centos 运行yum makecache生成缓存有时候会出现这个问题，
Not using downloaded repomd.xml because it is older than what we have
解决方法：清空/var/cache/yum/目录下面的文件

rm -rf /var/cache/yum/*

centos 运行yum makecache生成缓存有时候会出现这个问题，
Not using downloaded repomd.xml because it is older than what we have
解决方法：清空/var/cache/yum/目录下面的文件

rm -rf /var/cache/yum/*

Keepalived-Redis(主从高可用)方案

当系统中只有一台redis运行时，一旦该redis挂了，会导致整个系统无法运行，所以想到的办法自然就是备份。一台redis出现问题了，另一台redis可以继续提供服务。但由于redis目前只支持主从复制备份（不支持主主复制），当主redis挂了，从redis只能提供读服务，无法提供写服务。所以，还得想办法，当主redis挂了，我们让从redis升级成为主redis。这就需要自动故障转移，keepalived可以实现redis的双机热备作为过渡方案。

环境说明：
操作系统：CentOS release 6.8 (64)
Master IP：192.168.129.132
Slave IP：192.168.129.133
Virtural IP : 192.168.129.100
Redis Version: 3.2.28
Keepalived v1.2.13
前期准备：
1、下载包到/usr/local/src目录，配置yum源

curl -o /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-6.repo
wget -O /etc/yum.repos.d/epel.repo http://mirrors.aliyun.com/repo/epel-6.repo
yum makecahce
yum install -y gcc openssl-devel kernel-devel 

2、修改Hostname主机名，关闭selinux和iptables

[root@localhost ~]#  sed -i 's@SELINUX=enforcing@SELINUX=disabled@g' /etc/selinux/config
[root@localhost ~]# setenforce 0
[root@localhost ~]# /etc/init.d/iptables stop 

3、分别修改两台主机名为redis_master 和 redis_slave

[root@localhost ~]# vim /etc/sysconfig/network
HOSTNAME=redis_master
[root@localhost ~]# vim /etc/sysconfig/network
HOSTNAME=redis_slave 

4、禁用大内存页面，详细请了解此篇文章
http://blog.csdn.net/longwang155069/article/details/50897026

[root@redis_master ~]#  echo 'never' > /sys/kernel/mm/transparent_hugepage/enabled
[root@redis_master ~]# vi /etc/sysctl.conf    #编辑，在最后一行添加下面代码
vm.overcommit_memory = 1
[root@redis_master ~]# sysctl -p #使设置立即生效
 

Redis主从搭建
详细步骤
#下载Redis,两台机器都需要做相同操作

[root@redis_master ~]# wget http://download.redis.io/releases/redis-3.2.8.tar.gz
#解压
[root@redis_master ~]# tar -zxvf redis-3.2.8.tar.gz
[root@redis_master ~]# cd redis-3.2.8
[root@redis_master ~]# make
[root@redis_master ~]# make install PREFIX=/usr/local/redis

mkdir /usr/local/redis/etc 

#下载配置文件和启动脚本

wget http://soft.8090st.com/conf/redis.conf -O /usr/local/redis/etc/redis.conf
wget http://soft.8090st.com/shell/redis.sh -O /etc/init.d/redis
 

#添加redis用户

useradd -s /sbin/nologin redis
mkdir /usr/local/redis/var

chmod 777 /usr/local/redis/var
chmod 755 /etc/init.d/redis
chkconfig --add redis
chkconfig redis on

#启动redis测试是否正常

service redis start

#redis主从配置文件
①、主redis需要修改的文件及内容

[root@redis_master ~]# vi /usr/local/redis/etc/redis.conf
bind 0.0.0.0

其余都可以安装默认状态
②、从redis需要修改的文件及内容

[root@redis_slave ~]# vi /usr/local/redis/etc/redis.conf
bind 0.0.0.0
slaveof 192.168.129.132 6379 //指定主redis的地址与端口

如果master设置了验证密码，还需配置masterauth。如果master设置了验证密码为admin，应当配置masterauth admin。
配置完之后重新启动slave的Redis服务，OK，主从配置完成。下面测试一下：
在master和slave分别执行info命令，查看结果如下：

# 查看主从状态
Redis主

[root@redis_master ~]# redis-cli info |grep role -A 3
 

Redis从

[root@redis_slave ~]# ../bin/redis-cli info |grep role -A 3
 

测试现在redis主从是否同步数据

[root@redis_master bin]# redis-cli
127.0.0.1:6379> set a a
OK
 

在从上get查看a的值，结果和redis主的值相同。

[root@redis_slave bin]# redis-cli
127.0.0.1:6379> get a
"a"
 

在Redis从服务器上试试能不能插入数据。
redis-cli -p 6379 set hello world
(error) READONLY You can’t write against a read only slave.
成功配置主从redis服务器，由于配置中有一条从服务器是只读的，所以从服务器没法设置数据，只可以读取数据。

安装过程错误解决方法
zmalloc.h:50:31: error: jemalloc/jemalloc.h: No such file or directory
zmalloc.h:55:2: error: #error “Newer version of jemalloc required”
make[1]: *** [adlist.o] Error 1
#make MALLOC=libc

1. 安装和配置keepalived
在Master和Slave上安装Keepalived
这里以yum安装为例

$ yum install -y keepalived

keepalived安装完成后，我们需要修改它的配置文件：

首先，在Master上创建如下配置文件：

$ mv /etc/keepalived/keepalived.conf /etc/keepalived/keepalived.conf_bak

$ > /etc/keepalived/keepalived.conf
$ vim /etc/keepalived/keepalived.conf

! Configuration File for keepalived
global_defs {
router_id redis100
}
vrrp_script chk_redis
{
script “/etc/keepalived/scripts/redis_check.sh 127.0.0.1 6379”
interval 2
timeout 2
fall 3
}
vrrp_instance redis {
state MASTER # master set to SLAVE also
interface eth0
virtual_router_id 50
priority  150
nopreempt # no seize,must add
advert_int 1
authentication {   #all node must same
auth_type PASS
auth_pass 1111
}
virtual_ipaddress {
192.168.129.100/24 //定义虚拟浮动IP
}
track_script {
chk_redis
}
notify_master “/etc/keepalived/scripts/redis_master.sh 192.168.129.133 6379"
notify_backup “/etc/keepalived/scripts/redis_backup.sh 192.168.129.133 6379"
notify_fault /etc/keepalived/scripts/redis_fault.sh
notify_stop /etc/keepalived/scripts/redis_stop.sh
}

//192.168.129.133 定义redis从服务器IP
//interface eth0   定义网卡名称，有的网卡名不相同，请自行修改

然后，在Slave上创建如下配置文件：

! Configuration File for keepalived

global_defs {
router_id redis101
}
vrrp_script chk_redis
{
script “/etc/keepalived/scripts/redis_check.sh 127.0.0.1 6379”
interval 2
timeout 2
fall 3
}
vrrp_instance redis {
state BACKUP
interface eth0
virtual_router_id 50
priority  100
advert_int 1
authentication {   #all node must same
auth_type PASS
auth_pass 1111
}
virtual_ipaddress {
192.168.0.200/24
}
track_script {
chk_redis
}
notify_master “/etc/keepalived/scripts/redis_master.sh 192.168.129.132 6379"
notify_backup “/etc/keepalived/scripts/redis_backup.sh 192.168.129.132 6379"
notify_fault /etc/keepalived/scripts/redis_fault.sh
notify_stop /etc/keepalived/scripts/redis_stop.sh
}

//192.168.129.132 定义redis主服务器IP
//interface eth0   定义网卡名称，有的网卡名不相同，请自行修改

在Master和Slave上创建监控Redis的脚本

$ mkdir /etc/keepalived/scripts
$ vim /etc/keepalived/scripts/redis_check.sh
 

#!/bin/bash
ALIVE=`/usr/local/redis/bin/redis-cli -h $1 -p $2 PING`
LOGFILE="/var/log/keepalived-redis-check.log"
echo "[CHECK]" >> $LOGFILE
date >> $LOGFILE
if [ $ALIVE == "PONG" ]; then :
echo "Success: redis-cli -h $1 -p $2 PING $ALIVE" >> $LOGFILE 2>&1
exit 0
else
echo "Failed:redis-cli -h $1 -p $2 PING $ALIVE " >> $LOGFILE 2>&1
exit 1
fi


编写以下负责运作的关键脚本：
notify_master /etc/keepalived/scripts/redis_master.sh
notify_backup /etc/keepalived/scripts/redis_backup.sh
notify_fault /etc/keepalived/scripts/redis_fault.sh
notify_stop /etc/keepalived/scripts/redis_stop.sh

因为Keepalived在转换状态时会依照状态来呼叫：
当进入Master状态时会呼叫notify_master
当进入Backup状态时会呼叫notify_backup
当发现异常情况时进入Fault状态呼叫notify_fault
当Keepalived程序终止时则呼叫notify_stop

首先，在Redis Master上创建notity_master与notify_backup脚本：
$ vim /etc/keepalived/scripts/redis_master.sh

#!/bin/bash
REDISCLI="/usr/local/redis/bin/redis-cli -h $1 -p $3"
LOGFILE="/var/log/keepalived-redis-state.log"
echo "[master]" >> $LOGFILE
date >> $LOGFILE
echo "Being master...." >> $LOGFILE 2>&1
echo "Run MASTER cmd ..." >> $LOGFILE 2>&1
$REDISCLI SLAVEOF $2 $3 >> $LOGFILE
sleep 10 #delay 10 s wait data async cancel sync
echo "Run SLAVEOF NO ONE cmd ..." >> $LOGFILE
$REDISCLI SLAVEOF NO ONE >> $LOGFILE 2>&1

$ vim /etc/keepalived/scripts/redis_backup.sh

#!/bin/bash
REDISCLI="/usr/local/redis/bin/redis-cli"
LOGFILE="/var/log/keepalived-redis-state.log"
echo "[backup]" >> $LOGFILE
date >> $LOGFILE
echo "Run SLAVEOF cmd ..." >> $LOGFILE
$REDISCLI SLAVEOF $2 $3 >> $LOGFILE 2>&1
# echo "Being slave...." >> $LOGFILE 2>&1
sleep 15 #delay 15 s wait data sync exchange role

接着，在Redis Slave上创建notity_master与notify_backup脚本：

$ vim /etc/keepalived/scripts/redis_master.sh

#!/bin/bash
REDISCLI="/usr/local/redis/bin/redis-cli -h $1 -p $3"
LOGFILE="/var/log/keepalived-redis-state.log"
echo "[master]" >> $LOGFILE
date >> $LOGFILE
echo "Being master...." >> $LOGFILE 2>&1
echo "Run SLAVEOF cmd ... " >> $LOGFILE
$REDISCLI SLAVEOF $2 $3 >> $LOGFILE  2>&1
#echo "SLAVEOF $2 cmd can't excute ... " >> $LOGFILE
sleep 10 ##delay 15 s wait data sync exchange role
echo "Run SLAVEOF NO ONE cmd ..." >> $LOGFILE
$REDISCLI SLAVEOF NO ONE >> $LOGFILE 2>&1

$ vim /etc/keepalived/scripts/redis_backup.sh

#!/bin/bash
REDISCLI="/usr/local/redis/bin/redis-cli"
LOGFILE="/var/log/keepalived-redis-state.log"
echo "[BACKUP]" >> $LOGFILE
date >> $LOGFILE
echo "Being slave...." >> $LOGFILE 2>&1
echo "Run SLAVEOF cmd ..." >> $LOGFILE 2>&1
$REDISCLI SLAVEOF $2 $3 >> $LOGFILE
sleep 100 #delay 10 s wait data async cancel sync
exit(0)

然后在Master与Slave创建如下相同的脚本：
$ vim /etc/keepalived/scripts/redis_fault.sh

#!/bin/bash
LOGFILE=/var/log/keepalived-redis-state.log
echo "[fault]" >> $LOGFILE
date >> $LOGFILE

$ vim /etc/keepalived/scripts/redis_stop.sh

#!/bin/bash
LOGFILE=/var/log/keepalived-redis-state.log
echo "[stop]" >> $LOGFILE
date >> $LOGFILE
给脚本都加上可执行权限：
（这点很重要,最开始由于这不没做，运行后一直报错 “VRRP_Instance(Redis) Now in FAULT state”）
$ chmod +x /etc/keepalived/scripts/*.sh

脚本创建完成以后，我们开始按照如下流程进行测试：
1.启动Master上的Redis
[root@redis_master ~]# /etc/init.d/redis start
Starting redis-server: [ OK ]

2.启动Slave上的Redis
[root@redis_slave ~]# /etc/init.d/redis start
Starting redis-server: [ OK ]

3.启动Master上的Keepalived
[root@redis_master ~]# /etc/init.d/keepalived start
Starting keepalived: [ OK ]
启动后我们看下eth0这张网卡是否有VIP
[root@redis_master ~]# ip a

4.启动Slave上的Keepalived
[root@redis_slave ~]# /etc/init.d/keepalived start
Starting keepalived: [ OK ]

5.客户机尝试通过VIP连接Redis:
[root@localhost ~]# redis-cli -h 192.168.129.100 INFO ｜grep role -A 3

从图中我们可以看出当前从机器是192.168.129.133

6.尝试插入一些数据：
$ redis-cli -h 192.168.129.100 SET Hello Redis

从VIP读取数据
$ redis-cli -h 192.168.129.100 GET Hello

从Master读取数据
$ redis-cli -h 192.168.129.132 GET Hello

从Slave读取数据
$ redis-cli -h 192.168.129.133 GET Hello

接下来模拟故障产生：
将Master上的Redis停了
$ service redis stop

查看Master上的Keepalived日志
$ tailf /var/log/keepalived-redis-state.log

同时Slave上的日志显示：
$ tailf /var/log/keepalived-redis-state.log

然后我们可以发现，Slave已经接管服务，并且担任Master的角色了。
$ redis-cli -h 192.168.129.100 INFO

然后我们恢复Master的Redis进程
$ service redis start

查看Master上的Keepalived日志
$ tailf /var/log/keepalived-redis-state.log

同时Slave上的日志显示：
$ tailf /var/log/keepalived-redis-state.log

可以发现目前的Master已经再次恢复了Master的角色，故障切换以及自动恢复都成功了。

注意事项：主从的redis都要开启持续化本地备份，否则数据会丢失。
1.master slave IP、VIP位于同一个vlan
2. interface 网卡名称配置正确
3. virtual_router_id VRRP 的Id 不能与vlan 其他设备使用的冲突
4.配置2s检测一次，3次都失败才认为要切换

Q: 当在另一台机器上登录MySQL时出现如下错误：

ERROR 2003 (HY000): Can't connect to MySQL server on 'x.x.x.x' (111)

A: 原因是MySQL考虑到安全因素，默认配置只让从本地登录

打开 /etc/mysql/my.cnf 文件，找到 bind-address = 127.0.0.1 修改为 bind-address = 0.0.0.0

重启mysql : sudo /etc/init.d/mysql restart

可参考：

> I've already check my /etc/my.cnf file for a "binding"
> line.  Its not
> there.  I also found an item online that indicated
> adding:
>

Look for the option "skip-networking". This disables TCP/IP so the
server only accepts local connections via the Unix socket. This sounds1
like your situation.
Note that a "could not connect" error means just that. If the problem
was related to user privileges you would get an "access denied" error.

Q: 还一种情况出现类似下面的错误：

ERROR 1045 (28000): Access denied for user 'test'@'x.x.x.x' (using password: NO)

A: 原因是没有给登录用户名设置远程主机登录的权限。

在本地用 root 登录: mysql -u root -p

修改 MySQL 数据库中 user 表中 对应用户名的 Host 字段，将 localhost 改为 %

use mysql;
update user set Host = '%' where User = 'username';

[root@master ~]# vim /etc/sysconfig/network
[root@master ~]# vim /etc/hosts
[root@master ~]# cd /usr/local/src

[root@master ~]# wget https://mirrors.tuna.tsinghua.edu.cn/mysql/downloads/MySQL-5.6/mysql-5.6.35-linux-glibc2.5-x86_64.tar.gz
 

[root@master ~]# tar –zxvf mysql-5.6.35-linux-glibc2.5-x86_64.tar.gz
 

[root@master ~]# mv mysql-5.6.35-linux-glibc2.5-x86_64 /usr/local/mysql
 

[root@master ~]# useradd -s /sbin/nologin mysql -M
 

[root@master ~]# cd /usr/local/mysql
[root@master ~]# mkdir -p /data/mysql ; chown -R mysql.mysql /data/mysql
[root@master ~]# ./scripts/mysql_install_db --user=mysql --datadir=/data/mysql/
 

[root@master ~]# cp support-files/my-default.cnf /etc/my.cnf 

[root@master ~]# cp support-files/mysql.server /etc/init.d/mysql
[root@master ~]# chmod 755 !$
 

[root@master ~]# vim /etc/init.d/mysql
Datadir=
Basedir=

[root@master ~]# chkconfig --add mysql
[root@master ~]# chkconfig mysql on
 

[root@master ~]# service mysql start
Stating MySQL. SUCCESS!
 

[root@master ~]# vim /etc/profile.d/mysql.sh
export PATH=$PATH:/usr/local/mysql/bin
 

 
[root@master ~]# netstat -lntp |grep 3306
tcp 0 0 :::3306 :::* LISTEN 2057/mysqld

 
[root@master ~]# vim /usr/local/mysql/my.cnf

server-id=1
log-bin=mysql-bin

binlog-do-db=databasename1,databasename2
binlog-ignore-db=databasename1,databasename2

[root@master ~]# mysqladmin -uroot password ‘123456'
[root@master ~]# mysql -uroot -p123456
mysql> grant replication slave on *.* to 'slave'@'192.168.120.11' identified by 'hello123';
mysql> flush privileges; //刷新权限
 

[root@master ~]# service mysql restart //重启服务
mysql> flush tables with read lock; //锁定数据库，此时不允许更改任何数据
mysql> show master status; //查看状态，这些数据是要记录的，一会要在slave端用到
+------------------+----------+--------------+------------------+
| File | Position | Binlog_Do_DB | Binlog_Ignore_DB |
+------------------+----------+--------------+------------------+
| mysql-bin.000006 | 474952 | | |
+------------------+----------+--------------+------------------+
 

[root@slave ~]# mysql -uroot -p123456
mysql> stop slave;
mysql> change master to master_host='192.168.120.10', master_port=3306,
master_user='slave', master_password='hello123',
master_log_file='mysql-bin.000006', master_log_pos=474952;
mysql> start slave;

Slave_IO_Running: Yes
Slave_SQL_Running: Yes

[root@master ~]# mysql -uroot -p123456 -e "use db1;
truncate table db"
[root@master ~]# mysql -uroot -p123456 -e "use db1;
select count(*) from db"

[root@master ~]# mysql -uroot -p123456 -e "use db1; drop table db"
[root@slave ~]# mysql -uroot -pyourpassword -e "use db1; select count(*) from db"
ERROR 1146 (42S02) at line 1: Table 'db1.db' doesn't exist