回顾：

主要是MysqL-systemd-start脚本中的路径开始没修改，换这种启动方式后没注意到他，引出了初始化数据库的一堆折腾。

OS：Ubuntu16.04

MysqL:5.7.17

apt install之后默认datadir 为/var/lib/MysqL,希望修改下datadir的路径

修改/etc/MysqL/MysqL.conf.d/MysqLd.cnf中的datadir,并删除了原来的/var/lib/MysqL文件夹（也可将这个原来的内容mv过去，就不用初始化了），

修改/etc/apparmor.d/usr.sbin.MysqLd中的datadir路径为新的值， 并service apparmor reload重启服务。

在新路径下执行数据库初始化

zhujinhua@ThinkPad-E455:/webdata$ MysqLd --initialize
MysqLd: Can't create directory '/webdata/db/MysqL/' (Errcode: 13 - Permission denied)
2016-12-17T14:50:43.250752Z 0 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use --explicit_defaults_for_timestamp server option (see documentation for more details).
2016-12-17T14:50:43.261000Z 0 [ERROR] Aborting

http://bugs.MysqL.com/bug.PHP?id=82281

https://blogs.oracle.com/jsmyth/entry/apparmor_and_MysqL
了解到是apparmor的问题。但路径确实修改过了。

这个通过暂时停止apparmor的服务执行数据库初始化成功

启动MysqL服务，

zhujinhua@ThinkPad-E455:/webdata$ systemctl restart MysqL.service
Job for MysqL.service Failed because the control process exited with error code. See "systemctl status MysqL.service" and "journalctl -xe" for details.

zhujinhua@ThinkPad-E455:/webdata$ journalctl -xe
12月 17 23:22:26 ThinkPad-E455 systemd[1]: Stopped MysqL Community Server.
-- Subject: Unit MysqL.service has finished shutting down
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit MysqL.service has finished shutting down.
12月 17 23:22:26 ThinkPad-E455 systemd[1]: Starting MysqL Community Server...
-- Subject: Unit MysqL.service has begun start-up
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit MysqL.service has begun starting up.
12月 17 23:22:26 ThinkPad-E455 MysqL-systemd-start[31248]: MysqL system database not found. Please run MysqL_install_db tool.
12月 17 23:22:26 ThinkPad-E455 systemd[1]: MysqL.service: Control process exited,code=exited status=1
12月 17 23:22:26 ThinkPad-E455 systemd[1]: Failed to start MysqL Community Server.
-- Subject: Unit MysqL.service has Failed
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit MysqL.service has Failed.
-- 
-- The result is Failed.
12月 17 23:22:26 ThinkPad-E455 systemd[1]: MysqL.service: Unit entered Failed state.
12月 17 23:22:26 ThinkPad-E455 systemd[1]: MysqL.service: Failed with result 'exit-code'.
12月 17 23:22:27 ThinkPad-E455 systemd[1]: MysqL.service: Service hold-off time over,scheduling restart.
12月 17 23:22:27 ThinkPad-E455 systemd[1]: Stopped MysqL Community Server.
-- Subject: Unit MysqL.service has finished shutting down
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit MysqL.service has finished shutting down.
12月 17 23:22:27 ThinkPad-E455 systemd[1]: MysqL.service: Start request repeated too quickly.
12月 17 23:22:27 ThinkPad-E455 systemd[1]: Failed to start MysqL Community Server.
-- Subject: Unit MysqL.service has Failed
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit MysqL.service has Failed.
-- 
-- The result is Failed.

查看/usr/share/MysqL/MysqL-systemd-start文件

sanity () {
  if [ ! -r /etc/MysqL/my.cnf ]; then
    echo "MysqL configuration not found at /etc/MysqL/my.cnf. Please create one."
    exit 1
  fi

  if [ ! -d /var/lib/MysqL ] && [ ! -L /var/lib/MysqL ]; then
    echo "MysqL data dir not found at /var/lib/MysqL. Please create one."
    exit 1
  fi

  if [ ! -d /var/lib/MysqL/MysqL ] && [ ! -L /var/lib/MysqL/MysqL ]; then
    echo "MysqL system database not found. Please run MysqL_install_db tool."
    exit 1
  fi
}

sanity () {
  if [ ! -r /etc/MysqL/my.cnf ]; then
    echo "MysqL configuration not found at /etc/MysqL/my.cnf. Please create one."
    exit 1
  fi

 datadir=/webdata/db/MysqL sysdbdir=$datadir/MysqL
  if [ ! -d $datadir ] && [ ! -L $datadir ]; then
    echo "MysqL data dir not found at $datadir. Please create one."
    exit 1
  fi

  if [ ! -d $sysdbdir ] && [ ! -L $sysdbdir ]; then
    echo "MysqL system database $sysdatadir not found. Please run MysqL_install_db tool."
    exit 1
  fi
}

启动成功后从error.log中找到初始化时生产的密码，

2016-12-17T14:56:46.781127Z 1 [Note] A temporary password is generated for root@localhost: xxxxxx