ARM64 UBUNTU 18.04 更新失败

环境：
rk3399pro + ubuntu18.04.

问题：
修改ubuntu根文件系统时，不能apt-get update。

错误信息：

root@sams-desktop:/# apt-get update
Get:1 https://repo.huaweicloud.com/ubuntu-ports bionic InRelease [242 kB]
Get:2 https://repo.huaweicloud.com/ubuntu-ports bionic-security InRelease [88.7 kB]
Get:3 https://repo.huaweicloud.com/ubuntu-ports bionic-updates InRelease [88.7 kB]
Get:4 https://repo.huaweicloud.com/ubuntu-ports bionic-backports InRelease [74.6 kB]
Err:1 https://repo.huaweicloud.com/ubuntu-ports bionic InRelease
  Couldn't create temporary file /tmp/apt.conf.cBC7Lj for passing config to apt-key
Err:2 https://repo.huaweicloud.com/ubuntu-ports bionic-security InRelease
  Couldn't create temporary file /tmp/apt.conf.9QXhoc for passing config to apt-key
Err:3 https://repo.huaweicloud.com/ubuntu-ports bionic-updates InRelease
  Couldn't create temporary file /tmp/apt.conf.36WDOa for passing config to apt-key
Err:4 https://repo.huaweicloud.com/ubuntu-ports bionic-backports InRelease
  Couldn't create temporary file /tmp/apt.conf.DeFxma for passing config to apt-key
Reading package lists... Done
W: GPG error: https://repo.huaweicloud.com/ubuntu-ports bionic InRelease: Couldn't create temporary file /tmp/apt.conf.cBC7Lj for passing config to apt-key
E: The repository 'https://repo.huaweicloud.com/ubuntu-ports bionic InRelease' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
W: GPG error: https://repo.huaweicloud.com/ubuntu-ports bionic-security InRelease: Couldn't create temporary file /tmp/apt.conf.9QXhoc for passing config to apt-key
E: The repository 'https://repo.huaweicloud.com/ubuntu-ports bionic-security InRelease' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
W: GPG error: https://repo.huaweicloud.com/ubuntu-ports bionic-updates InRelease: Couldn't create temporary file /tmp/apt.conf.36WDOa for passing config to apt-key
E: The repository 'https://repo.huaweicloud.com/ubuntu-ports bionic-updates InRelease' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
W: GPG error: https://repo.huaweicloud.com/ubuntu-ports bionic-backports InRelease: Couldn't create temporary file /tmp/apt.conf.DeFxma for passing config to apt-key
E: The repository 'https://repo.huaweicloud.com/ubuntu-ports bionic-backports InRelease' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.

错误原因：
根文件系统中没有 tmp 目录。创建目录并分配权限，即可解决问题。

处理方法：

 /# mkdir tmp  
 /# chmod 777 /tmp 

ARM64 UBUNTU 更新源设置：
参考：
https://blog.csdn.net/c417469898/article/details/106412687/

使用华为源。

本文参考：
https://xie.infoq.cn/article/b81ac033bbe40fca501828302

完毕。