伺服器搭建（09）設定開機啟動腳本（ubuntu18.04後）

1 ubuntu18.04後啟動的原理變更

ubuntu-16.10 開始不再使用initd管理系統，改用systemd，systemd 就是用 systemctl 指令來替換了 service 和 chkconfig 的功能。

以前啟動 XXX服務用指令：

sudo service XXX start           

現在改用：

sudo systemctl start XXX.service           

開機啟動比以前複雜一些。systemd 預設是讀取 /etc/systemd/system 下的配置檔案，該目錄下的檔案會連結/lib/systemd/system/下的檔案。執行 ls /lib/systemd/system 你可以看到有很多啟動腳本，其中就有我們需要的 

rc.local.service。

打開該腳本，預設内容如下：

#  This file is part of systemd.
#
#  systemd is free software; you can redistribute it and/or modify it
#  under the terms of the GNU Lesser General Public License as published by
#  the Free Software Foundation; either version 2.1 of the License, or
#  (at your option) any later version.

# This unit gets pulled automatically into multi-user.target by
# systemd-rc-local-generator if /etc/rc.local is executable.
[Unit]
Description=/etc/rc.local Compatibility
ConditionFileIsExecutable=/etc/rc.local
After=network.target

[Service]
Type=forking
ExecStart=/etc/rc.local start
TimeoutSec=0
RemainAfterExit=yes           

該配置檔案主要分為3個部分：

1. [Unit] 段: 啟動順序與依賴關系 
2. [Service] 段: 啟動行為,如何啟動，啟動類型 
3. [Install] 段: 定義如何安裝這個配置檔案，即怎樣做到開機啟動

可以看到，預設的配置檔案中少了 Install 段，也就沒有定義如何做到開機啟動，是以顯然這樣配置是無效的。 是以我們的思路就是在後面幫他加上 [Install] 段。之後在rc.local中添加啟動腳本相關資訊，調試後重新開機 測試即可。

2 設定開機啟動腳本流程

@1 添加install字段

預設配置檔案為：

#  This file is part of systemd.
#
#  systemd is free software; you can redistribute it and/or modify it
#  under the terms of the GNU Lesser General Public License as published by
#  the Free Software Foundation; either version 2.1 of the License, or
#  (at your option) any later version.

# This unit gets pulled automatically into multi-user.target by
# systemd-rc-local-generator if /etc/rc.local is executable.
[Unit]
Description=/etc/rc.local Compatibility
ConditionFileIsExecutable=/etc/rc.local
After=network.target

[Service]
Type=forking
ExecStart=/etc/rc.local start
TimeoutSec=0
RemainAfterExit=yes           

添加install字段，添加後，配置檔案為：

[Unit]
Description=/etc/rc.local Compatibility
Documentation=man:systemd-rc-local-generator(8)
ConditionFileIsExecutable=/etc/rc.local
After=network.target

[Service]
Type=forking
ExecStart=/etc/rc.local start
TimeoutSec=0
RemainAfterExit=yes
GuessMainPID=no

[Install]
WantedBy=multi-user.target
Alias=rc-local.service           

@2 之後編輯檔案/etc/rc.local （沒有則建立）

把你需要啟動腳本寫入 /etc/rc.local ，如下所示：

#!/bin/sh -e
#
# rc.local
#
# This script is executed at the end of each multiuser runlevel.
# Make sure that the script will "exit 0" on success or any other
# value on error.
#
# In order to enable or disable this script just change the execution
# bits.
#
# By default this script does nothing.
echo "log test" > /usr/local/test.log
#添加需要開機啟動的腳本指令集合
exit 0           

之後 添權重限，如下所示：

sudo chmod +x /etc/rc.local           

@3 建立軟連結

 systemd 預設讀取 /etc/systemd/system 下的配置檔案, 是以還需要在 /etc/systemd/system 目錄下建立軟連結，如下所示：

ln -s /lib/systemd/system/rc.local.service /etc/systemd/system/           

@4 重新開機系統測試開機腳本是否生效

可以通過列印日志的方式，比如：

echo "test log..." > /usr/local/test.log
           

也可以直接看執行結果。