Linux notes

• ls list files
  
• ls -l long list with details
  
• ls -a show all files (including hidden ones)
  
• pwd present working directory
  
• cd change directory
  

• pushd Push the current directory into a stack so it can be popped later and cd into the given directory
  
• popd Pop the top directory from the stack and cd into it
  
• cd - cd into the last directory that was accessed using cd. Useful for alternating between two folders
  

Linux doesn't need file extension to correctly identify the type of file. You can see the type of a file that doesn't have an extension using the file command.

file translations.json
translations.json: UTF-8 Unicode text, with very long lines

Use the locate command when you know the name of a file, but are unsure about which directory it resides in. Make sure to run sudo updatedb, so that all the files are indexed.

The whereis command locates all the binaries of a command. Useful to know where multiple versions are installed.

The which command is used to locate a command and prints the full path of the command being executed. This is especially useful if you have different versions of the same command installed, and want to know which version is currently active. You can then maybe change your $PATH variable to make sure the right version gets picked up.

Use the find command to find directories and files within a directory. Some interesting flags:

• -type f Only find files
  
• -type d Only find directories
  
• -name <pattern> find files which match the pattern
  
• -iname <pattern> same a above, but ignore case
  
• -size +100K Only files above 100 kilobytes
  
• -not find files that don't match the given criteria
  
• -maxdepth <num> Maximum depth of directories to recurse under
  
• -exec <command> {} + Execute the given command on the found files
  

touch <filename> to create an empty file.
cat <filename> to display all the contents of a file.
cat >> <filename> to read input from stdin and append contents into <filename>. Use <C-d> to end input. Use cat > <filename> to replace contents
less <filename> read contents of a file in a more convenient form than cat. Has paging and searching capabilities.

apt is a more simplified version of apt-get. A lot of the apt-get commands have a corresponding command with apt, but this is not always the case. For most regular use cases, apt is sufficient. This specifically applies to Ubuntu distributions.

If you have a .deb file (Debian package), you can use the following command to install

sudo dpkg -i /path/to/file.deb

top Displays linux processes
htop Interactive process viewer
ps -ef | grep <pattern> Useful for listing processes that match the given pattern
pgrep <pattern> Only lists the process IDs for the processes that match the given pattern. A convenient alternative to ps -ef | grep <pattern> if you only need PIDs

Services are a certain kind of process that runs in the background
sudo service <servicename> start To start a service. Use stop or restart instead of start to do what it says

Instructions copied from here: https://github.com/elementary-tweaks/elementary-tweaks. You might get an 'add-apt-repository command not found' error. In that case, run:

sudo apt-get install software-properties-common
sudo apt-get update

To install UI tweaks tool, run:

sudo add-apt-repository ppa:philip.scott/elementary-tweaks
sudo apt install elementary-tweaks

You can now access the Tweaks tool under system settings. Note: You'll probably need to restart for the settings to take effect. At the very least, you'll need to restart the app

After switching to dark theme, some of the apps' title bars might still have the light variant, but I managed to fix this by following these steps:

• Install dconf-editor by running sudo apt install dconf-editor
  
• Download gtk-theme-variant-switcher from https://github.com/beachmachine/gtk-theme-variant-switcher, cd in to the folder and run make install
  
• Run dconf-editor from the applications menu and navigate to org/gtk/settings/theme-variant-switcher
  
• Select custom value and append a new array which consists of 3 values: WM_CLASS of a window, gtk theme variant, human readable description. To get the WM_CLASS of a window, run xprop WM_CLASS in the terminal and click on the window you want to modify. For my emacs application, I added the following array: ('emacs25', 'dark', 'Emacs').
  

Some people on the internet have mentioned modifying the app's .desktop file found in /usr/share/applications/ or in ~/.local/share/applications/ by appending env GTK_THEME=elementary:dark to the Exec value, but that didn't work for me.

• Right click issue on Firefox wherein the context menu gets activated on button press instead of button release. Go to about:config in Firefox and set ui.context_menus.after_mouseup to true
  
• When updating applications or packages from app center, it might not get past the "Waiting for package manager lock". Running sudo dpkg --configure -a should fix it.
  
• To enable Dropbox icon in the top panel, sudo vim /etc/xdg/autostart/indicator-application.desktop, Add ;Pantheon; to the end of OnlyShowIn, download wingpanel-indicator-ayatan from http://ppa.launchpad.net/elementary-os/stable/ubuntu/pool/main/w/wingpanel-indicator-ayatana/ and run install the .deb package using sudo dpkg -i Downloads/wingpanel-indicator-ayatana_2.0.3+r27+pkg17~ubuntu0.4.1.1_amd64.deb (change package name as necessary). Log out and log in, and you should see the Dropbox icon in the top panel. You might also see a duplicated Wifi indicator, no idea how to fix that yet.
  
• Touchpad on Acer stops working after resuming from suspend. Run the following command:
  

sudo /sbin/rmmod i2c_hid && sudo /sbin/modprobe i2c_hid

If that works, make it a more permanent solution:

touch /lib/systemd/system-sleep/touchpad

Add following contents to touchpad file

#!/bin/sh
case $1 in
  post)
    /sbin/rmmod i2c_hid && /sbin/modprobe i2c_hid 
  ;;
esac

Make file executable chmod +x /lib/systemd/system-sleep/touchpad and test (suspend computer and wake-up again)

Basic usage which fuzzy finds files in the current directory.

$ fzf

<C-r> interactive history search, but now with fuzzy pattern matching

cd /home/projects/**<TAB> fuzzy search files under /home/projects/

kill -9<TAB> fuzzy search pid to kill

You can select multiple entries using fzf -m and <TAB>

To use fd command with fzf, add the following to .bashrc:

export FZF_DEFAULT_COMMAND='fd --type f'
export FZF_CTRL_T_COMMAND="$FZF_DEFAULT_COMMAND"

Crazy fast search tool written in Rust, and runs searches in parallel by default. Ignores hidden files and files/folders mentioned under .gitignore file if one is present.
Basic usage:

rg <pattern>

Search for specific file type:

rg -thtml <pattern>
rg -Thtml <pattern> #exclude html type from search