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README.md

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-# Important-Linux-commands
+## Important-Linux-commands
+
+The commands which make life in cyberspace easier.
+
+In the shell, you have to imagine the jumps. Because the computer will only be 
+projecting code in your mind from your mind.
+
+You are a specific point on some system, when you are in the shell.
+you can see what is in the directory you are with the command
+
+# ls
+
+this command also can display other useful information. Of what is inside the directory 
+you are in.
+
+# cd
+
+The most important one.
+Instead to click, you change directories via command.
+that makes it possible to jump from one point to the other, especially with autocompletion.
+
+
+# man
+
+In general you can get the manual entries for each of the programs described here and much more.
+
+Just type 
+
+    man cd
+
+or type 
+    man ls
+
+and you will get the manual opened historically with nano or less.. not sure, both good old editors.
+
+# cp
+
+copy files from one place to another. (relatively from you)
+
+    cp /dirA/file1.py /dirB/file1.py
+
+when there is already file1.py in the destination directory, it gets overwritten.
+
+
+
+# Concept of piping with >
+
+in the shell you have standard input and standard output.
+Nothing more.
+to pipe the standard output from one program into a file, you write it like this:
+
+    ls > file.txt
+
+When you write like that, youll overwrite everything in the file with the output.
+
+If you want to append to a file what a program has as standard output, 
+you can use >> instead. Writing it like this:
+
+    ls >> file.txt
+
+This both is piping. There is another very important aspect of piping described later.
+
+# alias
+
+
+give your complicated commands easy remember commands.
+Or build the own language of your shell.
+
+    alias cls=clear
+
+This sets up an alias called cls. It will be another name for clear. When you type cls, it will clear the screen just as though you had typed clear. 
+
+On my Arch Linux, I can write these aliases in my bashrc config file. I need to issue the command 
+
+    source bash_profile
+
+to get the configuration loaded. On other linux there will be an analogon.
+
+
+
+# cat
+
+print out what you have in front of you on the standard output.
+
+also print several together
+
+for instance:
+
+    cat doc1.txt doc2.txt > doc1ANDdoc2.txt
+
+
+# chown
+
+On linux everything are only directories and (txt)files.
+All these objects have an owner, or also multiple ones.
+
+    sudo chown -R root /ole/ola/kp.txt
+
+gives root the ownership of kp.txt
+
+# chmod
+
+Every owner then has file permissions. That means he can read write or x (do) something.
+he can do all of them or some of them or none of them. Thats defined in codes, 777 gives them all and 660 doesnt completely.
+
+    sudo chmod 777 ole/oi/file.txt
+
+bzw
+
+    sudo chmod 660 ole/oi/file.txt
+
+
+ Just look it up what people say regarding permissions and certain directories.
+
+# history
+
+this lists all the commands of the shell you are in, that you have typed in lastly.
+
+# grep
+
+
+if you have some bigger output of some of the former commands for example. Or whatever big output. then use grep to filter out the lines that have a certain word in it.
+GRAB it.
+
+# piping with |
+
+here comes into account the piping with |.
+
+Directly combining it with the history command is pretty effective..
+
+    history | grep "whatsoevercommandIalreadyfiguredoutbutreallydontwanttosearchoutagain"
+
+here the output of history gets piped into the program grep.
+as the output of history gives one command per line, grep will filter out exactly the command in which the pattern "whatsoever" occur. 
+
+
+# getting some INFO about the system
+
+
+# df
+
+prints you out disc usage of your hardware
+
+    df -h
+
+does it in humanreadable
+
+
+# du 
+
+prints out the size of files around you
+
+    du -h -d 2
+
+prints in human readable with depth 2, that means in the directories and in their subdirectories.
+
+
+# lsblk
+
+prints you out all the hardware devices with memory
+
+
+# htop respectively top
+
+gives you a terminal graphics programm interface to see all running processes
+
+
+# tail -f
+
+with tail or also head, you can print out the last or the first lines of a file 
+
+When you use tail -f, you get a stream of the documents last lines.
+
+Thats perfect for some log files that get written.
+
+# journalctl -f
+
+this gives you a stream of the kernel messages, which are pretty a lot about a lot of different topics of the programs on your machine.
+
+The kernel is the ground software, running the hardware of the proper materia device.
+Its mostly in C.
+C is like the base of all languages. (if its not assembly)
+
+# uname (-a or -r or other)
+
+gives you general infos about system, OS, and stuff
+
+# systemctl
+
+some people do not like systemctl.
+I personally have parts of my structures that are managed by this software.
+with 
+
+    sudo systemctl status nginx.service
+
+I ask systemctl to give me the status of the nginx daemon, running in the background of my (and actually all of my machines there is running one nginx daemon) machine.
+
 
-The commands which make life in cyberspace easier