标题可能有点难以描述。举个例子。我有一个配置文件。

CONFIG = {
    'app_name': 'ZiXi',
    'mysql': {
        'host': '127.0.0.1',
    }
    'version': 'v2.0.11',
}

通常可以通过CONFIG['mysql']['host'] 这种方式访问，但我们还是想更简单点访问。如
CONFIG.mysql.host ，那么有几种方法。

话不多话，直接上菜:

1. 切回上一个工作目录

这条目录可以直接切回上一次cd的目录，避免复制和输入长目录了。

cd -

如下：切到了Misc， 想切加上一个Downloads目录，即用 cd -

~/Downloads ❯❯❯ cd Misc
~/D/Misc ❯❯❯ cd -
~/Downloads

netplan从/etc/netplan/ 目录读取配置文件，这个目录下有多个不同的文件，可能会有这样的文件

• 01-netcfg.yaml
• 50-cloud-init.yaml
• config.yaml

但不一定都有，我们可以修改来更改网络配置，如果在这个目录下你没找到文件可以通过这个命令sudo netplan generate来创建一个配置文件。

用的阿里的：

deb https://mirrors.aliyun.com/ubuntu-ports/ focal main restricted universe multiverse
deb-src https://mirrors.aliyun.com/ubuntu-ports/ focal main main restricted universe multiverse
deb https://mirrors.aliyun.com/ubuntu-ports/ focal-updates main restricted universe multiverse
deb-src https://mirrors.aliyun.com/ubuntu-ports/ focal-updates main restricted universe multiverse
deb https://mirrors.aliyun.com/ubuntu-ports/ focal-backports main restricted universe multiverse
deb-src https://mirrors.aliyun.com/ubuntu-ports/ focal-backports main restricted universe multiverse
deb https://mirrors.aliyun.com/ubuntu-ports/ focal-security main restricted universe multiverse
deb-src https://mirrors.aliyun.com/ubuntu-ports/ focal-security main restricted universe multiverse
# deb https://mirrors.aliyun.com/ubuntu-ports/ focal-proposed main restricted universe multiverse
# deb-src https://mirrors.aliyun.com/ubuntu-ports/ focal-proposed main restricted universe multiverse

首先说明下，本文是以树莓派作为客户端连接ss， 再用privoxy自动代理实现科学研究。
1 安装ss apt-get install shadowsocks-libev

2 禁用这个服务端服务 systemctl disable shadowsocks-libev

3 自动开启这个客户端连接服务 systemctl enable shadowsocks-libev-local@config

4 编辑ss的配置文件 vi /etc/shadowsocks-libev/config.json

事情源于在树莓派上写的定时脚本，定时获取停车费用信息。ubuntu重装后时区都用tzselect设置了，但仍在半夜收到消息通知。
于是发现需要这样设置下。

执行这个设置成中国时区 timedatectl set-timezone Asia/Shanghai

查看本地时间 timedatectl status

还有最重要的，要重启下crontab的服务. systemctl restart cron
有些系统中crontab服务为 crond。

更多关于timedatectl的帮助可以查看这个：

问题来源于raspberry pi4 安装了打印服务，但是cups服务有点异常报，/etc/securetty找不到。
查了下应该是ubuntu 20.04的bug.

root@ubuntu:~# systemctl status cups
● cups.service - CUPS Scheduler
     Loaded: loaded (/lib/systemd/system/cups.service; enabled; vendor preset: enabled)
     Active: active (running) since Wed 2020-07-01 00:58:26 CST; 12min ago
TriggeredBy: ● cups.path
             ● cups.socket
       Docs: man:cupsd(8)
   Main PID: 8324 (cupsd)
      Tasks: 2 (limit: 4434)
     CGroup: /system.slice/cups.service
             ├─8324 /usr/sbin/cupsd -l
             └─9318 /usr/lib/cups/notifier/dbus dbus://

Jul 01 01:08:15 ubuntu cupsd[8324]: pam_unix(cups:auth): Couldn't open /etc/securetty: No such file or directory
Jul 01 01:08:15 ubuntu cupsd[8324]: pam_unix(cups:auth): Couldn't open /etc/securetty: No such file or directory
Jul 01 01:08:22 ubuntu cupsd[8324]: pam_unix(cups:auth): Couldn't open /etc/securetty: No such file or directory
Jul 01 01:08:22 ubuntu cupsd[8324]: pam_unix(cups:auth): Couldn't open /etc/securetty: No such file or directory
Jul 01 01:08:27 ubuntu cupsd[8324]: pam_unix(cups:auth): Couldn't open /etc/securetty: No such file or directory
Jul 01 01:08:27 ubuntu cupsd[8324]: pam_unix(cups:auth): Couldn't open /etc/securetty: No such file or directory
Jul 01 01:08:29 ubuntu cupsd[8324]: pam_unix(cups:auth): Couldn't open /etc/securetty: No such file or directory
Jul 01 01:08:29 ubuntu cupsd[8324]: pam_unix(cups:auth): Couldn't open /etc/securetty: No such file or directory
Jul 01 01:08:39 ubuntu cupsd[8324]: pam_unix(cups:auth): Couldn't open /etc/securetty: No such file or directory
Jul 01 01:08:39 ubuntu cupsd[8324]: pam_unix(cups:auth): Couldn't open /etc/securetty: No such file or directory

解决的办法就是新建这个文件/etc/securetty，内容为

shell执行时报这个错

./shell/notify.sh: 7: ./shell/notify.sh: Syntax error: "(" unexpected

notify.sh 写了个方法如

function notify() {
  echo "hello"
}

在mac上执行没问题，但是jenkins下跑时报错了。原因查到在这：

shell中函数定义应该是这样，没有function

notify() {
  echo "hello"
}

如果你硬要加function，那就去掉括号()，如下

function notify {
  echo "hello"
}

程序中如果引用了空目录，但git提交的代码没有，有时会发生异常。
空目录通常git提交时给忽略了。
有个办法提交空目录即：在每个空目录中新增一个文件.gitignore

# Ignore everything in this directory
*
# Except this file
!.gitignore

至于为什么git不能提交空目录原因如下：https://git.wiki.kernel.org/index.php/GitFaq#Can_I_add_empty_directories.3F