Terminal (3/3): system administration

12 of september of 2021

In the previous parts we saw the fundamentals of the terminal and the network, compression and process utilities. In this final chapter we put on the administrator’s hat: **memory, disk and interface management**, **package handling**, **administration users and permissions**, **security**, **command scheduling** and some final **miscellaneous tricks**.

Disclaimer: This post has been translated to English using a machine translation model. Please, let me know if you find any mistakes.

📚 **This entry is part of the _Introduction to the terminal_ series**, divided into three chapters that are read in order:

> * Part 1: Navigation, files, and commands

* Part 2: Network, compression, and processes

* 👉 **Part 3: System administration**

RAM memory management

If we only want to obtain information from memory, we can use the free command

	
		
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		!free
	
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				              total       usado       libre  compartido búfer/caché  disponible
Memoria:    32774516     6563544    20091804      276296     6119168    25479600
Swap:       2097148           0     2097148

But since this information isn't very easy to digest, we added the -h (human) flag to make it easier to read

	
		
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		!free -h
	
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				              total       usado       libre  compartido búfer/caché  disponible
Memoria:        31Gi       6,3Gi        19Gi       270Mi       5,8Gi        24Gi
Swap:         2,0Gi          0B       2,0Gi

Hard Drive Management

To get information about the hard drive, we use the du command. If we only enter this command in the terminal, it will give us information about all the folders on our machine, so, in order not to get too much information, it is necessary to provide it with a path that we want to scan

	
		
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		!du ~/Documentos/web/portafolio/posts/
	
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				8	/home/wallabot/Documentos/web/portafolio/posts/__pycache__
1648	/home/wallabot/Documentos/web/portafolio/posts/notebooks_translated
4288	/home/wallabot/Documentos/web/portafolio/posts/html_files
336	/home/wallabot/Documentos/web/portafolio/posts/prueba/tocompress
1132	/home/wallabot/Documentos/web/portafolio/posts/prueba
16	/home/wallabot/Documentos/web/portafolio/posts/introduccion_python/__pycache__
28	/home/wallabot/Documentos/web/portafolio/posts/introduccion_python
11232	/home/wallabot/Documentos/web/portafolio/posts/

As before, we add the -h flag (human) to make it easier to read

	
		
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		!du ~/Documentos/web/portafolio/posts/ -h
	
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				8,0K	/home/wallabot/Documentos/web/portafolio/posts/__pycache__
1,7M	/home/wallabot/Documentos/web/portafolio/posts/notebooks_translated
4,2M	/home/wallabot/Documentos/web/portafolio/posts/html_files
336K	/home/wallabot/Documentos/web/portafolio/posts/prueba/tocompress
1,2M	/home/wallabot/Documentos/web/portafolio/posts/prueba
16K	/home/wallabot/Documentos/web/portafolio/posts/introduccion_python/__pycache__
28K	/home/wallabot/Documentos/web/portafolio/posts/introduccion_python
11M	/home/wallabot/Documentos/web/portafolio/posts/

Interface management

In Ubuntu, by default we start in a graphical interface, but we can open other interfaces, which will not be graphical, by pressing CTRL+ALT+F<num> where the number can range from 1 to 6. Only 2 will have the graphical interface and 1 will be the login prompt

When handling multiple interfaces, we may not know which one we are in, so by entering the tty command, it will tell us which one we are in

	
		
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		!tty
	
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				/dev/pts/0

Package management

PPA Repositories (Personal Package Archives)

In Linux, package management is done through repositories. This is a list of addresses where the binaries of our programs are located. Thus, when we want to update or install our programs (we will explain how later), what the operating system will do is look at the list of these repositories and go to the indicated addresses to search for the binaries

This list of repositories is located in /etc/apt/sources.list and inside the /etc/apt/sources.list.d folder. Let's take a look at this list.

	
		
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		terminal("cat /etc/apt/sources.list", max_lines_output=10)
	
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				# deb cdrom:[Ubuntu 20.04.2.0 LTS _Focal Fossa_ - Release amd64 (20210209.1)]/ focal main restricted
# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://es.archive.ubuntu.com/ubuntu/ focal main restricted
# deb-src http://es.archive.ubuntu.com/ubuntu/ focal main restricted
## Major bug fix updates produced after the final release of the
## distribution.
deb http://es.archive.ubuntu.com/ubuntu/ focal-updates main restricted
...
deb https://developer.download.nvidia.com/compute/cuda/repos/ubuntu2004/x86_64/ /
# deb-src https://developer.download.nvidia.com/compute/cuda/repos/ubuntu2004/x86_64/ /
deb https://apt.kitware.com/ubuntu/ focal main
# deb-src https://apt.kitware.com/ubuntu/ focal main

The first lines that include the word cd-rom are references to the installation CD; they always come with the words deb cdrom: even if the system was installed over the network or from a USB drive.

From here on, various lines begin to appear that start with deb or deb-src. deb contains the binaries, and deb-src contains the source code.

Every valid repository address has one of these formats:

deb http://server_address/folder_name version_name (main or universe or multiverse or main restricted, etc)
deb-src http://server_address/folder_name version_name (main or universe or multiverse or main restricted, etc)

The six types of Ubuntu repositories are:

Main

The Main repository is enabled by default and contains only free and open-source software or FOSS for its acronym in English (Free and Open-Source Software).

Universe

As Main, Universe also offers FOSS. The difference is that in this repository it is not Ubuntu that guarantees regular security updates, but rather the community that is responsible for its support. It comes enabled by default, but not always. Some operating systems have it disabled by default and we may need to enable it if we are running a Live Session. If we have not added it, we can do so with this command:

sudo add-apt-repository universe

What do we find in «Universe»? I’d say most of the worthwhile software, including VLC and OpenShot.

Multiverse

From here on come the Ubuntu repositories with less freedom. Multiverse contains software that is no longer FOSS, and Ubuntu cannot enable this repository by default due to legal and licensing issues. On the other hand, it also cannot provide patches and updates. With this in mind, we need to decide whether or not to add it, something we can do with this command:

sudo add-apt-repository multiverse

Restricted

In Ubuntu repositories we can find free and open-source software, but this is not possible when it comes to something related to hardware. In the Restricted repositories, we will find drivers, such as those for graphics cards, touchpads, or network cards.

sudo add-apt-repository restricted

Partner

This repository contains proprietary software compiled by Ubuntu from its partners.

Third-party Ubuntu repositories

Finally, we have third-party repositories. Ubuntu always tries to offer the best possible user experience, and that is one of the reasons why it rejects certain software. There are also developers who prefer to have total control over what they offer, and for that reason they create their own repositories.

Add repositories

If we are on Ubuntu, we can add a repository using the command add-apt-repository <repository>. But as in other distributions that are not Ubuntu, we do not have this command

Update the repositories

By using the apt update command, we can update to the latest versions of the packages we have in our repository.

Update the packages

Using the apt upgrade command, we can update the programs we have installed and whose repository we have previously updated.

Update the kernel

If we use the apt dist-upgrade command, kernel packages will also be updated

Warning!: Updating kernel packages can cause some packages to break

Reminder: When updating kernel packages, for them to take effect it is necessary to restart the computer

Package search

With the command apt search <package> we can find packages

	
		
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		terminal("apt search vlc", max_lines_output=10)
	
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				Ordenando...
Buscar en todo el texto...
anacrolix-dms/focal 1.1.0-1 amd64
  Go UPnP DLNA Digital Media Server with basic video transcoding
cubemap/focal 1.4.3-1build1 amd64
  scalable video reflector, designed to be used with VLC
dvblast/focal 3.4-1 amd64
  Simple and powerful dvb-streaming application
...
x264/focal 2:0.155.2917+git0a84d98-2 amd64
  video encoder for the H.264/MPEG-4 AVC standard

List of installed packages

To see which packages we have installed, we can use dpkg -l, which will give us a list of all the packages installed on our computer.

	
		
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		terminal("dpkg -l", max_lines_output=10)
	
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				Deseado=desconocido(U)/Instalar/eliminaR/Purgar/retener(H)
| Estado=No/Inst/ficheros-Conf/desempaqUetado/medio-conF/medio-inst(H)/espera-disparo(W)/pendienTe-disparo
|/ Err?=(ninguno)/requiere-Reinst (Estado,Err: mayúsc.=malo)
||/ Nombre                                     Versión                               Arquitectura Descripción
+++-==========================================-=====================================-============-===========================================================================================================================================================================================================================================================================================================================================================================================================================================
ii  accountsservice                            0.6.55-0ubuntu12~20.04.5              amd64        query and manipulate user account information
ii  acl                                        2.2.53-6                              amd64        access control list - utilities
ii  acpi-support                               0.143                                 amd64        scripts for handling many ACPI events
ii  acpid                                      1:2.0.32-1ubuntu1                     amd64        Advanced Configuration and Power Interface event daemon
ii  adduser                                    3.118ubuntu2                          all          add and remove users and groups
...
ii  zip                                        3.0-11build1                          amd64        Archiver for .zip files
ii  zlib1g:amd64                               1:1.2.11.dfsg-2ubuntu1.5              amd64        compression library - runtime
ii  zlib1g:i386                                1:1.2.11.dfsg-2ubuntu1.5              i386         compression library - runtime
ii  zlib1g-dev:amd64                           1:1.2.11.dfsg-2ubuntu1.5              amd64        compression library - development

If we want to check whether we have a package installed, we can use the previous command, create a pipe, and search for the package name with grep

	
		
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		terminal("dpkg -l | grep vlc")
	
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				Deseado=desconocido(U)/Instalar/eliminaR/Purgar/retener(H)
| Estado=No/Inst/ficheros-Conf/desempaqUetado/medio-conF/medio-inst(H)/espera-disparo(W)/pendienTe-disparo
|/ Err?=(ninguno)/requiere-Reinst (Estado,Err: mayúsc.=malo)
||/ Nombre         Versión      Arquitectura Descripción
+++-==============-============-============-=================================
ii  grep           3.4-1        amd64        GNU grep, egrep and fgrep
ii  vlc            3.0.9.2-1    amd64        multimedia player and streamer

Install downloaded packages and not from repositories

On some occasions, when you want to install a program, what they do is give you a .deb file, so to install it, we use the command dpkg -i <file.deb>

User Administrator

Active user information with `id`

Using the id command, I can see which user I am

	
		
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		!id
	
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				uid=1000(wallabot) gid=1000(wallabot) grupos=1000(wallabot),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),120(lpadmin),131(lxd),132(sambashare),998(docker)

With this command, I can see my id, the group ID gid, and the groups I belong to. In Debian-based distributions, users are assigned an ID starting from 1000, while the root user is assigned ID 0

Active user information with `whoami`

Another command to find out which user I am is whoami

	
		
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		!whoami
	
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				wallabot

File with information on all users

User information is in the /etc/passwd file

	
		
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		terminal("cat /etc/passwd", max_lines_output=10)
	
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				root:x:0:0:root:/root:/bin/bash
daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin
bin:x:2:2:bin:/bin:/usr/sbin/nologin
sys:x:3:3:sys:/dev:/usr/sbin/nologin
sync:x:4:65534:sync:/bin:/bin/sync
games:x:5:60:games:/usr/games:/usr/sbin/nologin
man:x:6:12:man:/var/cache/man:/usr/sbin/nologin
lp:x:7:7:lp:/var/spool/lpd:/usr/sbin/nologin
mail:x:8:8:mail:/var/mail:/usr/sbin/nologin
news:x:9:9:news:/var/spool/news:/usr/sbin/nologin
...
sshd:x:126:65534::/run/sshd:/usr/sbin/nologin
nvidia-persistenced:x:127:135:NVIDIA Persistence Daemon,,,:/nonexistent:/usr/sbin/nologin
fwupd-refresh:x:128:136:fwupd-refresh user,,,:/run/systemd:/usr/sbin/nologin
glances:x:129:137::/var/lib/glances:/usr/sbin/nologin

Change a user's password

If you want to change a user's password, you have to use the command passwd <user> <password>. If the user is not specified, it will use whatever the command whoami returns.

Create users with `useradd`

To create a new user, use the command useradd <user name>, let's create a new user

	
		
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		!sudo useradd usertest1
	
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Let's see if it is in the file with all the users

	
		
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		!cat /etc/passwd | grep usertest
	
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				usertest1:x:1001:1001::/home/usertest1:/bin/sh

As we can see, the user has been created with id 1001, the next one after the one my wallabot user had, which was the last one

However, when creating this user, it did not ask us to assign a password. In addition, if we look at what is inside home

	
		
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		!ls /home
	
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				wallabot

Only the wallabot user folder is present, but not the test1 user folder

Create users with `adduser`

Therefore, let's look at another command for creating users that does require a password and does create a folder in home. This command is adduser

	
		
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		!sudo adduser usertest2
	
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				[sudo] contraseña para wallabot:
Añadiendo el usuario `usertest2' ...
Añadiendo el nuevo grupo `usertest2' (1002) ...
Añadiendo el nuevo usuario `usertest2' (1002) con grupo `usertest2' ...
Creando el directorio personal `/home/usertest2' ...
Copiando los ficheros desde `/etc/skel' ...
Nueva contraseña:
Vuelva a escribir la nueva contraseña:
passwd: contraseña actualizada correctamente
Cambiando la información de usuario para usertest2
Introduzca el nuevo valor, o presione INTRO para el predeterminado
Nombre completo []:
Número de habitación []:
Teléfono del trabajo []:
Teléfono de casa []:
Otro []:
¿Es correcta la información? [S/n] s

If we look in the file with all the users

	
		
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		!cat /etc/passwd | grep usertest
	
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				usertest1:x:1001:1001::/home/usertest1:/bin/sh
usertest2:x:1002:1002:,,,:/home/usertest2:/bin/bash

We see that the user usertest2 has been created

	
		
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		!ls /home
	
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				usertest2  wallabot

And we can see that a folder has been created for it in home

To delete a user, use the command userdel <username>

	
		
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		!sudo userdel usertest1
	
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		!sudo userdel usertest2
	
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Let's see if they are in the file with all the users.

	
		
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		!cat /etc/passwd | grep usertest
	
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We see that nothing appears anymore; in fact, we see the end of that file.

	
		
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		!tail /etc/passwd
	
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				geoclue:x:122:127::/var/lib/geoclue:/usr/sbin/nologin
pulse:x:123:128:PulseAudio daemon,,,:/var/run/pulse:/usr/sbin/nologin
gnome-initial-setup:x:124:65534::/run/gnome-initial-setup/:/bin/false
gdm:x:125:130:Gnome Display Manager:/var/lib/gdm3:/bin/false
wallabot:x:1000:1000:wallabot,,,:/home/wallabot:/bin/bash
systemd-coredump:x:999:999:systemd Core Dumper:/:/usr/sbin/nologin
sshd:x:126:65534::/run/sshd:/usr/sbin/nologin
nvidia-persistenced:x:127:135:NVIDIA Persistence Daemon,,,:/nonexistent:/usr/sbin/nologin
fwupd-refresh:x:128:136:fwupd-refresh user,,,:/run/systemd:/usr/sbin/nologin
glances:x:129:137::/var/lib/glances:/usr/sbin/nologin

Make an administrator user

First, we are going to create a new user, who will not be an administrator at first.

	
		
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		!sudo adduser noadmin
	
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				Añadiendo el usuario `noadmin' ...
Añadiendo el nuevo grupo `noadmin' (1001) ...
Añadiendo el nuevo usuario `noadmin' (1001) con grupo `noadmin' ...
Creando el directorio personal `/home/noadmin' ...
Copiando los ficheros desde `/etc/skel' ...
Nueva contraseña:
Vuelva a escribir la nueva contraseña:
passwd: contraseña actualizada correctamente
Cambiando la información de usuario para noadmin
Introduzca el nuevo valor, o presione INTRO para el predeterminado
Nombre completo []:
Número de habitación []:
Teléfono del trabajo []:
Teléfono de casa []:
Otro []:
¿Es correcta la información? [S/n] s

Let's see which groups the user we just created belongs to; to do this, we use the command groups <user>

	
		
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		!groups noadmin
	
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				noadmin : noadmin

As we can see, it is only in the noadmin group, which is a group that was created when the user was created

Let's see which groups my user belongs to

	
		
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		!groups wallabot
	
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				wallabot : wallabot adm cdrom sudo dip plugdev lpadmin lxd sambashare docker

As we can see, my user belongs to several more groups, including one called sudo. Users who have access to this group have administrator privileges, so for the new user we have created to have these privileges, we need to add it to the sudo group.

To add a user to a group there are two ways: one is with the command gpasswd -a <user> <group>

	
		
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		!sudo gpasswd -a noadmin sudo
	
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				Añadiendo al usuario noadmin al grupo sudo

We now see which groups the noadmin user belongs to

	
		
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		!groups noadmin
	
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				noadmin : noadmin sudo

As we can see, it already belongs to the sudo group, so it would already have administrator privileges

We remove the user noadmin from the sudo group with the command gpasswd -d <user> <group>

	
		
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		!sudo gpasswd -d noadmin sudo
	
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				Eliminando al usuario noadmin del grupo sudo

We see that noadmin no longer belongs to the sudo group

	
		
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		!groups noadmin
	
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				noadmin : noadmin

The second command to add a user to a group is usermod -aG <group> <user>

	
		
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		!sudo usermod -aG sudo noadmin
	
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We return to see which groups the user noadmin belongs to

	
		
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		!groups noadmin
	
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				noadmin : noadmin sudo

We remove the user noadmin from the sudo group and delete it

	
		
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		!sudo gpasswd -d noadmin sudo
	
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				Eliminando al usuario noadmin del grupo sudo

	
		
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		!sudo userdel noadmin
	
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Command history

`history`

If we enter the history command in the terminal, we see a history of the commands used

	
		
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		!history
	
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				1009  docker build . nvidia/cuda
1010  docker build --help
1011  docker build --build-arg nvidia/cuda
1012  docker build --build-arg [nvidia/cuda]
1013  cd ../docker/
1014  docker ps -a
1015  docker rm boring_wescoff
1016  docker compose up -d
1017  docker compose exec deepstream61 bash
1018  cd ..
    ....
1996  ps
1997  ps aux
1998  camerasIP.sh
1999  sudo su
2000  sudo useradd usertest
2001  sudo userdel usertest
2002  sudo useradd usertest
2003  sudo userdel usertest
2004  sudo su
2005  sudo apt install history
2006  history
2007  clear
2008  history

If we want to execute one of the commands from the history, we do so using !<num command>, for example, if I want to re-run command 1996

	
		
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		! !1996
	
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				    PID TTY          TIME CMD
   6610 pts/0    00:00:00 bash
  20826 pts/0    00:00:00 ps

`reverse-i-search`

A more refined way to search through the history is to press CTRL+r. When you do this, the following message will appear in the console

	
		
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		!reverse-i-search)`':
	
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So as you type, commands matching what you’ve entered will appear. For example, if I type if, the last time I used ifconfig appears.

If we enter CTRL+r again, older matches will appear.

Remove commands from history

There are commands like ls, cd, and pwd that do not add much value if they are kept in the history, so it can be configured so they are not saved in the history. To do this, we modify the ~/.bashrc file and add the line HISTIGNORE="pwd:ls:cd"

Security

Firewall `ufw`

Ubuntu comes with the ufw firewall installed, but to verify it we use the following command

	
		
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		!sudo ufw status
	
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				Estado: inactivo

As we can see, by default it is inactive, so we are going to create a set of rules. For example, let’s start by opening port 22 (SSH). To do this, we use the command sudo allow <port> comment "<coment>", which lets us open a port and add a comment

	
		
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		!sudo ufw allow 22 comment 'ssh'
	
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				Regla añadida
Regla añadida (v6)

As we can see, it has opened port 22 for IPv4 and IPv6. Now let's activate ufw with the command ufw enable

	
		
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		!sudo ufw enable
	
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				El cortafuegos está activo y habilitado en el arranque del sistema

If we want to see the rules we have in the firewall, we use the ufw status command

	
		
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		!sudo ufw enable
	
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				Hasta                      Acción      Desde
-----                      ------      -----
22                         ALLOW       Anywhere                   # ssh
22 (v6)                    ALLOW       Anywhere (v6)              # ssh

We can also tell it to show us the numbered rules with the command ufw status numbered

	
		
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		!sudo ufw status numbered
	
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				Estado: activo
     Hasta                      Acción      Desde
     -----                      ------      -----
[ 1] 22                         ALLOW IN    Anywhere                   # ssh
[ 2] 22 (v6)                    ALLOW IN    Anywhere (v6)              # ssh

Since they are numbered, we can delete one using the command ufw delete <rule number>, so to remove the rule for IPv6 we do

	
		
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		!sudo ufw delete 2
	
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				Estado: activo
Borrando:
allow 22 comment 'ssh'
¿Continuar con la operación (s|n)? s
Regla eliminada (v6)

We see the status again

	
		
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		!sudo ufw status numbered
	
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				Estado: activo
     Hasta                      Acción      Desde
     -----                      ------      -----
[ 1] 22                         ALLOW IN    Anywhere                   # ssh

We see that rule number 2 has indeed been removed.

If we want to enable SSH access from a single IP, we use the from <IP> flag

	
		
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		!sudo ufw allow from 192.168.1.103 proto tcp to any port 22 comment 'ssh ip'
	
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				Regla añadida

We check the rules again

	
		
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		!sudo ufw status numbered
	
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				Estado: activo
     Hasta                      Acción      Desde
     -----                      ------      -----
[ 1] 22                         ALLOW IN    Anywhere                   # ssh
[ 2] 22/tcp                     ALLOW IN    192.168.1.103              # ssh ip

If we want to delete all the rules, we use the reset command

	
		
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		!sudo ufw reset
	
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				Estado: activo
Reiniciando todas las reglas a sus valores predeterminados instalados.
¿Continuar con la operación (s|n)? s
Respaldando «user.rules» en «/etc/ufw/user.rules.20221205_171730»
Respaldando «before.rules» en «/etc/ufw/before.rules.20221205_171730»
Respaldando «after.rules» en «/etc/ufw/after.rules.20221205_171730»
Respaldando «user6.rules» en «/etc/ufw/user6.rules.20221205_171730»
Respaldando «before6.rules» en «/etc/ufw/before6.rules.20221205_171730»
Respaldando «after6.rules» en «/etc/ufw/after6.rules.20221205_171730»

We check the status again

	
		
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		!sudo ufw status numbered
	
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				Estado: inactivo

We see that there are no more rules

To disable the firewall, we use the ufw disable command

	
		
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		!sudo ufw disable
	
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				El cortafuegos está detenido y deshabilitado en el arranque del sistema

We check the status again

	
		
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		!sudo ufw status
	
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				Estado: inactivo

Security audit with `Lynis`

To install Lynis, you have to use the command sudo apt install lynis

To perform an audit of your system, you need to use the command lynis audit system. This starts a scan of the entire system and reports it back to you.

I’m not going to show the result of my system scan so as not to expose my vulnerabilities on the Internet

Command Scheduling

Scheduling periodic commands with `cron`

With the cron command, we can schedule commands to run periodically. To do this, we need to edit the /etc/crontab file

	
		
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		!cat /etc/crontab
	
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				# /etc/crontab: system-wide crontab
# Unlike any other crontab you don't have to run the `crontab'
# command to install the new version when you edit this file
# and files in /etc/cron.d. These files also have username fields,
# that none of the other crontabs do.
SHELL=/bin/sh
PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin
# Example of job definition:
# .---------------- minute (0 - 59)
# |  .------------- hour (0 - 23)
# |  |  .---------- day of month (1 - 31)
# |  |  |  .------- month (1 - 12) OR jan,feb,mar,apr ...
# |  |  |  |  .---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat
# |  |  |  |  |
# *  *  *  *  * user-name command to be executed
17 *	* * *	root    cd / &amp;&amp; run-parts --report /etc/cron.hourly
25 6	* * *	root	test -x /usr/sbin/anacron || ( cd / &amp;&amp; run-parts --report /etc/cron.daily )
47 6	* * 7	root	test -x /usr/sbin/anacron || ( cd / &amp;&amp; run-parts --report /etc/cron.weekly )
52 6	1 * *	root	test -x /usr/sbin/anacron || ( cd / &amp;&amp; run-parts --report /etc/cron.monthly )
#

As can be seen, in this file there is a series of commands that are executed periodically. The format of these commands is as follows

<minute> <hour> <day of the month> <month> <day of the week> <user> <command>

To properly create the date and time when you want the command to run, there are plenty of online pages that help you write it correctly, such as crontab guru

One-time command scheduling with `at`

When we want a command to be executed in the future, but we do not want it to run periodically, only once, we can use the at command. For example, you start an Azure or Amazon machine, for which you are charged, and you want to make sure it will be turned off so you do not get a surprise on the bill; you can schedule it to shut down at night. That way, even if you forget to turn it off, it will shut itself down.

We do an ls to the /tmp folder

	
		
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		!ls -l /tmp
	
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				total 60
-rw------- 1 wallabot wallabot    0 sep 24 08:51 config-err-QM3AAe
-rw-r--r-- 1 root     root     2049 sep 24 08:51 glances-root.log
drwx------ 2 wallabot wallabot 4096 sep 24 09:06 pyright-9853-BG3nXEXw0Tao
drwxrwxr-x 3 wallabot wallabot 4096 sep 24 09:06 python-languageserver-cancellation
drwx------ 3 root     root     4096 sep 24 08:51 snap-private-tmp
drwx------ 2 wallabot wallabot 4096 sep 24 08:51 ssh-mHjlSPPoqCp7
drwx------ 3 root     root     4096 sep 24 08:51 systemd-private-371a1d9479324db8bd79b6844b8b589b-colord.service-rpjPri
drwx------ 3 root     root     4096 sep 24 08:51 systemd-private-371a1d9479324db8bd79b6844b8b589b-fwupd.service-FzPoQf
drwx------ 3 root     root     4096 sep 24 08:51 systemd-private-371a1d9479324db8bd79b6844b8b589b-geoclue.service-F6pMWi
drwx------ 3 root     root     4096 sep 24 08:51 systemd-private-371a1d9479324db8bd79b6844b8b589b-ModemManager.service-Orf6Bi
drwx------ 3 root     root     4096 sep 24 08:51 systemd-private-371a1d9479324db8bd79b6844b8b589b-switcheroo-control.service-1QXRqj
drwx------ 3 root     root     4096 sep 24 08:51 systemd-private-371a1d9479324db8bd79b6844b8b589b-systemd-logind.service-lL35tg
drwx------ 3 root     root     4096 sep 24 08:51 systemd-private-371a1d9479324db8bd79b6844b8b589b-systemd-resolved.service-iaswSi
drwx------ 3 root     root     4096 sep 24 08:51 systemd-private-371a1d9479324db8bd79b6844b8b589b-systemd-timesyncd.service-Yet8lj
drwx------ 3 root     root     4096 sep 24 08:51 systemd-private-371a1d9479324db8bd79b6844b8b589b-upower.service-oTL7Gg
drwx------ 2 wallabot wallabot 4096 sep 24 09:31 tracker-extract-files.1000

Now let’s program it to create a new file in /tmp within 5 minutes

	
		
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		!at 09:55 touch /tmp/at.txt
	
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				warning: commands will be executed using /bin/sh
at&gt; touch /tmp/at.txt
at&gt; &lt;EOT&gt;
job 1 at Sun Sep 24 09:55:00 2023

As we can see, you need to write at <time> and on the next line the command you want to run

We now see the files in /tmp

	
		
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		!ls -l /tmp
	
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				total 60
-rw-rw-r-- 1 wallabot wallabot    0 sep 24 09:55 at.txt
-rw------- 1 wallabot wallabot    0 sep 24 08:51 config-err-QM3AAe
-rw-r--r-- 1 root     root     2049 sep 24 08:51 glances-root.log
drwx------ 2 wallabot wallabot 4096 sep 24 09:06 pyright-9853-BG3nXEXw0Tao
drwxrwxr-x 3 wallabot wallabot 4096 sep 24 09:06 python-languageserver-cancellation
drwx------ 3 root     root     4096 sep 24 08:51 snap-private-tmp
drwx------ 2 wallabot wallabot 4096 sep 24 08:51 ssh-mHjlSPPoqCp7
drwx------ 3 root     root     4096 sep 24 08:51 systemd-private-371a1d9479324db8bd79b6844b8b589b-colord.service-rpjPri
drwx------ 3 root     root     4096 sep 24 08:51 systemd-private-371a1d9479324db8bd79b6844b8b589b-fwupd.service-FzPoQf
drwx------ 3 root     root     4096 sep 24 08:51 systemd-private-371a1d9479324db8bd79b6844b8b589b-geoclue.service-F6pMWi
drwx------ 3 root     root     4096 sep 24 08:51 systemd-private-371a1d9479324db8bd79b6844b8b589b-ModemManager.service-Orf6Bi
drwx------ 3 root     root     4096 sep 24 08:51 systemd-private-371a1d9479324db8bd79b6844b8b589b-switcheroo-control.service-1QXRqj
drwx------ 3 root     root     4096 sep 24 08:51 systemd-private-371a1d9479324db8bd79b6844b8b589b-systemd-logind.service-lL35tg
drwx------ 3 root     root     4096 sep 24 08:51 systemd-private-371a1d9479324db8bd79b6844b8b589b-systemd-resolved.service-iaswSi
drwx------ 3 root     root     4096 sep 24 08:51 systemd-private-371a1d9479324db8bd79b6844b8b589b-systemd-timesyncd.service-Yet8lj
drwx------ 3 root     root     4096 sep 24 08:51 systemd-private-371a1d9479324db8bd79b6844b8b589b-upower.service-oTL7Gg
drwx------ 2 wallabot wallabot 4096 sep 24 09:31 tracker-extract-files.1000

As we can see, there is an at.txt file that was created at 09:55

Keyboard shortcuts

Below are a few useful keyboard shortcuts for using the terminal

Ctrl+a: moves the cursor to the beginning of the command line.
Ctrl+e: moves the cursor to the end of the command line.
Ctrl+l: clears the terminal, similar to what the clear command does.
Ctrl+u: clears from the cursor position to the beginning of the line. If at the end, clears the entire line.
Ctrl+k: clears from the cursor position to the end of the line. If at the beginning, clears the entire line.
Ctrl+h: does the same as the backspace key, deletes the character immediately before the cursor position.
Ctrl+w: deletes the word immediately before the cursor.
Alt+d or Esc+d: deletes the next word after the cursor.
Ctrl+p: sets the command line to the last command entered.
Ctrl+r: starts the search for previously used commands, typing part of a previously used command that we have executed, including options and parameters. Perform a search by pressing the key combination again and we will find earlier matches.
Ctrl+c: ends the process that is running, useful for regaining control of the system.
Ctrl+d: exits the terminal, similar to the exit command.
Ctrl+z: suspends the execution of the process that is running and puts it in the background; with the fg command, we can resume its execution.
Ctrl+t: swaps the position of the two characters before the cursor, useful for correcting typos.
Esc+t: swaps the position of the two words before the cursor, useful for correcting typos.
Alt+f: moves the cursor to the beginning of the next word on the line, the same as Ctrl+right in the GNOME terminal.
Alt+b: moves the cursor to the beginning of the previous word on the line, the same as Ctrl+left in the GNOME terminal.
Tab: auto-completes commands or directory or file paths.
Ctrl+Shift+F: opens a dialog to search for text in the terminal output.
Ctrl+Shift+g: searches for the next occurrence of the previous search in the terminal.
Ctrl+Shift+h: searches for the previous occurrence of the previous search in the terminal.
Ctrl+Shift+c: copies the selected terminal text to the clipboard.
Ctrl+Shift+v: pastes the clipboard text into the command line.
Up: sets in the command line the previous command from the history, just like Ctrl+p.
Down: sets the next command from the history in the command line.
Left Mouse: selects lines of text from the terminal.
Ctrl+Left Mouse: selects blocks of text in the terminal.

Folder system in Linux

In the following image, we can see what the folder system in Linux looks like

This image has been taken from the post on LinkedIn by Roberto Morais

Oddities

You forgot to use sudo

Has it ever happened to you that you were about to use a command that needed to be run with sudo, but you forgot to type sudo? Well, after receiving the corresponding error, if you run sudo !!, the previous command will be executed with sudo

	
		
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		!apt update
	
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				Leyendo lista de paquetes... Hecho
E: No se pudo abrir el fichero de bloqueo «/var/lib/apt/lists/lock» - open (13: Permiso denegado)
E: No se pudo bloquear el directorio /var/lib/apt/lists/
W: Se produjo un problema al desligar el fichero /var/cache/apt/pkgcache.bin - RemoveCaches (13: Permiso denegado)
W: Se produjo un problema al desligar el fichero /var/cache/apt/srcpkgcache.bin - RemoveCaches (13: Permiso denegado)

As can be seen, when running sudo update we get an error, but if we now run sudo !! it will execute sudo apt update

	
		
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		!sudo !!
	
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				[sudo] contraseña para wallabot:

Kernel messages

With the dmesg command (display kernel ring buffer messages) we can view the kernel messages. For example, this is very useful for seeing whether a USB device has been connected, or for debugging hardware errors on our computer

	
		
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		!dmesg | tail
	
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				[   35.812312] input: LogiOps Virtual Input as /devices/virtual/input/input33
[   35.916406] input: LogiOps Virtual Input as /devices/virtual/input/input34
[   36.002064] input: LogiOps Virtual Input as /devices/virtual/input/input35
[   63.879806] input: MX Master 3 as /devices/virtual/misc/uhid/0005:046D:B023.0006/input/input36
[   63.879931] logitech-hidpp-device 0005:046D:B023.0006: input,hidraw3: BLUETOOTH HID v0.15 Keyboard [MX Master 3] on 4c:77:cb:1d:66:d0
[   63.902120] logitech-hidpp-device 0005:046D:B023.0006: HID++ 4.5 device connected.
[   69.604899] input: MX Keys Keyboard as /devices/virtual/misc/uhid/0005:046D:B35B.0007/input/input37
[   69.605221] input: MX Keys Mouse as /devices/virtual/misc/uhid/0005:046D:B35B.0007/input/input38
[   69.606204] hid-generic 0005:046D:B35B.0007: input,hidraw4: BLUETOOTH HID v0.13 Keyboard [MX Keys] on 4c:77:cb:1d:66:d0
[  188.285030] input: T9 (AVRCP) as /devices/virtual/input/input40

With the --follow flag, we can see in real time the new messages that are generated.

	
		
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		!dmesg --follow
	
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				[    0.000000] Linux version 5.15.0-84-generic (buildd@lcy02-amd64-005) (gcc (Ubuntu 9.4.0-1ubuntu1~20.04.2) 9.4.0, GNU ld (GNU Binutils for Ubuntu) 2.34) #93~20.04.1-Ubuntu SMP Wed Sep 6 16:15:40 UTC 2023 (Ubuntu 5.15.0-84.93~20.04.1-generic 5.15.116)
[    0.000000] Command line: BOOT_IMAGE=/boot/vmlinuz-5.15.0-84-generic root=UUID=59002381-d88d-44a6-b83d-8c5a226ce058 ro quiet splash vt.handoff=7
[    0.000000] KERNEL supported cpus:
[    0.000000]   Intel GenuineIntel
[    0.000000]   AMD AuthenticAMD
[    0.000000]   Hygon HygonGenuine
[    0.000000]   Centaur CentaurHauls
[    0.000000]   zhaoxin   Shanghai
[    0.000000] BIOS-provided physical RAM map:
[    0.000000] BIOS-e820: [mem 0x0000000000000000-0x000000000009ffff] usable
[    0.000000] BIOS-e820: [mem 0x00000000000a0000-0x00000000000fffff] reserved
[    0.000000] BIOS-e820: [mem 0x0000000000100000-0x0000000009d01fff] usable
[    0.000000] BIOS-e820: [mem 0x0000000009d02000-0x0000000009ffffff] reserved
[    0.000000] BIOS-e820: [mem 0x000000000a000000-0x000000000a1fffff] usable
[    0.000000] BIOS-e820: [mem 0x000000000a200000-0x000000000a20bfff] ACPI NVS
[    0.000000] BIOS-e820: [mem 0x000000000a20c000-0x00000000b8983fff] usable
[    0.000000] BIOS-e820: [mem 0x00000000b8984000-0x00000000b8acdfff] reserved
[    0.000000] BIOS-e820: [mem 0x00000000b8ace000-0x00000000b8c56fff] ACPI data
[    0.000000] BIOS-e820: [mem 0x00000000b8c57000-0x00000000b9107fff] ACPI NVS
[    0.000000] BIOS-e820: [mem 0x00000000b9108000-0x00000000ba55cfff] reserved
[    0.000000] BIOS-e820: [mem 0x00000000ba55d000-0x00000000bcffffff] usable
[    0.000000] BIOS-e820: [mem 0x00000000bd000000-0x00000000bfffffff] reserved
[    0.000000] BIOS-e820: [mem 0x00000000f8000000-0x00000000fbffffff] reserved
...
[   35.916406] input: LogiOps Virtual Input as /devices/virtual/input/input34
[   36.002064] input: LogiOps Virtual Input as /devices/virtual/input/input35
[   63.879806] input: MX Master 3 as /devices/virtual/misc/uhid/0005:046D:B023.0006/input/input36
[   63.879931] logitech-hidpp-device 0005:046D:B023.0006: input,hidraw3: BLUETOOTH HID v0.15 Keyboard [MX Master 3] on 4c:77:cb:1d:66:d0
[   63.902120] logitech-hidpp-device 0005:046D:B023.0006: HID++ 4.5 device connected.
[   69.604899] input: MX Keys Keyboard as /devices/virtual/misc/uhid/0005:046D:B35B.0007/input/input37
[   69.605221] input: MX Keys Mouse as /devices/virtual/misc/uhid/0005:046D:B35B.0007/input/input38
[   69.606204] hid-generic 0005:046D:B35B.0007: input,hidraw4: BLUETOOTH HID v0.13 Keyboard [MX Keys] on 4c:77:cb:1d:66:d0
[  188.285030] input: T9 (AVRCP) as /devices/virtual/input/input40

>_ Output

^C

Hardware Information

With lshw we can see information about our computer's hardware

	
		
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		!lshw
	
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				AVISO: debería ejecutar este programa como superusuario.
wallabot
    descripción: Computer
    anchura: 64 bits
    capacidades: smp vsyscall32
  *-core
       descripción: Motherboard
       id físico: 0
     *-memory
          descripción: Memoria de sistema
          id físico: 0
          tamaño: 32GiB
...
          producto: PnP device PNP0501
          id físico: 6
          capacidades: pnp
          configuración: driver=serial
     *-pnp00:05
          producto: PnP device PNP0c02
          id físico: 7
          capacidades: pnp
          configuración: driver=system
AVISO: la salida puede ser incompleta o imprecisa, debería ejecutar este programa como superusuario.

Cowsay

There is a command called cowsay that takes a text as a parameter and draws a cow saying that text.

It’s possible that you don’t have it installed, so to install it, you need to enter the command

sudo apt install cowsay

	
		
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		terminal("cowsay MaximoFN")
	
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>_ Output

			
				__________
< MaximoFN >
----------
        \   ^__^
         \  (oo)\_______
            (__)\       )\/\
                ||----w |
                ||     ||

If you add the -f dragon flag, the speaker is a dragon.

	
		
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		terminal("cowsay -f dragon MaximoFN")
	
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>_ Output

			
				__________
< MaximoFN >
----------
      \                    / \  //\
       \    |\___/|      /   \//  \\
            /0  0  \__  /    //  | \ \
           /     /  \/_/    //   |  \  \
           @_^_@'/   \/_   //    |   \   \
           //_^_/     \/_ //     |    \    \
        ( //) |        \///      |     \     \
      ( / /) _|_ /   )  //       |      \     _\
    ( // /) '/,_ _ _/  ( ; -.    |    _ _\.-~        .-~~~^-.
  (( / / )) ,-{        _      `-.|.-~-.           .~         `.
(( // / ))  '/\      /                 ~-. _ .-~      .-~^-.  \
(( /// ))      `.   {            }                   /      \  \
  (( / ))     .----~-.\        \-'                 .~         \  `. \^-.
             ///.----..>        \             _ -~             `.  ^-`  ^-_
               ///-._ _ _ _ _ _ _}^ - - - - ~                     ~-- ,.-~
                                                                  /.-~

	
		
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		terminal("cowsay -f dragon-and-cow MaximoFN")
	
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>_ Output

			
				__________
< MaximoFN >
----------
                       \                    ^    /^
                        \                  / \  // \
                         \   |\___/|      /   \//  .\
                          \  /O  O  \__  /    //  | \ \           *----*
                            /     /  \/_/    //   |  \  \          \   |
                            @___@`    \/_   //    |   \   \         \/\ \
                           0/0/|       \/_ //     |    \    \         \  \
                       0/0/0/0/|        \///      |     \     \       |  |
                    0/0/0/0/0/_|_ /   (  //       |      \     _\     |  /
                 0/0/0/0/0/0/`/,_ _ _/  ) ; -.    |    _ _\.-~       /   /
                             ,-}        _      *-.|.-~-.           .~    ~
            \     \__/        `/\      /                 ~-. _ .-~      /
             \____(oo)           *.   }            {                   /
             (    (--)          .----~-.\        \-`                 .~
             //__\\  \__ Ack!   ///.----..<        \             _ -~
            //    \\               ///-._ _ _ _ _ _ _{^ - - - - ~

Cleaning

Since the prueba folder has been created, we delete it to leave everything as we found it.

	
		
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		!rm -r prueba
	
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Continue reading

Deep Research with LangGraph (3/3): the Writer agent and final report

Third and final part of the Deep Research with LangGraph series. Implement the Writer agent that drafts the final report from the research, assemble the full deep researcher graph, and run the complete assistant end to end.

Deep Research with LangGraph (2/3): the multi-agent Research Supervisor

Second part of the Deep Research with LangGraph series. Build the Research Supervisor that coordinates several Researche...

Deep Research with LangGraph (1/3): Scope and Researcher agents

First part of the series on building an AI research assistant with LangGraph. Learn the system architecture and build th...

Last posts -->

Have you seen these projects?

Gymnasia

Horeca chatbot

Naviground

View all projects -->

>_ Available for projects

Do you have an AI project?

Let's talk.

maximofn@gmail.com

Machine Learning and AI specialist. I develop solutions with generative AI, intelligent agents and custom models.

Write me LinkedIn

Do you want to watch any talk?

Tomorrow's Agents: Deciphering the Mysteries of Planning, UX and Memory

AI agents, powered by LLMs, promise to transform applications. But are they simple executors today or future intelligent collaborators? To reach their...

Create your own Apple intelligence

Learn to create an IA system to execute efficiently on a device

Last talks -->

Do you want to improve with these tips?

Best practices building agents with Claude Code

Technical talk: skills, subagents, slash commands and MCPs in Claude Code

o1 prompt engineering

Create better prompts for o1 following an example

Memory profiler

See the memory usage of a script

Last tips -->

Use this locally

Hugging Face spaces allow us to run models with very simple demos, but what if the demo breaks? Or if the user deletes it? That's why I've created docker containers with some interesting spaces, to be able to use them locally, whatever happens. In fact, if you click on any project view button, it may take you to a space that doesn't work.

Flow edit

FLUX.1-RealismLora

token_hmr

View all containers -->

>_ Available for projects

Do you have an AI project?

Let's talk.

maximofn@gmail.com

Machine Learning and AI specialist. I develop solutions with generative AI, intelligent agents and custom models.

Write me LinkedIn

Do you want to train your model with these datasets?

short-jokes-dataset

HuggingFace

Dataset with jokes in English

Use: Fine-tuning text generation models for humor

231K rows 2 columns 45 MB

View on HuggingFace →

opus100

HuggingFace

Dataset with translations from English to Spanish

Use: Training English-Spanish translation models

1M rows 2 columns 210 MB

View on HuggingFace →

netflix_titles

HuggingFace

Dataset with Netflix movies and series

Use: Netflix catalog analysis and recommendation systems

8.8K rows 12 columns 3.5 MB

View on HuggingFace →

View more datasets -->

RAM memory management

Hard Drive Management

Interface management

Package management

PPA Repositories (Personal Package Archives)

Add repositories

Update the repositories

Update the packages

Update the kernel

Package search

List of installed packages

Install downloaded packages and not from repositories

User Administrator

Active user information with id

Active user information with whoami

File with information on all users

Change a user's password

Create users with useradd

Create users with adduser

Make an administrator user

Command history

history

reverse-i-search

Remove commands from history

Security

Firewall ufw

Security audit with Lynis

Command Scheduling

Scheduling periodic commands with cron

One-time command scheduling with at

Keyboard shortcuts

Folder system in Linux

Oddities

You forgot to use sudo

Kernel messages

Hardware Information

Cowsay

Cleaning

Continue reading

Deep Research with LangGraph (3/3): the Writer agent and final report

Deep Research with LangGraph (2/3): the multi-agent Research Supervisor

Deep Research with LangGraph (1/3): Scope and Researcher agents

Have you seen these projects?

Do you have an AI project?

Do you want to watch any talk?

Tomorrow's Agents: Deciphering the Mysteries of Planning, UX and Memory

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Do you want to improve with these tips?

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o1 prompt engineering

Memory profiler

Use this locally

Do you have an AI project?

Do you want to train your model with these datasets?

short-jokes-dataset

opus100

netflix_titles

Active user information with `id`

Active user information with `whoami`

Create users with `useradd`

Create users with `adduser`

`history`

`reverse-i-search`

Firewall `ufw`

Security audit with `Lynis`

Scheduling periodic commands with `cron`

One-time command scheduling with `at`