Difference between service and systemctl / method of modifying path / a command to view IP address, gateway and DNS server

One .service and systemctl The difference between

Linux Two ways of service management ：service and systemctl

service The order is actually to /etc/init.d Under the table of contents , To execute relevant procedures ,init.d The directory contains many start and stop scripts for various services of the system . When Linux Startup time , Will look for service scripts in these directories , And according to the script run level Determine the different boot levels .

This method has two disadvantages ：

• First, it takes a long time to start .init Process is serial start , Only the previous process started , To start the next process .
• Second, the startup script is complex .init The process just executes the startup script , Whatever else . Scripts need to deal with all kinds of situations themselves , This tends to make scripts very long

Systemd It was born to solve the above problems . Its design goal is , Provide a complete set of solutions for system startup and management . according to Linux practice , Letter d It's the daemons （daemon） Abbreviation . Systemd The meaning of the name , It's about guarding the whole system . Used Systemd, There's no need to use init 了 .Systemd To replace the initd, Become the first process of the system （PID be equal to 1）, Other processes are its children .

[[email protected] system]# pwd

/usr/lib/systemd/system        

systemctl Can manage /usr/lib/systemd/system All in this directory are marked with .service The end of the service , for example Network.service,nginx.service

Essentially systemctl Or execute an executable file to manage that service , It's just convenient , adopt systemctl To manage , We don't need to find that file to execute

[[email protected] system]# cat NetworkManager.service 

ExecStart=/usr/sbin/NetworkManager --no-daemon         # for example systemctl start NetworkManager Is to /usr/sbin/NetworkManager To execute that file 

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Two . modify PATH Method of environment variable

1. The method of temporary modification

export PATH= Variable path :$PATH Or directly PATH= Variable path :$PATH

2. Permanent modification

modify /root/.bashrc In the document PATH Variable

3. Permanent modification

modify /etc/profile file , add to PATH=/sc:$PATH, Just add in the first line . Effective for all users , We all know the installation path of your program

3、 ... and . Write a script , Realize that you can view at the same time through one command IP Address 、 gateway 、DNS The server , And it is set to be used directly wherever you enter this command

[[email protected] shell-test]# pwd
/lianxi/shell-test
[[email protected] shell-test]# cat ip.sh 
#!/bin/bash
# get IP Address 
ip=`ip add|awk -F' ' 'NR==9 {print $2}'` 
# Get gateway 
route=`ip route|awk 'NR==1 {print $3}'`
# get DNS The server 
dns=`cat /etc/resolv.conf|awk 'NR==3 {print $2}'`
echo "IP The address is ："$ip,"GATEWAY by ："$route,"DNS The server is ："$dns
[[email protected] shell-test]# bash ip.sh 
IP The address is ：192.168.2.43/24,GATEWAY by ：192.168.2.1,DNS The server is ：114.114.114.114

The above simple function has been realized , But only in /lianxi/shell-test This specified location implements , Other locations cannot be achieved . Next we add aliases and modify PATH Variable , Achieve input at any position in the system ipa This command can get the above effect

[[email protected] shell-test]# vim /root/.bashrc
[[email protected] shell-test]# cat /root/.bashrc
# .bashrc

# User specific aliases and functions

alias rm='rm -i'
alias cp='cp -i'
alias mv='mv -i'
alias ipa=`bash /lianxi/shell-test/ip.sh`        # Set an alias for the script just now , Input ipa You can get the same effect 

# Source global definitions
if [ -f /etc/bashrc ]; then
	. /etc/bashrc
fi
PATH=/lianxi/shell-test/:/usr/local/sclilin99/sbin:/lianxi:    # modify path Variable , Add the path where your script is located 
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/root/bin
[[email protected] shell-test]# ipa 
IP The address is ：192.168.2.43/24,GATEWAY by ：192.168.2.1,DNS The server is ：114.114.114.114
[[email protected] shell-test]# cd ~
[[email protected] ~]# ipa        # Now the above functions can be realized in any position 
IP The address is ：192.168.2.43/24,GATEWAY by ：192.168.2.1,DNS The server is ：114.114.114.114