broken image path in linux basics
This commit is contained in:
Kalyanasundaram Somasundaram
parent
ef0416983e
commit
d08cd1479e
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@ -18,7 +18,7 @@ for manual pages.
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Using \--help to show the documentation for ls command.
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## File System Organization
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@ -28,7 +28,7 @@ present inside the root directory stores file related to the system.
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These directories in turn can either store system files or application
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files or user related files.
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bin | The executable program of most commonly used commands reside in bin directory
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sbin | This directory contains programs used for system administration.
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@ -62,12 +62,12 @@ At any given moment of time, we will be standing in a certain directory.
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To get the name of the directory in which we are standing, we can use
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the pwd command in linux.
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We will now use the cd command to move to a different directory and then
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print the working directory.
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### cd (change directory)
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@ -77,7 +77,7 @@ command, you can move from one directory to another.
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In the below example, we are initially in the root directory. we have
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then used the cd command to change the directory.
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### ls (list files and directories)**
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@ -87,12 +87,12 @@ down all the files and folders present in the given directory.
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If we just type ls in the shell, it will list all the files and
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directories present in the current directory.
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We can also provide the directory name as argument to ls command. It
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will then list all the files and directories inside the given directory.
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## Commands for Manipulating Files
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@ -125,7 +125,7 @@ General syntax of using touch command
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touch <file_name>
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```
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### mkdir (create new directories)
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@ -138,7 +138,7 @@ General syntax of using mkdir command
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mkdir <directory_name>
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```
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### rm (delete files and directories)
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@ -158,7 +158,7 @@ Let's try to understand the rm command with an example. We will try to
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delete the file and directory we created using touch and mkdir command
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respectively.
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### cp (copy files and directories)
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@ -178,18 +178,18 @@ command to create a new directory named "test_directory". We will now
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try to copy the "\_test_runner.py" file to the directory we created just
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now.
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Do note that nothing happened to the original "\_test_runner.py" file.
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It's still there in the current directory. A new copy of it got created
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inside the "test_directory".
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We can also use the cp command to copy the whole directory from one
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location to another. Let's try to understand this with an example.
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We again used the mkdir command to create a new directory called
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"another_directory". We then used the cp command along with an
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@ -214,7 +214,7 @@ already exists in "test_directory". The mv command will just replace it.
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**Do note that the original file doesn't exist in the current directory
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after mv command ran successfully.**
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We can also use the mv command to move a directory from one location to
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another. In this case, we do not need to use the '-r' flag that we did
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@ -227,7 +227,7 @@ directories. Let's see how we can use this command for renaming.
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We have first changed our location to "test_directory". We then use the
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mv command to rename the ""\_test_runner.py" file to "test.py".
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## Commands for Viewing Files
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@ -247,7 +247,7 @@ online bash shell.
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We will create a new file called "numbers.txt" and insert numbers from 1
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to 100 in this file. Each number will be in a separate line.
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Do not worry about the above command now. It's an advanced command which
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is used to generate numbers. We have then used a redirection operator to
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@ -261,7 +261,7 @@ The most simplest use of cat command is to print the contents of the file on
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your output screen. This command is very useful and can be used for many
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other purposes. We will study about other use cases later.
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You can try to run the above command and you will see numbers being
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printed from 1 to 100 on your screen. You will need to scroll up to view
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@ -276,13 +276,13 @@ from the top.
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In this example, we are only able to see the first 10 lines from the
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file when we use the head command.
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By default, head command will only display the first 10 lines. If we
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want to specify the number of lines we want to see from start, use the
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'-n' argument to provide the input.
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### tail
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@ -290,13 +290,13 @@ The tail command displays the last 10 lines of the file by default. We
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can include additional arguments to display as many lines as we want
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from the end of the file.
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By default, the tail command will only display the last 10 lines. If we
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want to specify the number of lines we want to see from the end, use '-n'
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argument to provide the input.
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In this example, we are only able to see the last 5 lines from the file
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when we use the tail command with explicit -n option.
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@ -310,7 +310,7 @@ programming languages.
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The echo command prints the given input string on the screen.
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## Text Processing Commands
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@ -339,7 +339,7 @@ online bash shell.
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We will create a new file called "numbers.txt" and insert numbers from 1
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to 10 in this file. Each number will be in a separate line.
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### grep
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@ -357,7 +357,7 @@ grep <word_to_search> <file_name>
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In this example, we are trying to search for a string "1" in this file.
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The grep command outputs the lines where it found this string.
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### sed
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@ -373,7 +373,7 @@ sed 's/<text_to_replace>/<replacement_text>/' <file_name>
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Let's try to replace each occurrence of "1" in the file with "3" using
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sed command.
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The content of the file will not change in the above
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example. To do so, we have to use an extra argument '-i' so that the
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@ -386,12 +386,12 @@ argument. By default, it will sort in increasing order.
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Let's first see the content of the file before trying to sort it.
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Now, we will try to sort the file using the sort command. The sort
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command sorts the content in lexicographical order.
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The content of the file will not change in the above
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example.
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@ -415,12 +415,12 @@ I/O redirection is a very powerful feature.
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In the below example, we have used the '>' operator to redirect the
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output of ls command to output.txt file.
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In the below example, we have redirected the output from echo command to
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a file.
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We can also redirect the output of a command as an input to another
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command. This is possible with the help of pipes.
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@ -428,13 +428,13 @@ command. This is possible with the help of pipes.
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In the below example, we have passed the output of cat command as an
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input to grep command using pipe(\|) operator.
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In the below example, we have passed the output of sort command as an
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input to uniq command using pipe(\|) operator. The uniq command only
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prints the unique numbers from the input.
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I/O redirection -
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[https://tldp.org/LDP/abs/html/io-redirection.html](https://tldp.org/LDP/abs/html/io-redirection.html)
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@ -110,7 +110,7 @@ system by a package manager.
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## Linux Architecture
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- The Linux kernel is monolithic in nature.
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@ -12,7 +12,7 @@ commands on your own.
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- We will be running all the commands on Red Hat Enterprise Linux (RHEL) 8 system.
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- We will run most of the commands used in this module in the above docker container.
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@ -41,12 +41,12 @@ id command can be used to find the uid and gid associated with an user.
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It also lists down the groups to which the user belongs to.
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The uid and gid associated with the root user is 0.
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A good way to find out the current user in linux is to use the whoami
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command.
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**"root" user or superuser is the most privileged user with**
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**unrestricted access to all the resources on the system. It has UID 0**
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@ -58,11 +58,11 @@ command.
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| /etc/shadow | Stores the password associated with the users |
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| /etc/group | Stores information about different groups on the system |
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If you want to understand each filed discussed in the above outputs, you can go
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through below links:
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@ -94,13 +94,13 @@ has been created by tailing the /etc/passwd file. The uid and gid are
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is /home/shivam and the login shell assigned is /bin/bash. Do note that
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the user home directory and login shell can be modified later on.
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If we do not specify any value for attributes like home directory or
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login shell, default values will be assigned to the user. We can also
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override these default values when creating a new user.
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### passwd
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@ -112,11 +112,11 @@ In the above examples, we have not assigned any password for users
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\"!!\" in an account entry in shadow means the account of an user has
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been created, but not yet given a password.
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Let's now try to create a password for user "shivam".
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Do remember the password as we will be later using examples
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where it will be useful.
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@ -125,7 +125,7 @@ Also, let's change the password for the root user now. When we switch
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from a normal user to root user, it will request you for a password.
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Also, when you login using root user, the password will be asked.
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### usermod
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@ -134,7 +134,7 @@ home directory or the shell.
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Let's try to modify the login shell of user "amit" to "/bin/bash".
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In a similar way, you can also modify many other attributes for a user.
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Try 'usermod -h' for a list of attributes you can modify.
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@ -147,7 +147,7 @@ user, all the information related to that user will be removed.
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Let's try to delete the user "amit". After deleting the user, you will
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not find the entry for that user in "/etc/passwd" or "/etc/shadow" file.
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## Important commands for managing groups
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@ -160,11 +160,11 @@ Commands for managing groups are quite similar to the commands used for managing
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| groupdel \<group_name\> | Deletes a group |
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| gpasswd \<group_name\> | Modifies password for group |
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We will now try to add user "shivam" to the group we have created above.
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## Becoming a Superuser in Linux
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@ -175,11 +175,11 @@ described in the above section.**
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The su command can be used to switch users in linux. Let's now try to
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switch to user "shivam".
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Let's now try to open the "/etc/shadow" file.
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The operating system didn't allow the user "shivam" to read the content
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of the "/etc/shadow" file. This is an important file in linux which
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@ -201,7 +201,7 @@ need to be a part of the sudo group.
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Let's first switch to the root user using su command. Do note that using
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the below command will need you to enter the password for the root user.
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In case, you forgot to set a password for the root user, type "exit" and
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you will be back as the root user. Now, set up a password using the
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@ -211,7 +211,7 @@ passwd command.
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sudo**. In redhat operating systems, this file is not present by
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default. We will need to install sudo.
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We will discuss the yum command in detail in later sections.
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@ -220,23 +220,23 @@ information. This file stores the rules that users must follow when
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running the sudo command. For example, root is allowed to run any
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commands from anywhere.
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One easy way of providing root access to users is to add them to a group
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which has permissions to run all the commands. "wheel" is a group in
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redhat linux with such privileges.
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Let's add the user "shivam" to this group so that it also has sudo
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privileges.
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Let's now switch back to user "shivam" and try to access the
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"/etc/shadow" file.
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We need to use sudo before running the command since it can only be
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accessed with the sudo privileges. We have already given sudo privileges
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@ -253,15 +253,15 @@ allowed to access the files and resources of another user.
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To see the permissions of a file, we can use the ls command. Let's look
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at the permissions of /etc/passwd file.
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Let's go over some of the important fields in the output that are
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related to file permissions.
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### Chmod command in linux
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@ -285,13 +285,13 @@ allowed and 0 representing False or not allowed.
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We will now create a new file and check the permission of the file.
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The group owner doesn't have the permission to write to this file. Let's
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give the group owner or root the permission to write to it using chmod
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command.
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Chmod command can be also used to change the permissions of a directory
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in the similar way.
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@ -303,14 +303,14 @@ directories in linux.
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Command syntax: chown \<new_owner\> \<file_name\>
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**In case, we do not have sudo privileges, we need to use sudo
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command**. Let's switch to user 'shivam' and try changing the owner. We
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have also changed the owner of the file to root before running the below
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command.
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Chown command can also be used to change the owner of a directory in the
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similar way.
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@ -321,7 +321,7 @@ The chgrp command can be used to change the group ownership of files or
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directories in linux. The syntax is very similar to that of chown
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command.
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Chgrp command can also be used to change the owner of a directory in the
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similar way.
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@ -354,19 +354,19 @@ Steps for setting up a passwordless authentication with a remote host:
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Install openssh package which contains all the commands related to ssh.
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Generate a key pair using the ssh-keygen command. One can choose the
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default values for all prompts.
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After running the ssh-keygen command successfully, we should see two
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keys present in the \~/.ssh directory. Id_rsa is the private key and
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id_rsa.pub is the public key. Do note that the private key can only be
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read and modified by you.
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2. Transferring the public key to the remote host
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@ -374,23 +374,23 @@ Steps for setting up a passwordless authentication with a remote host:
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We will look at one of the most common ways of doing it using the
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ssh-id-copy command.
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Install the openssh-clients package to use ssh-id-copy command.
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Use the ssh-id-copy command to copy your public key to the remote host.
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Now, ssh into the remote host using the password authentication.
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Our public key should be there in \~/.ssh/authorized_keys now.
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\~/.ssh/authorized_key contains a list of public keys. The users
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associated with these public keys have the ssh access into the remote
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@ -401,13 +401,13 @@ Steps for setting up a passwordless authentication with a remote host:
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General syntax: ssh \<user\>@\<hostname/hostip\> \<command\>
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### How to transfer files from one host to another host ?
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General syntax: scp \<source\> \<destination\>
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## Package Management
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@ -435,17 +435,17 @@ the successor to YUM which is now used in Fedora for installing and
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managing packages. DNF may replace YUM in the future on all RPM based
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linux distributions.
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|
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|
||||
|
||||
We did find an exact match for the keyword httpd when we searched using
|
||||
yum search command. Let's now install the httpd package.
|
||||
|
||||
|
||||
|
||||
|
||||
After httpd is installed, we will use the yum remove command to remove
|
||||
httpd package.
|
||||
|
||||
|
||||
|
||||
|
||||
## Process Management
|
||||
|
||||
|
|
@ -457,7 +457,7 @@ used to monitor the processes on linux systems.
|
|||
The ps command is used to know the information of a process or list of
|
||||
processes.
|
||||
|
||||
|
||||
|
||||
|
||||
If you get an error "ps command not found" while running ps command, do
|
||||
install **procps** package.
|
||||
|
|
@ -468,17 +468,17 @@ processes on the system by using the below command.
|
|||
Reference:
|
||||
[https://unix.stackexchange.com/questions/106847/what-does-aux-mean-in-ps-aux](https://unix.stackexchange.com/questions/106847/what-does-aux-mean-in-ps-aux)
|
||||
|
||||
|
||||
|
||||
|
||||
We can use an additional argument with ps command to list the
|
||||
information about the process with a specific process ID.
|
||||
|
||||
|
||||
|
||||
|
||||
We can use grep in combination with ps command to list only specific
|
||||
processes.
|
||||
|
||||
|
||||
|
||||
|
||||
### top
|
||||
|
||||
|
|
@ -486,7 +486,7 @@ The top command is used to show information about linux processes
|
|||
running on the system in real time. It also shows a summary of the
|
||||
system information.
|
||||
|
||||
|
||||
|
||||
|
||||
For each process, top lists down the process ID, owner, priority, state,
|
||||
cpu utilization, memory utilization and much more information. It also
|
||||
|
|
@ -504,19 +504,19 @@ The free command is used to display the memory usage of the system. The
|
|||
command displays the total free and used space available in the RAM
|
||||
along with space occupied by the caches/buffers.
|
||||
|
||||
|
||||
|
||||
|
||||
free command by default shows the memory usage in kilobytes. We can use
|
||||
an additional argument to get the data in human-readable format.
|
||||
|
||||
|
||||
|
||||
|
||||
### vmstat
|
||||
|
||||
The vmstat command can be used to display the memory usage along with
|
||||
additional information about io and cpu usage.
|
||||
|
||||
|
||||
|
||||
|
||||
## Checking Disk Space in Linux
|
||||
|
||||
|
|
@ -528,19 +528,19 @@ used to view disk space on linux.
|
|||
The df command is used to display the free and available space for each
|
||||
mounted file system.
|
||||
|
||||
|
||||
|
||||
|
||||
### du (disk usage)
|
||||
|
||||
The du command is used to display disk usage of files and directories on
|
||||
the system.
|
||||
|
||||
|
||||
|
||||
|
||||
The below command can be used to display the top 5 largest directories
|
||||
in the root directory.
|
||||
|
||||
|
||||
|
||||
|
||||
## Daemons
|
||||
|
||||
|
|
@ -562,7 +562,7 @@ The below examples shows the unit configuration files available at
|
|||
We are more interested in the configuration file that ends with service
|
||||
as these are service units.
|
||||
|
||||
|
||||
|
||||
|
||||
### Managing System Services
|
||||
|
||||
|
|
@ -584,7 +584,7 @@ which can be very useful for viewing system logs and applications logs
|
|||
in linux. These logs can be very useful when you are troubleshooting on
|
||||
the system.
|
||||
|
||||
|
||||
|
||||
|
||||
## Applications in SRE Role
|
||||
|
||||
|
|
|
|||
Loading…
Reference in New Issue