Directory Structure
Directory Structure Preliminary Knowledge
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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)
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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
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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 |
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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)
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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
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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
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Different hostname profiles for different versions
Version command path centos6 /etc/sysconfig/network centos7 /etc/hostname -
Modify hostname
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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.
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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
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Local domain name resolution file /etc/hosts
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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
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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
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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
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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
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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
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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
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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
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Operation and maintenance operation specification (operation and maintenance personnel == firefighters)
①Check before operation
② Backup before operation
③Confirm after operation
④Summary after the operation
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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
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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
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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
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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
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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)
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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
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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
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Aliases simplify complex commands
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'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)
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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
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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
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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
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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 |
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/var/log/messages | Service operation information, system operation or abnormal information |
/var/log/secure | User login information save file |
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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
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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
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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
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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