Ubuntu / Debian

CLI basics

Sudo

Suck it Up and Do as Ordered.

Add a user to the duoers file (so he can use Sudo to force commands).

sudo nano /etc/sudoers

Sudo bang bang

If you forgot the add 'sudo' before a command, the easy way is not rewrite the whole command but to add the following (!! [bang bang] means: 'add this to my previous command, first this than the previous command).

sudo !!

The !! parameter represents the latest CLI command.

Show technical server (hardware) information

To show information about the linux system hardware, run the following command.

sudo lshw

Source: https://www.tecmint.com/commands-to-collect-system-and-hardware-information-in-linux/

Wget

GNU Wget is a free utility for non-interactive download of files from the Web. It supports HTTP, HTTPS, and FTP protocols, as well as retrieval through HTTP proxies.

Wget is non-interactive, meaning that it can work in the background, while the user is not logged on. This allows you to start a retrieval and disconnect from the system, letting Wget finish the work. By contrast, most of the Web browsers require constant user's presence, which can be a great hindrance when transferring a lot of data.

Wget has been designed for robustness over slow or unstable network connections; if a download fails due to a network problem, it will keep retrying until the whole file has been retrieved. If the server supports regetting, it will instruct the server to continue the download from where it left off.

Source: Ubuntu ManPages > Wget

Create a complete website mirror through CLI
wget -mk https://www.copy-this-site.com/

Functions

Language errors

To reconfigure the language issue within Ubuntu / Devian, run the following code and you have a 50/50 chance it will fix the bloody error message.

dpkg-reconfigure tzdata
Reverse search in last used commands

You can search in previously used commands inside the CLI interface.

ctrl + R

Server security

Tutsplus Basic Security

Compress and extract TAR files

The tar command on Linux is often used to create .tar.gz or .tgz archive files, also called “tarballs.” This command has a large number of options, but you just need to remember a few letters to quickly create archives with tar. The tar command can extract the resulting archives, too.

The GNU tar command included with Linux distributions has integrated compression. It can create a .tar archive and then compress it with gzip or bzip2 compression in a single command. That’s why the resulting file is a .tar.gz file or .tar.bz2 file.

Compress an Entire Directory or a Single File

Use the following command to compress an entire directory or a single file on Linux. It’ll also compress every other directory inside a directory you specify–in other words, it works recursively.

tar -czvf name-of-archive.tar.gz /path/to/directory-or-file

Here’s what those switches actually mean:

Let’s say you have a directory named “stuff” in the current directory and you want to save it to a file named archive.tar.gz. You’d run the following command:

tar -czvf archive.tar.gz stuff

Or, let’s say there’s a directory at /usr/local/something on the current system and you want to compress it to a file named archive.tar.gz. You’d run the following command:

tar -czvf archive.tar.gz /usr/local/something

Compress Multiple Directories or Files at Once

RELATED: How to Manage Files from the Linux Terminal: 11 Commands You Need to Know

While tar is frequently used to compress a single directory, you could also use it to compress multiple directories, multiple individual files, or both. Just provide a list of files or directories instead of a single one. For example, let’s say you want to compress the /home/ubuntu/Downloads directory, the /usr/local/stuff directory, and the /home/ubuntu/Documents/notes.txt file. You’d just run the following command:

tar -czvf archive.tar.gz /home/ubuntu/Downloads /usr/local/stuff /home/ubuntu/Documents/notes.txt

Just list as many directories or files as you want to back up.

Exclude Directories and Files

In some cases, you may wish to compress an entire directory, but not include certain files and directories. You can do so by appending an --exclude switch for each directory or file you want to exclude.

For example, let’s say you want to compress /home/ubuntu, but you don’t want to compress the /home/ubuntu/Downloads and /home/ubuntu/.cache directories. Here’s how you’d do it:

tar -czvf archive.tar.gz /home/ubuntu --exclude=/home/ubuntu/Downloads --exclude=/home/ubuntu/.cache

The --exclude switch is very powerful. It doesn’t take names of directories and files–it actually accepts patterns. There’s a lot more you can do with it. For example, you could archive an entire directory and exclude all .mp4 files with the following command:

tar -czvf archive.tar.gz /home/ubuntu --exclude=*.mp4

Use bzip2 Compression Instead

While gzip compression is most frequently used to create .tar.gz or .tgz files, tar also supports bzip2 compression. This allows you to create bzip2-compressed files, often named .tar.bz2, .tar.bz, or .tbz files. To do so, just replace the -z for gzip in the commands here with a -j for bzip2.

Gzip is faster, but it generally compresses a bit less, so you get a somewhat larger file. Bzip2 is slower, but it compresses a bit more, so you get a somewhat smaller file. Gzip is also more common, with some stripped-down Linux systems including gzip support by default, but not bzip2 support. In general, though, gzip and bzip2 are practically the same thing and both will work similarly.

For example, instead of the first example we provided for compressing the stuff directory, you’d run the following command:

tar -cjvf archive.tar.bz2 stuff

Extract an Archive

Once you have an archive, you can extract it with the tar command. The following command will extract the contents of archive.tar.gz to the current directory.

tar -xzvf archive.tar.gz

It’s the same as the archive creation command we used above, except the -x switch replaces the -c switch. This specifies you want to extract an archive instead of create one.

You may want to extract the contents of the archive to a specific directory. You can do so by appending the -C switch to the end of the command. For example, the following command will extract the contents of the archive.tar.gz file to the /tmp directory.

tar -xzvf archive.tar.gz -C /tmp

If the file is a bzip2-compressed file, replace the “z” in the above commands with a “j”.


This is the simplest possible usage of the tar command. The command includes a large number of additional options, so we can’t possibly list them all here. For more information. run the info tar command at the shell to view the tar command’s detailed information page. Press the q key to quit the information page when you’re done. You can also read tar’s manual online.

If you’re using a graphical Linux desktop, you could also use the file-compression utility or file manager included with your desktop to create or extract .tar files. On Windows, you can extract and create .tar archives with the free 7-Zip utility.


Source: HowToGeek - https://www.howtogeek.com/248780/how-to-compress-and-extract-files-using-the-tar-command-on-linux/

Cyber Security

Logged in users

W displays information related to users that are currently logged in. Following is its syntax:

w

Output should look like:

myname@server:~$ w
 23:22:10 up 1 day, 19 min,  1 user,  load average: 0,54, 0,83, 0,97
USER     	TTY      FROM             LOGIN@   IDLE   JCPU   PCPU WHAT
myname     	:0       :0                za23   ?xdm?  38:42   0.01s /usr/lib/gdm3/gdm-x-session --run-script
myname@server:~$