Linux Study Group 5th: Directory Manipulation, Links and Inodes

Preface

Good evening. This is the 5th in-house study session. Due to the influence of Corona, it became a remote study session, but let's do it again this time without losing! !!

Prologue

--Directory operation --Move and view working directory (cd, pwd) --Go back and forth between directories (pushd, popd) --Check disk usage (du) --Display disk capacity information (df) --Links and inodes --Link setting (ln)

Directory manipulation

Move and view working directory (cd, pwd)

[2nd](https://qiita.com/onukid007/items/149dd210bd96cd43bb21#%E7%89%B9%E6%AE%8A%E3%81%AA%E3%83%87%E3%82%A3 % E3% 83% AC% E3% 82% AF% E3% 83% 88% E3% 83% AA% E8% A8% 98% E5% 8F% B7), but it is a review. cd command (Change working Directory): Command to change the position of the current directory pwd command (Print Working Directory): Command to display the name of the current directory

#Move by absolute specification
$ cd /home/una/hoge/fuga

#View current directory
$ pwd
/home/una/hoge/fuga

#Go to the piyo directory
$ cd piyo

$ pwd
/home/una/hoge/fuga/piyo

Special directory symbols are present to facilitate path specification. Since ~- is convenient, I often use it after learning. You don't have to do cd ../../ anymore ... !!

#Return to the previous directory
cd ~-

#One level up(parent)Move to the directory of
cd ..

#Move to your home directory
cd ~

#Same as above
cd

Go back and forth between directories (pushd, popd)

pushed command: A command to save the history of the working directory in a stacking expression and move to the specified directory. popd command: move folders according to recorded history

$ pwd
/home/una/hoge

#When stacking directories in a stack format....
$ pushd fuga/
~/hoge/fuga ~

#It was piled up under hoge
$ pwd
/home/una/hoge/fuga

#When popping....
$ popd
~/hoge ~

#fuga is now the retrieved stack contents
$ pwd
/home/una/hoge


I'm ashamed to say that this was the first command I knew. I thought it was an ancient command, but it played an important role as the basis of the computer as follows.

A stack is one of the basic data structures used in computers, and holds data in a last in first out (LIFO: Last In First Out; FILO: First In Last Out) structure. https://ja.wikipedia.org/wiki/%E3%82%B9%E3%82%BF%E3%83%83%E3%82%AF

Display disk capacity information (df)

df command (Disk Free): A command to display the free disk space I think that there are many opportunities to use it as a set with the du command introduced later.

For example, suppose your server is nearly full. When investigating the cause, you can use df to check the disk usage status and du to find out which file is squeezing the disk.

$ df
Filesys 1K-Block can be used can be used%Mount position
devtmpfs            485712       0  485712    0% /dev
tmpfs               503664       0  503664    0% /dev/shm
tmpfs               503664     624  503040    1% /run
tmpfs               503664       0  503664    0% /sys/fs/cgroup
/dev/xvda1         8376300 1724520 6651780   21% /
tmpfs               100736       0  100736    0% /run/user/1000

#The h option makes the unit easy to see.
$ df -h
File system size used Remaining used%Mount position
devtmpfs         475M     0  475M    0% /dev
tmpfs            492M     0  492M    0% /dev/shm
tmpfs            492M  656K  492M    1% /run
tmpfs            492M     0  492M    0% /sys/fs/cgroup
/dev/xvda1       8.0G  1.7G  6.4G   21% /
tmpfs             99M     0   99M    0% /run/user/1000

Check disk usage (du)

du command (Disk Usage): A command that displays the size of disk usage.

option Customized content
-a Also shows the usage of each file in the directory
-b Display in bytes
-k Display in kilobytes(Default)
-s Display only total size
$ du
304	./dir1  #Total size of dir1 used(Unit kilo)
656	./dir2  #Total size of dir2 used
960	.       #Total size

#Kilobytes
$ du -k
152     ./dir1  
328     ./dir2 
480     .

#All directories
$ du -a  
304	    ./dir1
656	    ./dir2
   ~abridgement~
960	    .  

#Total size
$ du -s
960     .

Links and inodes

Link settings (ln)

ln command (LiNk): Command to set the link

There are two types of links: hard links and symbolic links.

Symbolic link: sample_s points to sample1. sample1 points to the file entity Hard link: sample_h and sample2 point to the same file entity

The superficial features are the same, but flexible symlinks are now the mainstream. The reason is as follows.

--Symbol links can also link directories --Symlinks can also link to files on another file system

This time I will touch on symbolic links.

option Customized content
-s Make it a symbolic link( -sHard link without)
-i Confirm and execute when "Alias path name" already exists
-f Force execution when "Alias path name" already exists

Link settings

#sample file creation
$ echo This is sample1 > sample1

#Set a symbolic link
$ ln -s sample1 sample_s

#View files using symbolic links
$ cat sample_s
This is sample1

Confirmation of link method


#View list
$ ls -F
sample1  [email protected]  #@Is a symbolic link mark

#See list details
$ ls -l
total 8
-rw-r--r--  1 una  staff  16  3 10 06:45 sample1
lrwxr-xr-x  1 una  staff   7  3 10 06:45 sample_s -> sample1  #Symbolic links are displayed as pointers

Directory name link

$ cat hoge/fuga
This is sample3

#Make piyo which is a link of hoge
$ ln -s hoge piyo

#Display fuga using piyo
$ cat piyo/fuga
This is sample3

Links between directories

Create a link name in the current directory

#Make a link with the same name
$ ln -s hoge/sample1 .

#Make a link called sample2
$ ln -s hoge/sample1 sample2

#Link content
$ ls -l
lrwxrwxrwx 1 una staff 12 March 10 06:55 sample1 -> hoge/sample1
lrwxrwxrwx 1 una staff 12 March 10 06:56 sample2 -> hoge/sample1

#Display specification with a link with the same name
$ cat sample1   
This is sample1. # hoge/Displaying sample1

#Display specification with the link name sample2
$ cat dfile2    
This is sample1. #This is also the same

Create a link name in a different directory

$ cat sample3
This is sample3

#Make piyo
$ mkdir piyo

#Specify with a relative path (no problem with an absolute path)
$ ln -sf ../sample3 piyo/sample4

#Link destination
$ ls -l piyo
Total 0
lrwxrwxrwx 1 una staff 9 March 10 07:01 sample4 -> ../sample3

#Can be displayed..!!
$ cat piyo/sample4
This is sample3

Link setting is a must-have command to become a linux chat deck. I used it somehow, but when I learned it again, I noticed a lot of new things ....

Summary

I think that the commands taken up this time are also basic commands. However, it was very interesting because there were options and backgrounds that I didn't know even with the commands I use every day. Even if you don't know the ancient commands, there may be some convenient ways to use them. In order not to forget, I would like to actively use it and let it soak into my body! !!

Click here for links to past study sessions

-Linux study session 1st: Virtual console and file operation -Linux study session 2nd: File operation -Linux study session 3rd: File deletion prohibition setting and search function -Linux study session 4th: File operation and directory operation

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