Linux is always tough for newbies but trust me if you treat linux more than OS at the initial stages, you will be so intimated by its power that you may not get use to it easily. So my suggestion linux is just an operating System.
Linux is one of the must to know things in computer science as most of the servers are linux based and one or the other day you have to interact with it. SO lets start with things that you should know to be able to handle servers easily.
Make directory, change directory , copy, move and remove commands.
Yes this are the basic commands are same as they are in windows command prompt.
For creating a directory use
mkdir directory_name
for changing the directory use
cd path_to_directory
Read more about cd options here .
for copying from one location to another
cp [options] source dest
Read more about cp Options here .
for moving from one location to another
mv [options] source dest
Read more about mv options here .
for removing a file or directory
rm filename
rm -R directory_name
Read more about rm here.
How to install packages in Linux.
You can install the packages in linux using commands with respective modification of OS. like for Ubuntu you use
apt-get install package-name
Similarly for other the commands are there just use the commands you can easily find on internet.
Permissions in linux
Here comes the tough part, Permissions, Lets talk about it and make it simple to understand.
Linux permissions are managed by Permissions Groups and Permission Types.
There are three Permission Groups.
Owner – The Owner permissions apply only the owner of the file or directory, they will not impact the actions of other users
Group – The Group permissions apply only to the group that has been assigned to the file or directory, they will not effect the actions of other users.
All users – The All Users permissions apply to all other users on the system, this is the permission group that you want to watch the most.
And the permission types are
Read – The Read permission refers to a user’s capability to read the contents of the file.
Write – This permission allows User to write to the file or not.
Execute – This allows the user to execute the file.
To see the permission go to directory and type
ls -l -a
ls will list files -l will list permissions and -a will list hidden files also
When you see a permission of any file it will be something like this
rw_rw_rwx
Here the first three characters are for owner, next three for group and last three for all users. r is for read, w for write and x for execute.
So for above case.
Owner as permission to read and write, group has permission to read and write, but all users have permission to read, write and execute.
Now how to set permissions, It is done using chmod command like
chmod 640 file_name
Wait wait now you must be thinking what is 640 here. 640 is the representation of permissions in numbers.
It is calculated like below.
r - 4 w - 2 x - 1
Now why 4 2 and 1 why not anything else its because of binary representation see here, when we write the permissions for group or owner or all users it was like rwx or rw_ or something similar.
Here there are three positions first for r second for w and third for x. Now if we see the places in binary and put 1 in these positions it will be like 111 for rwx 110 for rw_. Now if we convert the binary to number 100 is for read this 4 is for read 010 is for write thus 2 is for write and 001 is for execute thus 1 is for execute.
From above 640 means 6 for owner, 6 = 110 thus read and write permission for owner. 4 is for group thus 4 = 100 thus only read for group and 0 thus no permission for all users.
Now you understand the permission for linux and how to change them using chmod.
If you wanna dig deeper into permission try reading this article on linux permissions.
Command to start stop and restart various server.
There is nothing to tell about this. Generally in linux server are added as a service so say you want to start an nginx server you just have to type
sudo service nginx start/restart/stop
sudo service mysql start/restart/stop for mysql.
All the commands are like this only and if there is any diversion you can easily get the commands from their documentation.
Now that you learned basics, permissions and few more commands lets get into GREP.
grep Command
When you are working with servers you have to keep a close watch on logs, search them and analyze them. Now comes the grep which make it very easy to search in directory of file.
grep [options] pattern [files]
Simplest example is lets say we have to find word hello in file test.html
then command will be like
grep hello test.html
Now you want it to be highlighted use
grep --color hello test.html
Say you want to see line number also then type
grep -n --color hello test.html
Grep search is case sensitive, to perform case insensitive search use -i flag
grep -n --color -i hello test.html
Searching in more than one file with extension .html
grep -n --color -i hello *.html
It will search in all the files with extension .html
Now searching in subdirectories, use the -r flag.
grep -n --color -i -r hello *.html
These are few of the basic examples you can read about more here.
Getting Process Id and killing it.
This is important in handling servers as sometimes it may happen you run a script and it started consuming all your resources in that case you have to kill that process.
For getting the process id for firefox
ps ax | grep firefox
This will give process id for all process of firefox.
Now kill the process
kill -9 pid or kill -KILL pid
here pid is Process ID
VIM text editor.
Why Vim is important is that generally on servers you don’t have GUI thus if you need to edit any file you will come across one such CLI editors. VIM is one of those. Here Ill tell some basic things in Vim
For opening a file in VIM
vim path_to_file
For starting editing in file
press i and start changing.
for saving the file
press ESC -> : -> w
it will write changes to the file.
for closing the file
press ESC -> : -> q
Deleting a line
press d
Undo changes
press u
Redo Changes
CTRL + u
For searching
press ? then pattern
These are the things that you must know to handle the servers easily in linux.
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