Welcome to Linux! If you’re a new user, this notes can serve as a quick introduction, as well as a guide to common and practical commands. If you have Linux experience, feel free to skip the introductory material.
Here’s an example command that counts lines of text in a file, myfile
> wc -l myfileHere we will cover the most important Linux commands for the average user, such as ls(list files), grep(search for text),
mplayer(play audio and video files), and df(measure free disk space).
Linux is a popular, open source operating system that competes with Microsoft Windows and Mac OS X. Like these other operating systems, Linux has a graphical user interface with win‐dows, icons, and mouse control. However, the real power of Linux comes from its command-line interface, called the shell,for typing and running commands like the preceding wc.
A Linux command typically consists of a program name followed by options and arguments, typed within a shell, like this:
> wc -l myfileHere the program name wc, short for word count refers to a program somewhere on disk that the shell will locate and run. Options, which usually begin with a dash, affect the behavior of the program. In the preceding command, the -l option tells wc to count lines and not words. The argument myfile specifies the file that wc should read and process.
Commands can have multiple options and arguments. Options may be given individually:
> wc -l -w myfile # Two individual argumentsof command after a single dash:
> wc -lw myfile # same as -l -wor, can take multiple files
> wc -lw myfile myfile2 # count lines in two filesOptions are not standardized. They may be a single dash and one character (say,
-l), two dashes and a word (--lines), or several other formats. Some options are followed by a value, such as-s 10, and space between them might not be required(-s10). Likewise, arguments are not standardized. They usually representfilenames forinput or output, but they can be other things too, likedirectory namesorregular expressions.
Before you can type a command, you must wait for the shell to display a special symbol, called a prompt. A prompt means, “Iam waiting for your next command.”
Your prompt:
>or a complex string of text containing your computer name, username, and possibly other information and symbols
localhost:~rucse$Some command will print text on the screen as they run.
> wc -l myfile
18 filesSome commands are successfully only by an administrator, a special user with permission to do anything on the system (called superuser or root)
> sudo superuser commands goes hereExample:
> wc -l /etc/shadow # This will fail
wc: /etc/shadow: Permission denied> sudo wc -l /etc/shadow
Password: ******
51 /etc/shadowTo give you a feel for Linux, here are 10 simple commands you can try right now.
Note: commands name, options are case sensitive
Display a calender for April 2017
> cal apr 2017
April 2017
Su Mo Tu We Th Fr Sa
1
2 3 4 5 6 7 8
9 10 11 12 13 14 15
16 17 18 19 20 21 22
23 24 25 26 27 28 29
30List the contents of the /bin directory, which contains many commands
> ls /bin
2to3-2.7 more xmodmap
7z most xmore
7za mount Xorg
...........................................................................................Count the number of visible items in your home directory(represented here by a special variable HOME that we will discuss later):
> ls $HOME | wc -l
11See how much space is used on a partition of your hard disk:
> df -h /
Filesystem Size Used Avail Use% Mounted on
/dev/sda2 99G 39G 55G 42% /Watch the processes running on your computer (type "q" to quit):
> top -d1
top - 10:18:21 up 54 min, 1 user, load average: 1.55, 1.17, 1.10
Tasks: 277 total, 1 running, 276 sleeping, 0 stopped, 0 zombie
%Cpu(s): 15.4 us, 5.5 sy, 0.5 ni, 78.6 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
MiB Mem : 7868.2 total, 912.4 free, 4134.5 used, 2821.3 buff/cache
MiB Swap: 3898.0 total, 3890.6 free, 7.4 used. 2859.2 avail Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
19764 nahid 20 0 4851096 309860 107112 S 27.2 3.8 6:12.87 chrome
17490 nahid 20 0 628468 141360 77776 S 3.9 1.8 4:15.79 chrome
8250 nahid 20 0 901892 74332 43840 S 2.9 0.9 2:24.24 Xorg
28419 nahid 20 0 12320 3900 3256 R 2.9 0.0 0:00.09 top
22420 nahid 20 0 4589808 468632 42172 S 1.9 5.8 2:07.70 Microsoft.+
4596 root 35 15 12032 8716 2212 S 1.0 0.1 0:05.04 preload
12532 nahid 20 0 4938516 310452 106932 S 1.0 3.9 2:58.63 gnome-shell
15208 nahid 20 0 1098316 327840 170164 S 1.0 4.1 1:30.69 chrome
16269 nahid 20 0 923528 57860 40620 S 1.0 0.7 0:09.93 gnome-term+
16414 nahid 20 0 18.6g 284488 119140 S 1.0 3.5 3:22.70 code
17535 nahid 20 0 4646264 186248 57052 S 1.0 2.3 0:50.80 code See how long you've been logged in:
> last -1 $USER
nahid :0 :0 Fri Oct 23 09:25 still logged inDownload a file sample.pdf from this book’s website to your current directory, without needing a web browser:
> wget http://linuxpocketguide.com/sample.pdDisplay information about you computer's IP address
> ip addr show eth0
...
inet 192.168.1.21See who owns the domain name oreilly.com (press the space bar to move forward page by page, and type “q” to quit):
> whois oreilly.com | less
Domain Name: OREILLY.COM
Registrar: GODADDY.COM, LLCFinally, clear the windows:
> clearGeneral usage in a simple format:
ls [options..] [files..]
-
stdin: The command reads from standard input (i.e., your key‐board), by default. See “Input and Output” on page 15. -
stdout: The command writes to standard output (i.e., your screen), by default. See “Input and Output” on page 15. -
file: When given a dash (-) argument in place of an input file‐name, the command reads from standard input;
> echo My dog has fleas
My dog has fleas
> echo My name is $USER # Here USER is shell variable
My name is nahid.Sometimes, a command will be too lengthy to fit on one line in the book. In these cases, we’ll split the command onto multiple lines that end with a backward slash character:
> echo This is a long command that does not fit on \
one line
This is a long command that does not fit on one line