1.先在服务器下建文件夹以下3个文件夹：/bak、/bak/bakmysql、/bak/bakmysqlold。
[root@server21 ~]# mkdir -p /bak/bakmysql{,old}
在/bak/bakmysql文件夹下建一个shell脚本：
[root@server21 ~]# touch /bak/bakmysql/backup.sh
给文件授权：
[root@server21 ~]# chmod 755 /bak/bakmysql/backup.sh

2.编辑shell脚本：
[root@server21 ~]# vim /bak/bakmysql/backup.sh
#!/bin/bash
cd /bak/bakmysql
echo "You are in bakmysql directory "
mv bakmysql* /bak/bakmysqlold
echo "Old databases are moved to bakmysqlold folder "
Now=$(date +"%Y-%m-%d")
File=bakmysql-$Now.sql
mysqldump -uroot -p'password' db_bbs > $File
echo "Your database backup successfully completed "
SevenDays=$(date -d -7day +"%Y-%m-%d")
if [ -f /bak/bakmysqlold/bakmysql-$SevenDays.sql ]; then
rm -rf /bak/bakmysqlold/bakmysql-$SevenDays.sql
echo "You have delete 7days ago backup file "
else
echo "7 days ago backup file not exist "
fi

3.Shell脚本mysqldump -uroot -p'password' db_bbs > $File语句中的红色字体请分别换为自己的mysql数据库用户、密码和database名。脚本先将/bak/bakmysql文件夹下bakmysql为文件名开头的备份文件移至/bak/bakmysqlold，再生成最新的备份文件，最后再判断/bak/bakmysqlold文件夹中七天前的文件是否存在，存在则删除，最后结束。这样就能自动备份最近七天的数据库脚本。


4.设置每天自动执行shell脚本:
[root@server21 ~]# vim /etc/crontab 在最后加入这样一行（具体含义请自行参考/etc/crontab中的注释）
0 0 * * * root /bak/bakmysql/backup.sh
重启crontab：
[root@server21 ~]# /sbin/service crond restart
如果没有设置crontab为开机自启动可以如下设置其开机自启动：
[root@server21 ~]# chkconfig –level 35 crond on