Basic Linux CLI commands

sudo: Executing Commands with Elevated Privileges

• Most of the following commands will need to be prefaced with the sudo command. This elevates privileges to the root-user administrative level temporarily, which is necessary when working with directories or files not owned by your user account. When using sudo you will be prompted for your password. Only users with sudo (administrative) privileges will be able to use this command. You should never use normal sudo to start graphical applications as Root (Please see RootSudo for more information on using sudo correctly.)

File & Directory Commands

• The tilde (~) symbol stands for your home directory. If you are user, then the tilde (~) stands for /home/user
• pwd: The pwd command will allow you to know in which directory you’re located (pwd stands for “print working directory”). Example: “pwd” in the Desktop directory will show “~/Desktop”. Note that the Gnome Terminal also displays this information in the title bar of its window. A useful gnemonic is “present working directory.”
• ls: The ls command will show you (‘list’) the files in your current directory. Used with certain options, you can see sizes of files, when files were made, and permissions of files. Example: “ls ~” will show you the files that are in your home directory.
• cd: The cd command will allow you to change directories. When you open a terminal you will be in your home directory. To move around the file system you will use cd. Examples:
  • To navigate into the root directory, use “cd /”
  • To navigate to your home directory, use “cd” or “cd ~”
  • To navigate up one directory level, use “cd ..”
  • To navigate to the previous directory (or back), use “cd -“
  • To navigate through multiple levels of directory at once, specify the full directory path that you want to go to. For example, use, “cd /var/www” to go directly to the /www subdirectory of /var/. As another example, “cd ~/Desktop” will move you to the Desktop subdirectory inside your home directory.
• cp: The cp command will make a copy of a file for you. Example: “cp file foo” will make an exact copy of “file” and name it “foo”, but the file “file” will still be there. If you are copying a directory, you must use “cp -r directory foo” (copy recursively). (To understand what “recursively” means, think of it this way: to copy the directory and all its files and subdirectories and all their files and subdirectories of the subdirectories and all their files, and on and on, “recursively”)
• mv: The mv command will move a file to a different location or will rename a file. Examples are as follows: “mv file foo” will rename the file “file” to “foo”. “mv foo ~/Desktop” will move the file “foo” to your Desktop directory but will not rename it. You must specify a new file name to rename a file.
  • To save on typing, you can substitute ‘~’ in place of the home directory.
  • Note that if you are using mv with sudo you can use the ~ shortcut, because the terminal expands the ~ to your home directory. However, when you open a root shell with sudo -i or sudo -s, ~ will refer to the root account’s home directory, not your own.
• rm: Use this command to remove or delete a file in your directory.
• rmdir: The rmdir command will delete an empty directory. To delete a directory and all of its contents recursively, use rm -r instead.
• mkdir: The mkdir command will allow you to create directories. Example: “mkdir music” will create a directory called “music”.
• man: The man command is used to show you the manual of other commands. Try “man man” to get the man page for man itself. See the “Man & Getting Help” section down the page for more information.
• sudo: The sudo command is used to perform file operations on files that the Root User would only be allowed to change. An example would be trying to move one of your documents that another user accidentally moved to / back to your documents directory. Normally, to move the file, you would type mv /mydoc.odt ~/Documents/mydoc.odt, but you are not allowed to modify files outside of your home directory. To get around this, you would type sudo mv /mydoc.odt ~/Documents/mydoc.odt. This will successfully move the file back to its correct location, provided that you are not a standard user, who has less (administrative) ability than an administrator. Be aware, though, that by using the sudo command, you need to be extra careful. It is easier to damage your system by using the sudo command. For more information about the sudo command, click here.

Running a File Within a Directory

So you’ve decided to run a file using the command-line? Well… there’s a command for that too!

• ./filename.extension

After navigating to the file’s parent directory, this command will enable any Ubuntu user to parse files compiled via gcc or any other programming language. Keep in mind that the ‘extension’ will vary depending upon the language the source code is written in. For example: “.c” for C source, “.cpp” for C++, “.rb” for Ruby, “.py” for python, etc. Also, remember that (in the case of interpreted languages like Ruby & Python) you must have a version of that language installed on Ubuntu before trying to run files written with it.

System Information Commands

Filesystem disk space usage

• df: The df command displays filesystem disk space usage for all mounted partitions. “df -h” is probably the most useful – it uses megabytes (M) and gigabytes (G) instead of blocks to report. (-h means “human-readable”)
• du: The du command displays the disk usage for a directory. It can either display the space used for all subdirectories or the total for the directory you run it on. Example:

user@users-desktop:~$ du /media/floppy
1032    /media/floppy/files
1036    /media/floppy/
user@users-desktop:~$ du -sh /media/floppy
1.1M    /media/floppy/

• -s means “Summary” and -h means “Human Readable”

How to check directories size:

50 biggest directories in /some/path, biggest on top:

du -m /some/path | sort -nr | head -n 50

• free: The free command displays the amount of free and used memory in the system. “free -m” will give the information using megabytes, which is probably most useful for current computers.
• top: The top (‘table of processes’) command displays information on your Linux system, running processes and system resources, including CPU, RAM & swap usage and total number of tasks being run. To exit top, press “q”.
• uname -a: The uname command with the -a option prints all system information, including machine name, kernel name & version, and a few other details. Most useful for checking which kernel you’re using.
• lsb_release -a: The lsb_release command with the -a option prints version information for the Linux release you’re running, for example:

user@computer:~$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 11.10
Release:        11.10
Codename:       oneiric

• ip addr reports on your system’s network interfaces.

Adding A New User

• “adduser newuser” command will create a new general user called “newuser” on your system, and to assign a password for the newuser account use “passwd newuser”.

Options

The default behaviour for a command may usually be modified by adding a —option to the command. The ls command for example has an -s option so that “ls -s” will include file sizes in the listing. There is also a -h option to get those sizes in a “human readable” format.

Options can be grouped in clusters so “ls -sh” is exactly the same command as “ls -s -h”. Most options have a long version, prefixed with two dashes instead of one, so even “ls –size –human-readable” is the same command.

“Man” and getting help

man command, info command and command –help are the most important tools at the command line.

Nearly every command and application in Linux will have a man (manual) file, so finding them is as simple as typing “man “command”” to bring up a longer manual entry for the specified command. For example, “man mv” will bring up the mv (Move) manual.

Move up and down the man file with the arrow keys, and quit back to the command prompt with “q”.

“man man” will bring up the manual entry for the man command, which is a good place to start!

“man intro” is especially useful – it displays the “Introduction to user commands” which is a well-written, fairly brief introduction to the Linux command line.

There are also info pages, which are generally more in-depth than man pages. Try “info info” for the introduction to info pages.

Some software developers prefer info to man (for instance, GNU developers), so if you find a very widely used command or app that doesn’t have a man page, it’s worth checking for an info page.

Virtually all commands understand the -h (or –help) option which will produce a short usage description of the command and it’s options, then exit back to the command prompt. Try “man -h” or “man –help” to see this in action.

Caveat: It’s possible (but rare) that a program doesn’t understand the -h option to mean help. For this reason, check for a man or info page first, and try the long option –help before -h.

Searching for man files

If you aren’t sure which command or application you need to use, you can try searching the man files.

• man -k foo will search the man files for foo. Try “man -k nautilus” to see how this works.
  • Note that this is the same as doing apropos command.
• man -f foo searches only the titles of your system’s man files. Try “man -f gnome”, for example.
  • Note that this is the same as doing whatis command.

Other Useful Things

Prettier Manual Pages

Users who have Konqueror installed will be pleased to find they can read and search man pages in a web browser context, prettified with their chosen desktop fonts and a little colour, by visiting man:/command in Konqueror’s address bar. Some people might find this lightens the load if there’s lots of documentation to read/search.

Pasting in commands

Often, you will be referred to instructions that require commands to be pasted into the terminal. You might be wondering why the text you’ve copied from a web page using ctrl+C won’t paste in with ctrl+V. Surely you don’t have to type in all those nasty commands and filenames? Relax. ctrl+shift+V pastes into a Gnome terminal; you can also do Middle Button Click on your mouse (both buttons simultaneously on a two-button mouse) or Right Click and select Paste from the menu. However, if you want to avoid the mouse and yet paste it, use “Shift+Insert”, to paste the command. If you have to copy it from another terminal / webpage, you can use “Ctrl+Insert” to copy.

Save on typing

Up Arrow or ctrl+p	Scrolls through the commands you’ve entered previously.
Down Arrow or ctrl+n	Takes you back to a more recent command.
Enter	When you have the command you want.
tab	A very useful feature. It autocompletes any commands or filenames, if there’s only one option, or else gives you a list of options.
ctrl+r	Searches for commands you’ve already typed. When you have entered a very long, complex command and need to repeat it, using this key combination and then typing a portion of the command will search through your command history. When you find it, simply press Enter.
History	The history command shows a very long list of commands that you have typed. Each command is displayed next to a number. You can type !x to execute a previously typed command from the list (replace the X with a number). If you history output is too long, then use history | less for a scrollable list.

• Example: you ran history and found you want to use command 1967 . Simply enter

!1967

Change the text

The mouse won’t work. Use the Left/Right arrow keys to move around the line.

When the cursor is where you want it in the line, typing inserts text – ie it doesn’t over type what’s already there.

ctrl+a or Home	Moves the cursor to the start of a line.
ctrl+e or End	Moves the cursor to the end of a line.
esc+b	Moves to the beginning of the previous or current word.
ctrl+k	Deletes from the current cursor position to the end of the line.
ctrl+u	Deletes from the start of the line to the current cursor position.
ctrl+w	Deletes the word before the cursor.
alt+b	Goes back one word at a time.
alt+f	Moves forward one word at a time.
ctrl+w	Deletes the word before the cursor.
alt+c	Capitalizes letter where cursor is and moves to end of word.

More ways to run a terminal

You can also get it with a function key

You can run more than one – in tabs or separate windows

You can also install guake (Gnome), tilda (XFCE / LXDE) or yakuake (KDE) and have a terminal which appears and hides on shortcut key. This can be particularly useful if you use terminal a lot

An extremely handy tool :: Incremental history searching

in terminal enter:

gksudo gedit  ~/.inputrc

• then copy paste and save

"\e[A": history-search-backward
"\e[B": history-search-forward
"\e[C": forward-char
"\e[D": backward-char

• FROM now on and many agree this is the most useful terminal tool saves you a lot of writing/memorizing… all you need to do to find a previous command is to enter say the first 2 or 3 letters and upward arrow will take you there quickly say i want:

for f in *.mid ; do timidity "$f"; done

all i need to do is enter

fo

• and hit upward arrow command will soon appear