Shell script controls the startup and shutdown of services - with detailed cases

background

One of the functions involved in the automation script used in recent work is through shell Script to control process restart ( Because I have written before , But because the conclusion is not in place , The original notes cannot be found ) You can only search the general information on the Internet , Then I rearranged it according to my own understanding , I also reviewed the basic shell Script writing , Learn new things from the old !

Demand this time : Achieve one shell Script to control the start of the service , If the service has not been run before , This script allows the service to run ; If the service is already running , Then the script can restart the service !

The deployment environment

The services used in this article are tomcat Service as an example , After all, the service is relatively easy to download, install and deploy

tomcat Download address

https://downloads.apache.org/tomcat/tomcat-9/v9.0.62/bin/

tomcat Deploy

1. Unzip the file first tar -zxvf apache-tomcat-9.0.62.tar.gz
2. Entry directory , function tomcat cd apache-tomcat-9.0.62/bin

1. function Start command : sh startup.sh Closing order : sh shutdown.sh
2. Expected results + There may be a mistake

「 Expected results 」 adopt ps -ef|grep tomcat command , You can see tomcat Process information

「 The most common error reports 」 8080 The port is occupied , because tomcat The default port is 8080 At this time, you can use the lsof -i:8080, Find the pid, then kill -9 pid You can end the process , Rerun sh startup.sh that will do

restart tomcat Of shell Script

The final version code debugged by yourself is as follows

pid=$(ps -ef | grep tomcat|grep -v grep| awk '{print $2}')

if [ ! -z "$pid" ];then
  echo " Currently running tomcat Service pid yes : ${pid}"
  kill -9 ${pid}
  echo -e " The current... Has ended tomcat service ~\n"
else
  echo -e " Currently not running tomcat service !\n" 
fi

sh startup.sh

echo -e "\n"
pid1=$(ps -ef | grep tomcat|grep -v grep| awk '{print $2}')

if [ ! -z "$pid1" ];then
  echo " Restarted tomcat service ( *￣▽￣)"
  echo "tomcat New service pid yes : ${pid1}"
else
  echo " restart tomcat Service failure ,  Please check if 8080 The port is occupied (＞﹏＜)"
fi

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Name the above code restart.sh, On the tomcat Of bin Under the table of contents

• Test scenarios - Before 「 not 」 Start the service , Run the script at this time

• Test scenarios - Before 「 has 」 Start the service , Run the script at this time

this shell Code knowledge points

ps -ef The explanation of that long list of commands

ps -ef | grep tomcat|grep -v grep| awk '{print $2}'

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1. First ps -ef | grep tomcat Is to filter the current system , with tomcat Keyword for all processes

1. Visible from above , Find out 2 Processes , One is expected tomcat process , The other is what we filter grep process . We need to take grep Process filtering , So use grep -v grep

• remarks : grep -v It means reverse search , such as grep -v grep Is to find no grep Row of field

1. After the above operations , We only found one expected process , Our goal is to get the second column of data separated by spaces 27851 This process number , So I used awk command

• remarks : Hearsay Linux There are three swordsmen : grep, sed, awk. What we use here awk yes linux One of the three swordsmen ！
• awk The usage scenario of is to obtain data separated by a separator , This separator defaults to a space . print $2 The representative takes the third 2 Columns of data , The process number of the current scenario 27851

shell Assign values to variables in and Value

It uses () and Variable These two usages

1. Basic examples

a=$(date)
echo $a  # Wed Apr 20 20:50:48 CST 2022

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1. tomcat Of shell Script

pid=$(ps -ef | grep tomcat|grep -v grep| awk '{print $2}') That is, the result of various operations pid Assign a value to pid Variable

shell Sentenced to empty

if [ ! -z "$pid" ];then This code uses the usage of judging null , If from pid The value of the variable is null , that if [ -z "$pid" ];then for True, add !, On behalf of the negative is False

pid=$(ps -ef | grep tomcat|grep -v grep| awk '{print $2}')

if [ ! -z "$pid" ];then
  echo " Currently running tomcat Service pid yes : ${pid}"
  kill -9 ${pid}
  echo -e " The current... Has ended tomcat service ~\n"
else
  echo -e " Currently not running tomcat service !\n" 
fi

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In this code block , If you can find tomcat Of pid, that if [ -z "$pid" ];then by Fasel, Go for True, Enter into then The following judgment statement , according to tomcat Of pid The end of the fall tomcat process

shell Other small details of

1. 「 Double quotes and The difference between single quotation marks 」

Double quotes : Variables can be called inside , It is equivalent to using variables dynamically .if [ ! -z "$pid" ] It can be dynamically obtained pid The value of the variable is put into the judgment statement

Single quotation marks : Consider the contents as a string , Will not dynamically use the value of the variable inside . for example ,echo 'pid', The output is pid

1. 「shell Output newline characters in the script 」

At first, I thought it was OK to do this directly echo "hello world\n", Discovery can't be , It has to be used this way echo -e "hello world\n". among -e The parameter represents the active escape character