This module introduces Linux commands to beginers. Intermediate and experts can go through this module slectively to augment their linux skills. There three ways to go through these lessons:
- Register for a free account at https://webminal.org and using the in-browser terminal, complete the lessons 1-8.
- If you are using a Windows desktop/laptop, download and install VirtualBox and install a Linux distro on it eg. Ubuntu. Use the linux Virtual Machine (VM) to go through the lessons.
- If you are using Windows 10 or 11, Windows Subsystem for Linux (WSL) is a great option.
- LESSONS
- Lesson 1: Basic commands to navigate directories.
- Lesson 2: Create files, display contents and stats.
- Lesson 3: Copy, rename, delete files.
- Lesson 4: Basic process commands.
- Lesson 5: Manipulate or parse file contents.
- Lesson 6: Changing file attributes.
- Lesson 7: Locate file and its type.
- Lesson 8: System and user details.
Simply type
$ pwd
and press enter key and read on :) title: pwd
Can you see the output similar to /home/yourname ? cool,you have found your current working directory. Congrats,You have joined exclusive club of linux commandline users :)
As you realized typing
pwd
will display your current working directory. Yeah,your home is a directory. Now lets try to create a new directory. Type the following on the prompt
mkdir -v dir1
and press enter key. title: mkdir
Did it say?
mkdir: created directory dir1
Wow, now you created a new directory. Lets say you want to create more than one directory instead of invoking mkdir multiple(three) times-like.
mkdir -v dir2
mkdir -v dir2/dir3
mkdir -v dir2/dir3/dir4
you can simply use
mkdir -vp dir2/dir3/dir4
-p option will create parent directories for dir4 as needed. In this case, it creates dir2,dir3 automatically. Now we have created 4 directories.How to view them?
To view type ls and press enter
ls
title: ls
listed dir1 dir2 as directory content right? Thats exactly what we wanted
dumb tutor: yes, the guy with blue-t-shirt, Yeah, you, why you look so confused?
blue-t-shirt :I created 4 directories, where is the missing
dir3,dir4?Good question.They are created inside
dir2they won't be listed with simple command likels. You need to use complex command to view them. Try this:
ls -R
really "complex" isn't it :P , btw -R stands for recursive.
Okay,we have created new directories and listed them. Now lets move into a new directory.
cd dir2
title: cd
cool,you have changed to dir2 Now confirm this location by using previously learned pwd command. To move into next directory dir3
cd dir3
will place you under "dir3" directory.
Tips and tricks: Typing
cd ..
will move to parent directory.i.e dir2. Now type,
cd -
will move you to previous working directory i.e dir3 Cool ,isn't it? and a simple
cd
will move to the your home directory.
That's it.You have successfully completed lesson1 Now to start next lesson.
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During Lesson1,you have learned how to create directories.
Lets learn to create a new file,
touch file1.txt
and press enter key and read on :)
title: touch
touch command will create a new file or change time stamp of an existing file. Now try again,
touch file1.txt
this time it will change file1.txt created/last access and modified time to current time.
touch file2.txt
will create an empty new file, if the file is not already exists. to view directory contents ,you can also use
dir
title: dir
dir is used to list directory contents. Yeah,as you guessed it correctly, dir is equivalent to ls -C -b (I know you didn't guess that :P)
that is, by default files are listed in columns, sorted vertically, and special characters are represented by backslash escape sequences. To clear a screen, the command is
clear
title: clear
Viola! terminal screen is cleared!!! Lets print some message on the terminal,
echo "hello"
title: echo
Cool! the message is displayed on the screen. Lets redirect the message to a new file instead of screen.
echo "hello" > hello.txt
To append data you must use >> not just >
echo "linux" >> hello.txt
echo "world" >> hello.txt
Done. to view the file content, do
cat hello.txt
title: cat
so now you have viewed the file content. cat is used to display the entire file content.
To view only first two lines from the file
head -2 hello.txt
title: head
see, it showed us first two lines from files. By default, head will display the first 10 lines when you run,
head hello.txt
Now how to view last two lines?. Its simple, use tail
tail -2 hello.txt
title: tail
cool. Thus head will be used to display lines from begining and tail will be used to display last few lines. As with head
tail hello.txt
by default will display last 10 lines from the line.
Lets check some stats of the files and directories we have create so far.
stat hello.txt
title: stat
carefully examine few important fields the output. The first line shows the filename. second line says its a regular file with size as 18. Third line shows Inode number and no. of links to that inode. Fourth one,says owner(Uid), group(Gid) who has read-write permission but other have read permission. Final three lines show access, modified and change time. They mean:
- access - when the file was last accessed/read.
- modified - when the contents was last modified written.
- change - denotes changes to files metadata like changing user permission.
Now lets do a stat on directory.
stat dir1
Compare the previous stat "hello.txt" output with "dir1", before you move. especially find out "dir1" type. That marks the end of lesson2!. Well done!!
Now move to lesson-3.
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On Lesson-1, you learned about directories. With Lesson-2, you learned about files. Now lets learn general file operations.
Now check this command
du
title: du
It displays the disk usage of current directory. (Please note the current total of du output). Use the h switch to output in a human readable format and the x switch to exclude other file systems and ~ denotes your home.
du -xh ~
Tips and tricks:
du can take a long time so you can specify the max. directory depth using --max-depth option.
du --max-depth 3 ~
Now lets copy hello.txt to dir2 directory.
cp -v hello.txt dir2
title: cp
Now file is copied to new location. Now compute the usage again using, du now you should see usage has been increased by file size.
Tips and tricks:
cp -v hello.txt dir2/file2.txt
This will copy hello.txt into dir2 at the same time, rename it as file2.txt.
cp -vr dir2/*.txt dir2/dir3
This will copy all files ending with .txt from dir2 into dir2/dir3.
cp -vr dir2/dir3
This will copy the directory named dir3 to current directory.
Use ls, it should show you dir3.
Now we have copied few files, how do we verify its file integrity? simple cat should be enough. But If its large file or binary file, we can't use cat. We have to use,
md5sum hello.txt
title: md5sum
b8d5079c5d6a9dbb3294b31d318d74c0 is the calculated checksum for a file. This helps with detecting accidental or deliberate file corruption.
When transfering a file from machine to another or downloading files from internet, to verify the file integrity compare md5sum on source and destination machines,
md5sum dir2/hello.txt
should be same as
md5sum hello.txt
now lets move to another command,
mv hello.txt dir2/dir3/dir4/hi.txt
will move a file into directory dir4 and names it as hi.txt. so how mv is different from cp?. Try ls it will not show hello.txt.
When you use cp there exists two copies of a file (similar to copy-paste "ctrl-c" and "ctrl-v") with mv there is one copy (its cut-paste ctrl-x and ctrl-v). unlike (cp, rm) other commands mv don't need -r for directories.
create a new directory dir5
mkdir dir5
now
mv dir2/*.txt dir5
mv dir5 dir50
will move all \*.txt files under dir2 into dir5. then rename the directory dir5 as dir50.
with mv command we moved hello.txt under dir4, instead of accessing them as dir2/dir3/dir4/hi.txt everytime, we can create a link and after that, you can access or edit dir2/dir3/dir4/hi.txt file as simply hello
ln dir2/dir3/dir4/hi.txt hello
Great! you have created a link. There are two types of links, hardlinks. where a same inode pointed by two different names and softlinks which work more like shortcuts.
Hard links are created by default.
stat hello
and perform
stat dir2/dir3/dir4/hi.txt
see both uses same inode and link count shown as 2. Soft links are created using the -s switch.
ln -s dir2/dir3/dir4/hi.txt softlink
again do
stat softlink
and examine its output. New inode is created for this new symbolic link "softlink" but link count remains as 1. To remove individual file use
rm -i file2.txt
will prompt you with a message. rm: remove regular empty file 'file2.txt'? type y to delete the file. To remove directory, first remove it's contents using option -r,
rm -ri dir50/*
Tips and tricks:
If you want to remove files content without begin prompted for confirmation use -f option. It's extremely dangerous to use rm -rf, because you may delete very important files by mistake-so make sure you delete correct files before running rm -rf
rm -rf junk/*
rmdir dir50
rmdir will remove an empty directory. so thats end of lesson3. Good keep going :) Time for lesson4.
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In Lesson 1, you learned about directories. With Lesson 2, you learned about files. With Lesson 3, you have learned about Copying,renaming,deleting files. Now lets learn basic process-related commands.
Now check this widely used
ps
output is nothing but a snapshot of the currently running processes. lets create a new process.
sleep 60 &
can you see process id on screen? Now again do
ps
you can see the sleeping process, now-right? lets see how to stop/kill this process replace 12345 will your sleeping process id, you got above
kill 12345
Check again the running process list with
ps
sleeping process is Gone! right?
Sometimes process won't die with simple kill command, in such cases scream die!die!die! while running kill command. (hehe..just kidding) you have to use -9 option.
kill -9 12345
start two process like
sleep 30 &
sleep 30 &
checking with ps, we can see we have two process named sleep, now type
killall sleep
did it gave an output like
Terminated sleep 30
right? thus killall terminates processes by process name.
Tips and tricks:
killall -u webminal
This kills only processes owned by user webminal
killall -w find
Wait for all find process to die. killall checks once per second if any of the killed processes still exist and only returns if none are left. Note that killall may wait forever if the signal was ignored, had no effect. To find a process id (pid) of a process you can use,
pidof bash
provides the process ID of a running program bash
Tips and tricks:
pidof -s bash
returns only one process id , instead of all process running as bash. You can adjust the pripority of your process by starting a process like,
nice -n 19 sleep 30 &
runs a program with modified scheduling priority. nice runs a command with an adjusted niceness, which affects process scheduling. Nicenesses range from -20 (most favorable scheduling) to 19 (least favorable-the affected processes will run only when nothing else in the system wants to). Only root can increase the priority ,for example setting process nice to -20 others can lower the priority of processes they own.
how to adjust priority of currently running process with pid 12345?
renice -n 19 12345
changes priority of running processes.
renice +1 3176
3176: old priority 0, new priority 1
renice +4 3176
3176: old priority 1, new priority 4
Only root can increase the priority, for example setting process nice to -20. Others can lower the priority of processes they own.
note with renice command, Non super-users can not increase scheduling priorities of their own processes, even if they were the ones that decreased the priorities in the first place.
To adjust priority for all process owned by a user webminal,
renice +1 -u webminal
to display running process, you can also use
top
see it provides a dynamic real-time view of a running system. spend sometime, examining the output. To quit from the top command, press q. To display commands in a tree like structure, type
pstree
display a tree of processes, to display pid, use -p option with pstree.
pstree -p
below command will let us know how long it took to complete a command.
time ls -l
time gives statistics about the program it ran.
real- the elapsed real time between invocation and termination.user- the user CPU time .sys- the system CPU time .
Thanks, you have completed Lesson 4.
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Lets try this widely used
grep "linux" hello
grep searches for matching words or line on the file To search entire directory of files, supply the directory name
grep -r 'Hello'
By default grep is case sensitive (a is not the same as A) but you can ignore case by using the -i switch
grep -i 'lINUX' hello
Tips and tricks:
To display line numbers:
grep -n 'linux' hello
To display lines that don't match the pattern:
grep -v 'world' hello
To count no. of words, lines and character on a file use wc hello title: wc
thus wc counts lines/words/bytes in a file. first field is no. of lines, second column is no.of words and third column denotes no. of bytes.
Tips and tricks:
wc -L hello
to find the length of longest line in the file. Lets create a file with some contents with echo.
echo -e "col1 col2 r1\ncol5 col6 r2\ncol3 col4 r3 " >> new.txt
echo -e "Hello\nlinux\nProgrammers paradise" >> linux.txt
Okay,you have two files new.txt, linux.txt now, lets cut it ! :D
cut -f1 -d' ' new.txt
So it extracted the first column from the file and to extract the third column
cut -f3 -d' ' new.txt
As you have noticed -f can be used to mention the column number and -d is used to specify the delimiter. Now we have seen how to cut a file lets check out the another one ,
paste hello new.txt
paste merges the lines of files
Tips and tricks:
to paste one file at time,
paste -s hello new.txt
In order to sort a file content, we could use
sort new.txt
File contents are sorted. Remember, we have two files new.txt and linux.txt. lets compare them
diff hello linux.txt
Compare files line by line. < denotes first file(hello) and > denotes second file(linux.txt). you can compare three files with
diff3 hello new.txt linux.txt
I'll let you to analyze the output :D we have reached end of lesson-5. move on to lesson-6.
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Lets begin with a command that manipulates pathname,
dirname dir2/dir3/dir4/hi.txt
strip non-directory suffix from path name, gave you the output
dir2/dir3/dir4
lets use the same path with different command this time
basename dir2/dir3/dir4/hi.txt
this strips directory and suffix from pathname and gives the last entry.
hi.txt
Pretty useful commands :D lets change file access permission
chmod -v 666 file1.txt
You should have seen a output like mode of file1.txt changed to 0666 (rw-rw-rw-)
That will set the file file1.txt to be "world writeable". This means the owner, group and others can read and write into file. The same effect can be achived (remember you can verify it by using stat file1.txt) by
chmod a+rw file1.txt
where as below makes it so that no one can read or write into this file, not even it's owner!
chmod a-rw file1.txt
with next command only owner can read or write into this file.
chmod u+rw file1.txt
Tips and tricks:
To change permission for more than one file use the -R switch
chmod -R 644 ~/chmod_dir
now to change file owner,
chown root file1.txt
chown: changing ownership of file1.txt: Operation not permitted
oh,thats expected error message, you can use chown only as root user, but anyway thats the syntax/usage of chown command. Now we can change file owner and group, by
chown root:staff file1.txt
Tips and tricks:
To change permission on all files and sub-directories, use the -R switch.
chown root:staff -R ~/dir2
Use option --from to change files that belongs to specific user group.
chown --from=webminal:webminal root:staff -R ~/dir2
will change the files the belong to webminal user and webminal group to root and other user files left as it is. Lets change the group alone.
chgrp root file1.txt
chgrp: changing group of file1.txt: Operation not permitted
hehe..again thats expected error message :) ,you can use chgrp only as root user, but anyway thats the syntax/usage of chgrp command.
Tips and tricks:
To change the group of dir2 and subfiles to "root".
chgrp -hR root dir2
Thats it we have completed lesson6.
Often we need to figure out a file type,for such task, we can use
file linux.txt
determines the type of a file as ASCII text
file /dev/null
/dev/null: characater special says,its a character device.
Tips and tricks:
You can also find about file system details of special devices. (below command listed here for sake of completeness, you will get permission denied error message)
file -s /dev/sda2
says /dev/sda2: x86 boot sector, code offset 0x52, OEM-ID "NTFS ", sectors/cluster 8, reserved sectors 0, Media descriptor 0xf8, heads 255, hidden sectors 161792, dos < 4.0 BootSector (0x80)
often we need to find the location of a certain file
whereis ls
you should see an output
ls: /bin/ls /usr/share/man/man1p/ls.1p.gz /usr/share/man/man1/ls.1.gz
whereis command will locate source files and binaries, lets see another example, finding source file
whereis stdio.h
will give you
stdio: /usr/include/stdio.h /usr/share/man/man3/stdio.3.gz
Assume, you have installed two version a php (php4 and php5), when you simply type
php
which version will get executed?we don't know. In order to find it out,we use
which php
To locate a binary file or if you have two version of a binary file installed, you can find "which" one is currently used with this command.
Can we use which command to search for a file on a given directory? No, we can't. "which" searches only pre-defined directories shown by echo $PATH.
so in order to search a file on any directory,
find ~ -name "linux.txt"
Searches for files in a directory hierarchy.
Tips and tricks:
To find regular files and invoke the file command on the results, run
find . -type f -exec file '{}' \;
To find regular files and display their attributes using the ls command, run
find . -type f -exec ls -l '{}' \;
To find files over 20 bytes in size and list them out, run
find ~ -type f -size +20c -exec ls -hl {} \;
What this last command does is left as an exercise for you.
find ~ -type f -size +20c -exec cp dir1 {} \;
After you have practised above commands,move to our final lesson see you later.
Use below command to find out how long this system has been up and running,
uptime
uptime gives, the current time, how long the system has been running, how many users are currently logged on, and the system load averages for the past 1, 5,and 15 minutes.
To know current date and time simply use
date
Okay that display the current time of server running webminal.org website.
To display details about currently logged users
who
can you see other linux users ? :)
who -a
print information about users who are currently logged into the system. You can also use a single letter command,
w
see it gives more detailed informatio than who. w can display information about the users currently on the machine, and their processes.The header shows, in this order,the current time,how long the system has been running, how many users are currently logged on, and the system load averages for the past 1, 5, and 15 minutes.
Displays list of mounted file system
mount
provides list of mounted file systems.
Tips and tricks:
to view only ext4 file system,
mount -t ext4
to display free disk space on mounted devices.
df -h
-h switch makes the output more headable for humans. so we found df finds disk usage, but to find memory usage, we need to use
free -m
displays the total amount of free and used physical and swap memory in the system, as well as the buffers used by the kernel.
Wow!Cool,
You have completed the lesson.
TBD