This section covers some very basic commands to efficiently work with a Linux system. They should be available on all standard installations. Although many modern Linux variants offer an advanced GUI, it is advisable to be able to control a Linux system from command line.

• ls

  lists files in current directory. Use

  ls -al

  to list all files (including hidden = starting with .) in a long listing.

• mkdir

  creates a directory. Specify the directory name after the command.

• rm

  removes files and directories. If directories need to be removed, the

  -r

  option must be specified. To force operation, add

  -f

  . The last parameters are the files and directories that are to be deleted. Make sure that there are no wrong directories listed! A call to

  rm -rf /

  as root is not a good thing.

• file

  reveals what content type a file is. Use it to test if a file is text, image, binary or whatever.

• sudo

  starts a process with super user (=root) capabilities. To start a root shell, use

  sudo su

  . If

  sudo

  is not installed, use

  su

  instead. It requires not the current user's password but the root password.

• less

  helps to look at what a file stores.

• cat

  reads a file and prints it to

  stdout

  (the console if invoked as-is.)

• locate

  locates all files that contain a given string.

• grep

  searches input for matching lines. To search all files in the current directory (and sub directories), use

  grep -r . -e "text"

  .

• man

  shows the manual for some command. Sometimes

  info

  shows a more detailed documentation.

• dmesg

  prints kernel messages.

The output of one command can be piped into the input of another command. This is done by the pipe operator

|

. To search kernel messages for some string, use

dmesg | grep string

.