[Linux cheatsheet] Very very many trivial things

linux-cheatsheet.md

Table of contents

I create a custom GitOpenSourceApps, AppImagesApplication in home folder

Duplicate /snap/bin directory in $PATH remove

https://askubuntu.com/questions/1349900/duplicate-system-path-variable-snap-bin-snap-bin

systemctl

• Start on boot sudo systemctl enable <service>
• Disable perminent sudo systemctl disable <service>
• Start (reset after login) sudo systemctl start <service>

Fish

• Remove greeting set -U fish_greeting
• Print current OS type $(uname)
• Print status code $status (in bash, it's $?
• Set $EDITOR to gedit to be used when ran funced
• Break long-line command Alt+Enter

Some trivial things I learn when learning Fish shell

• print default shell echo $SHELL
• list all shells installed cat /etc/shells
• change default shell chsh -s /usr/bin/fish (remember to log out to see effect)

MySQL

• Check authentication method for each MySQL user accounts SELECT user,authentication_string,plugin,host FROM mysql.user;
• Create new user CREATE USER 'sammy'@'localhost' IDENTIFIED WITH caching_sha2_password BY 'password';
• Change user auth method ALTER USER 'sammy'@'localhost' IDENTIFIED WITH mysql_native_password BY 'password';
• Grant privileges GRANT ALL PRIVILEGES ON *.* TO 'sammy'@'localhost' WITH GRANT OPTION;

systemctl

• Check systemctl is-active <service_name>

Identify IP

• ip a
• ip addr show <network_interface> | grep inet | awk '{ print $2; }' | sed 's/\/.*$//'

ufw

• Enable sudo ufw enable

• Disable sudo ufw disable

• Reset sudo ufw reset (fresh start, disable and remove all custom rules)

• Check status sudo ufw status [verbose] [numbered]

• Allow/Deny sudo ufw allow/deny <port>

• Allow/Deny by name defined in /etc/services sudo ufw allow/deny <service_name>

• Delete by number sudo ufw delete <num>

• Delete by actual rule sudo ufw delete allow ssh

Ref: https://www.digitalocean.com/community/tutorials/how-to-set-up-a-firewall-with-ufw-on-ubuntu-22-04

ssh

• Begin SSH-ing ssh <user-name>@<ip address>

• Enable service sudo systemctl start ssh
• Check service sudo systemctl status ssh
• Disable service sudo systemctl disable --now ssh
• Re-enable service sudo systemctl enable --now ssh
• Restart service sudo systemctl restart ssh

• Open SSH port via ufw sudo ufw allow ssh
• Generate SSH key ssh-keygen -t rsa -b 4096 -C "some comment" (ssh-keygen generate default RSA-3072)
• Automatic add SSH key ssh-copy-id <user_name>@<server_IPaddress>
• Manual add SSH key cat ~/.ssh/id_rsa.pub | ssh user_name@server_ipaddress "mkdir -p ~/.ssh && chmod 700 ~/.ssh && cat >> ~/.ssh/authorized_keys && chmod 600 ~/.ssh/authorized_keys"
• Check SSH key ls ~/.ssh/id_*

• Disable SSH password authentication In sshd_config, set PasswordAuthentication no

Ref:

• https://linuxize.com/post/how-to-enable-ssh-on-ubuntu-20-04/
• https://linuxize.com/post/using-the-ssh-config-file/
• sshd_config file setup https://serverfault.com/a/994935
• client config file setup https://linuxize.com/post/using-the-ssh-config-file/
• permission denied (publickey) error https://www.tecmint.com/ssh-permission-denied-publickey/

tmux

Prefix hotkey Ctrl+b

• List running sessions tmux ls (or tmux list-sessions)

• New session with name tmux new -s <session-name>

• Attach to session tmux attach -t <session-name>

• Kill session tmux kill-session -t <session-name>

• Detach from session Ctrl+b then D

• Create new win Ctrl+b then C

• Cycle prev win Ctrl+b then P

• Cycle next win Ctrl-b then N

• Kill current win Ctrl-b then & (or just exit)

• Manual select wins Ctrl-b then W

• Rename Ctrl-b then ,

• Split ver Ctrl-b then %

• Split hor Ctrl-b then "

• List keybindings Ctrl-b then ?

• Type command Ctrl-b then : (e.g. to split var, use split-screen, to split hor, use split

Ref: https://gist.github.com/andreyvit/2921703

git

• Clone a specific tag git clone --depth 1 --branch <tag_name> <repo_url> NOTE: --depta 1 is optional, only used when need the state at the 1 revision, no download history. Some people downloads whole history for nothing :v Ref: https://stackoverflow.com/a/24102558

Diffrence between bashrc and bash profile

https://superuser.com/questions/183870/difference-between-bashrc-and-bash-profile/183980#183980 (24/08/23)

The meaning of $-

https://stackoverflow.com/questions/42757236/what-does-mean-in-bash (23/08/23)

The meaning of i)

https://stackoverflow.com/questions/40747576/need-help-understanding-a-strange-bashrc-expression (23/08/23)

flatpak

• Update flatpak update
• The rest https://docs.flatpak.org/en/latest/using-flatpak.html#the-flatpak-command

snap

• Search snap find <package_name>
• Install sudo snap install <package_name>
• List install snap list
• List install + Old package snap list --all (reveal old ver marked as disabled)
• Get info snap info <package_name>
• Uninstall sudo snap remove <package_name> --purge
• Uninstall + Delete snap shot sudo snap remove <package_name> --purge
• Uninstall disabled package sudo snap remove <package_name> --revision=<rev name>

AppImageLauncher

• Desktop entry files ~/.local/share/applications

Terminal

https://askubuntu.com/questions/3167/what-is-difference-between-the-options-autoclean-autoremove-and-clean -sudo apt remove --purge <package_name> -sudo apt autoclean -sudo apt clean -sudo apt autoremove

Keyboard remapping