Basic Linux: 200 Essential Terminal Commands

Every server you will administer, every container you will debug and a good part of the tools you use run on Linux. Learning the terminal stops being optional very quickly.

These 200 commands are the foundation: navigating, reading, editing, granting permissions, killing a process, installing a package, checking the disk, testing the network, archiving and searching. The examples use Debian/Ubuntu as the reference, with the RHEL/Fedora variation noted where it differs.

A tip that saves hours: Tab completes names, Ctrl+R searches the history and man command (or command --help) answers before Google does.

Contents

• 1–25 · Navigation and files
• 26–45 · Viewing and editing content
• 46–63 · Permissions and ownership
• 64–75 · Users and groups
• 76–93 · Processes
• 94–108 · Packages and programs
• 109–123 · Disk and space
• 124–138 · Basic networking
• 139–153 · Archiving and transfer
• 154–173 · Finding files and content
• 174–190 · The shell day to day
• 191–200 · Date, time and system information

Navigation and files

Where you are, what is here and how to move things around.

1. pwd — where am I

Shows the current directory in full.

pwd

2. ls — list

The most used command in the terminal.

ls

3. ls -l — detailed listing

Permissions, owner, size and date of each item.

ls -l

4. ls -la — include hidden files

Files starting with a dot only show up with -a.

ls -la

5. ls -lh — readable size

-h swaps bytes for KB, MB and GB.

ls -lh

6. ls sorted by date

Most recent first — great for finding what has just changed.

ls -lt
ls -ltr   # oldest first

7. cd — change directory

Navigates to the given path.

cd /var/log

8. cd shortcuts

Home, previous, up. The three you use the most.

cd ~     # the user's home
cd -     # the previous directory
cd ..    # one level up

9. Absolute vs relative path

Starting with / is absolute; without it, it starts from where you are.

cd /etc/nginx        # absolute
cd nginx/conf.d      # relative

10. mkdir — create a directory

Creates a folder.

mkdir projetos

11. mkdir -p — create the tree

Creates any missing parents and does not complain if it already exists.

mkdir -p projetos/api/src

12. touch — create an empty file

Creates the file or updates its modification date.

touch notas.txt

13. cp — copy

Copies a file, keeping the original.

cp origem.txt destino.txt

14. cp -r — copy a directory

-r is mandatory for folders.

cp -r projetos/ backup-projetos/

15. cp preserving attributes

-a keeps permissions, owner and dates. The right way to copy a backup.

cp -a /var/www/ /backup/www/

16. mv — move and rename

The same command does both.

mv antigo.txt novo.txt
mv relatorio.pdf ~/Documentos/

17. rm — remove

There is no recycle bin. What goes from here is gone.

rm arquivo.txt

18. rm -r — remove a directory

Removes recursively.

rm -r pasta-antiga/

19. rm -i — confirm first

Asks about each file. The habit is worth having on a server.

rm -i *.log

20. Careful with rm -rf

One extra space wipes the system. Check the path twice before Enter.

rm -rf /caminho/certo    # check first
# rm -rf / caminho      <- the space here wipes everything

21. ln -s — symbolic link

A shortcut pointing at another path.

ln -s /var/www/site /home/user/site

22. tree — directory tree

Visualises the structure; -L limits the depth.

tree -L 2

23. basename and dirname

They separate the file name from the path. Heavily used in scripts.

basename /var/log/syslog    # syslog
dirname /var/log/syslog     # /var/log

24. realpath — the real path

Resolves links and relative paths down to the absolute path.

realpath ../projeto

25. Wildcards (globbing)

The shell expands the pattern before the command runs.

ls *.log            # ends in .log
ls arquivo?.txt     # any single character
ls dados[1-3].csv   # a range

Viewing and editing content

Reading a big file without freezing the terminal and editing without leaving SSH.

26. cat — show the file

Dumps the whole content. Careful with a large file.

cat /etc/hostname

27. cat -n — number the lines

Makes it easier to talk about line X of the file.

cat -n script.sh

28. less — paged reader

The right way to open a large file. q exits, / searches, G goes to the end.

less /var/log/syslog

29. head — the start of the file

The first 10 lines by default.

head arquivo.csv
head -n 50 arquivo.csv

30. tail — the end of the file

The last lines — where the recent error usually is.

tail -n 100 /var/log/nginx/error.log

31. tail -f — follow live

Follows the file as it grows. The on-call command.

tail -f /var/log/nginx/access.log

32. tail -F

Like -f, but it survives log rotation.

tail -F /var/log/app.log

33. wc — count

Lines, words and bytes.

wc -l acesso.log     # lines
wc -w texto.txt      # words
wc -c arquivo.bin    # bytes

34. nano — simple editor

For when you just need to edit and get out. Ctrl+O saves, Ctrl+X exits.

nano /etc/hosts

35. vim — the omnipresent editor

It is on any server. i inserts, Esc leaves the mode, :wq saves and closes, :q! exits without saving.

vim /etc/nginx/nginx.conf

36. sort — sort

Sorts the lines; -n numeric, -r reverse.

sort nomes.txt
sort -nr valores.txt

37. uniq — remove repeats

It only works on adjacent lines — combine it with sort.

sort acessos.log | uniq
sort acessos.log | uniq -c | sort -nr   # a ranking

38. cut — cut out columns

Extracts fields by delimiter or position.

cut -d: -f1 /etc/passwd        # users
cut -c1-10 arquivo.txt         # the first 10 characters

39. tr — swap characters

Converts or removes characters from the stream.

echo "texto" | tr 'a-z' 'A-Z'
tr -d '\r' < arquivo-windows.txt > arquivo-unix.txt

40. diff — compare files

Shows what changed between two files.

diff config-antigo.conf config-novo.conf
diff -u a.txt b.txt   # unified format, as in git

41. nl — number the lines

Like cat -n, with more formatting options.

nl arquivo.txt

42. split — split a file

Breaks a large file into pieces.

split -l 1000 grande.csv parte_

43. md5sum and sha256sum

They verify the integrity of a download.

sha256sum imagem.iso
sha256sum -c checksums.txt

44. file — what type of file is it

Finds out the real type, ignoring the extension.

file documento.pdf
file *

45. stat — metadata

Size, permissions, owner and the file's three dates.

stat arquivo.txt

Permissions and ownership

The Unix security model: who can read, write and execute what.

46. Reading the permissions

-rwxr-xr--: type, owner, group and others. r=4, w=2, x=1.

ls -l arquivo.sh
# -rwxr-xr--  owner: rwx (7) | group: r-x (5) | others: r-- (4)

47. Numeric chmod

The most common form: three digits, one per class.

chmod 644 arquivo.txt    # owner reads/writes, the rest read
chmod 755 script.sh      # everyone executes, only the owner writes
chmod 600 ~/.ssh/id_ed25519   # only the owner, and nothing else

48. Symbolic chmod

Adds or removes a permission without recalculating everything.

chmod +x script.sh
chmod u+w,go-w arquivo.txt
chmod a-x binario

49. Recursive chmod

Applies to the whole tree. Take care not to hand out 777 on the server.

chmod -R 755 /var/www/site

50. Different permissions for folders and files

A directory needs x to be traversed; a file does not.

find /var/www -type d -exec chmod 755 {} \;
find /var/www -type f -exec chmod 644 {} \;

51. chown — change the owner

Only root can hand a file to another user.

sudo chown www-data arquivo.html
sudo chown www-data:www-data -R /var/www

52. chgrp — change the group

Changes only the owning group.

sudo chgrp desenvolvedores projeto/

53. umask — default permissions

Defines what is subtracted from the permissions of new files.

umask         # 0022 is the default
umask 0077    # new files for the owner only

54. The SUID bit

Runs with the file's owner, not with whoever called it. That is why passwd works.

ls -l /usr/bin/passwd    # -rwsr-xr-x
sudo chmod u+s programa

55. The SGID bit

On a directory, it makes every file created inherit the folder's group.

sudo chmod g+s /projetos/compartilhado

56. The sticky bit

In a shared folder, only the owner deletes their own file. It is what protects /tmp.

ls -ld /tmp      # drwxrwxrwt
sudo chmod +t /pasta-compartilhada

57. ACL — fine-grained permissions

It goes beyond owner/group/others: permissions per specific user.

setfacl -m u:jhonatan:rw arquivo.txt
getfacl arquivo.txt

58. Attributes with chattr

+i makes the file immutable — not even root can change it without removing the attribute.

sudo chattr +i /etc/resolv.conf
lsattr /etc/resolv.conf
sudo chattr -i /etc/resolv.conf

59. sudo — run as root

It asks for your password and records in the log who did what.

sudo apt update

60. sudo -i and su

They open a root shell. Prefer a targeted sudo command.

sudo -i
su - outro-usuario

61. Repeat the last command with sudo

The most satisfying shortcut in the terminal.

sudo !!

62. See what you are allowed to run

Lists your user's sudo permissions.

sudo -l

63. Never use 777

Full permission for any user on the system. There is nearly always an owner/group combination that solves it.

# instead of: chmod -R 777 /var/www
sudo chown -R www-data:www-data /var/www
sudo chmod -R 755 /var/www

Users and groups

Who exists on the machine and what each one can do.

64. whoami and id

Who you are and which groups you belong to.

whoami
id
id jhonatan

65. who and w

Who is connected right now; w also shows what they are running.

who
w

66. last — login history

The last accesses to the machine — the first stop in an audit.

last
last -n 20

67. useradd / adduser

adduser (Debian) is interactive and creates a home; useradd is the raw command.

sudo adduser maria
sudo useradd -m -s /bin/bash maria

68. passwd — set a password

Changes your own password or another user's (as root).

passwd
sudo passwd maria

69. usermod — modify a user

Adds to groups, changes the shell, moves the home.

sudo usermod -aG sudo maria      # -a is mandatory so as NOT to remove the other groups
sudo usermod -s /bin/zsh maria

70. userdel — remove a user

-r also deletes the home folder.

sudo userdel maria
sudo userdel -r maria

71. groupadd and groups

Creates a group and lists a user's groups.

sudo groupadd desenvolvedores
groups maria

72. /etc/passwd and /etc/group

Where users and groups are recorded (the password lives in /etc/shadow).

cat /etc/passwd | cut -d: -f1,3,7
cat /etc/group

73. Lock and unlock an account

Prevents login without deleting the user.

sudo usermod -L maria    # locks
sudo usermod -U maria    # unlocks

74. Password expiry

A policy of periodic changes.

sudo chage -l maria
sudo chage -M 90 maria   # expires in 90 days

75. A service user

No shell and no login: an application does not need interactive access.

sudo useradd -r -s /usr/sbin/nologin app

Processes

What is running, how much it consumes and how to stop it.

76. ps aux — everything that is running

The full process listing, with CPU and memory.

ps aux

77. ps with a filter

Combined with grep, it finds the specific process.

ps aux | grep nginx

78. ps as a tree

Shows the hierarchy of parents and children.

ps auxf
pstree -p

79. top — real-time monitor

It refreshes on its own. q exits, k kills, M sorts by memory.

top

80. htop — a better top

Colourful, with scrolling and mouse support. Worth installing on every server.

htop

81. kill — terminate a process

Sends SIGTERM (15): it asks the process to shut down properly.

kill 12345

82. kill -9 — force it

SIGKILL cannot be ignored, but the process saves nothing. Use it last.

kill -9 12345

83. pkill and killall

They kill by name, with no need for the PID.

pkill nginx
killall firefox

84. pgrep — find the PID

Looks for a process by name.

pgrep -a nginx

85. Run in the background

& releases the process; jobs lists them; fg brings one back.

./script-longo.sh &
jobs
fg %1

86. nohup — survive the logout

The process keeps going after you close the SSH session.

nohup ./backup.sh > backup.log 2>&1 &

87. Ctrl+Z and bg

Suspends the foreground process and resumes it in the background.

# Ctrl+Z suspends
bg      # continues in the background
fg      # brings it back

88. nice — priority

Runs at a lower priority, so as not to disturb the rest.

nice -n 19 ./tarefa-pesada.sh
renice -n 10 -p 12345

89. timeout — limit the duration

Kills the command if it runs over time.

timeout 30s ./script.sh

90. watch — repeat a command

Runs it every N seconds and shows the updated result.

watch -n 2 'df -h /'

91. lsof — open files

Finds out who is using a file or a port.

lsof /var/log/app.log
sudo lsof -i :8080

92. uptime and load average

How long the machine has been up and the load over 1, 5 and 15 minutes.

uptime

93. free — memory

Memory used, free and cached. available is the number that matters.

free -h

Packages and programs

Installing, updating and removing software on your distribution.

94. apt update

Updates the package list. It does not install anything.

sudo apt update

95. apt upgrade

Updates the installed packages.

sudo apt upgrade
sudo apt full-upgrade

96. apt install

Installs one or several packages.

sudo apt install -y htop curl git

97. apt remove and purge

remove takes the program away; purge takes the configuration files with it.

sudo apt remove nginx
sudo apt purge nginx

98. apt autoremove

Removes dependencies that have been left orphaned.

sudo apt autoremove

99. apt search and show

Searches for and details a package before installing it.

apt search postgresql
apt show postgresql-16

100. apt list --installed

Everything installed on the machine.

apt list --installed | less

101. dnf / yum — RHEL and Fedora

The equivalents of apt in the Red Hat world.

sudo dnf install htop
sudo dnf update
sudo dnf remove htop

102. pacman — Arch

Arch Linux's package manager.

sudo pacman -S htop
sudo pacman -Syu

103. dpkg and rpm

They install a local package, without resolving dependencies automatically.

sudo dpkg -i pacote.deb
sudo apt install -f        # fixes the dependencies
sudo rpm -i pacote.rpm

104. snap and flatpak

Universal formats, with the application sandboxed.

sudo snap install code --classic
flatpak install flathub org.gimp.GIMP

105. which and whereis

Where the binary that will run actually is.

which python3
whereis nginx

106. type — what is this

Tells you whether it is a binary, an alias, a function or a shell builtin.

type ls
type cd

107. Repository and key

Adds a third-party source with its signing key.

curl -fsSL https://exemplo.com/key.gpg | sudo gpg --dearmor -o /usr/share/keyrings/exemplo.gpg
echo "deb [signed-by=/usr/share/keyrings/exemplo.gpg] https://exemplo.com/apt stable main" | sudo tee /etc/apt/sources.list.d/exemplo.list

108. Clear the apt cache

Frees space on a tight server.

sudo apt clean
sudo apt autoclean

Disk and space

The most common question on a server: who filled the disk?

109. df -h — space per partition

An overview of the disk. The first command when something stops writing.

df -h

110. df -i — inodes

A disk can fill up with files even with free space. Millions of tiny files exhaust the inodes.

df -i

111. du — directory size

How much each folder takes up.

du -sh /var/log

112. du sorted

The recipe for finding the space villain.

du -h --max-depth=1 /var | sort -hr | head -20

113. ncdu — space browser

Interactive: you browse and delete right there. Worth installing.

ncdu /var

114. The biggest files

Finds the large files in one go.

find / -type f -size +500M -exec ls -lh {} \; 2>/dev/null

115. lsblk — disks and partitions

A tree of block devices.

lsblk
lsblk -f   # with the filesystem and UUID

116. mount — mount

Connects a device to a directory.

sudo mount /dev/sdb1 /mnt/dados
mount | column -t

117. umount — unmount

It fails if something is using it; lsof reveals who.

sudo umount /mnt/dados
sudo lsof +D /mnt/dados

118. /etc/fstab

Mounts applied at boot. A mistake here can stop the machine from coming up.

cat /etc/fstab
sudo mount -a   # tests fstab without rebooting

119. Space taken by logs

Logs are usually the first suspect.

sudo du -sh /var/log/*
sudo journalctl --disk-usage

120. File deleted but the space does not come back

A process still holding the file open keeps the space until it is restarted.

sudo lsof | grep deleted

121. Clear the system cache

Space that is easy to recover in an emergency.

sudo apt clean
sudo journalctl --vacuum-time=7d

122. Create a test file

Generates a file of a set size to test the disk.

dd if=/dev/zero of=teste.img bs=1M count=100
fallocate -l 1G teste.img

123. Write speed

A quick I/O test of the disk.

dd if=/dev/zero of=teste bs=1M count=1024 oflag=direct

Basic networking

Finding out the IP, testing the connection and seeing what is listening.

124. ip a — addresses

The modern replacement for ifconfig.

ip a
ip -br a   # the short version

125. ip r — routes

Shows the default gateway and the configured routes.

ip r

126. ping — does the host answer?

The first connectivity test.

ping -c 4 google.com

127. curl — HTTP request

The Swiss army knife of the web on the command line.

curl https://api.exemplo.com/status
curl -I https://exemplo.com          # the headers only
curl -s -o /dev/null -w "%{http_code}\n" https://exemplo.com

128. curl with a method and a body

Tests an API without leaving the terminal.

curl -X POST https://api.exemplo.com/itens \
  -H "Content-Type: application/json" \
  -d '{"nome":"teste"}'

129. wget — download a file

A resilient download, with resume.

wget https://exemplo.com/arquivo.tar.gz
wget -c https://exemplo.com/grande.iso   # continues an interrupted download

130. ss — ports and connections

The replacement for netstat. It shows who is listening.

ss -tuln
sudo ss -tulpn   # with the process owning the port

131. Find out who is using the port

The answer to "address already in use".

sudo ss -tulpn | grep :8080
sudo lsof -i :8080

132. dig — query DNS

Resolves a name and shows the full answer.

dig exemplo.com
dig +short exemplo.com
dig @8.8.8.8 exemplo.com

133. host and nslookup

Simpler DNS queries.

host exemplo.com
nslookup exemplo.com

134. traceroute

Shows the path to the destination and where the latency shows up.

traceroute exemplo.com
mtr exemplo.com   # a continuous traceroute

135. Public IP

The address your machine appears with on the internet.

curl -s ifconfig.me
curl -s https://api.ipify.org

136. hostname

The machine's name on the network.

hostname
hostname -I         # IPs
sudo hostnamectl set-hostname servidor01

137. /etc/hosts

Local resolution, before DNS. Great for testing before pointing the domain.

cat /etc/hosts
# 192.168.0.10  meu-site.local

138. Test a remote port

Checks whether the port is open on the other side.

nc -zv exemplo.com 443
timeout 3 bash -c "</dev/tcp/exemplo.com/443" && echo aberta

Archiving and transfer

Packing, compressing and moving files between machines.

139. tar — create an archive

creates, z compresses with gzip, verbose, file.

tar -czvf backup.tar.gz pasta/

140. tar — extract

x extracts. -C chooses the destination.

tar -xzvf backup.tar.gz
tar -xzvf backup.tar.gz -C /destino

141. tar — list without extracting

Check the contents before unpacking.

tar -tzvf backup.tar.gz

142. tar excluding folders

A backup without node_modules or .git.

tar -czvf app.tar.gz --exclude=node_modules --exclude=.git app/

143. Stronger compression

xz and zstd compress better; zstd is much faster.

tar -cJvf backup.tar.xz pasta/
tar --zstd -cvf backup.tar.zst pasta/

144. gzip and gunzip

Compresses a single file (replacing the original).

gzip arquivo.log
gunzip arquivo.log.gz
zcat arquivo.log.gz | less   # reads it without decompressing

145. zip and unzip

A universal format, compatible with Windows.

zip -r pasta.zip pasta/
unzip pasta.zip -d destino/

146. scp — copy over SSH

Transfers between machines using the SSH connection.

scp arquivo.txt usuario@servidor:/caminho/
scp -r pasta/ usuario@servidor:/caminho/
scp usuario@servidor:/caminho/arquivo.txt .

147. rsync — synchronise

Copies only the difference and resumes where it left off. Better than scp for volume.

rsync -avz pasta/ usuario@servidor:/destino/

148. rsync with deletion

Mirrors the destination, deleting whatever no longer exists at the source.

rsync -avz --delete --exclude=node_modules ./site/ usuario@servidor:/var/www/site/

149. rsync simulating

--dry-run shows what it would do, without doing it. Always use it before --delete.

rsync -avzn --delete origem/ destino/

150. rsync with progress

Follows the transfer of a large file.

rsync -avz --progress grande.iso usuario@servidor:/dados/

151. sftp

An interactive transfer session over SSH.

sftp usuario@servidor
# get arquivo.txt / put local.txt / ls / bye

152. Transfer with tar over SSH

Packs, sends and unpacks on the other side, with no intermediate file.

tar -czf - pasta/ | ssh usuario@servidor "tar -xzf - -C /destino"

153. Backup with the date in the name

A simple pattern that avoids overwriting a backup.

tar -czf backup-$(date +%F-%H%M).tar.gz /var/www

Finding files and content

find searches by attributes; grep searches inside the content.

154. find by name

The most common search.

find /var -name "*.log"
find . -iname "readme*"   # without distinguishing case

155. find by type

File (f), directory (d) or link (l).

find /etc -type f -name "*.conf"
find /var -type d -name "cache"

156. find by size

+ larger, - smaller.

find / -type f -size +100M
find . -type f -size -1k

157. find by date

Modified in the last days or minutes.

find /var/log -mtime -1      # the last 24 h
find /tmp -mmin -30          # the last 30 min

158. find by owner and permission

Auditing: files belonging to a user or with a dangerous permission.

find /home -user maria
find / -perm -4000 -type f 2>/dev/null   # SUID binaries

159. find with an action

-exec runs a command on each result; -delete removes it.

find /tmp -name "*.tmp" -mtime +7 -delete
find . -name "*.sh" -exec chmod +x {} \;

160. find with xargs

Faster than -exec on many files. -print0/-0 handles names with spaces.

find . -name "*.log" -print0 | xargs -0 rm

161. find limiting the depth

Avoids sweeping the whole tree.

find /var -maxdepth 2 -name "*.conf"

162. locate — instant search

It queries an index; far faster, but out of date until the next updatedb.

locate nginx.conf
sudo updatedb

163. grep — search for text

Looks for the pattern inside the files.

grep "erro" /var/log/syslog

164. Recursive grep

Sweeps the entire directory tree.

grep -r "TODO" src/

165. grep without distinguishing case

-i ignores the case.

grep -i "error" app.log

166. grep with the line number

-n says where it is.

grep -n "senha" config.py

167. Inverted grep

-v shows what does not match — great for filtering out noise.

grep -v "DEBUG" app.log

168. grep with context

Lines before and after the hit.

grep -B 3 -A 5 "Exception" app.log
grep -C 3 "Exception" app.log

169. grep counting

-c counts the occurrences; -l lists only the files.

grep -c "404" access.log
grep -rl "senha" /etc

170. grep with a whole word

-w stops test matching inside testing.

grep -w "test" arquivo.txt

171. grep with extended regex

-E enables |, + and ? without escaping.

grep -E "erro|falha|timeout" app.log

172. grep across several files

Prefixes each result with the file name.

grep "database" /etc/*.conf

173. ripgrep — the modern grep

Far faster and it already respects .gitignore.

rg "getThemeSelection"
rg -t ts "useState"

The shell day to day

Shortcuts, history and help — what makes you type less.

174. Tab — complete

Completes a command, a path and a file name. Two presses list the options.

cd /var/lo<Tab>   # becomes /var/log/

175. history — the history

Every command you have run.

history
history | grep docker

176. Repeat from the history

!! repeats the last one; !123 runs number 123.

!!
!123
!docker    # the last one starting with docker

177. Ctrl+R — search the history

The shortcut that saves the most typing. Keep pressing it to go further back.

# Ctrl+R and start typing part of the command

178. Line-editing shortcuts

Moving and deleting without the arrow keys.

# Ctrl+A start | Ctrl+E end
# Ctrl+U deletes to the start | Ctrl+K to the end
# Ctrl+W deletes the previous word | Ctrl+L clears the screen

179. Ctrl+C and Ctrl+D

Interrupts the current command; ends the input/session.

# Ctrl+C cancels
# Ctrl+D sends EOF (exits the shell)

180. alias — create a shortcut

A long command becomes a short word.

alias ll='ls -lah'
alias gs='git status'
alias ..='cd ..'

181. Make the alias permanent

Put it in your shell's profile file.

echo "alias ll='ls -lah'" >> ~/.bashrc
source ~/.bashrc

182. Environment variables

Viewing, creating and exporting them to child processes.

echo $HOME
export API_URL="https://api.exemplo.com"
printenv | sort

183. PATH

Where the shell looks for executables.

echo $PATH
export PATH="$HOME/bin:$PATH"

184. man — the manual

The official documentation for each command. / searches, q exits.

man tar
man 5 crontab   # section 5: file formats

185. --help

A quick summary, without opening the manual.

tar --help | less

186. tldr — practical examples

A condensed manual, with the common uses only. Worth installing.

tldr tar
tldr find

187. apropos — look for a command

Searches the manual by what the command does.

apropos compress

188. clear and reset

Clears the screen; reset fixes a terminal messed up by binary output.

clear
reset

189. Chaining commands

; always, && if it succeeded, || if it failed.

cd /tmp; ls
mkdir dados && cd dados
ping -c1 host || echo "sem resposta"

190. Redirecting the output

> overwrites, >> appends, 2> is the error stream.

ls > lista.txt
echo "linha" >> log.txt
comando > saida.txt 2> erros.txt
comando > tudo.txt 2>&1

Date, time and system information

Knowing what you are standing on before touching anything.

191. date — date and time

Shows and formats the date. Heavily used in file names.

date
date +"%Y-%m-%d %H:%M:%S"
date +%s   # Unix timestamp

192. cal — calendar

The calendar for the month or the year.

cal
cal 2026

193. timedatectl — time zone and clock

Configures the time zone and NTP synchronisation.

timedatectl
sudo timedatectl set-timezone America/Sao_Paulo

194. uname — kernel and architecture

Which kernel and which architecture the machine uses.

uname -a
uname -r   # just the kernel version

195. Which distribution

The name and version of the system.

cat /etc/os-release
lsb_release -a

196. CPU

Model, cores and frequency.

lscpu
nproc   # just the number of cores

197. Memory and hardware

An inventory of what the machine has.

free -h
sudo lshw -short
sudo dmidecode -t memory

198. PCI and USB devices

Network card, GPU, connected devices.

lspci
lsusb

199. Uptime and reboots

How long it has been up and the history of restarts.

uptime -p
last reboot | head

200. Shut down and reboot

Always warn whoever is connected first.

sudo shutdown -h now
sudo shutdown -r +5 "Reinício em 5 minutos"
sudo shutdown -c   # cancels