Directory Structure

Directory Structure Preliminary Knowledge

• Structural Features Description

  1. The directory under the linux root is a hierarchical tree structure

  2. Each directory of linux can be mounted on a different device (disk)

  What is mount:

  like a disk-Equipment (room) Want to store things to enter from the door>:directory (mount point)
  Disk device "-- mount --> Portal (directory)
  

• Practical operation to realize the mounting process

  First step: owning a storage device (optical drive)

  The second step: find the corresponding optical drive device

   [root@jasonNB ~]# ls /dev/cdrom/dev/cdrom
   [root@jasonNB ~]# ls -l /dev/cdrom
   lrwxrwxrwx. 1 root root 3 Dec 6 09:07/dev/cdrom -> sr0
  

  The third process: carry out the mount operation

  mount /dev/cdrom /mnt/ (the mount point directory must exist)

  The fourth step: confirm whether the mount is successful ----> ls /mnt

  Fifth process: unmount ----> umount /mnt

  

Directory Structure Description

• The evolution of the directory structure

  ​ One disk: root directory

  ​ Two disks: /usr directory

  ​ Extension: FHS file system directory specification

  ​

Important Directory Data Information Notes

NIC configuration file

Order	instruction
network card configuration file	/etc/sysconfig/network-scripts/ifcfg-eth0 or ens33
Backup in advance when editing network card files	cp xxx /tmp/xxx.bak
Invoke the last parameter information of the previous command	ps:esc + .
After the network card file is modified, restart the network service	systemctl restart network

Initialize software installation yum install -y vim tree bashcompletion (provides command parameter completion function systemctl)

• Information about the internal field data of the network card configuration file

  BOOTPROTO=none 	Start the agreement Get IP How to get the address automatically dhcp Manually
   set up
  DEFROUTE=yes 	The default route network is enabled (default route dynamic route static route
   Depend on)
  NAME=eth0 		Network card logical name
  UUID=... 		Identify some hardware device information in the virtualization software
  DEVICE=eth0 	Network card device name
  ONBOOT=yes 		Make sure the network card is active
  IPADDR=10.0.0.200 IP address settings
  PREFIX=24 		Set the subnet mask to ensure how many hosts can be connected to a local area network Default 253
  GATEWAY=10.0.0.254 Gateway information The necessary gateway for communication between different LANs 
  					required and in the virtual editor nat The network card settings remain the same
  IPV6_PRIVACY=no
  DNS=114.114.114.114 DNS Domain Name Resolution Service 
  
  

DNS service setting method

1. Set as the address of the Alibaba Cloud dns server

223.5.5.5
223.6.6.6

2. Generic dns server address

114.114.114.114
114.114.114.119

3. Use mobile dns server (Google dns server)

8.8.8.8

4. Use the gateway address as the dns server address

10.0.0.254

Network card domain name resolution configuration file / etc/resolv.conf

• Editing command operations of the configuration file of network card domain name resolution

  vi /etc/resolv.conf
  nameserver 114.114.114.114
  nameserver 223.5.5.5
  

  After the configuration is completed, it will take effect immediately. The dns configuration of the network card takes precedence over the configuration in the resolv.conf file

hostname profile

• Different hostname profiles for different versions

  Version	command path
  centos6	/etc/sysconfig/network
  centos7	/etc/hostname

• Modify hostname

  • The first step: modify the host name using the command (temporary modification)

    hostname jasonNB
    

    After the modification is completed, you need to reconnect for the command to take effect.

  • The second step: Edit and modify the configuration file (permanent modification)

    vi /etc/hostname
    centos7 There are special ways to modify the host name:
     hostnamectl set-hostname oldboyds05
    

Local domain name resolution file /etc/hosts

• Website page information change

  Small companies directly debug online servers Usually operate at night with few users, easy to maintain

  Large enterprises Directly debug and test server test access Simulate real environment access

• Large business case

  ​ JD online website server address 112.65.34.1

  ​ JD.com offline website server address 10.0.0.200

  Modulate the local domain name

  [root@jasonNB ~]# vi /etc/hosts
  10.0.0.200 www.jd.com # Specify the mapping relationship
  

Network failure troubleshooting process

1. Confirm whether the gateway address is unblocked

2. Confirm whether the network card configuration is correct

3. Confirm that the network management service is closed

systemctl stop NetworkManager
systemctl disable NetworkManager

Important data files in the etc directory

/etc/fstab

​ filesystem table system mount information table

Disk --- Partition formatting --- Disk device can be seen in the system --- Mount (open a page)

All storage devices must be mounted before they can be used

• Mounting is divided into temporary mounting and permanent mounting

  ​ Temporary mount: mount /dev/cdrom /mnt

  ​ Permanent mount: Modify a configuration file /etc/fstab related to auto-mounting at boot

• settings file

  device file	mount point
  /dev/first partition	/boot
  /dev/ second partition	swap
  /dev/ third partition	/

  View the file content: cat /etc/fstab

  View disk partition: blkid

• Summarize

  Realize disk storage devices, mount operations take effect permanently, and automatically load mount information when booting

/etc/rc.local

​ This file can only store linux system command operation information

• This file operation process

  ①The system is loaded and started normally

  ②Read the rc.local file

  ③The file mainly saves command information

  ④Execute the command in the file

  ⑤The system starts successfully

• Automatic backup at boot

  cp /etc/sysconfig/network-scripts/ifcfg-eth0/tmp/ifcfg-eth0.bak
  
  
  echo "cp /etc/sysconfig/network-scripts/ifcfgeth0 /tmp/ifcfg-eth0.bak" >> /etc/rc.local
  

  centos6: Just follow the instructions above

  centos7: chmod +x /etc/rc.d/rc.local

• Operation and maintenance operation specification (operation and maintenance personnel == firefighters)

  ①Check before operation

  ② Backup before operation

  ③Confirm after operation

  ④Summary after the operation

• specific operation

  ①Check whether there is a backup file in the corresponding path. There is a backup file: delete it

  ② Test execution on the command line first

  ③ Edit the configuration file rc.local to automatically load the command at startup

  ④Restart the system to confirm

/etc/inittab centos6 vs centos7

• system startup runlevel

  A System startup: Network service running, Security service running, Storage service running Level 01
  B System startup: Security service running Storage service running Level 02
  C System startup: storage service running level 03
  

  Three systems: different startup levels

• centos6 (7 runlevels)

   0 shutdown level ( init 0)  
   1 Single user mode (reset user password information root Repair system) rescue mode 
   2 multi-user mode NFS (no internet service) 
   3 Multi-User Mode (Command Line Mode) 
   4 unknown unused 
   5 Graphical interface mode ( init 5) 
   6 restart level
  

• centos7 (target target)

  ls /usr/lib/systemd/system/runlevel*target -l
   poweroff.target
   rescue.target
   multi-user.target
   multi-user.target
   multi-user.target
   graphical.target
   reboot.target
  

• Adjust system runlevel

  1.centos6

  ​ init level information Temporary modification

  ​ vim /etc/inittab permanent modification

  2.centos7

  ​ systemctl get-default Get level information

  ​ systemctl set-default modified the level

/etc/profile

Configure environment variable information or alias information file (important)

• Environment Variable Characteristics

  1. All environment variables are represented by uppercase letters.

  2. Environment variables can be used by all users

  3. The environment is generally set up after system installation

• Mileage of environment variables

  Step 1: Defining Variables

  [root@jasonNB ~]# oldboy=123
  

  The second process: call variable information

  [root@jasonNB ~]# echo $oldboy
  

  The third step: adjust the variable value information

  [root@jasonNB ~]# oldboy=456
  [root@jasonNB ~]# echo $oldboy
  

/etc/bashrc

​ Specially used to set alias information

• Aliases simplify complex commands

• 'The definition of aliases can be set either in profile or in bashrc

  /etc/profile national law 
   /etc/bashrc national law
   ~/.bashrc House rules
   ~/.bash_profile House rules
  

/etc/motd

​ Prompt information after the user logs in to the system

/etc/issue /etc/issue.net(centos7 more)

​ Prompt information before the user logs in to the system

Important data files in the usr directory

/usr/local/ is used to save user-installed software program information

How to install software in linux system (four ways)

• 1.yum installation software

  ​ Can resolve software dependencies

  E.g:

  Everything you need to buy takeaway is ready to be collected:
  yum install -y tree vim bash-completion
   For the software in question, you can reinstall it to fix:
  yum reinstall -y tree vim bash-completion
  

• 2. Install software in rpm package

  A software installation package is required in the system

  Unable to resolve software dependencies 
  rpm -ivh xxx.rpm
  -i install Install
  -v verbose show details
  -h human Display information in a way that is better understood by humans
  
  rpm -qa tree
  -q query Inquire
  -a all All software information 
  
  rpm -ql vim-enhanced
  -l list Displays list information of software installation directories
  
  rpm -e tree Uninstall software
  	-e erase wipe out==delete
  

  ps:yum remove tree Do not use this method to uninstall

• 3. Compile and install the software

  ​ Installation software is more flexible

  eg: buy raw materials (non-finished products) for cooking, you can flexibly adjust the taste of the food

  Set the software installation path Specify the software function information

• 4. Binary package installation software

  ​ Install software and deploy efficiently

  eg: small zero instant ready-to-use convenient and simple

  CS software installation package (green version free installation)

Important data files in the var directory

Frequently changing files are stored in variable

Frequently changing files >>>: log file

Order	effect
/var/log/messages	Service operation information, system operation or abnormal information
/var/log/secure	User login information save file

• Check log information regularly

  [root@jasonNB ~]# grep # Three Musketeers Central Three 
   [root@jasonNB ~]# grep "Failed" /var/log/secure
  # If the log file is too large, it must be cut
   cat /etc/services >> a.txt # continuous append
   cat a.txt # Check for stuttering
   secure-0k > secure-100k > Size range 10 M > cut securebak01 secure
   ls -l /var/log/secure* # View Default Cut Policy Cut by Days
  
  

Important data files in the proc directory

Log some hardware usage Hardware details

​ CPU # /proc/cpuinfo

• Command to view CPU information

  lscpu
   CPU(s): 4 How many cores does the entire server have
   Core(s) per socket: 2 each CPU how many cores
   Socket(s): 2 There are several servers CPU
  

• Command to view memory information

  cat /proc/meminfo
   MemTotal: 2030172 kB --- The total memory capacity of the server
   MemFree: 1755372 kB --- server unused CPU capacity
   MemAvailable: 1728900 kB --- The server can also use
   Buffers: 2076 kB 
   Cached: 86716 kB
   real-time usage
   free,free -h
  

• Command to view disk information

  df -h
   Check the load
   cat /proc/loadavg
      
   	0.00	 					0.01			 0.03
   Average load per minute 				Average 5 minute load 	Average 15 minute load
   The value of the load cannot exceed the number of cores of the server 	8 nuclear			 7(threshold)
      
  Use commands to view load information
   [root@oldboysh03 ~]# w
   15:39:53 up 43 min, 	2 users, load average: 0.00,0.01, 0.03
   Current time Server running time Number of connected users Average load	
  
  View mount information
   df -h
   cat /proc/mounts # Record system mount information