System Commands Reference

How to display all environment variables

printenv

Manual: printenv

How to stop/start the local PostgreSQL

sudo systemctl status postgresql
sudo systemctl stop postgresql
sudo systemctl start postgresql

Manual: systemctl

How to print all `.py` files in a project folder except some folders

find . -type d \( -path ./.tox -o -path ./venv_py39 -o -path ./venv_py310 \) -prune -o -name '*.py' -print

How to find all folders and files where the word "telegram" occurs

find / -iname "*telegram*" 2>/dev/null

How to display a tree of directories and files of a Python project

# Using
tree -a -I 'venv_py310|.idea|.git|.pytest_cache|.mypy_cache|.hypothesis|.coverage|__pycache__|docs|tests|src|*.sql|*.xml' --dirsfirst --sort=name -n -A

How to get detailed statistics on the size of folders and files

How to get detailed statistics on the size of folders and files with a depth of no more than 2 and a size of at least 10 GB and sort by size in descending order:

sudo du -h --max-depth=1 ./ | awk '$1 ~ /[0-9]+G/ && $1+0 >= 10 {print $0}' | sort -hr

How to display the operating system version

lsb_release -a

No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 20.04.3 LTS
Release:    20.04
Codename:   focal

How to find the currently running shell

ls -l /proc/$$/exe

# /proc/19624/exe -> /usr/bin/bash

How to get information about the default shell

echo $SHELL

# /bin/bash

Manual: grep

kubectl explain pod --recursive | grep -A5 tolerations

How to find out the IP addresses of a host

ip address show
nmcli show

Manual: ip-address

How do I find out what is currently listening on which port

 Active Proto tcp tcp tcp tcp tcp6 tcp6 tcp6 udp udp udp udp udp6 udp6 udp6 udp6

$ sudo netstat -tulpn Internet connections (only servers) Recv-Q Send-Q Local Address Foreign Address State PID/Program name 0 0 127.0.0.53:53 0.0.0.0:* LISTEN 917/systemd-resolve 0 0 127.0.0.1:631 0.0.0.0:* LISTEN 952/cupsd 0 0 127.0.0.1:5432 0.0.0.0:* LISTEN 1186/postgres 0 0 127.0.0.1:8000 0.0.0.0:* LISTEN 25428/python 0 0 127.0.0.1:63342 :::* LISTEN 8920/java 0 0 ::1:631 :::* LISTEN 952/cupsd 0 0 127.0.0.1:6942 :::* LISTEN 8920/java 0 0 0.0.0.0:57025 0.0.0.0:* 948/avahi-daemon: r 0 0 127.0.0.53:53 0.0.0.0:* 917/systemd-resolve 0 0 0.0.0.0:631 0.0.0.0:* 1050/cups-browsed 0 0 0.0.0.0:5353 0.0.0.0:* 948/avahi-daemon: r 0 0 :::41301 :::* 8920/java 0 0 :::8976 :::* 8920/java 0 0 :::60237 :::* 948/avahi-daemon: r 0 0 :::5353 :::* 948/avahi-daemon: r target="_blank">Manual: netstat

How to create a string hash

echo -n 'Some text' | base64
# Output: U29tZSB0ZXh0

How to replace a file with content from another file?

cp -f [source_file] [destination_file]

Copies the original file and overwrites the target file (hence -f which stands for "force").

In case you are attempting to copy just the content of the file try:

cat /first/file/same_name > /second/file/same_name

This will overwrite all the content of the second file with the content from the first. However, your owner, group, and permissions of the second file will be unchanged.

How to see which services start when the system starts

systemctl list-unit-files --type=service --state=enabled

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