在 Oracle Cloud 建立首個虛擬主機

Oracle Cloud 資安要求嚴謹，首次註冊即強制要求啟動雙因子驗證。每次登入除了帳號密碼外，皆需搭配特定手機軟體(Oracle Mobile Authenticator)方能進入主控台。

主控台最基礎操作就從建立虛擬機(VM compute instance)開始，節點會以用戶的家鄉區(Home Region)作為預設值。基本上 Always Free 方案能選的項目不多，處理器部份固定是 E2.micro 然後作業系統有 Oracle Linux,Ubuntu, CentOS 等。

Oracle 雲端免費資源(Cloud Always Free)

Oracle Cloud 相較於 Google Cloud Platform(GCP) 除了同樣提供免費運算資源外，機房區域多了東京可以選擇，對於亞太區傳輸延遲顯得更有優勢。另外 Oracle Cloud 登入強制啟用 2FA(Oracle Mobile Authenticator) 認證！

The Home Region(家鄉區)

When you sign up for Oracle Cloud Infrastructure, Oracle creates a tenancy for you in one region. This is your home region. Your home region is where your IAM resources are defined. Your home region contains your account information and identity resources.It is not changeable after your tenancy is provisioned. (區域列表)

Always Free Resources

All Oracle Cloud Infrastructure accounts (whether free or paid) have a set of resources that are free of charge in the home region of the tenancy, for the life of the account. These resources display the Always Free label in the Console (for Ampere A1 Compute shapes, see Compute). (圖例)

Compute(免費運算節點只能在家鄉區建立！)

All tenancies get a set of Always Free resources in the Compute service for creating compute virtual machine (VM) instances. You must create the Always Free compute instances in your home region.

• Micro instances (AMD processor): All tenancies get up to two Always Free VM instances using the VM.Standard.E2.1.Micro shape, which has an AMD processor.(節點規格, 流量計價)
• Ampere A1 Compute instances (Arm processor): All tenancies get the first 3,000 OCPU hours and 18,000 GB hours per month for free for VM instances using the VM.Standard.A1.Flex shape, which has an Arm processor.

Idle Compute Instances(閒置的節點會被收回)
Idle Always Free compute instances may be reclaimed by Oracle. Oracle will deem virtual machine and bare metal compute instances as idle if, during a 7-day period, the following are true:

• CPU utilization for the 95th percentile is less than 20%
• Network utilization is less than 20%
• Memory utilization is less than 20% (applies to A1 shapes only)

[OpenVZ] /proc/self/oom_adj: Operation not permitted

採用 OpenVZ 架構的主機，一直噴錯誤訊息：

error writing /proc/self/oom_adj: Operation not permitted

修正兩個檔案，把 SSHD_OOM_ADJUST 那行註解：

1. /etc/init.d/ssh
2. /etc/default/ssh