升级步骤

1. 更新系统软件

   [email protected]:~# apt-get update 
   [email protected]:~# apt-get upgrade -y 
   [email protected]:~# apt-get dist-upgrade
   

2. 移除不必要软件

   [email protected]:~# apt-get autoremove
   

3. 安装更新管理器

   [email protected]:~# apt-get install update-manager-core
   

4. 更新系统

   注意，不要ssh登录执行，使用vnc来操作。

   [email protected]:~# do-release-upgrade
   

5. 我的系统是16.04的，执行完是升级到18.04，如果要升级到20.04就再重复一遍上面的步骤即可。

遇到的问题

1. do-release-upgrade 执行一半提示 /boot 空间不足，没办法清理boot空间，删多余的内核吧。

   • 查看当前系统使用的内核

     [email protected]:~# uname -a
     Linux koomu.cn 4.15.0-142-generic #146~16.04.1-Ubuntu SMP Tue Apr 13 09:27:15 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux
     

   • 查看安装的内核

     [email protected]:~# dpkg --get-selections |grep linux-image|grep -v deinstall
     linux-image-4.15.0-139-generic			install
     linux-image-4.15.0-140-generic			install
     linux-image-4.15.0-142-generic			install
     linux-image-generic-hwe-16.04			install
     

   • 删除旧内核

     [email protected]:~# apt-get remove linux-image-4.15.0-139-generic linux-image-4.15.0-140-generic linux-image-generic-hwe-16.04
     

   • 清理无用包

     [email protected]:~# apt-get autoremove
     

   等空间释放后，再次执行更新命令即可。

2. 中间过程会有选择提示，比如是否要保留现有配置啥的，一定要保留啊，要不就等着重新配置现有的服务啥的吧。

3. 从16.04升级后DNS失效问题

   Ubuntu20.04 LTS 版本安装之后网络管理方式变了，导致原来设置的DNS失效。

   • 首先修改 /etc/systemd/resolved.conf

     [email protected]:~# cat /etc/systemd/resolved.conf
     #  This file is part of systemd.
     #
     #  systemd is free software; you can redistribute it and/or modify it
     #  under the terms of the GNU Lesser General Public License as published by
     #  the Free Software Foundation; either version 2.1 of the License, or
     #  (at your option) any later version.
     #
     # Entries in this file show the compile time defaults.
     # You can change settings by editing this file.
     # Defaults can be restored by simply deleting this file.
     #
     # See resolved.conf(5) for details
     
     [Resolve]
     DNS=8.8.8.8 8.8.4.4
     #FallbackDNS=
     #Domains=
     #LLMNR=no
     #MulticastDNS=no
     #DNSSEC=no
     #DNSOverTLS=no
     #Cache=no-negative
     #DNSStubListener=yes
     #ReadEtcHosts=yes
     

   • 以root身份执行

     [email protected]:~# systemctl restart systemd-resolved
     [email protected]:~# systemctl enable systemd-resolved
     [email protected]:~# mv /etc/resolv.conf  /etc/resolv.conf.bak
     [email protected]:~# ln -s /run/systemd/resolve/resolv.conf /etc/