Useful commands

  • Important for installations in the console
    For selection fields press the space bar to mark fields.
  • Search in files
    git grep "[SEARCH]"
  • Unzip files
    tar -xzvf *.gz
    tar -jxvf *.bz2
  • Show current Linux version
    lsb_release -a
  • Update short form
    apt update && apt upgrade -y && apt full-upgrade -y && apt autoremove -y
    The individual commands
    apt update
    apt upgrade
    apt full-upgrade === apt-get dist-upgrade
    apt autoremove
  • Service systems
    Which system does my operating system use? SysVInit or SystemD?
    ps -p 1
    SystemD, New
    systemctl status [SERVICE]
    SystemD, the path to the command is specified explicitly
    /bin/systemctl status [SERVICE]
    SysVInit, Deprecated
    /etc/init.d/[SERVICE] status
    SysVInit, service often associated with /etc/init.d/
    service [SERVICE] status
  • Service commands
    systemctl status [SERVICE]
    systemctl start [SERVICE]
    systemctl stop [SERVICE]
    systemctl restart [SERVICE]
    systemctl enable [SERVICE] (add to autostart)
    systemctl disable [SERVICE]

VirtualBox guest extension

  1. Switch to root user
    su -
  2. Update software
    apt update && apt upgrade -y && apt full-upgrade -y && apt autoremove -y
    Restart when a new Linux kernel has been installed.
  3. Install packages for building kernel modules
    apt install build-essential module-assistant dkms
  4. Preparation for creating kernel modules
    m-a prepare
  5. Insert guest extension
    Devices -> insert guest additions ...
    Run (CD is mounted)
  6. Install guest extension
    sh /media/cdrom0/
  7. Check modules
    lsmod or grep -io vboxguest or xargs modinfo or grep -iw version
  8. Only members of the vboxsf group have access to automatically integrated folders
    vboxsf = VirtualBox shared folder
    sudo adduser [USER] vboxsf
  9. Restart -> Done


  • Show all users
    cat /etc/passwd | cut -d: -f1
  • Switch to root user
    su -
  • Create new user
    adduser [USER]
  • Change user
    su [USER]
  • Add user to group
    adduser [USER] [GROUP]
  • Remove user from group
    deluser [USER] [GROUP]
  • Show groups of the user
    groups [USER]
  • List all groups
  • Delete user
    deluser [USER] --remove-home --remove-all-files
  • Delete group
    delgroup [GROUP]
    visudo ([GROUP] ALL=(ALL:ALL) ALL -> Delete lines if any)
  • Login as www-data
    su -s /bin/bash www-data (no password is set; www-data, to-www or auto-www)

Owners and Rights

  • chown -R [USER]:[GROUP] [FOLDER/FILE]
  • chmod -R 775 [FOLDER/FILE]
  • chmod g+s

Symbolic (umask u=rwx,g=rx,o=)
u = User
g = Group
o = Other
r = read
w = write
x = execute

Octal (umask 022)
0 = read, write and execute
1 = read and write
2 = read and execute
3 = read only
4 = write and execute
5 = write only
6 = execute only
7 = no permissions

Cron Jobs

  • View root cron jobs
    crontab -l
  • Cron jobs are saved here
  • Software specific cron jobs
  • Add cron job
    crontab -u [USERNAME] -e
    crontab -u xoobit -e
    Select editor and insert job entry at the bottom.
  • Control cron jobs
    crontab -u [USERNAME] -l
  • Change cron job
    crontab -u [USERNAME] -e
  • Delete cron job
    crontab -u [USERNAME] -r


  1. Download package
  2. Unzip
    tar -xzvf truecrypt-7.1a-linux-x86.tar.gz
  3. Install
    sudo ./truecrypt-7.1a-setup-x86
  4. Uninstall
  5. Execute


  • apt install filezilla


  • apt install lftp

Run *.sh file

  • chmod +x [FILENAME]
  • ./[FILENAME]

Convert line endings

DOS/Windows line break (CR LF), in Unix System (LF) convert end of line / line break.

  • apt install dos2unix
  • Now you can convert the line endings in both directions
    dos2unix [FILE]
    unix2dos [FILE]
  • Testing
    vi [FILE]
    :x! to leave vi

JDK for NetBeans is already installed

  • Testing
    java -version
  • Folder

Compare two folders

  • diff -rq [FOLDER1] [FOLDER2]
  • -r = Recursively compare any subdirectories found.
  • -q = Output only whether files differ.

Symbolic Link


Uninstall a package

  • dpkg --list
  • Check dependencies
    apt-cache depends [PACKAGE]
  • Remove package
    apt remove [PACKAGE]
  • Remove package and its configuration files
    apt purge [PACKAGE]

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