====== Ubuntu ======
  * [[http://www.ubuntu.com|Official site]]
===== Snap =====
  * [[https://cn.ubuntu.com/blog/what-is-snap-application|What is snap application]]
===== Audio =====
  * [[https://linuxhint.com/pulse_audio_sounds_ubuntu/|pulse_audio_sounds_ubuntu]]

===== Tips =====
  * 搜索软件包：http://packages.ubuntu.com/
  * Ubuntu18.04 后网络管理：[[https://netplan.io/|netplan]] ''/etc/netplan/'' -> **NetworkManager** [[https://www.cnblogs.com/liuhedong/p/10695969.html|nmcli]]
  * Ubuntu20.04 更新 openssl : [[https://code.luasoftware.com/tutorials/linux/upgrade-openssl-on-ubuntu-20/|upgrade-openssl-on-ubuntu-20]]<code bash>
# check version
openssl version -a
# backup
sudo cp -R /usr/lib/ssl /usr/lib/ssl-1.1.1h
# download latest version https://www.openssl.org/source/
wget https://www.openssl.org/source/openssl-1.1.1m.tar.gz
# check 
wget https://www.openssl.org/source/openssl-1.1.1m.tar.gz.sha256
echo "$(cat openssl-1.1.1m.tar.gz.sha256) openssl-1.1.1m.tar.gz" | sha256sum --check
# install
sudo apt update && sudo apt install build-essential -y
tar -zxvf openssl-1.1.1m.tar.gz
cd openssl-1.1.1m
./config
make
sudo make install
sudo mv /usr/bin/openssl /usr/bin/openssl-1.1.1f
sudo ln -s /usr/local/bin/openssl /usr/bin/openssl
sudo ldconfig
# check current version
openssl version -a
# fix cert
cd /usr/local/ssl
sudo rmdir certs
sudo ln -s /etc/ssl/certs
sudo rmdir private/
sudo ln -s /etc/ssl/private
sudo mv openssl.cnf openssl.cnf.original
sudo ln -s /etc/ssl/openssl.cnf
# check cert
wget https://www.google.com
</code>
  * 修改时区 [[https://www.server-world.info/en/note?os=Ubuntu_16.04&p=timezone|timedatectl]] <code bash>
# display settings
timedatectl
# display timezone list
timedatectl list-timezones
# set timezone
timedatectl set-timezone Asia/Shanghai
</code>
  * 查看版本:<code bash>lsb_release -a</code>
  * 修改主机名称: <code bash>sudo vim /etc/hostname </code>
  * 增加 sudo 权限 <code>
$ visudo
#添加
username ALL=(ALL) NOPASSWD:ALL
 </code>
  * 添加账户''useradd'' ''passwd'' ''usermod'' ''usermod -aG''
  * 彻底删除帐户：''userdel -r user''
  * 要在禁止所有用户通过ssh以用户名+密码的方式远程登录系统，修改/etc/ssh/sshd_config文件，把允许密码验证这一行改为no：<code bash>
# Change to no to disable tunnelled clear text passwords
PasswordAuthentication no</code>然后重启ssh服务<code bash>sudo service sshd restart</code>如果只是要禁止部分用户以密码登入ssh服务，则可以使用passwd命令中的锁定用户的密码，以user用户为例：<code>
passwd -l user</code>
  * 有时候 ''sudo apt-get update'' 会失败， 以下处理可能解决问题<code bash>
sudo rm -rf /var/lib/apt/lists/* 
sudo apt-get update
</code>详见 [[https://askubuntu.com/questions/41605/trouble-downloading-packages-list-due-to-a-hash-sum-mismatch-error|Failed to fetch update on Ubuntu 14.04 LTS ]]
  * 登录之后的欢迎信息来自 ''/etc/update-motd.d/'' 下脚本动态生成的 ''/run/motd.dynamic''
  * ubuntu 应用列表配置信息目录为 ''/usr/share/application''
  * 双系统启动选项的配置，ubuntu下修改grub选项 ''sudo vim /etc/default/grub'', 配置<code>
GRUB_DEFAULT=saved
GRUB_SAVEDEFAULT=true
</code>, 然后执行 ''sudo update-grub'', 就可实现启动的默认选项保存为上一次手动选择的结果。
  * ubuntu 的时间同步用的是 timesyncd , 可用  ''timedatectl'' 来查看时间同步状态
    * 关闭时间同步：''sudo timedatectl set-ntp no''
    * 开启时间同步: ''sudo timedatectl set-ntp on''
==== 备忘 ====
  * <code bash>
# 添加账户
useradd oak -s /bin/bash -m -l -G sudo
# ssh 登录， /home/oak/.ssh/authorized_keys
# visudo 
# 修改密码
passwd oak
</code>
  * 18.04 最小化安装开启远程桌面： <code bash>
# 安装 vino
sudo apt-get install vino
# 配置 vino
gsettings set org.gnome.Vino enabled true
gsettings set org.gnome.Vino require-encryption false
gsettings set org.gnome.Vino prompt-enabled false
gsettings set org.gnome.Vino view-only false
gsettings set org.gnome.Vino authentication-methods "['vnc']"
gsettings set org.gnome.Vino vnc-password $(echo -n "mypassword"|base64)
# 启动
/usr/lib/vino/vino-server --display=:0
</code> 使用 vnc-viewer 客户端来连接
  * 无人值守安全补丁更新：https://www.cyberciti.biz/faq/set-up-automatic-unattended-updates-for-ubuntu-20-04/ <code bash>
sudo apt install unattended-upgrades
sudo dpkg-reconfigure -plow unattended-upgrades  # select yes
sudo vi /etc/apt/apt.conf.d/50unattended-upgrades  
# Unattended-Upgrade::Automatic-Reboot "true";
sudo unattended-upgrades --dry-run -d  # test
sudo unattended-upgrades -d  # manual upgrade.
</code>