tricks-linux.txt

Allow executable to run sudo w/o password prompt
	1.	Execute:
		sudo visudo
	2.	Add line:
		<username> ALL=NOPASSWD:/path/to/executable


Apt
	Auto purge:
		apt autoremove --purge
	Download debs to '/var/cache/apt/archives/':
		sudo apt install --download-only <package-name>
	Export GPG key from deprecated keyring:
		1.	List existing keys:
			sudo apt-key list
			Warning: apt-key is deprecated. Manage keyring files in trusted.gpg.d instead (see apt-key(8)).
			/etc/apt/trusted.gpg
			--------------------
			pub   rsa4096 2017-05-08 [SCEA]
						1EDD E2CD FC02 5D17 F6DA  9EC0 ADAE 6AD2 8A8F 901A
			uid           [ unknown] Sublime HQ Pty Ltd <support@sublimetext.com>
			sub   rsa4096 2017-05-08 [S]

			pub   rsa2048 2015-10-28 [SC]
						BC52 8686 B50D 79E3 39D3  721C EB3E 94AD BE12 29CF
			uid           [ unknown] Microsoft (Release signing) <gpgsecurity@microsoft.com>
		2.	Export a key:
			sudo apt-key export BE1229CF | sudo gpg --dearmour -o /usr/share/keyrings/microsoft.gpg
			* Note:	The BE1229CF value comes from the last 8 characters of the pub code.
		3.	Update corresponding apt source file for the repository, adding a signed-by tag:
			deb [arch=amd64 signed-by=/usr/share/keyrings/microsoft.gpg] https://packages.microsoft.com/repos/edge/ stable main
		4.	Update apt to confirm warning is gone
			sudo apt update
		5.	Remove the original signature
			sudo apt-key del BE1229CF
	Fix: 'add-apt-repository: command not found'
		sudo apt install software-properties-common
		* Note: Also install dirmngr
	Hold/Unhold packages:
		Hold:
			sudo apt-mark hold <package-name>
		Unhold:
			sudo apt-mark unhold <package-name>
		Show packages on hold
			apt-mark showhold
	List installed packages:
		apt list --installed
	List installed packages matching a pattern:
		apt list --installed "pattern*"
	List upgradeable packages:
		apt list --upgradable
	Mark to prevent autoremove:
		sudo apt-mark manual <package-name>
	Update offline:
		1.	Copy .deb files from '/var/cache/apt/archives/' after
		'apt dist-upgrade'/'apt full-upgrade'/'apt upgrade'.
		2.	Copy 'apt update' downloaded repository info from '/var/lib/apt/lists/'.
		3.	Run 'apt dist-upgrade'/'apt full-upgrade'/'apt upgrade'.


Backup MBR
	sudo dd status=progress if=/dev/sda of=/path/to/mbr.raw bs=512 count=1


Base Conversion
	Binary to Decimal:
		echo "ibase=2; 101010" | bc
	Decimal to Binary:
		echo "ibase=10; obase=2; 42" | bc
	Decimal to Hexadecimal:
		echo "obase=16; 42" | bc
	Hexadecimal to Decimal:
		echo "ibase=16; 2A" | bc
	Hexadecimal to Base64:
		echo <hex-string> | xxd -r -p | base64


Beep:
	echo -ne "\a"


Build; Packages required
	GQRX-Scanner:
		•	To build/install:
			cmake .
			make
			sudo make install
		•	Dependencies:
			cmake
		•	To uninstall:
			sudo make uninstall
	Gradio:
		•	To build/install:
			meson build .
			cd build/
			ninja
			sudo ninja install
		•	Dependencies:
			libgstreamer1.0-dev
			libgstreamer-plugins-base1.0-dev
			libgtk-3-dev
			libjson-glib-dev
			libsoup2.4-dev
			libsqlite3-dev
			meson
			ninja-build
			valac


Change Partition Sequence Number
	1.	Get copy of partition table:
		sudo sfdisk --dump /dev/sdX > sdX.old
	2.	Create copy for new partition table:
		cp --verbose sdX.old sdX.new
	3.	Edit the file for new partition table, changing only the line order and
	partition number.
	4.	Write new partition table:
		sudo sfdisk /dev/sdX < sdX.new
		* In case the above does not work:
			sudo sfdisk --no-reread --force /dev/sdX < sdX.new


Check script/command execution time
	time /path/to/script


CheckInstall - Build Linux packages from source code
	1.	Install:
		sudo checkinstall
		* This is same as: sudo checkinstall make install
	2.	Create package:
		sudo checkinstall --install=no


Chromium - always run in Incognito
	1.	Set Chromium as default in:
		sudo update-alternatives --config x-www-browser
	2.	Edit file as root:
		sudo --edit /etc/chromium-browser/default
	3.	Change line reading CHROMIUM_FLAGS="" to CHROMIUM_FLAGS="--incognito".


Chroot
	1.	Into device/image:
		sudo mount /dev/sdXY /mnt/
		sudo mount /dev/sdXY /mnt/boot/ # If applicable
			...or...
		sudo mount /dev/sdXY /mnt/boot/efi/ # For EFI based systems
		for i in /dev/ /proc/ /run/ /sys/ /usr/ /var/ ; do sudo mount --bind "$i" "/mnt$i"; done
		chroot /mnt
	2.	Fix no internet access in chroot environment:
		Copy host '/etc/resolv.conf' to chroot environment.

ClamAV
	1.	Update database:
		sudo freshclam
		* You may need to stop clamav service (restart later):
			sudo service clamav-freshclam stop
	2.	To scan:
		clamscan --allmatch --bell --infected --recursive <path> &


Cleanup $HOME
	1.	ClamTk
		sudo sed --in-place 's/\/\.clamtk/\/.local\/share\/clamtk/g' \
		/usr/share/perl5/ClamTk/App.pm /usr/share/perl5/ClamTk/Schedule.pm
	2.	Eclipse.
		a.	In 'eclipse.ini' add:
			-Duser.home=.config
		b.	Eclipse will create '.eclipse', '.p2' directories in '$HOME/.config/'.


Clear Logs
	for i in $(sudo find /var/log/ -type f); do sudo \cp -v /dev/null $i; done


Clear Recent Files for GTK File Chooser:
	rm ~/.local/share/recently-used.xbel


Connect to a serial device
	screen /dev/ttyUSB0 <optional baud-rate>
	* Note:
	1.	To detach: 'Ctrl-D'.
	2.	To kill session: 'Ctrl-A' then 'K'.
	3.	To scroll: 'Ctrl-A' then 'Esc'. Scroll using arrow keys. When done hit
	'Q'/'Esc'.


Convert EFI to BIOS
	1.	Do changes in partition(s).
	2.	Update '/etc/fstab' i.e. remove '/boot/efi' and/or update UUIDs.
	3.	Chroot (with /, /boot/, /boot/efi/, /dev/, /proc/, /run/, /sys/, /usr/, /var/) to the root of device to convert.
	4.	grub-install /dev/sda
	5.	update-grub


Copy preserving ownership/permissions
	cp --archive --verbose /path/to/source /path/to/destination # Note: No trailing '/'
		...or...
	rsync --archive --progress --verbose /path/to/source /path/to/destination


Copy Entire Filesystem
	rsync -axHAX --numeric-ids --info=progress2 /media/old-disk /media/new-disk
		-a	all files, with permissions, etc
		-x	stay on one file system
		-H	preserve hard links (not included with -a)
		-A	preserve ACLs/permissions (not included with -a)
		-X	preserve extended attributes (not included with -a)


Count total number of lines in set of files
	find . -type f -name '*.java' | xargs wc -l
	find -L . -type f -name '*.java' | xargs wc -l # Follow symbolic links


Create Loopback device for an image
	udisksctl loop-setup --file /path/to/image.img
	udisksctl loop-setup --read-only --file /path/to/image.img
	udisksctl loop-delete --block-device /dev/loopX
		...or...
	1.	Enable loopback if not already enabled:
		sudo modprobe loop
	2.	Request a new (free) loopback device:
		sudo losetup --find
		* Note the path to the free loopback device
	3.	Create device of image:
		sudo losetup --verbose /dev/loopX /path/to/image.img
		* Where X is the number of loopback device returned earlier
	4.	Ask kernel to load partitions in device:
		sudo partprobe --summary /dev/loopX
	5.	Unloading the loopback device:
		sudo losetup --verbose --detach /dev/loopX


Dconf/Dconf-editor:
	1.	Increase maximum recent files for text editors:
		dconf write /org/x/editor/preferences/ui/max-recents "'20'"
			...or...
		dconf-editor:
			Under ' /org/x/editor/preferences/ui/' set 'max-recents' to '20'.
	2.	Set maximum compression for file-roller:
		dconf write /org/gnome/file-roller/general/compression-level "'maximum'"
			...or...
		dconf-editor: Under 'org/gnome/file-roller/general' set 'compression-level'
		to 'maximum'.


Disable GUI
	1.	Edit '/etc/default/grub' with your favourite editor and change:
		GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
			to
		GRUB_CMDLINE_LINUX_DEFAULT="text"
	2.	Update GRUB:
		sudo update-grub
	3.	Tell systemd to not load the graphical login manager:
		sudo systemctl enable multi-user.target --force
		sudo systemctl set-default multi-user.target
	4.	You will still be able to use X by typing 'startx' after you logged in.


Disable Hibernation
	1.	Remove/delete the file 'com.ubuntu.enable-hibernate.pkla' from
	'/etc/polkit-1/localauthority/50-local.d/'.
	2.	Content of the file for Linux Mint Cinnamon 18.3:
		[Re-enable hibernate by default]
		Identity=unix-user:*
		Action=org.freedesktop.upower.hibernate
		ResultActive=yes

		[Re-enable hibernate by default in logind]
		Identity=unix-user:*
		Action=org.freedesktop.login1.hibernate
		ResultActive=yes


Disk image
	1.	Create (empty):
		a.	Create blank file of required size (here 1GiB):
			sudo dd if=/dev/zero of=/path/to/image.img iflag=fullblock bs=1M count=1024 status=progress && sync
		b.	Create loopback device for disk image:
			sudo losetup --verbose /dev/loopX /path/to/image.img
		c.	Run GParted for loopback device:
			gparted /dev/loopX
		d.	Detach loopback device:
			sudo losetup --verbose --detach /dev/loopX
	2.	Enlarge:
		a.	Add space to the image:
			sudo dd if=/dev/zero bs=1M count=1024 status=progress >> /path/to/image.img
		b.	Load image as a loopback and edit with GParted to enlarge partition(s):
			sudo gparted /dev/loopX
		c.	Unload the loopback:
			sudo losetup --detach /dev/loopX
	3.	Shrink:
		a.	Load image as a loopback and edit with GParted:
			sudo gparted /dev/loopX
		b.	Unload the loopback:
			sudo losetup --detach /dev/loopX
		c.	Find end of partition(s):
			i.	Execute:
				fdisk --list /path/to/image.img
			ii.	Will give output like:
				Disk myimage.img: -- MB, -- bytes, -- sectors
				Units = sectors of 1 * -- = X bytes
				Sector size (logical/physical): -- bytes / -- bytes
				I/O size (minimum/optimal): -- bytes / -- bytes
				Disk identifier: --
					          Device Boot      Start         End      Blocks   Id  System
				/path/to/image.img1              --           Y          --    -      --
		* Note:
			i.	Block-size, here X (and generally 512byts)
			ii.	Ending of partition, here: Y
		d.	Run truncate with above noted values:
			truncate --size=$[X*(Y+1)] /path/to/image.img # 'Y+1' as block count starts at 0


Disable root account
	1.	Remove the root password:
		sudo passwd --delete root

	2.	Lock the account:
		sudo passwd --lock root


Dump1090-mutability - Fix service exiting
	sudo wget --output-documen /etc/udev/rules.d/rtl-sdr.rules "https://raw.githubusercontent.com/osmocom/rtl-sdr/master/rtl-sdr.rules"
	sudo reboot


dpkg
	1.	List packages with size
		dpkg-query -Wf '${Installed-Size}\t${Package}\n'
	2.	Find package of executable
		dpkg-query -S <path to executable>


Echo To File As root
	echo 'Hello, world!' | sudo tee /path/to/file.txt > /dev/null
		...or...
	echo 'Hello, world!' | sudo tee --append /path/to/file.txt > /dev/null


EFI/UEFI
	Check if system is EFI/UEFI:
		Check existence of '/sys/firmware/efi/' folder.
	List entries:
		efibootmgr --verbose
	Add entry:
		sudo efibootmgr --create --verbose -d /dev/sda -p 1 -l \\EFI\\ubuntu\\grubx64.efi -L "Linux"
	Delete entry:
		sudo efibootmgr --bootnum --verbose <bootnum> -B


Encrypt Home Partition (Post install)
	1.	Install the encryption utilities:
		sudo apt install ecryptfs-utils cryptsetup
	2.	Login with a different account than the one to be encrypted.
	3.	Encrypt home:
		sudo ecryptfs-migrate-home -u <username>
	4.	Login to the original account without reboot to complete process!
	5.	Follow the instruction to add a password to the newly encrypted folder.
	If you don't see it, enter:
		ecryptfs-add-passphrase
	3.	Note: A copy of original home directory is made.


Execute command on list of files/directories
	for file in <one> <two> <three>; do <command> $file; done


exFAT
	1.	Format:
		sudo mkfs.exfat -n LABEL /dev/sdXn
			...or...
		sudo mkexfatfs -n LABEL /dev/sdXn
	2.	Change label:
		sudo exfatlabel /dev/sdXn NEW_LABEL
	3.	Get filesystem info:
		sudo dumpexfat /dev/sdXn
	4.	To check the partition:
		sudo fsck.exfat /dev/sdXn
			...or...
		sudo exfatfsck /dev/sdXn


Metadata Removal
	1.	EXIF
		exiftool -all= /path/to/file
	2.	PDF
		mat2 /path/to/file


Extract Eltorito Boot Image from CD-ROM image
	1.	Get info from image:
		isoinfo -d -i /path/to/bootable-cd.iso
	2.	This will output with something like this:
			Eltorito defaultboot header:
				Bootid 88 (bootable)
				Boot media 2 (1.44MB Floppy)
				Load segment 0
				Sys type 0
				Nsect 1
				Bootoff 1D 29
	3.	The last line tells that offset of boot image is 29 (0x1D in decimal).
	ISO9660 sectors are 2048 bytes. So we would use dd as follows:
		dd if=/path/to/bootable-cd.iso of=/path/to/bootable-floppy.img bs=2048 skip=29 count=720
		* Count as per size of floppy?


Extract icon from Windows executable (EXE)
	sudo apt install icoutils
	wrestool --extract --type 14 source.exe > output.ico

FFMPEG
	1.	Convert M4V to AVI:
		ffmpeg -i foo.mp4 -q:v 3 bar.avi
			* Lower Q values will increase quality and file size
		...or...
		a.	First pass:
			ffmpeg -i foo.m4v -c:v libxvid -c:a libmp3lame -r 30 -threads 12 -pass 1 -f rawvideo -y /dev/null
		b.	Second pass:
			ffmpeg -i foo.m4v -c:v libxvid -c:a libmp3lame -r 30 -ar 44100 -b:a 128k -qscale 1 -threads 12 -pass 2 -passlogfile ffmpeg2pass bar.avi
	2.	Change speed of video:
		ffmpeg -i foo.mp4 -filter:v "setpts=0.5*PTS" foo-double-speed.mp4
	3.	Extract mp3 cover art:
		ffmpeg -i file.mp3 file.jpg
	4.	Convert to mp3:
		ffmpeg -i input-file.ext -c:a libmp3lame -b:a 128k output-file.mp3
	5.	Clip a video:
		ffmpeg -ss 00:01:23 -to 00:23:45 -i foo.m4v -o foo.m4v
	6.	Convert m4v to mp4:
		ffmpeg -i input-file.m4v -c copy output-file.mp4
	7.	Replace audio:
		ffmpeg -i input-file.mp4 -i input-file.wav -c:v copy -map 0:v:0 -map 1:a:0 output-file.mp4
	

Find
	1.	Execute command on directories only in current directory:
		find . -maxdepth 1 -type d -exec echo {} \;
	2.	Execute command on files only in current directory:
		find . -maxdepth 1 -type f -exec echo {} \;
	3.	Chmod all directories beginning from the current directory:
		find . -type d -exec chmod 700 {} \;
	4.	Chmod all files beginning from the current directory:
		find . -type f -exec chmod 600 {} \;
	5.	Chmod specified file pattern:
		find . -type f -name "*.sh" -exec chmod --verbose +x {} \;
	6.	Chmod multiple file pattern:
		find . -type f \( -iname \*.pl -o -iname \*.sh \) -exec chmod --verbose +x {} \;
		* '-iname' is like '-name' but case insensitive
	7.	Find all files with specified permissions:
		find . -type f -perm 777
	8.	Rename to lowercase:
		find . -exec rename -verbose 's!([^/]*\Z)!lc($1)!e' {} +
	9.	Rename to uppercase:
		find . -exec rename 's!([^/]*\Z)!uc($1)!e' {} +
	10.	Delete symbolic links:
		find . -type l -delete
	11.	Find ELF files:
		find /path/to/search/ -exec file {} \; | grep -i "lsb executable"
	12.	Print filenames:
		find /path/to/search/ -printf '%p' -exec grep foo {} \;

Find duplicate files
	find . ! -empty -type f -exec md5sum {} + | sort | uniq -w32 -dD
	find -not -empty -type f -printf "%s\n" | sort -rn | uniq -d | xargs -I{} -n1 find -type f -size {}c -print0 | xargs -0 md5sum | sort | uniq -w32 --all-repeated=separate


Find duplicate lines in two files
	sort /path/to/file1 /path/to/file2 | uniq -d


Find file with text
	1.	Simple search:
		grep -rnw /path/to/somewhere/ -e 'pattern'
			-r or -R	Recursive
			-n	Display line number
			-w	Match whole word
			-l	Only give filenames of matching files
	2.	Along with these, --exclude, --include, --exclude-dir flags could be used
	for efficient searching:
		a.	Only search through those files which have .c or .h extensions:
			grep --include=\*.{c,h} -rnw '/path/to/somewhere/' -e "pattern"
		b.	Exclude searching all the files ending with .o extension:
			grep --exclude=*.o -rnw '/path/to/somewhere/' -e "pattern"
		c.	For directories it's possible to exclude a particular directory(ies)
		through --exclude-dir parameter. For e.g, this will exclude the dirs dir1/,
		dir2/ and all of them matching *.dst/:
			grep --exclude-dir={dir1,dir2,*.dst} -rnw '/path/to/somewhere/' -e "pattern"


Find MAC addresses:
	sudo ifconfig -a


Find process locking a file
	sudo lsof /path/to/file


Fix Fastboot 'no permissions, verify udev rules' (Android devices)
	1.	Determine vendor id.
		a.	Execute 'lsusb'.
		b.	Output will be of form:
			Bus XXX Device XXX: ID [vendor_id]:[device_id] [device_name]
	2.	Add an entry for the vendor in file '/etc/udev/rules.d/51-android.rules':
		# Vendor name
		SUBSYSTEM=="usb", ATTR{idVendor}=="[vendor_id]", MODE="0666", GROUP="plugdev"
	3.	Execute:
		sudo udevadm control --reload-rules && sudo udevadm trigger && sudo service udev restart


Fix '* failed to open vchiq instance'
	sudo chmod 777 /dev/vchiq


Fix Kazam Not Showing System Speaker
	sudo sed "s/time.clock()/time.perf_counter()/g" -i /usr/lib/python3/dist-packages/kazam/pulseaudio/pulseaudio.py


Fix Public Key Not Available
	1.	To Fix error:
		Failed to fetch http://foo.org/ubuntu/dists/bionic/InRelease The following
		signatures couldn't be verified because the public key is not available:
		NO_PUBKEY 1234ABCD5678EFGH
	2.	Run:
		sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-key 1234ABCD5678EFGH


Flash Storage (SD Card/USB Drive)/SSD Install)
	1.	Turn off recording of access timestamps by adding noatime mount option in
	'/etc/fstab'. E.g.:
		UUID=01234567-89ab-cdef-0123-456789abcdef / ext4 defaults,noatime,errors=remount-ro 0 1
	2.	Use tmpfs for /tmp, /run, /var/spool, /var/tmp in '/etc/fstab'. E.g.:
		tmpfs /tmp       tmpfs noatime,nodev,nosuid,mode=1777 0 0
		tmpfs /run       tmpfs noatime,nodev,nosuid,mode=1777 0 0
		tmpfs /var/spool tmpfs noatime,nodev,nosuid,mode=1777 0 0
		tmpfs /var/tmp   tmpfs noatime,nodev,nosuid,mode=1777 0 0
	3.	Reduce swappiness by adding in '/etc/sysctl.conf':
		vm.swappiness=10
	4.	In case of SD Card/USB Drive, avoid swap file/partition if possible.


Flatpak
	1.	To install Flatpak:
		sudo add-apt-repository ppa:alexlarsson/flatpak
		sudo apt update
		sudo apt install flatpak
		# Optional Flatpak plugin for the Ubuntu Software app:
		sudo apt install gnome-software-plugin-flatpak
	2.	Add Flathub repostory:
		flatpak remote-add --if-not-exists flathub https://flathub.org/repo/flathub.flatpakrepo
	3.	To search:
		flatpak search gimp
	4.	To install:
		flatpak install flathub org.gimp.GIMP
	5.	To run:
		flatpak run org.gimp.GIMP
	6.	To uninstall:
		flatpak uninstall org.gimp.GIMP
	* Other Flatpaks apart from GIMP:
		Gradio - de.haeckerfelix.gradio
		Frog - com.github.tenderowl.frog


For with iterator
	for i in {0..4}; do echo "$i"; done # Outputs: 0, 1, 2, 3, 4
		...or...
	for i in {0..9..2}; do echo "$i"; done # Outputs: 0, 2, 4, 6, 8
		...or...
	for (( i=0; i<5; i++ )); do echo "$i"; done
	* Note: You can also use break (to break out of loop) and continue (to skip
	to next iteration.


Get CPU temperature
	cat /sys/class/thermal/thermal_zone*/temp


Grep PDF:
	find /path/to/search/ -iname '*.pdf' -exec pdfgrep foo {} +


GRUB
	1.	Change timeout:
		a.	Edit '/etc/default/grub'.
		b.	Change 'GRUB_TIMEOUT'.
		c.	Run 'sudo update-grub'.
	2.	Disable probing for other OSes:
		a.	In the file '/etc/default/grub' add:
			GRUB_DISABLE_OS_PROBER=true
		b.	Run 'sudo updage-grub'.
	3.	Remove hidden timeout:
		a.	Edit '/etc/default/grub'.
		b.	Change 'GRUB_TIMEOUT_STYLE' to 'menu'.
		c.	Run 'sudo update-grub'.
	4.	Verbose Boot:
		a.	Edit '/etc/default/grub'. Change 'GRUB_CMDLINE_LINUX_DEFAULT', removing
		'splash quiet' and adding '--verbose nosplash'.
		b.	Edit '/etc/grub.d/10_linux'. Change 'quiet_boot="1"' to
		'quiet_boot="0"'.
		c.	Run 'sudo update-grub'.


Hostname
	Change:
		hostnamectl set-hostname new_hostname


Ignore lid switch
	Open file '/etc/UPower/UPower.conf'.
	Change 'IgnoreLid=false' to 'IgnoreLid=true'.


Imagemagick
	Fix error 'convert-im6.q16: attempt to perform an operation not allowed by the
	security policy `PDF' @ error/constitute.c/IsCoderAuthorized/408.' when trying
	to create PDF
		1.	Edit file '/etc/ImageMagick-6/policy.xml'.
		2.	Comment out line:
			<policy domain="coder" rights="none" pattern="PDF" />


Install Nodejs
	curl -sL https://deb.nodesource.com/setup_10.x | sudo -E bash -
	sudo apt install -y nodejs


Iterate over file lines
	1.	Simple:
		while read i; do echo "$i"; done < /path/to/file
	2.	Robust:
		while IFS='' read -r line || [[ -n "$line" ]]; do echo "$line"; done < /path/to/file


Iterate over files
	for f in *.mp3; do ln -s "/source/$f" "/destination/$f"; done;


Infinite loop
	while true; do echo "Hello, world!"; sleep 1; done


Hardware Information
	dmidecode
	lshw
	lspci -vv
	lsusb


Journaling
	1.	Check status. Look for absence/presence of flag 'hash_journal'
		sudo dumpe2fs /dev/sdXY | grep "Filesystem features"
	2.	Disable journaling:
		sudo tune2fs -O ^has_journal /dev/sdXY
	3.	Clear journal:
		sudo tune2fs -o discard /dev/sdXY
	4.	Enable journaling:
		sudo tune2fs -O has_journal /dev/sdXY


Kill a process
	sudo pkill --echo -15 --exact <pattern>


LibreOffice
	English (India) Support in LibreOffice:
		1.	'English (India)' (en_IN) is equivalent to 'English (UK)' (en_GB).
		2.	Hunspell (Spell check):
				for e in aff dic; do sudo ln -sv /usr/share/hunspell/en_GB.$e /usr/share/hunspell/en_IN.$e; done
		3.	Mythes (Thesaurus):
			cd /usr/share/mythes
			for e in idx dat; do sudo ln -s th_en_US_v2.$e th_en_GB_v2.$e; sudo ln -s th_en_US_v2.$e th_en_IN_v2.$e; done


LightDM
	1.	Enable autologin:
		a.	In file '/etc/lightdm.d/lightdm.conf' uncomment & set:
			[Seat:*]
			autologin-user=<username>
			autologin-user-timeout=0
		b.	Add the user to the group 'autologin':
			sudo groupadd --system autologin # Create group
			sudo usermod -aG autologin <username> # Add user to 'autologin' group
	2.	Show user list: In file '/etc/lightdm.d/lightdm.conf' uncomment & set:
		[Seat:*]
		greeter-hide-users=false



List installed kernels
	dpkg -l | grep linux-image


List lines in file 'foo.txt' but not in file 'bar.txt'
	awk 'NR==FNR{a[$0]=1;next}!a[$0]' bar.txt foo.txt
		...or...
	comm -23 foo.txt bar.txt # For sorted lines


List only directories
	Current directory:
		ls -d */
	Specified directory:
		ls -d /path/to/specified/directory/*/


Local/UTC time in BIOS
	Run 'sudo timedatectl set-local-rtc 1' (0 is default i.e. UTC).


Location of application files
	/usr/share/applications/
	~/.local/share/applications/


Location of icons
	/usr/share/icons
	~/.local/share/icons


Location of mime List (File-Application association)
	~/.config/mimeapps.list


MinGW
	For x86 Windows:
		i686-w64-mingw32-gcc
		* Package: gcc-mingw-w64-x86-64
	For x64 Windows:
		x86_64-w64-mingw32-gcc
		*	Package: gcc-mingw-w64-i686


Mount
	1.	Directory (bind mount):
		mount --bind /some/where /else/where
	2.	Disk/partition image:
		mount -o loop file.img /media/dir
	3.	R/W overlay over a R/O mount:
		a.	Create required directories:
			mkdir -p /tmp/mount/{image,tmpfs,rw}
		b.	Mount readonly mount:
			mount -o ro -o loop /path/to/image /tmp/mount/image
		c.	Create & mount tmpfs overlay:
			mount -v -t tmpfs -o size=64M none /tmp/mount/tmpfs/
		d.	Combine readonly and overlay:
			mount -v -t aufs -o br:/tmp/mount/tmpfs/:/tmp/mount/image/=ro none /tmp/mount/rw
	4.	Unmount File Manage (Nemo etc) mounted device:
		udisksctl unmount --block-device=/dev/whatever


NPM
	1.	Install module globally
		sudo npm -g install <module>
	2.	List globally installed modules:
		npm list -g --depth=0
	3.	List globally installed outdated modules:
		npm -g outdated
	4.	Uninstall globally installed module:
		sudo npm -g uninstall <module>
	5.	Update all globally installed modules:
		sudo npm -g update


Nvidia GPU Temperature
	LD_PRELOAD=/usr/lib/nvidia-384/libnvidia-ml.so nvidia-smi -q -d temperature


Open SSL
	1.	Keys:
		a.	Generate RSA private key in file 'private.pem':
			i.	Without passphrase (encryption):
				openssl genpkey -out /path/to/private.pem -algorithm rsa -pkeyopt rsa_keygen_bits:2048
				openssl genrsa -out /path/to/private.pem 2048
				* Note:	2048-bit is minimum recommended
			ii.	With passphrase (encryption):
				openssl genpkey -out /path/to/private.pem -algorithm rsa -pkeyopt rsa_keygen_bits:2048 -des3
				openssl genrsa -des3 -out /path/to/private.pem 2048
				*	Supported encryption algorithms: aes128, aes192, aes256, camellia128,
					camellia192, camellia256, des (definitely avoid), des3 or idea
		b.	Generate RSA public key in file 'public.pem' from private key in file
		'private.pem':
			openssl rsa -in /path/to/private.pem -outform PEM -pubout -out /path/to/public.pem
		c.	Add passphrase (encryption) to private key:
			openssl rsa -aes256 -in private-clear.pem -out private-encrypted.pem
		d.	Remove passphrase (encryption) from private key:
			openssl rsa -in private-encrypted.pem -out private-clear.pem
	2.	Encode file:
		a.	Generate private and public keys.
		b.	Generate random password file:
			openssl rand -out /path/to/password.bin 64 # 64 is size in bytes
			Note:	Create a unique password for each exchange!
		c.	Encode file with random key:
			openssl enc -aes-256-cbc -salt -in /path/to/file -out /path/to/file.enc -pass file:/path/to/password.bin
		d.	Encode random key with public key:
			openssl pkeyutl -encrypt -pubin -inkey /path/to/public.pem -in /path/to/password.bin -out /path/to/password.bin.enc
			openssl rsautl -encrypt -oaep -inkey /path/to/public.pem -pubin -in /path/to/password.bin -out /path/to/password.bin.enc
		e.	Decode encrypted random key with private key:
			openssl pkeyutl -decrypt -inkey /path/to/private.pem -in /path/to/password.bin.enc -out /path/to/password.bin
			openssl rsautl -decrypt -oaep -inkey /path/to/private.pem -in /path/to/password.bin.enc -out /path/to/password.bin
		f.	Decode file with decrypted random key:
			openssl enc -d -aes-256-cbc -in /path/to/file.enc -out /path/to/file -pass file:/path/to/password.bin
	3.	Digitally signing:
		a.	Create a signature file:
			openssl dgst -sha256 -sign /path/to/file/private.pem -out /path/to/file/signature.txt /path/to/file
		b.	Verify a signature file:
			openssl dgst -sha256 -verify /path/to/file/public.pem -signature /path/to/file/signature.txt /path/to/file


PDF
	1.	Remove all raster images:
		gs -o output-no-images.pdf -sDEVICE=pdfwrite -dFILTERIMAGE input.pdf
	2.	Remove all text elements:
		gs -o output-no-texts.pdf -sDEVICE=pdfwrite -dFILTERTEXT input.pdf
	3.	Remove all vector elements:
		gs -o output-no-vectors.pdf -sDEVICE=pdfwrite -dFILTERVECTOR input.pdf


Process Multiline Text
	echo "Hello,
	world!" | while read -r l; do echo $l; done


Pkexec - Add application
	For eg to enable 'xed'...
	1.	Create a policy file: '/usr/share/polkit-1/actions/com.linuxmint.xed.policy':
		<?xml version="1.0" encoding="UTF-8"?>
		<!DOCTYPE policyconfig PUBLIC
			"-//freedesktop//DTD PolicyKit Policy Configuration 1.0//EN"
			"http://www.freedesktop.org/standards/PolicyKit/1.0/policyconfig.dtd">
		<policyconfig>
			<vendor>xed</vendor>
			<vendor_url>xed</vendor_url>
			<icon_name>accessories-text-editor</icon_name>
			<action id="org.freedesktop.policykit.pkexec.xed">
			 <description>Run 'xed'</description>
			 <message>Authentication is required to run Text Editor</message>
			 <defaults>
				 <allow_any>no</allow_any>
				 <allow_inactive>no</allow_inactive>
				 <allow_active>auth_admin_keep</allow_active>
			 </defaults>
				 <annotate key="org.freedesktop.policykit.exec.path">/usr/bin/xed</annotate>
				 <annotate key="org.freedesktop.policykit.exec.allow_gui">true</annotate>
			 </action>
		</policyconfig>
	2.	Create a script to call xed with pkexec and use it:
		#!/bin/bash
		pkexec /usr/bin/xed "$@"


Read
	1.	Text entry prompt:
		read -p "Enter name: " name; echo $name
	2.	Filename entry prompt:
		read -p "File: " -i "/" -e file; echo $file
	3.	Pause i.e. prompt Press a key to continue
		read -n1 -rs -p "Press any key to continue..."


Read-only bind mount
	In '/etc/fstab':
		/path/to/source/ /path/to/dest/ none bind,ro


Reduce Footprint
	1.	Remove unnecessary locale:
		a.	Edit '/etc/default/locale' and remove unnecessary locales.
		b.	Delete unnecessary locale directories under '/usr/share/locale/'.
	2.	Remove foreign manpages:
		sudo rm -frv /usr/share/man/?? /usr/share/man/??_*
	3.	Remove foreign help:
		for d in /usr/share/help/*/; do if [[ ! $d =~ '/C/' ]]; then sudo rm -frv $d; fi; done


Rename with all '.' except the last one replaced with space
	rename 's/\.(?=[^.]*\.)/ /g' '{}'


Remount Read/Write
	sudo mount -o remount,rw /partition/identifier /mount/point


Remove 'Amazon' launcher on Ubuntu
	sudo apt purge ubuntu-web-launchers


Remove Duplicate lines
	sort /path/to/input-file.txt | uniq | tee /path/to/output-file.txt
		...or to eliminate all lines with duplicates...
	sort /path/to/input-file.txt | uniq -u | tee /path/to/output-file.txt


Remove LibreOffice
	sudo apt purge fonts-opensymbol libreoffice libreoffice-* \
			openoffice.org-dtd-officedocument1.0 python*-uno uno-libs3-* ure ure-dbg


Repair Grub
	1.	Chroot (with /, /boot/, /boot/efi/, /dev/, /proc/, /run/, /sys/, /usr/, /var/)
	2.	update-grub
	3.	grub-install /dev/sda # To reinstall grub if required


Replace text in file
	sed -i 's/original/new/g' /path/to/file


Run Perl/Swift file with Notpadqq's 'Run' option
	Beautify JS:
		bash -c "uglifyjs -b beautify %path% | zenity --text-info --title='Beautify JS - %filename%' --font='DejaVu Sans Mono' --height=600 --width=900"
	CSS Lint:
		bash -c "csslint --format=compact %path% | sed 's|%path%: ||' | zenity --text-info --title='CSS Lint - %filename%' --font='DejaVu Sans Mono' --height=600 --width=900 --no-wrap"
	G++:
		x-terminal-emulator -e "bash -c \"g++ %path% -o %path%.out; %path%.out; read -n1 -s -r -p $'\nPress any key to continue...'\""
	HTML Hint:
		bash -c "htmlhint --format=compact --nocolor %path% | zenity --text-info --title='HTML Hint' --font='DejaVu Sans Mono' --height=600 --width=900 --no-wrap"
	Perl:
		x-terminal-emulator -e "bash -c \"perl %path%; read -n1 -s -r -p $'\nPress any key to continue...'\""
	Swift:
		x-terminal-emulator -e "bash -c \"swift %path%; read -n1 -s -r -p $'\nPress any key to continue...'\""
	Uglify JS:
		bash -c "uglifyjs -m eval %path% | zenity --text-info --title='Uglify JS - %filename%' --font='DejaVu Sans Mono' --height=600 --width=900"


Samba
	Allow anonymous/guest access from Windows for directory with parents without
	global access:
		1.	Edit '/etc/samba/smb.conf' as root.
		2.	Below 'workgroup = WORKGROUP' under '[global' add:
			force user = <linux-user-name>


Snap:
	sudo snap find
		To list the available packages
	sudo snap install <package name>
		To install a package
	sudo snap list
		To view all the installed snap packages
	sudo snap changes
		To view a list of logged actions
	sudo snap refresh <package name>
		To upgrade a package to its latest available version
	sudo snap remove
		To uninstall a package


SquashFS:
	Create a squash FS:
		mksquashfs squashfs-root/ filesystem.squashfs \
				-b 1024k -comp xz -Xbcj x86 -Xdict-size 100% -e boot
	Extract a squash FS:
		sudo unsquashfs filesystem.squashfs


SSH
	1.	Avoid host verification for IP range:
		Add/create entry in file '~/.ssh/config':
			Host 192.168.0.*
				StrictHostKeyChecking no
				UserKnownHostsFile=/dev/null
	2.	Password less login
		a.	Create private/public key on the client:
			ssh-keygen -b 4096 -t rsa
			Note:	It asks you to set a passphrase which will interrupt when
			setting up automated processes. Therefore, press Enter to skip.
		b.	Copy public key to the remote host:
			ssh-copy-id -i ~/.ssh/id_rsa.pub remote-user@remote-host-ip
			Note:	'~/.ssh/id_rsa.pub' is the default location of the file with public
			key.
		c.	Disable password authentication on host:
			i.	Edit '/etc/ssh/sshd_config'.
			ii.	Add/set:
				PasswordAuthentication no
			iii.	Restart ssh service:
				sudo service ssh restart


Sudo - Display asterisk for passwords
	In the file '/etc/sudoers', change:
		Defaults	env_reset
	...to...
		Defaults	env_reset,pwfeedback


Suspend System
	systemctl suspend


Swap File
	1.	Add:
		a.	Create empty file:
			sudo dd status=progress if=/dev/zero of=/swapfile bs=1K count=4M # Size 1K * 4M = 4 GiB
			sudo chmod 600 /swapfile
		b.	Convert newly created file into a swap space file.
			sudo mkswap /swapfile
		c.	Enable file for paging and swapping.
			sudo swapon -v /swapfile
		d.	Verify by:
			swapon -s
				...or...
			top -bn1 | grep -i swap
		e.	Add entry to '/etc/fstab':
			/swapfile none swap sw 0 0
		f.	Re-test swap file on startup by:
			sudo swapoff -v /swapfile
			sudo swapon -va
	2.	Resize existing:
		a.	Disable swap file.
			sudo swapoff -v /swapfile
		b.	Increase the size of swap file.
			sudo dd if=/dev/zero of=/swapfile bs=1M count=1024 oflag=append conv=notrunc status=progress
			* Above command will append 1GiB of zero bytes at end of swap file.
		c.	Convert newly created file into a swap space file.
			sudo mkswap /swapfile
		d.	Enable file for paging and swapping.
			sudo swapon -v /swapfile


Swap Partition
	1.	Add
		a.	Create an empty partition, say 'sdXY'.
		b.	Format the partition:
			sudo mkswap /dev/sdXY
		c.	Find UUID of partition:
			sudo blkid /dev/sdXY
		d.	Mount partition as swap:
			sudo swapon -U UUID
		e.	Add the partition entry in '/etc/fstab':
			UUID=xxx none swap sw 0 0
	2.	Remove cryptswap:
		a.	Disable swap:
			sudo swapoff -a
		b.	Remove crypt swap:
			cryptsetup remove cryptswap1
		c.	Edit '/etc/crypttab' and remove entry for cryptswap.


Symbolic Links
	1.	To create a new symlink (will fail if symlink already exists):
		ln -s /path/to/file /path/to/symlink
	2.	To create or update a symlink:
		ln -sf /path/to/file /path/to/symlink
	3.	Find symbolic link(s) to a file:
		find -L /dir/to/start -samefile /dir/of/original/file
	4.	List symbolic link(s) in current path:
		find . -type l


TeamViewer
	1.	Disable service:
		sudo teamviewer --daemon stop
		sudo teamviewer --daemon disable
	2.	Setup headless:
		a.	Get latest deb:
			wget https://dl.teamviewer.com/download/linux/version_14x/teamviewer-host_14.2.8352_armhf.deb
		b.	Install:
			sudo apt install teamviewer-host_14.2.8352_armhf.deb
		c.	With account:
			Configure account:
				sudo teamviewer setup
		d.	Without account:
			i.	Get ID:
				cat /etc/teamviewer/global.conf | grep ClientID
			ii.	Set password:
				teamviewer passwd <password>


tune2fs:
	1.	See partition info (including reserved blocks):
		tune2fs -l /dev/sdXY
	2.	Set partition uuid:
		tune2fs -U <uuid> /dev/sdXY
	3.	Set reserved space on partition as percentage
		tune2fs -m X /dev/sdYZ
		* X is percent of space to reserve
	4.	Set reserved space on partition as block count
		tune2fs -r X /dev/sdYZ
		* X is block count of space to reserve


Type Arbitrary Unicode Character
	Use:	Shift + Ctrl + U and then Unicode value


Ufw
	1.	Add rule to allow local traffic:
		sudo ufw allow from 192.168.0.0/24 comment 'Allow local traffic'
		sudo ufw allow from 192.168.1.0/24 comment 'Allow local traffic'
	2.	Add rule to open port:
		sudo ufw allow <port>/tcp comment 'Comment'
	3.	Remove rule:
		a.	List rules:
			sudo ufw status numbered
		b.	Remove rule as per number:
			sudo ufw delete [rule-number]
	4.	Enable firewall
		sudo ufw enable


User/Group
	1.	User:
		a.	Add:
			sudo adduser <username>
				...or...
			sudo adduser <username> <usergroup>
		b.	Add user to group:
			sudo usermod -aG <group> <username>
		c.	Remove user from group:
			sudo deluser <username> <usergroup>
		d.	Delete:
			sudo deluser <username>
				...or...
			sudo deluser --remove-all-files <username>
		e.	Change password:
			sudo passwd <username>
		f.	Change username:
			sudo usermod -l <newName> <oldName>
		g.	Change full name:
			sudo usermod -c "Full Name" <username>
				...or...
			sudo chfn -f "Full Name" <username>
		h.	Change directory:
			sudo usermod -d /home/newHomeDir -m <username>
		j.	List all users:
			cut -d: -f1 /etc/passwd | sort
		k.	Delete user password (no account password):
			sudo passwd --delete <username>
	2.	Group:
		a.	Rename group:
			groupmod -n <newName> <oldname>
		b.	List all groups available:
			cut -d: -f1 /etc/group | sort
		c.	List groups of current user:
			groups


VeraCrypt - Run fsck on a container
		# Decrypt without mounting:
		sudo veracrypt --filesystem=none --protect-hidden=no /path/to/container
		# Get list to find mapper
		sudo veracrypt -l
		# Run fsck
		sudo fsck -fVy /dev/mapper/veracryptX
		# Unmount
		sudo veracrypt -d /path/to/container


VLC
	1.	Enable running as root:
		sudo sed -i 's/geteuid/getppid/' /usr/bin/vlc
	2.	Fix interface being too big on other screen:
		a.	Create a file '/etc/profile.d/gnome-qt.sh' with following:
			export QT_AUTO_SCREEN_SCALE_FACTOR=0
		b.	Restart system.


Wget
	1.	Download a page & all files necessary files to properly display HTML:
		wget --page-requisites http://example.com/your/page.html
	2.	Download with Cookie file:
		wget --cookies=on --load-cookies=<cookie-file> --continue <path>


WiFi
	1.	Connect to hidden network:
		nmcli c add type wifi con-name <connect name> ifname wlan0 ssid <ssid>
		nmcli con modify <connect name> wifi-sec.key-mgmt wpa-psk
		nmcli con modify <connect name> wifi-sec.psk <password>
		nmcli con up <connect name>
	2.	Passwords:
		/etc/NetworkManager/system-connections/


Wine
	1.	Installing Adobe Acrobat Pro XI:
		a.	Use a 64-bit/32-bit prefix.
		b.	Install WineTricks: atmlib, corefonts, vcrun2010
			WINEPREFIX=/path/to/prefix/ winetricks atmlib corefonts vcrun2010
		c.	Copy directories and registry entries from an install on a Windows 7 VM.

	2.	Installing Adobe CS6 (DreamWeaver, Photoshop):
		a.	Use a 64-bit/32-bit prefix.
		b.	Install WineTricks: atmlib, corefonts, msxml6, riched30, vcrun2010
			WINEPREFIX=/path/to/prefix/ winetricks atmlib corefonts msxml6 riched30 vcrun2010
		c.	Copy directories and registry entries from an install on a Windows 7 VM.

	2.	Installing CorelDRAW X3:
		a.	Do an install on a VM/Windows machine, and...
			i.	Copy the directory 'C:\Program Files\Corel\'.
			ii.	Export the registry key 'HKEY_LOCAL_MACHINE\Software\Corel\'.
		b.	Create a 32-bit Wine prefix:
			WINEARCH=win32 WINEPREFIX=/path/to/prefix/ winecfg
		c.	Install WineTricks: gdiplus, ie8, msxml4, vb6run
			WINEPREFIX=/path/to/prefix/ winetricks gdiplus ie8 msxml4 vb6run
		d.	Install CorelDraw X3.
		e.	Replace installed files with ones copied in step a. i..
		f.	In Wine regedit, import the REG file exported in step a. ii..

	3.	Installing Office 2013 x32:
		a.	Install 'winbind' and 'winetricks' apart from 'wine':
			sudo apt install winbind winetricks
		b.	Create 32-bit prefix:
			WINEARCH=win32 WINEPREFIX=/path/to/prefix/ winecfg
		c.	Set the windows version as 'Windows 7' for above.
		d.	Install WineTricks: corefonts, msxml6, riched20:
			WINEPREFIX=/path/to/prefix/ winetricks corefonts msxml6 riched20
		e.	In Wine registry under 'HKEY_CURRENT_USER\Software\Wine\Direct3D' set
		the value of DWORD 'MaxVersionGL' as '30002' (hex).
		f.	KMS activation:
			i.	Open regedit and navigate to 'HKLM\Software\Microsoft\OfficeSoftwareProtectionPlatform\'
			and add string values 'KeyManagementServiceName' with server address and
			'KeyManagementServicePort' with 1688.
			ii.	Now open and exit any office application. A new key should have been
			created under 'HKEY_USERS\S-1-5-20\Software\Microsoft\OfficeSoftwareProtectionPlatform'.
			iii.	Under this new key now add a new binary value 'VLRenewalSchedule'
			with any value.
			iv.	Create a new VB script 'ospp-act.vbs' and execute:
				Set objWMI = GetObject("winmgmts:" _
						& "{impersonationLevel=impersonate}!\\" & "." & "\root\cimv2")

				ExecuteQuery "ID, ApplicationId, PartialProductKey, Description,
				Name","PartialProductKey null","OfficeSoftwareProtectionProduct"

				Function ExecuteQuery(strSelect,strWhere,strClass)

					Err.Clear

					If strWhere = "" Then
						Set productinstances = objWMI.ExecQuery("SELECT " & strSelect & " FROM " &
						strClass)
					Else
						Set productinstances = objWMI.ExecQuery("SELECT " & strSelect & " FROM " &
						strClass & " WHERE " & strWhere)
					End If

					sppErrHandle ""

				End Function


				Set count = productinstances.Count

				For index = 0 to count
					set instance = productinstances.Item(index)
					If (LCase(instance.ApplicationId) = OfficeAppId) Then
						If instance.PartialProductKey "" Then
							i = i + 1
						End If
						instance.Activate
						SppErrHandle(strCommand)
					End If
				Next

	4.	Running Microsoft Flight Simulator X:
		a.	Use a 32-bit prefix.
		b.	Install WineTricks:
			WINEPREFIX=/path/to/prefix/ winetricks corefonts d3dx10_43 d3dx9 dinput8 dxdiag quartz vcrun2005
		c.	Install 'msxml4_sp2' (manually).
		d.	In Libraries for 'dinput8' set (builtin, native).

	5.	Running uBlock u-Centre:
		a.	Copy files under 'C:\Program Files (x86)\' from installation on Windows
		machine/VM.
		b.	Ensure username is part of 'dialout' group:
			sudo adduser $(whoami) dialout
		c.	On connection ublox receiver, it should appear as '/dev/ttyUSB0'.
		'com33' is a symbolic link created for the same by Wine.
		d.	Connect to the ublox receiver using 'com33'.


Zip
	1.	Create Windows compatible password protected ZIP archive:
		zip -9 --encrypt -r --verbose archive.zip /path/to/zip/
	2.	Test integrity:
		unzip -t /path/to/file.zip

Brilliant!