最近在进行debian根文件系统移植时，参考网上的例子使用debootstrap抽取了一个debian stretch根文件系统，之后得到了一个文件夹。

但是当我使用指令，将根文件系统下的所有内容复制到SD卡分区时，开机启动开发板，出现如下报警。

[FAILED] Failed to start Network Time Synchronization.
See 'systemctl status systemd-timesyncd.service' for details.
[  OK  ] Reached target System Time Synchronized.
[  OK  ] Stopped Network Time Synchronization.
[FAILED] Failed to start Network Time Synchronization.
See 'systemctl status systemd-timesyncd.service' for details.
[  OK  ] Started Update UTMP about System Boot/Shutdown.
[  OK  ] Stopped Network Time Synchronization.
[FAILED] Failed to start Network Time Synchronization.
See 'systemctl status systemd-timesyncd.service' for details.
[  OK  ] Stopped Network Time Synchronization.
[FAILED] Failed to start Network Time Synchronization.
See 'systemctl status systemd-timesyncd.service' for details.
[  OK  ] Stopped Network Time Synchronization.
[FAILED] Failed to start Network Time Synchronization.
See 'systemctl status systemd-timesyncd.service' for details.
[  OK  ] Stopped Network Time Synchronization.
[FAILED] Failed to start Network Time Synchronization.
See 'systemctl status systemd-timesyncd.service' for details.
[  OK  ] Started udev Coldplug all Devices.
[  OK  ] Reached target System Initialization.
[  OK  ] Started Daily Cleanup of Temporary Directories.
[  OK  ] Started Daily apt download activities.
[  OK  ] Started Daily apt upgrade and clean activities.
[  OK  ] Reached target Timers.
[  OK  ] Listening on D-Bus System Message Bus Socket.
[  OK  ] Reached target Sockets.
[  OK  ] Reached target Basic System.
         Starting Telephony service...
         Starting System Logging Service...
[  OK  ] Started D-Bus System Message Bus.
[    6.983851] RTL8211E Gigabit Ethernet e6800000.ethernet-ffffffff:00: attached PHY driver [RTL8211E Gigabit Ethernet] (mii_bus:phy_addr=e6800000.ethernet-ffffffff:00, irq=161)
[  OK  ] Started Telephony service.
         Starting DUN service...
         Starting Connection service...
         Starting Save/Restore Sound Card State...
         Starting Login Service...
[  OK  ] Started Regular background program processing daemon.
[  OK  ] Started System Logging Service.
[  OK  ] Started Save/Restore Sound Card State.
[  OK  ] Found device /dev/ttySC0.
[    7.665906] random: crng init done
[    7.669368] random: 7 urandom warning(s) missed due to ratelimiting
[  OK  ] Started DUN service.
[  OK  ] Started Connection service.
[  OK  ] Started Login Service.
         Starting Bluetooth service...
[  OK  ] Started Bluetooth service.
[  OK  ] Reached target Bluetooth.
[FAILED] Failed to start Hostname Service.
See 'systemctl status systemd-hostnamed.service' for details.

给大家提炼一下，就是集中在两个错误上
1、Failed to start Network Time Synchronization.
2、Failed to start Hostname Service.
当你进行展开，查看错误缘由时，你是查不到任何地址或者命令错误的。
之后经过我多次google发现，原来是由于/var/下面缺少了tmp文件夹，导致此错误发生。
修改方式：1，使用sudo cp -arf debian_stretch/* /media/******/rootfs/ (即重新完整复制根文件系统)
2，手动 mkdir /var/tmp (没试过，不推荐)
经过重新复制根文件系统后，问题解决。启动无报错。

问题解决，一片祥和。