Linux Command

Privileges

sudo command - run command as root
sudo su - open a root shell
sudo su user - open a shell as user
sudo -k - forget sudo passwords
gksudo command - visual sudo dialog (GNOME)
kdesudo command - visual sudo dialog (KDE)
sudo visudo - edit /etc/sudoers
gksudo nautilus - root file manager (GNOME)
kdesudo konqueror - root file manager (KDE)
passwd - change your password


Display

sudo /etc/init.d/gdm restart - restart X (GNOME)
sudo /etc/init.d/kdm restart - restart X (KDE)
(file) /etc/X11/xorg.conf - display configuration
sudo dpkg-reconfigure -phigh xserver-xorg - reset X configuration
Ctrl+Alt+Bksp - restart X display if frozen
Ctrl+Alt+FN - switch to tty N
Ctrl+Alt+F7 - switch back to X display

This command will usually tell you the vendor and model of your graphic card
list
lspci
lspci -v
lspci -v | less

System Services

start service - start job service (Upstart)
stop service - stop job service (Upstart)
status service - check if service is running (Upstart)
/etc/init.d/service start - start service (SysV)
/etc/init.d/service stop - stop service (SysV)
/etc/init.d/service status - check service (SysV)
/etc/init.d/service restart - restart service (SysV)
runlevel - get current runlevel


Package Management

apt-get update - refresh available updates
apt-get upgrade - upgrade all packages
apt-get dist-upgrade - upgrade Ubuntu version
apt-get install pkg - install pkg
apt-get remove pkg - uninstall pkg
apt-get autoremove - remove obsolete packages
apt-get -f install - try to fix broken packages
dpkg –configure -a - try to fix broken packages
dpkg -i pkg.deb - install file pkg.deb
(file) /etc/apt/sources.list - APT repository list


Network

ifconfig - show network information
iwconfig - show wireless information
sudo iwlist scan - scan for wireless networks
sudo /etc/init.d/networking restart - reset network
(file) /etc/network/interfaces - manual configuration
ifup interface - bring interface online
ifdown interface - disable interface


Special Packages

ubuntu-desktop - standard Ubuntu environment
kubuntu-desktop - KDE desktop
xubuntu-desktop - XFCE desktop
ubuntu-minimal - core Ubuntu utilities
ubuntu-standard - standard Ubuntu utilities
ubuntu-restricted-extras - non-free, but useful
kubuntu-restricted-extras - KDE of the above
xubuntu-restricted-extras - XFCE of the above
build-essential - packages used to compile programs
linux-image-generic - latest generic kernel image
linux-headers-generic - latest build headers


Firewall

ufw enable - turn on the firewall
ufw disable - turn off the firewall
ufw default allow - allow all connections by default
ufw default deny - drop all connections by default
ufw status - current status and rules
ufw allow port - allow traffic on port
ufw deny port - block port
ufw deny from ip - block ip adress


Application Names

nautilus - file manager (GNOME)
dolphin - file manager (KDE)
konqueror - web browser/filemanager (KDE)
kate - text editor (KDE)
gedit - text editor (GNOME)


System

Recovery - Type the phrase “REISUB” while
holding down Alt and SysRq (PrintScrn) with
about 1 second between each letter. Your system
will reboot.
lsb_release -a - get Ubuntu version
uname -r - get kernel version
uname -a - get all kernel information

Moving around in the file system

pwd "Print working directory" - show what dir you're in.
ls -List the contents of a dir.
ls -l -List the contents of a dir and show additional info of the files.
ls -a -List all files, including hidden files.
cd -Change directory.
cd .. -Go to the parent directory.


Manipulating files and directories

cp -Copy a file.
cp -i -Copy a file and ask before overwriting.
cp -r -Copy a directory with its contents.
mv -Move or rename a file.
mv -i -Move or rename a file and ask before overwriting.
rm -Remove a file.
rm -r -Remove a directory with its contents.
rm -i -Ask before removing a file. Good to use with the -r option.
mkdir -Make a directory.
rmdir -Remove an empty directory.


zipping/taring

tar -cvzf mytar.tar.gz sourcefilesordir - creates a new tar file, verbose options on, runs it through gnuzip,f is the filename
tar -xvf mytar.tar.gz destination - extracts a tar file (this example is compressed with gzip), verbosely, f is the filename
gzip fileordir - compresses a file with gzip.
gunzip file.gz - decompresses a file with gzip.
NB gzip only compresses files, it doesn’t collect them into a single file like a tarball does.


More Commands

Arrow Up: scrolls and edits the command history, press enter to activate.
Shift+pgup: scrolls terminal output up
Shift+pgdown: scrolls terminal output down
CTRL-ALT+DEL reboots the system
Shutdown -h now turns the system off
CTRL C kills the current process
CTRL S Stops the tranfer to the terminal
CTRL Q Resumes the transfer to the terminal
CTRL Z Puts the current process in the background.


hostname - Shows the host name of the system you are on
whoami Displays your login name
date - Displays what your machine thinks the date is
who - Shows who is logged into the machine
rwho-a -Shows all users logged into the server network
finger Shows info on chosen user
last - Show the last users logged into the machine
uptime - Shows the systems uptime
PS - Shows the current user processes
PS -A - Shows all process on the system
uname -A -Displays all info on your host.
free -Shows the free memory in KB
df -h -Shows the disk space details
cat/proc/cpuinfo -Shows the CPU information
cat/proc/filesystems -Shows the file system information in use
cat/etc/printcap -Shows if any printers are hooked up
lsmod -Shows the kernel modules loaded


Malicious Commands
You Should (NOT USE) unless you know what you're doing.

This commands will erase your hard drive:
sudo mkfs (This will format your hard drive)
sudo mkfs.ext3 (This will format your hard drive)
sudo mkfs.bfs (This will format your hard drive)
sudo mkfs.cramfs (This will format your hard drive)
sudo mkfs.ext2 (This will format your hard drive)
sudo mkfs.minix (This will format your hard drive)
sudo mkfs.msdos (This will format your hard drive)
sudo mkfs.reiserfs (This will format your hard drive)
sudo mkfs.vfat (This will format your hard drive)

This commands can damage your operating system.

sudo rm -rf / (This will delete all your files on your system)
sudo rm -rf * (This will delete all the files in the current folder)
rm -rf * or rm -rf *.* (This will delete all the files in the current folder)
rm -rf ~/ & (This will destroy your home directory)

If you cannot add contacts on my msn....

Delete your Contacts cache folder
If your contact list is empty or incomplete after you upgrade to Windows Live Messenger, the cached contact list may not have updated correctly. Before you can delete your Contacts cache folder, make sure you can view your complete folder list in Windows Explorer.
View your complete folder list
On the taskbar, right-click Start, and then select Explore.
Click on Tools, and then select Folder Options.
In the Folder Options window, click the View tab.
In the Advanced Settings list, select Show hidden files and folders, make sure Hide extensions for known file types is not selected, and then click OK.
In the Windows Explorer window, click View, select Explorer Bar, and then verify that Folders is checked.

Delete your Contacts cache folder
After changing your Windows Explorer settings:
On the taskbar, right-click Start, and then select Explore.
In the folder list on the left-hand pane, navigate to the folder C:\Documents and Settings\Your Windows logon name\Contacts\Your Messenger email address.
Delete all of the files within the folder Your Messenger email address.
In the folder list on the left-hand pane, navigate to the folder C:\Documents and Settings\Your Windows logon name\Local Settings\Application Data\Microsoft\Windows Live Contacts\Your Messenger email address.
In the Your Messenger email address folder, delete the real and shadow folders.
Close Windows Explorer and try to sign in to Messenger again