• Kernel state and user state

• Memory management and address conversion

  

• Thread-pool

  Concurrency

• ACID

  (Atomicity, Consistency, Isolation, Durability) is a set of properties of database transactions

在企业型的大型网关设备上常见Unix操作系统，TTL=255.

在个人型的小型路由器、交换机上常见Linux操作系统，TTL=63.

通过端口扫描可得到目标主机上开放的端口、运行的服务，进而推断操作系统。

ssh常用端口为22，telnet常用端口为23.

• Prevent boot into Windows automatically when boot from SSD

  Rename or remove the /EFI/Microsoft in the EFI partition.

• Why the bash replied “fdisk/mkfs command not found?”

  Because /sbin is not appended to the $PATH.