/sbin/keepalived $KEEPALIVED_OPTIONS
然后重新加载service：
systemctl daemon-reload
整体的思路就是，
1. 通过systemctl start keepalived去启动；
2. 启动keepalived的时候，会去读service的配置文件：/lib/systemd/system/keepalived.service；
3. 在service的配置文件时：
3.1 启动文件路径ExecStart=/sbin/keepalived $KEEPALIVED_OPTIONS，即启动方式是带环境变量文件中参数来启动；
3.2 读取环境变量参数EnvironmentFile=/etc/sysconfig/keepalived。
4. $KEEPALIVED_OPTIONS参数是在/etc/sysconfig/keepalived的配置；我们配置的是KEEPALIVED_OPTIONS="-D -d -S 0"；而-S是syslog的facility，0表示放在local0，在/etc/rsyslog.conf 中配置local0.* /var/log/keepalived.log
5. 所以，写日志就去/var/log/keepalived.log了。
