sudo apt update報錯：

Reading package lists… Done E: Release file for
https://mirrors.tuna.tsinghua.edu.cn/ubuntu/dists/focal-updates/InRelease
is not valid yet (invalid for another 9d 23h 6min 27s). Updates for
this repository will not be applied. E: Release file for
https://mirrors.tuna.tsinghua.edu.cn/ubuntu/dists/focal-backports/InRelease
is not valid yet (invalid for another 9d 23h 6min 47s). Updates for
this repository will not be applied. E: Release file for
https://mirrors.tuna.tsinghua.edu.cn/ubuntu/dists/focal-security/InRelease
is not valid yet (invalid for another 9d 23h 6min 16s). Updates for
this repository will not be applied.

sudo apt install -f報錯

Preparing to unpack …/libgl-dev_1.3.1-1_amd64.deb …
Unpacking libgl-dev:amd64 (1.3.1-1) …
dpkg: error processing archive /var/cache/apt/archives/libgl-dev_1.3.1-1_amd64.deb (–unpack):
trying to overwrite ‘/usr/include/GL/gl.h’, which is also in package mesa-common-dev:amd64 20.0.8-0ubuntu1~18.04.1
dpkg-deb: error: paste subprocess was killed by signal (Broken pipe)
Preparing to unpack …/libglx-dev_1.3.1-1_amd64.deb …
Unpacking libglx-dev:amd64 (1.3.1-1) …
dpkg: error processing archive /var/cache/apt/archives/libglx-dev_1.3.1-1_amd64.deb (–unpack):
trying to overwrite ‘/usr/include/GL/glx.h’, which is also in package mesa-common-dev:amd64 20.0.8-0ubuntu1~18.04.1
Errors were encountered while processing:
/var/cache/apt/archives/libgl-dev_1.3.1-1_amd64.deb
/var/cache/apt/archives/libglx-dev_1.3.1-1_amd64.deb
E: Sub-process /usr/bin/dpkg returned an error code (1)

sudo dpkg --configure -a報錯

$ sudo dpkg --configure -a
[sudo] password for wjc:
dpkg: dependency problems prevent configuration of libglvnd-dev:amd64:
libglvnd-dev:amd64 depends on libgl-dev (>= 1.3.0-1); however:
Package libgl-dev:amd64 is not installed.
libglvnd-dev:amd64 depends on libglx-dev (>= 1.3.0-1); however:
Package libglx-dev:amd64 is not installed.

dpkg: error processing package libglvnd-dev:amd64 (–configure):
dependency problems - leaving unconfigured dpkg: dependency problems
prevent configuration of libglvnd-core-dev:amd64:
libglvnd-core-dev:amd64 depends on libglvnd-dev; however: Package
libglvnd-dev:amd64 is not configured yet.

dpkg: error processing package libglvnd-core-dev:amd64 (–configure):
dependency problems - leaving unconfigured Errors were encountered
while processing: libglvnd-dev:amd64 libglvnd-core-dev:amd64

解決：

可能是系統時間出問題了
手動修改服務器時間：

啟用網絡時間協議：
為了保證時間的準確性，推薦使用NTP網絡時間協議來同步時間。對的，跟windows中的 Internet 時間同步是一樣一樣的。

NTP（Network Time Protocol，網絡時間協議）是用來使網絡中的各個計算機時間同步的一種協議。NTP可以使計算機時鐘與 Internet 時間服務器同步。 這意味著可以更新計算機上的時鐘，以與時間服務器上的時鐘匹配，這有助于確保計算機上的時鐘是準確的。它的用途是把計算機的時鐘同步到世界協調時間UTC，其精度在局域網內可達0.1ms，在互聯網上絕大多數的地方其精度可以達到1-50ms。

運行以下命令，啟用NTP：

sudo timedatectl set-ntp true

啟用NTP以后，時間就是正常的嗎？我們來通過date命令來查看當前時間：

date

若沒對上現在時間，說明時區不正常
使用以下命令修改本地時區：

sudo dpkg-reconfigure tzdata

在“Configuring tzdata”中，依次選擇Asia、Chongqing，回車確認，出現了以下提示信息：

cp: cannot create regular file '/etc/localtime.dpkg-new': Read-only file system                                  

Current default time zone: 'Asia/Chongqing'
Local time is now:      Mon Apr  6 08:49:52 UTC 2015.
Universal Time is now:  Mon Apr  6 08:49:52 UTC 2015.

debconf: DbDriver "config": could not write /var/cache/debconf/config.dat-new: Read-only file system

簡單來說，就是文件系統是只讀的，不能創建etc/localtime.dpkg-new文件和不能寫config.dat-new文件。

當前默認的時區是已經改成了我們想要的’Asia/Chongqing’，但是本地時間和世界時間還是一樣的，這里還有問題，應該就是只讀文件系統造成時區沒有完全配置。

使得文件系統可寫
通過askubuntu找到了Read-only file system問題的解決辦法，運行以下命令使得文件系統可寫。

重復第二步修改時區
這一次重新配置時區就比較順利了。本地時間變成了CST時間，也就是China Standard Time UTC+8:00 中國沿海時間(北京時間)。

Current default time zone: 'Asia/Chongqing'
Local time is now:      Mon Apr  6 55 55 173)">173)">16:55:50 CST 2015.
Universal Time is now:  Mon Apr  6 08:55:50 UTC 2015.

ubuntu@localhost:/etc$ date
Mon Apr  6 55 173)">17:55 173)">19:56 CST 2015
ubuntu@localhost:/etc$ timedatectl status
      Local time: Mon 2015-04-06 55 173)">17:55 173)">36:55 173)">36 CST
  Universal time: Mon 2015-04-06 09:55 173)">36:55 173)">36 UTC
        RTC time: n/a
       Time zone: Asia/Chongqing (CST, +0800)
     NTP enabled: yes
NTP synchronized: yes
 RTC in local TZ: no
      DST active: n/a