1.1. Linux Commands

Here is a list of some commands in Linux

1.1.1. How to remove a non-empty directory?



$ rm -rf directory-name

Removes directory-name forcefully (f) and recursively (r)

1.1.2. How to unzip tar.gz files?



$ tar -zxvf file.tar.gz

Unzips a tar.gz file

1.1.3. How to move files from Downloads to a new folder?



$ mv $HOME/filename.txt $HOME/new-folder/filenname.txt

Moves one file from $HOME to $HOME/new-folder

$ mv $HOME/*.* $HOME/new-folder

Moves all files with names and extensions from $HOME to $HOME/new-folder

1.1.4. SSH login without password

Your aim You want to use Linux and OpenSSH to automate your tasks. Therefore you need an automatic login from host A / user a to Host B / user b. You don’t want to enter any passwords, because you want to call ssh from a within a shell script.

How to do it First log in on A as user a and generate a pair of authentication keys. Do not enter a passphrase:

a@A:~> ssh-keygen -t rsa
Generating public/private rsa key pair.
Enter file in which to save the key (/home/a/.ssh/id_rsa):
Created directory '/home/a/.ssh'.
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /home/a/.ssh/id_rsa.
Your public key has been saved in /home/a/.ssh/id_rsa.pub.
The key fingerprint is:
3e:4f:05:79:3a:9f:96:7c:3b:ad:e9:58:37:bc:37:e4 a@A

Now use ssh to create a directory ~/.ssh as user b on B. (The directory may already exist, which is fine):

a@A:~> ssh b@B mkdir -p .ssh
b@B's password:

Finally append a’s new public key to b@B:.ssh/authorized_keys and enter b’s password one last time:

a@A:~> cat .ssh/id_rsa.pub | ssh b@B 'cat >> .ssh/authorized_keys'
b@B's password:

From now on you can log into B as b from A as a without password:

a@A:~> ssh b@B

A note from one of our readers: Depending on your version of SSH you might also have to do the following changes:

Put the public key in .ssh/authorized_keys2 Change the permissions of .ssh to 700 Change the permissions of .ssh/authorized_keys2 to 640