Linux study notes file system (organized and shared)

This article brings you relevant knowledge about the file system in Linux, including some directory descriptions and related issues about file operations. I hope it will be helpful to you.

Memory usage

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Partial directory description

• /bin

  • bin is the abbreviation of Binary. This directory stores the most commonly used commands

• /boot

  • Stores some core files used when starting Linux, including some connection files and image files

• /etc

  • is used to store All configuration files and subdirectories required by the system administrator

• /lib

  • store the most basic dynamic link shared libraries of the system. The function is similar to the DLL file in Windows. Almost all applications require these shared libraries.

• /lost found

  • Normally it is empty. When the system is shut down illegally, some files are stored here

• /media

  • The Linux system will automatically recognize some devices, such as U disks, CD-ROM drives, etc. After recognition, Linux will mount the recognized devices. Go to this directory

• /mnt

  • The system provides this directory to allow users to temporarily mount other file systems. You can put the optical drive Mount it to /mnt/, and then enter the directory to view the contents of the optical drive

• /opt

  • This is for the host The directory where additional installed software is placed. For example, if you install an ORACLE database, you can put it in this directory. It is empty by default.
• ##/proc
  This directory is a virtual directory. It is a mapping of system memory. You can obtain the system memory by directly accessing this directory. information.
  • The contents of this directory are not on the hard disk but in the memory. Some files in it can be modified directly.
  • For example, you can use the following command to block the ping command of the host so that others cannot ping your machine

echo 1 > /proc/sys/net/ipv4/icmp_echo_ignore_all

• /root
  This directory is the user home directory of the system administrator, also known as the super privileged person
• /sbin
  s means Super user. The system management program used by the system administrator is stored here.
• /srv
  This directory stores Some data that need to be extracted after starting some services
##/sys

• This is a big change in the linux2.6 kernel. In this directory Installed sysfs, a new file system in the 2.6 kernel.
  • The sysfs file system integrates the information of the following three file systems, the proc file system for process information, the devfs file system for devices, and the devpts file system for pseudo terminals. The file system is a visual reflection of the kernel device tree.
  • When a kernel object is created, the corresponding files and directories are also created in the kernel object subsystem
/tmp

• This directory is used to store some temporary files
/usr

• This is a very important directory for users Many applications and files are placed in this directory, similar to the program files directory under Windows
/usr/bin

• System Applications used by users
/usr/sbin

• Relatively advanced management programs and system daemons used by super users
/usr/src

• Default placement directory for kernel source code
/var

• This directory stores ever-expanding things. It is customary to place directories that are frequently modified in this directory, including various log files
/run

• is a temporary file system that stores information other than system startup. When the system restarts, the files in this directory should be deleted or cleared.

File operations

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ll

File attributes:

Linux files are basically divided into 3 attributes: readable (r), writable (w), executable (x) . The sorting order of permission positions is (taking -rw-r--r-- as an example): -rw (user)-r (user group in the same group)--r (other users)--

User can read and write, users in the same group can read, and other users can read

Number of files:

If it is a file, the number of files is 1; if it is a directory , the number of files is the number of files in the directory

The group it belongs to:

Each owner can have more than one group, but most users should only belong to the same group group, only when the system administrator wants to give the user special permissions, he may give him another group

File size:File size is expressed in bytes. Empty directories are generally 1024byte

Creation date:In the format of "month, day and time"

• cd

##cd	Change directory command
cd /	Return to the root directory
cd /home	Switch to the home directory
cd ..	Return to the upper level directory '.' indicates the current directory
cd /var/ftp/pub	Switch to the pub directory at one time
cd /root	Switch to the root user directory (Note: the root user directory is displayed as "~")
	Directory operations are available Use absolute paths (starting from the root directory) or relative paths (starting from the current directory). In order to change directories quickly and accurately, directory operations should be good at using the TAB key to automatically complete directory names

• cp

cp	Copy command
cp 123 /var/ftp/pub	Copy the file named 123 to the pub directory
cp 123 /var/ftp/pub/456	Copy the file named 123 to the pub directory and rename it to 456
cp -r /var/ftp/pub /home	Copy the pub directory to the home directory

• mv

##mvMove commandmv 123 /var/ftp/pubMove the file named 123 to pub Under the directory mv 123 /var/ftp/pub/456Move the file named 123 to pub directory and rename it to 456mv /var/ftp/pub /homeMove the pub directory Go to the home directory##mv 123 456Rename file 123 in the current directory to 456

• rm

##rm	Delete Command
rm 123	Delete the file named 123 in the directory (the file exists), you need to press y to confirm
rm -f 123	Delete the file, force deletion, no confirmation required
rm -r abc	Delete the directory named abc under the directory (the directory exists), you need to press y to confirm
rm -fr abc	Forcibly delete the directory without confirmation
rm -f a*	#Forcibly delete all files starting with a in the directory, no confirmation is required

• touch

##touchCreate filetouch 123Create a file named 123touch a b cCreate multiple files

stat

Inode: File identifier

Links: Link to Inode

Access: The last time the file contents were viewed

Modify: The time when the file content was last modified

Change: The time when the file permissions or other file attributes were last modified

Use stat to make the above three times consistent again

• ln

##ln##ln -s yyy syyyln yyy hyyy

Link (shortcut)
Create a link to yyy ( Soft link) syyy, and then use cat syyy to view the content in yyy
Create The link (hard link) of yyy is hyyy, and then use cat hyyy to view the content in yyy

cat/tac/less

##cat/less

View text content command

cat /etc/passwd

View the text file passwd Content, you can only view the last page, only suitable for viewing small text files within one screen

less /etc/passwd

You can use the up and down cursor keys and page up and down to scroll through the entire contents of the text file passwd. After viewing, press q to exit

tac

is similar to the cat command, except that the content is displayed from back to front

•  head/tail

head -3 yyy	显示yyy文件的前三行内容
tail -3 yyy	显示yyy文件的后三行内容
head -3 yyy | tail -1	显示yyy文件第三行的内容
tail -f yyy	监控yyy的内容（监控Inode，当文件删除后，监控就停止，再次创建同名文件时，不会继续监控）
tail -F yyy	监控yyy文件的内容（监控文件名，当文件删除后，监控会暂停，再次创建同名文件时，监控会继续）

移除yyy后

tail -F yyy停止

因为还有一个hyyy指向和yyy一样的Inode，所以

tail -f yyy还在继续监控

 移除hyyy后

tail -f yyy停止监控

 再次创建yyy后，并向yyy中追加“hello”

tail -F yyy追加hello

tail -f yyy没有反应

 再次向yyy中追加数据

ping www.baidu.com >> yyy//将ping的内容追加到yyy文件中

tail -F yyy继续追加新的信息

• find

find / -name yyy	全局搜索yyy文件的位置
find /ect -name yyy	在etc目录及子目录查找yyy文件
find /etc -name a*a	在etc目录及子目录查找a开头a结尾的文件

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