When you make the switch from one environment to another-and therefore from one IP address to another-people who have the DNS entry cached will continue to try to use the old environment.
The -l switch prefixes each trace entry with the process ID, while the -d switch displays a timestamp relative to the start of the trace.
l开关在每个跟踪条目前面加上进程ID作为前缀，- d开关显示相对于跟踪起点的时间戳。
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From the menu, you may press e on an entry to edit it, c to switch to a GRUB command line, b to boot the system, p to enter a password, and Esc to return to the menu or to the previous step.
在菜单中的条目上按 e 键将编辑条目，按 c 键切换到 GRUB 命令行，按 b 键引导系统，按 p 键输入密码，按 Esc 键返回菜单或上一步。