Useful Linux commands and tricks

- 32 mins

Disk operations (low level)

Do a MBR backup

With partition table:

dd if=/dev/hda of=/dev/fd0/mbr.bin bs=512 count=1 status=progress && sync

Without partition table:

dd if=/dev/hda of=/dev/fd0/mbr.bin bs=446 count=1 status=progress && sync

Restore a MBR backup

With partition table:

dd if=/dev/fd0/mbr.bin of=/dev/hda bs=512 count=1 status=progress && sync

Without partition table:

dd if=/dev/fd0/mbr.bin of=/dev/hda bs=446 count=1 status=progress && sync

Clone disks

PS.: the parameter bs=16M can be faster to clone HDDs. To clone HDDs with failures, use the parameter conv=noerror.

dd if=/dev/sdb of=image.bin bs=32M status=progress && sync

Partition and filesystem operations

Make a MD5 sum of a directory’s contents as one sum

find [DIRECTORY] -type f -exec md5sum {} \; | sort -k 2 | md5sum

Copy files recursively with ‘rsync’


Check partition filesystem

PS.: the partition must be unmounted in all cases.

Check a FAT32 partition:

sudo dosfsck -a -r -w -v /dev/sdb1

Check a NTFS partition:

sudo ntfsfix /dev/sdb1

Check a EXT4 partition:

sudo fsck.ext4 -f /dev/sda1

Scan for badblocks

Scans for bad blocks by writing some patterns (0xaa, 0x55, 0xff, 0x00) on every block of the device read/write/corruption errors. And corruption means comparison with previously written data.

sudo badblocks -s -w /dev/sdb

List the UUID of all partitions

sudo blkid

Change the UUID of a partition

sudo tune2fs /dev/[DEVICE] -U [NEW_UUID]

Or if you want generate it randomly:

sudo tune2fs /dev/[DEVICE] -U random

Change the UUID of a SWAP partition

sudo swaplabel -U [NEW_UUID] /dev/sda3

Build a floppy disk image

dd if=/dev/zero of=floppy.img bs=1440k count=1 status=progress && sync
mkfs.msdos -F 12 -n "LABEL" floppy.img

To mount:

sudo mkdir /mnt/floppy/
sudo mount -o loop floppy.img /mnt/floppy/

Image file with multiple partitions

To mount:

sudo losetup --find --partscan Lakka-Generic.x86_64-2.3.2.img

To umount:

sudo losetup --detach /dev/loopX

List mounted partitions


Or also:


Mount a directory in the RAM

Edit the file /etc/fstab and add:

tmpfs /tmp tmpfs rw,nosuid,noatime,nodev,size=4G,mode=1777 0 0

The common parameters on mount command or fstab file are:

Param Description
defaults Use default settings. Equivalent to rw, suid, dev, exec, auto, nouser, async.
rw / ro Mount (read-write) / (read-only).
suid / nosuid (Permit) / (Do not permit) the operation of suid, and sgid bits.
dev / nodev (Interpret) / (Do not interpret) character or block special devices on the file system.
exec / noexec (Permit) / (Do not permit) the execution of binaries from the filesystem.
user / nouser (Permit) / (Do not permit) any user to mount the filesystem.
sync / async All I/O to the file system should be done (a)synchronously.
auto / noauto The filesystem (can be) / (will not) be automatically mounted at startup.
noatime Do not update inode access times on this filesystem.
umask= Mask out the given permissions from all inodes read from the filesystem.
mode= Permissions of all directory inodes read from the filesystem.
errors= Behavior when an error is encountered. Can be: continue, remount-ro, panic.

Mount a ISO CD image

sudo mount -t iso9660 -o loop "image.iso" /mnt

Build a ISO CD image from a directory

PS.: this command build a ISO with the filesystem: ISO9660 + Rock Ridge + Joliet.

genisoimage -o "image.iso" -V "My Label" -A "Application ID" -sysid "System ID" -R -J [DIRECTORY]

Build a ISO image from a disc

isoinfo -d -i /dev/cdrom | grep -i -E 'block size|volume size'
dd if=/dev/cdrom of=output.iso status=progress bs=[BLOCK_SIZE_FROM_ABOVE] count=[VOLUME_SIZE_FROM_ABOVE]

Make a hybrid ISO from a bootable ISO (to boot with an USB flashdrive)

isohybrid "image.iso"

Make a USB flashdrive bootable (Windows or Linux)

sudo apt install extlinux wimtools curl
curl -L -O
chmod +x bootiso
sudo ./bootiso image.iso

Boot a ISO image inside a filesystem

Edit the file /etc/grub.d/40_custom and add:

menuentry "ISO Ubuntu 19.10 Custom" {
    # Insert modules needed in order to access the iso-file
    insmod part_gpt
    #insmod part_msdos

    #insmod ntfs
    insmod ext2

    # Insert module needed in order to find partition
    insmod search_fs_uuid

    # Set UUID of partition with the iso-image
    # and let grub2 find the partition
    # (save it's identifier to the variable $root)
    set uuid="0af7c1cc-23b0-4c62-bf66-ee3264d83f43"
    search --no-floppy --set=root --fs-uuid $uuid

    # Mount the iso image by addressing it with (partition)/path
    set iso="/Isos/Linux/ubuntu-20.04.1-desktop-amd64.iso"
    loopback loop ($root)$iso

    linux (loop)/casper/vmlinuz boot=casper iso-scan/filename=${iso} quiet splash
    initrd (loop)/casper/initrd

And update the GRUB configuration with:

sudo update-grub

Change the partition numbers (e.g.: ‘sda3’ to ‘sda2’)

sudo sfdisk -d /dev/sdb > table.conf
sudo sfdisk /dev/sdb < table.conf

Read SMART data from HDDs

sudo smartctl --attributes /dev/sda

GRUB tricks

Repair the GRUB with a livecd

Mount the devices and do a chroot:

# The sda2 is the root partition
sudo mount /dev/sda2 /mnt

# The sda1 is the EFI partition
sudo mount /dev/sda1 /mnt/boot/efi

for i in /dev /dev/pts /proc /sys; do sudo mount -B $i /mnt$i; done

# Makes the network available (if you want)
sudo cp /etc/resolv.conf /mnt/etc/

# Make sure this is loaded
modprobe efivars

# Do a chroot
sudo chroot /mnt

Reinstall and update GRUB:

grub-install --recheck /dev/sda

Exit chroot pressing CTRL+D.

Unmount everything:

for i in /sys /proc /dev/pts /dev; do sudo umount /mnt$i; done
sudo umount /mnt/boot/efi
sudo umount /mnt

Add a key shortcut for a entry menu in GRUB

Edit the file /boot/grub/grub.cfg and add --hotkey=w for a specific entry. And update the GRUB configuration with:

sudo update-grub

Kernel and hardware

Workarounds using kernel parameters

Edit the file /etc/default/grub and add the following parameters on the variable GRUB_CMDLINE_LINUX_DEFAULT.

Param Description
amd_iommu=off solve problem with iommu in AMD Ryzen processors.
max_loop=256 Increase the number of ‘loop’ devices.

And update the GRUB configuration with:

sudo update-grub

For my Lenovo Ideapad S145 Laptop, with Ubuntu 20.04, I use: amd_iommu=off i8042.noaux trace_clock=local notsc

For more information, see:

View module options loaded into the kernel

PS.: each file below is an option of the module, and its content is its value.


To initialize a module with a particular option (example):

sudo echo "options ath9k nohwcrypt=1" > /etc/modprobe.d/ath9k.conf

List loaded modules (and sort by size)

lsmod | sort -k 2,2n

Display information about a module

modinfo [MODULE_NAME]

Remove a module (don’t use the example)

rmmod --all --stacks [MODULE_NAME]

Load a module

modprobe [MODULE_NAME]

Load modules at startup

For loading modules during boot, edit the file /etc/initramfs-tools/modules.

For loading modules after boot, edit the file /etc/modules.

Then run:

sudo update-initramfs -u

Add a specific module to the blacklist

Edit the file /etc/modprobe.d/blacklist.conf and put the module to blacklist. The folder contains other blacklist files as well.

Then run:

sudo update-initramfs -u

Test input device events (hid, mouse, keyboard)


Remapping keyboard button events

Edit the file /lib/udev/hwdb.d/60-keyboard.hwdb then run:

sudo udevadm hwdb --update

Get information about serial ports

dmesg | egrep --color 'serial | ttyS'

Connect to a system through the serial port

screen /dev/ttyS0 19200

Or also:


Or also:

cu -l /dev/ttyS0 -s 19200

Or also:


Allow the user to access the USB serial port

sudo usermod -a -G dialout $USER

Display monitor resolution and refresh rate


List number of processors

nproc --all

Get information about processors

grep "^model name.*:" /proc/cpuinfo

Get information about RAM

grep "^Mem.*:" /proc/meminfo

Adjust swappiness

Uses 90% of RAM before Linux kernel begins swapping:

sudo echo "vm.swappiness=10" >> /etc/sysctl.conf

Debian package operations

Install ‘.deb’ package

dpkg -i [PACKAGE_FILE]

Uninstall ‘.deb’ package

dpkg -r [PACKAGE_FILE]

Remove residual configs

apt remove --purge -y "$(dpkg -l | grep '^rc' | awk '{print $2}')"

List history of installed packages

zgrep " install " /var/log/dpkg.*

List installed packages

dpkg -l | tail -n +6 | cut -f 3 -d ' '

Or also:

dpkg --get-selections | grep -v "deinstall" | sed 's/\t.*//g'

Or also:

apt --installed list | grep -v "Listing..." | sed 's/\/.*//g'

Create a Debian binary package

debuild -us -uc

Create a Debian source package

debuild -S

Debian packing: clean temporary files

debuild clean

Debian packing: submit packages to the Launchpad

dput ppa ../*.changes

P.S.: You need create the file ~/ with content:

fqdn =
method = ftp
incoming = ~cfgnunes/test
login = anonymous

Forces to remove a package without removing its dependencies

sudo dpkg -r --force-depends [PACKAGE_NAME]

Add missing public keys

sudo apt-key adv --keyserver --recv-key A040830F7FAC5991

Hold (pin) a version of a package

sudo apt-mark hold [PACKAGE_NAME]

Main apt directories


To clean all apt lists, run:

sudo rm -rf /var/lib/apt/lists/archive*
sudo rm -rf /var/lib/apt/lists/security*

Check which package a particular command is from

dpkg -S "$(whereis expand | cut -f 2 -d ' ')"


Iptables firewall: list all rules

sudo iptables -L

Iptables firewall: example that enables the ports 80, 8180, 5432 only for IP

# Remove all rules before
iptables -P INPUT ACCEPT
iptables -t nat -F
iptables -t mangle -F
iptables -F
iptables -X

# Allow establishment of connections initialised by my outgoing packets
iptables -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT

# Accept anything on localhost
iptables -A INPUT -i lo -j ACCEPT

# Individual ports tcp
iptables -A INPUT -p tcp --dport 22 -j ACCEPT # SSH
iptables -A INPUT -p tcp --dport 5432 -s -j ACCEPT # Postgresql
iptables -A INPUT -p tcp --dport 80 -s -j ACCEPT # HTTP
iptables -A INPUT -p tcp --dport 443 -s -j ACCEPT # HTTPS
iptables -A INPUT -p tcp --dport 8180 -s -j ACCEPT

# Drop everything else
iptables -A INPUT -j DROP

# Redirection rules (allowing forwarding from localhost)
#iptables -t nat -A OUTPUT -o lo -p tcp --dport 80 -j REDIRECT --to-port 8180

# Redirection http
#iptables -t nat -A PREROUTING -p tcp -m tcp --dport 80 -j REDIRECT --to-ports 8180

Iptables firewall: make changes permanent

P.S.: Need install the package iptables-persistent.

sudo iptables-save > /etc/iptables/rules.v4
sudo ip6tables-save > /etc/iptables/rules.v6

Change the hostname

sudo nano /etc/hostname
sudo nano /etc/hosts
sudo hostname [NEW_HOSTNAME]

Configures a network interface


Configures a wireless interface


Detailed information about the wireless interface


WPA/WPA2 and WPS cracking

airmon-ng start wlan0
wash -i wlan0mon
reaver -i wlan0mon -b [BSSID] -c [CHANNEL] -vv -K 1 / bully wlan0mon -b [BSSID] -c [CHANNEL]

If you already have the PIN:

reaver -i wlan0mon --b [BSSID] -c [CHANNEL] -vv -p [PIN] / bully wlan0mon -b [BSSID] -c [CHANNEL] -p [PIN]

Enable Wireshark capture

sudo setcap cap_net_raw,cap_net_admin=eip /usr/bin/dumpcap

New method to enable it:

sudo dpkg-reconfigure wireshark-common
sudo usermod -a -G wireshark $USER

Check active hosts on the network

nmap -sP

Check the open ports on a specific IP


Identify a host’s operating system

nmap -O

List open ports from within a server

netstat -ntlp

Sharing and security

Share files with NFS

In the server, install the package nfs-kernel-server. And then:

# Edit the file: /etc/exports
/home/user    *(ro,sync,no_root_squash,no_subtree_check)

# Run the command:
sudo exportfs -a

# Start the service:
sudo /etc/init.d/nfs-kernel-server start

In the client, install the package nfs-common. And then:

# Mount the directory:

Share files with SSH

In the server, install the package openssh-server.

In the client, install the package openssh-client and sshfs. And then:

# Mount the directory:

# You can umount the directory:
fusermount -u [DIRECTORY_TO_MOUNT]

Access terminal with SSH

In the server, install the package openssh-server.

In the client, install the package openssh-client. And then:

# To connect:

Generating an SSH key

ssh-keygen -t rsa -C ""

Or also (for a key with 4096 bits):

ssh-keygen -t rsa -b 4096 -C ""

Change SSH key password

ssh-keygen -m 'PEM' -p -f ~/.ssh/id_rsa

Import an SSH key

mkdir ~/.ssh
chmod 700 ~/.ssh
chmod 600 ~/.ssh/
chmod 600 ~/.ssh/id_rsa
chmod 600 ~/.ssh/config
ssh-add ~/.ssh/id_rsa

SSH connection without password between client and server

Disclose public key generated by the client:

ssh-copy-id -i ~/.ssh/ [REMOTE_HOST]

Export a GPG key

gpg -ao publickey.asc --export 17A6EE6D
gpg -ao privatekey.asc --export-secret-keys 17A6EE6D

Import a GPG key

gpg --import privatekey.asc
gpg --import publickey.asc

Change GPG key password

gpg --edit-key 17A6EE6D
> passwd
> save

File manipulation

Find duplicate files

List duplicate files (recursively):

fdupes -r [DIRECTORY]

List duplicate files (recursively) and asks the user which file to delete:

fdupes -r -d [DIRECTORY]

Renames multiple files

Make a simulation:

rename -n "s/[OLD_STRING]/[NEW_STRING]/" [FILES]

Performs the rename operation:


Set permissions recursively

find . -type f -exec chmod 644 {} \;
find . -type d -exec chmod 755 {} \;
find . -iname "*.sh" -type f -exec chmod +x {} \;

Delete empty directories

find . -type d -empty -exec rmdir {} \;

Or also:

find . -type d -empty -delete

Find directories with write permission

find . -type d -writable 2>/dev/null

Change file modification date

touch -t 200404281200 [FILES]

Batch execution

Run batch command with the find command

This example do: ls 01.jpg and then ls 02.jpg:

find . -iname '*.jpg' -exec ls {} \;

This example do: ls 01.jpg 02.jpg:

find . -iname '*.jpg' -exec ls {} \+

Run commands in parallel

Using xargs command (maximum number of processes):

ls -1 *.svg | xargs -P0 -I{} 7z a -mx9 {}.7z {}

Using xargs command (4 processes):

ls -1 *.svg | xargs -P4 -I{} 7z a -mx9 {}.7z {}

Using parallel command (maximum number of processes):

ls -1 *.svg | parallel "7z a -mx9 {.}.7z {}"

Using parallel command (4 processes):

ls -1 *.svg | parallel --jobs 4 "7z a -mx9 {.}.7z {}"

Create scripts that run commands in parallel

Follow the idea:

command1 &
command2 &
command3 &
command4 &

Run a command every 3 seconds

P.S: If you don’t specify the parameter n, the default is 2 seconds.

watch -n 3 echo "Hello world!"

File compression (archiving)

Group files in ‘tar’ file

tar -v -cf file.tar [FILES]

Decompress ‘tar.gz’ files

tar -xzf file.tar.gz

Create a ‘zip’ file from the current directory

zip -r .

Operations on ‘zip’ files

Displays file informations:

zipinfo -v

Ultra compression:

7z a -mx9 file.nes

Unzips multiple files:

unzip '*.zip'

MP3 files

Normalize audio from MP3 files

mp3gain -c -p -r -s s [FILENAME]

Repair MP3 files

mp3val -f -si -nb -t [FILENAME]

Displays MP3 file informations

mp3val [FILENAME]

MIDI files

List MIDI ports

aplaymidi -l

Play MIDI file through the port

aplaymidi --port 24:00 [FILENAME]

Text manipulation

Extract translation strings

xgettext -d wxlame -s -o wxlame.po -k_ *.cpp *.h

Remove accents in a text

cat file.txt | iconv -f ISO-8859-1 -t ascii//TRANSLIT > output.txt

Convert TABS to SPACES

expand -t 4 file.txt

Search for strings within files recursively

Case insensitive:

grep -r -i "STRING" [DIRECTORY]

Case sensitive:


With regex:

grep -r -P "REGEX" [DIRECTORY]
grep -r -i --include "*.h" --include "*.cpp" "STRING" [DIRECTORY]

Find files with a specific encoding

find . -type f -exec file --mime {} \; | grep -v "charset=utf-8"

Or also:

find . -type f -exec file -i {} \; | grep "utf-8"

Replace strings in files

find . -type f -iname "*.cpp" -exec sed -i -e "s|wxLame|wxMP3val|g" {} \;

Logs and system information

Display multiple system informations

uname -a > uname-a.log
cat /proc/version_signature > version.log
dmesg > dmesg.log
lspci -vnvn > lspci-vnvn.log
lsusb -v > lsusb-v.log

Display hardware informations (generate a hardware report)

sudo lshw -html > relatorio.html

Display BIOS informations

sudo dmidecode

System administration

Configure the keyboard layout

sudo dpkg-reconfigure keyboard-configuration

To check the configuration, see the file /etc/default/keyboard.

Configure the time zone

sudo dpkg-reconfigure tzdata

Clear all logs (truncate)

sudo find /var/log/* -type f -iname "*log" -exec truncate -s 0 {} \;

Find system files in the system database

locate [FILENAME]

Find a system command path


Creates a file with the history of all commands executed on all users’ machines

find /home -name '.bash_history' -exec cat {} \; > 'bash_history.txt'
cat '/root/.bash_history' >> 'bash_history.txt'
sort 'bash_history.txt' | sed "s/sudo\ //g"| uniq > 'bash_history_filtered.txt'

View scheduled tasks on ‘cron’

crontab -l
ls /etc/cron.hourly/
ls /etc/cron.daily/
ls /etc/cron.weekly/
ls /etc/cron.monthly/

Change the user password

passwd [USER]

Allow passwords less than 4 digits

Edit the file /etc/pam.d/common-password and make this change:

# From
password    [success=1 default=ignore] obscure sha512
# To
password    [success=1 default=ignore] obscure sha512 minlen=4

P.S.: To allow simple passwords, just remove the term “obscure” from the line above.

List the 5 largest directories and files

du -a . | sort -n -r | head -n 5

List the 5 largest files

find . -type f -printf "%k KB\t%p\n" | sort -n -r | head -n 5

Run 32-bit applications on Ubuntu

sudo dpkg --add-architecture i386
sudo apt-get update
sudo apt-get install libc6:i386 libncurses5:i386 libstdc++6:i386

Clear bash history

history -c
history -w

System services

Creating and manage a system service with ‘systemd’

Create service the file:


Or also (for system packages):


Enable and install the service:

sudo systemctl enable [SERVICE_NAME]

Start the service:

sudo systemctl [SERVICE_NAME] start

Check the service status:

sudo systemctl status [SERVICE_NAME]

Creating a scheduled service (timer) with ‘systemd’ for a user

Create the file ~/.config/systemd/user/my_service.service with content:

Description=Run my script


Create the file ~/.config/systemd/user/my_service.timer with content:

Description=Run my script every 30 seconds



Enable and install the service:

systemctl --user enable my_service.timer

Start the service:

systemctl --user start my_service.timer

Display a load time report for each service (systemd)

systemd-analyze blame

Produce a image graph:

systemd-analyze plot > image.svg

Creating and manage a system service with ‘System V init’

Create service the file:


Enable and install the service (this command creates symbolic links at /etc/rc?.d/):

sudo update-rc.d [SERVICE_NAME] defaults

Start the service:

sudo /etc/init.d/[SERVICE_NAME] start
# Or also
sudo service [SERVICE_NAME] start

If you would like to disable the service:

sudo update-rc.d -f [SERVICE_NAME] disable

If you would like to remove the service:

sudo update-rc.d -f [SERVICE_NAME] remove

Check the status of all services:

sudo service --status-all

Forensic techniques

Recover deleted files

Analyzes the file system, has a wizard (comes with testdisk package):


Recovers various types of files:

foremost -T -v -t all -i /dev/sdb

Program based on the foremost. You must configure the file scalpel.conf (based on the file /usr/local/etc/foremost.conf).

scalpel /dev/sdb -c scalpel.conf -o DirOutput

Erase data (anti-forensic)

Clean the disk by creating a large file in the free space:

sfill -v [DIRECTORY]

Clean the disk by creating a large file in the free space (fast mode and filling it with zeros at the end):

sfill -f -l -l -z -v [DIRECTORY]

Safely remove files:

srm -v [FILE]

Clear the entire disk with zero values:

sudo dd if=/dev/zero of=/dev/sdb bs=1M status=progress && sync

Clear the entire disk with random values (slower):

sudo dd if=/dev/urandom of=/dev/sdb bs=1M status=progress && sync

Operations on digital images

Process images in batch

convert -verbose -resize 100x100 -quality 80% *.jpg output.jpg
convert -verbose -resize 50%x50% -quality 80% *.jpg output.jpg
convert *.png -crop 1050x1500+10+120 output.png
convert *.png -density 300 output.jpg

Convert SVG to PDF

inkscape -f q10_16.svg -A q10_16.pdf

Convert a list of images to GIF format

convert -delay 20 -loop 0 *.jpg myimage.gif

Remove all EXIF from a JPEG image

exiftool -all= image.jpg

Remove all data (EXIF / IPTC / PhotoShop / ICC / XMP) from a JPEG image

jpegoptim --strip-all image.jpg

Operations on PDF files

Encrypt PDF

qpdf --encrypt "" "[PASSWORD]" 128 --accessibility=n --extract=n --print=none --modify=none -- file.pdf output.pdf

Convert PDF to grayscale

gs -q -dNOPAUSE -dBATCH -dSAFER -sDEVICE=pdfwrite -dEmbedAllFonts=true -dSubsetFonts=true -dAutoRotatePages=/None -sColorConversionStrategy=Gray -dProcessColorModel=/DeviceGray -sOutputFile=output.pdf input.pdf

Compress PDF to high resolution (high quality, color preserving, 300 dpi imgs)

gs -q -dNOPAUSE -dBATCH -dSAFER -sDEVICE=pdfwrite -dEmbedAllFonts=true -dSubsetFonts=true -dAutoRotatePages=/None -dPDFSETTINGS=/prepress -sOutputFile=output.pdf input.pdf

Compress PDF to low resolution (low quality, 150 dpi images)

gs -q -dNOPAUSE -dBATCH -dSAFER -sDEVICE=pdfwrite -dEmbedAllFonts=true -dSubsetFonts=true -dAutoRotatePages=/None -dPDFSETTINGS=/ebook -sOutputFile=output.pdf input.pdf

Extract images from a PDF file

pdfimages file.pdf imagem

Convert PDF to image

convert -verbose -density 300 file.pdf output.png

Create a PDF file from multiple images

convert -verbose *.jpg file.pdf
convert -verbose -resize 50%x50% -density 300 -quality 80% *.jpg file.pdf

Merge (join) multiple PDF files

pdfunite file_{01..26}.pdf output.pdf

Or also (too slow, much memory):

convert file_{01..26}.pdf output.pdf

Convert PDF to text

pdftotext input.pdf output.txt

Optimize a PDF file for web viewing (PDF linearize)

qpdf --linearize input.pdf output.pdf

Uncompress a PDF file stream

qpdf --stream-data=uncompress input.pdf uncompressed.pdf

Compress a PDF file stream

qpdf --stream-data=compress uncompressed.pdf output.pdf

Replace strings in a PDF file

qpdf --stream-data=uncompress input.pdf uncompressed.pdf
sed -i "s/ORIGINALSTRING/NEWSTRING/g" uncompressed.pdf
qpdf --stream-data=compress uncompressed.pdf output.pdf

Remove strings in PDF’s (recursively and in batch)

find . -iname "*.pdf" ! -iname "*_compressed*" ! -iname "*_temp*" -type f -exec qpdf --stream-data=uncompress "{}" {}_temp.pdf \;
find . -iname "*_temp.pdf" -type f -exec sed -i "s/ORIGINALSTRING///g" {} \;
find . -iname "*_temp.pdf" ! -iname "*_compressed*" -type f -exec qpdf --stream-data=compress --linearize "{}" {}_compressed.pdf \;
find . -iname "*_temp.pdf" -type f -exec rm "{}" \;

Operations on DOC files

Convert DOC to text

libreoffice --headless --convert-to "txt:Text (encoded):UTF8" file.doc

Video operations

Video operations with ‘ffmpeg’

H264 video suitable for Android smartphones with 320x480 resolution:

ffmpeg -threads 4 -y -i "input.mp4" -c:v libx264 -preset slow -tune fastdecode -profile:v baseline -level 3.0 -crf 25.0 -filter:v "scale=iw*sar*min(480/(iw*sar)\,320/ih):ih*min(480/(iw*sar)\,320/ih)" -c:a libvo_aacenc -b:a 128k "output.mp4"

Video compatible with Windows XP without codecs (run with Windows Media Player):

ffmpeg -threads 4 -y -i "input.mp4" -c:v wmv1 -b:v 450k -c:a wmav1 "output.wmv"

Video compatible with cell phones - 3gp:

ffmpeg -threads 4 -y -i "input.mp4" -c:v h263 -r 25 -s qcif -c:a libopencore_amrnb -b:a 12.20k -ar 8000 -ac 1 "output.3gp"

Extract MP3 audio from video files:

ffmpeg -threads 4 -y -i "input.mp4" -c:a libmp3lame -b:a 192k -ac 2 -vn "output.mp3"

Extract original audio from video files:

ffmpeg -threads 4 -y -i "input.mp4" -vn -acodec copy audio.aac

Crop start and end of a video:

ffmpeg -threads 4 -y -ss 50 -t 88 -i "input.mp4" -c:a copy -c:v copy "output.mp4"

Mix video and audio (also adds a 1.2 second audio delay):

ffmpeg -threads 4 -y -i "input.mp4" -itsoffset 1.2 -i "audio.wav" -map 0:0 -map 1:0 -shortest "output.mp4"

Video for Instagram (mix audio and video):

ffmpeg -threads 4 -y -i "input.mp4" -i "audio.wav" -c:v libx264 -preset slow -tune fastdecode -profile:v baseline -level 3.0 -crf 25.0 -r 30 -b:a 128k -filter:v "scale=iw*sar*min(1280/(iw*sar)\,720/ih):ih*min(1280/(iw*sar)\,720/ih)" -map 0:0 -map 1:0 -shortest "output.mp4"


Untrack files already added to GIT repository based on .gitignore

Step 1: Remove everything from the repository:

git rm -r --cached .

Step 2: Re add everything:

git add .

Step 3: Commit:

git commit -m ".gitignore fix"

Advanced GIT commands

Compress the repository:

git gc --aggressive

Pulls and fetches all tags:

git pull --tags

Modify the last 10 commits:

git rebase -i HEAD~10

Restores everything to the last commit:

git reset --hard origin/master

Add alias in GIT

git config --global checkout
git config --global branch
git config --global commit
git config --global status

Set other settings in GIT

git config --global merge.tool meld
git config --global diff.external meld

Delete remote and local TAG in GIT

git push --delete origin tagname
git tag --delete tagname

Reverse engineering in executables

Display information from an ELF executable

readelf --all file.bin
readelf -p .comment file.bin

Display miscellaneous information about a file

file file.binshared object dependencies
mediainfo file.bin
identify file.bin
identify -verbose file.bin
isoinfo -d -i file.iso

List symbols from object files

nm file.bin

Remove binary symbols and other data from object files

strip -s file.bin

View an executable’s shared object dependencies

ldd file.bin

Extract strings in binary files

strings --all --encoding=b file.bin > output_b.txt
strings --all --encoding=B file.bin > output_B.txt
strings --all --encoding=l file.bin > output_l.txt
strings --all --encoding=L file.bin > output_L.txt
strings --all --encoding=s file.bin > output_s.txt
strings --all --encoding=S file.bin > output_S.txt

Perform dissassembly of the object file (and executables)

objdump -DF executable.bin > "output.txt"

List calls to external libraries from an executable

ltrace ./executable.bin

List calls to system functions from an executable

strace ./executable.bin

Identify the process number using the filename

fuser /bin/bash

List all open files



Create virtual environment

python3 -m venv [DIRECTORY]

Install dependencies from a ‘requirements.txt’ file

pip3 install --upgrade --requirement requirements.txt

Install dependencies for the local user

pip3 install [PACKAGE_NAME] --user

Produce a binary executable from the code

pyinstaller --onefile --windowed --icon=resource/icon-app.ico


Compiling and installing an application with the CMake

mkdir build
cd build
cmake -DCMAKE_INSTALL_PREFIX:PATH=~/.local/ ..
sudo make install

Compiling and installing an application with the Make

mkdir build
cd build
../configure --prefix=~/.local/
sudo make install


Operations on XEN Server

List all VM’s:

xe vm-list

Open the interactive console:


Start a VM:

xe vm-start vm=[UUID]

Shutdown a VM:

xe vm-shutdown vm=[UUID]

List all parameters of a VM:

xe vm-param-list uuid=[UUID]

Changing the size of a VM’s RAM:

xe vm-param-set uuid=[UUID] memory-static-min=256MiB
xe vm-param-set uuid=[UUID] memory-dynamic-min=256MiB
xe vm-param-set uuid=[UUID] memory-static-max=512MiB
xe vm-param-set uuid=[UUID] memory-dynamic-max=512MiB
xe vm-memory-limits-set uuid=[UUID] static-min=16GiB dynamic-min=16GiB dynamic-max=16GiB static-max=16GiB

Change a VM’s CPU amount:

xe vm-param-set uuid=[UUID] platform:cores-per-socket=6
xe vm-param-set uuid=[UUID] VCPUs-max=6
xe vm-param-set uuid=[UUID] VCPUs-at-startup=6

Secure passwords


secret-tool store --label='Password for archives' archive myarchives

Read the stored password:

secret-tool lookup archive myarchives

Compile translation files

msgfmt minha_traducao.po -o

Convert DER certificates to PEM (binary to text)

openssl x509 -in input_cert.crt -inform der -outform pem -out output_cert.pem

Redirect the audio from the microphone to the speaker

pactl load-module module-loopback

Make it possible to use USB in the virtualbox

Edit the file /etc/group and make this change:


Scanning an image (scanner)

scanimage --mode Color --resolution 600 > file.ppm

Copy the text from a tty5 terminal

cat /dev/vcs5 > output.txt

Change user directory paths (Xdg user directories)

Edit the file ~/.config/user-dirs.dirs.

If you want change the language, you can also edit ~/.config/user-dirs.locale.

Define the default Java to be used

sudo update-alternatives --config java
Cristiano Nunes

Cristiano Nunes

A warrior of the light.

comments powered by Disqus
rss facebook twitter github gitlab youtube spotify instagram linkedin medium stackoverflow reddit quora pinterest researchgate download mail skoob scholar scholar