From d08cd1479eac05386e6e6415076ce347ebfc4dff Mon Sep 17 00:00:00 2001 From: Kalyanasundaram Somasundaram Date: Tue, 17 Nov 2020 16:09:40 +0530 Subject: [PATCH] broken image path in linux basics --- courses/linux_basics/command_line_basics.md | 62 +++++----- courses/linux_basics/intro.md | 2 +- .../linux_server_administration.md | 114 +++++++++--------- 3 files changed, 89 insertions(+), 89 deletions(-) diff --git a/courses/linux_basics/command_line_basics.md b/courses/linux_basics/command_line_basics.md index f4d4ea2..54845ff 100644 --- a/courses/linux_basics/command_line_basics.md +++ b/courses/linux_basics/command_line_basics.md @@ -18,7 +18,7 @@ for manual pages. Using \--help to show the documentation for ls command. -![](/images/linux/commands/image19.png) +![](images/linux/commands/image19.png) ## File System Organization @@ -28,7 +28,7 @@ present inside the root directory stores file related to the system. These directories in turn can either store system files or application files or user related files. -![](/images/linux/commands/image17.png) +![](images/linux/commands/image17.png) bin | The executable program of most commonly used commands reside in bin directory sbin | This directory contains programs used for system administration. @@ -62,12 +62,12 @@ At any given moment of time, we will be standing in a certain directory. To get the name of the directory in which we are standing, we can use the pwd command in linux. -![](/images/linux/commands/image2.png) +![](images/linux/commands/image2.png) We will now use the cd command to move to a different directory and then print the working directory. -![](/images/linux/commands/image20.png) +![](images/linux/commands/image20.png) ### cd (change directory) @@ -77,7 +77,7 @@ command, you can move from one directory to another. In the below example, we are initially in the root directory. we have then used the cd command to change the directory. -![](/images/linux/commands/image3.png) +![](images/linux/commands/image3.png) ### ls (list files and directories)** @@ -87,12 +87,12 @@ down all the files and folders present in the given directory. If we just type ls in the shell, it will list all the files and directories present in the current directory. -![](/images/linux/commands/image7.png) +![](images/linux/commands/image7.png) We can also provide the directory name as argument to ls command. It will then list all the files and directories inside the given directory. -![](/images/linux/commands/image4.png) +![](images/linux/commands/image4.png) ## Commands for Manipulating Files @@ -125,7 +125,7 @@ General syntax of using touch command touch ``` -![](/images/linux/commands/image9.png) +![](images/linux/commands/image9.png) ### mkdir (create new directories) @@ -138,7 +138,7 @@ General syntax of using mkdir command mkdir ``` -![](/images/linux/commands/image11.png) +![](images/linux/commands/image11.png) ### rm (delete files and directories) @@ -158,7 +158,7 @@ Let's try to understand the rm command with an example. We will try to delete the file and directory we created using touch and mkdir command respectively. -![](/images/linux/commands/image18.png) +![](images/linux/commands/image18.png) ### cp (copy files and directories) @@ -178,18 +178,18 @@ command to create a new directory named "test_directory". We will now try to copy the "\_test_runner.py" file to the directory we created just now. -![](/images/linux/commands/image23.png) +![](images/linux/commands/image23.png) Do note that nothing happened to the original "\_test_runner.py" file. It's still there in the current directory. A new copy of it got created inside the "test_directory". -![](/images/linux/commands/image14.png) +![](images/linux/commands/image14.png) We can also use the cp command to copy the whole directory from one location to another. Let's try to understand this with an example. -![](/images/linux/commands/image12.png) +![](images/linux/commands/image12.png) We again used the mkdir command to create a new directory called "another_directory". We then used the cp command along with an @@ -214,7 +214,7 @@ already exists in "test_directory". The mv command will just replace it. **Do note that the original file doesn't exist in the current directory after mv command ran successfully.** -![](/images/linux/commands/image26.png) +![](images/linux/commands/image26.png) We can also use the mv command to move a directory from one location to another. In this case, we do not need to use the '-r' flag that we did @@ -227,7 +227,7 @@ directories. Let's see how we can use this command for renaming. We have first changed our location to "test_directory". We then use the mv command to rename the ""\_test_runner.py" file to "test.py". -![](/images/linux/commands/image29.png) +![](images/linux/commands/image29.png) ## Commands for Viewing Files @@ -247,7 +247,7 @@ online bash shell. We will create a new file called "numbers.txt" and insert numbers from 1 to 100 in this file. Each number will be in a separate line. -![](/images/linux/commands/image21.png) +![](images/linux/commands/image21.png) Do not worry about the above command now. It's an advanced command which is used to generate numbers. We have then used a redirection operator to @@ -261,7 +261,7 @@ The most simplest use of cat command is to print the contents of the file on your output screen. This command is very useful and can be used for many other purposes. We will study about other use cases later. -![](/images/linux/commands/image1.png) +![](images/linux/commands/image1.png) You can try to run the above command and you will see numbers being printed from 1 to 100 on your screen. You will need to scroll up to view @@ -276,13 +276,13 @@ from the top. In this example, we are only able to see the first 10 lines from the file when we use the head command. -![](/images/linux/commands/image15.png) +![](images/linux/commands/image15.png) By default, head command will only display the first 10 lines. If we want to specify the number of lines we want to see from start, use the '-n' argument to provide the input. -![](/images/linux/commands/image16.png) +![](images/linux/commands/image16.png) ### tail @@ -290,13 +290,13 @@ The tail command displays the last 10 lines of the file by default. We can include additional arguments to display as many lines as we want from the end of the file. -![](/images/linux/commands/image22.png) +![](images/linux/commands/image22.png) By default, the tail command will only display the last 10 lines. If we want to specify the number of lines we want to see from the end, use '-n' argument to provide the input. -![](/images/linux/commands/image10.png) +![](images/linux/commands/image10.png) In this example, we are only able to see the last 5 lines from the file when we use the tail command with explicit -n option. @@ -310,7 +310,7 @@ programming languages. The echo command prints the given input string on the screen. -![](/images/linux/commands/image24.png) +![](images/linux/commands/image24.png) ## Text Processing Commands @@ -339,7 +339,7 @@ online bash shell. We will create a new file called "numbers.txt" and insert numbers from 1 to 10 in this file. Each number will be in a separate line. -![](/images/linux/commands/image8.png) +![](images/linux/commands/image8.png) ### grep @@ -357,7 +357,7 @@ grep In this example, we are trying to search for a string "1" in this file. The grep command outputs the lines where it found this string. -![](/images/linux/commands/image5.png) +![](images/linux/commands/image5.png) ### sed @@ -373,7 +373,7 @@ sed 's///' Let's try to replace each occurrence of "1" in the file with "3" using sed command. -![](/images/linux/commands/image31.png) +![](images/linux/commands/image31.png) The content of the file will not change in the above example. To do so, we have to use an extra argument '-i' so that the @@ -386,12 +386,12 @@ argument. By default, it will sort in increasing order. Let's first see the content of the file before trying to sort it. -![](/images/linux/commands/image27.png) +![](images/linux/commands/image27.png) Now, we will try to sort the file using the sort command. The sort command sorts the content in lexicographical order. -![](/images/linux/commands/image32.png) +![](images/linux/commands/image32.png) The content of the file will not change in the above example. @@ -415,12 +415,12 @@ I/O redirection is a very powerful feature. In the below example, we have used the '>' operator to redirect the output of ls command to output.txt file. -![](/images/linux/commands/image30.png) +![](images/linux/commands/image30.png) In the below example, we have redirected the output from echo command to a file. -![](/images/linux/commands/image13.png) +![](images/linux/commands/image13.png) We can also redirect the output of a command as an input to another command. This is possible with the help of pipes. @@ -428,13 +428,13 @@ command. This is possible with the help of pipes. In the below example, we have passed the output of cat command as an input to grep command using pipe(\|) operator. -![](/images/linux/commands/image6.png) +![](images/linux/commands/image6.png) In the below example, we have passed the output of sort command as an input to uniq command using pipe(\|) operator. The uniq command only prints the unique numbers from the input. -![](/images/linux/commands/image28.png) +![](images/linux/commands/image28.png) I/O redirection - [https://tldp.org/LDP/abs/html/io-redirection.html](https://tldp.org/LDP/abs/html/io-redirection.html) diff --git a/courses/linux_basics/intro.md b/courses/linux_basics/intro.md index e2c6c69..94e01d7 100644 --- a/courses/linux_basics/intro.md +++ b/courses/linux_basics/intro.md @@ -110,7 +110,7 @@ system by a package manager. ## Linux Architecture -![](/images/linux/commands/image25.png) +![](images/linux/commands/image25.png) - The Linux kernel is monolithic in nature. diff --git a/courses/linux_basics/linux_server_administration.md b/courses/linux_basics/linux_server_administration.md index 601186d..9da1e44 100644 --- a/courses/linux_basics/linux_server_administration.md +++ b/courses/linux_basics/linux_server_administration.md @@ -12,7 +12,7 @@ commands on your own. - We will be running all the commands on Red Hat Enterprise Linux (RHEL) 8 system. - ![](/images/linux/admin/image19.png) + ![](images/linux/admin/image19.png) - We will run most of the commands used in this module in the above docker container. @@ -41,12 +41,12 @@ id command can be used to find the uid and gid associated with an user. It also lists down the groups to which the user belongs to. The uid and gid associated with the root user is 0. -![](/images/linux/admin/image30.png) +![](images/linux/admin/image30.png) A good way to find out the current user in linux is to use the whoami command. -![](/images/linux/admin/image35.png) +![](images/linux/admin/image35.png) **"root" user or superuser is the most privileged user with** **unrestricted access to all the resources on the system. It has UID 0** @@ -58,11 +58,11 @@ command. | /etc/shadow | Stores the password associated with the users | | /etc/group | Stores information about different groups on the system | -![](/images/linux/admin/image23.png) +![](images/linux/admin/image23.png) -![](/images/linux/admin/image21.png) +![](images/linux/admin/image21.png) -![](/images/linux/admin/image9.png) +![](images/linux/admin/image9.png) If you want to understand each filed discussed in the above outputs, you can go through below links: @@ -94,13 +94,13 @@ has been created by tailing the /etc/passwd file. The uid and gid are is /home/shivam and the login shell assigned is /bin/bash. Do note that the user home directory and login shell can be modified later on. -![](/images/linux/admin/image41.png) +![](images/linux/admin/image41.png) If we do not specify any value for attributes like home directory or login shell, default values will be assigned to the user. We can also override these default values when creating a new user. -![](/images/linux/admin/image54.png) +![](images/linux/admin/image54.png) ### passwd @@ -112,11 +112,11 @@ In the above examples, we have not assigned any password for users \"!!\" in an account entry in shadow means the account of an user has been created, but not yet given a password. -![](/images/linux/admin/image13.png) +![](images/linux/admin/image13.png) Let's now try to create a password for user "shivam". -![](/images/linux/admin/image55.png) +![](images/linux/admin/image55.png) Do remember the password as we will be later using examples where it will be useful. @@ -125,7 +125,7 @@ Also, let's change the password for the root user now. When we switch from a normal user to root user, it will request you for a password. Also, when you login using root user, the password will be asked. -![](/images/linux/admin/image39.png) +![](images/linux/admin/image39.png) ### usermod @@ -134,7 +134,7 @@ home directory or the shell. Let's try to modify the login shell of user "amit" to "/bin/bash". -![](/images/linux/admin/image17.png) +![](images/linux/admin/image17.png) In a similar way, you can also modify many other attributes for a user. Try 'usermod -h' for a list of attributes you can modify. @@ -147,7 +147,7 @@ user, all the information related to that user will be removed. Let's try to delete the user "amit". After deleting the user, you will not find the entry for that user in "/etc/passwd" or "/etc/shadow" file. -![](/images/linux/admin/image34.png) +![](images/linux/admin/image34.png) ## Important commands for managing groups @@ -160,11 +160,11 @@ Commands for managing groups are quite similar to the commands used for managing | groupdel \ | Deletes a group | | gpasswd \ | Modifies password for group | -![](/images/linux/admin/image52.png) +![](images/linux/admin/image52.png) We will now try to add user "shivam" to the group we have created above. -![](/images/linux/admin/image33.png) +![](images/linux/admin/image33.png) ## Becoming a Superuser in Linux @@ -175,11 +175,11 @@ described in the above section.** The su command can be used to switch users in linux. Let's now try to switch to user "shivam". -![](/images/linux/admin/image37.png) +![](images/linux/admin/image37.png) Let's now try to open the "/etc/shadow" file. -![](/images/linux/admin/image29.png) +![](images/linux/admin/image29.png) The operating system didn't allow the user "shivam" to read the content of the "/etc/shadow" file. This is an important file in linux which @@ -201,7 +201,7 @@ need to be a part of the sudo group. Let's first switch to the root user using su command. Do note that using the below command will need you to enter the password for the root user. -![](/images/linux/admin/image44.png) +![](images/linux/admin/image44.png) In case, you forgot to set a password for the root user, type "exit" and you will be back as the root user. Now, set up a password using the @@ -211,7 +211,7 @@ passwd command. sudo**. In redhat operating systems, this file is not present by default. We will need to install sudo. -![](/images/linux/admin/image3.png) +![](images/linux/admin/image3.png) We will discuss the yum command in detail in later sections. @@ -220,23 +220,23 @@ information. This file stores the rules that users must follow when running the sudo command. For example, root is allowed to run any commands from anywhere. -![](/images/linux/admin/image8.png) +![](images/linux/admin/image8.png) One easy way of providing root access to users is to add them to a group which has permissions to run all the commands. "wheel" is a group in redhat linux with such privileges. -![](/images/linux/admin/image25.png) +![](images/linux/admin/image25.png) Let's add the user "shivam" to this group so that it also has sudo privileges. -![](/images/linux/admin/image48.png) +![](images/linux/admin/image48.png) Let's now switch back to user "shivam" and try to access the "/etc/shadow" file. -![](/images/linux/admin/image56.png) +![](images/linux/admin/image56.png) We need to use sudo before running the command since it can only be accessed with the sudo privileges. We have already given sudo privileges @@ -253,15 +253,15 @@ allowed to access the files and resources of another user. To see the permissions of a file, we can use the ls command. Let's look at the permissions of /etc/passwd file. -![](/images/linux/admin/image40.png) +![](images/linux/admin/image40.png) Let's go over some of the important fields in the output that are related to file permissions. -![](/images/linux/admin/image31.jpg) +![](images/linux/admin/image31.jpg) -![](/images/linux/admin/image57.png) +![](images/linux/admin/image57.png) ### Chmod command in linux @@ -285,13 +285,13 @@ allowed and 0 representing False or not allowed. We will now create a new file and check the permission of the file. -![](/images/linux/admin/image15.png) +![](images/linux/admin/image15.png) The group owner doesn't have the permission to write to this file. Let's give the group owner or root the permission to write to it using chmod command. -![](/images/linux/admin/image26.png) +![](images/linux/admin/image26.png) Chmod command can be also used to change the permissions of a directory in the similar way. @@ -303,14 +303,14 @@ directories in linux. Command syntax: chown \ \ -![](/images/linux/admin/image6.png) +![](images/linux/admin/image6.png) **In case, we do not have sudo privileges, we need to use sudo command**. Let's switch to user 'shivam' and try changing the owner. We have also changed the owner of the file to root before running the below command. -![](/images/linux/admin/image12.png) +![](images/linux/admin/image12.png) Chown command can also be used to change the owner of a directory in the similar way. @@ -321,7 +321,7 @@ The chgrp command can be used to change the group ownership of files or directories in linux. The syntax is very similar to that of chown command. -![](/images/linux/admin/image27.png) +![](images/linux/admin/image27.png) Chgrp command can also be used to change the owner of a directory in the similar way. @@ -354,19 +354,19 @@ Steps for setting up a passwordless authentication with a remote host: Install openssh package which contains all the commands related to ssh. - ![](/images/linux/admin/image49.png) + ![](images/linux/admin/image49.png) Generate a key pair using the ssh-keygen command. One can choose the default values for all prompts. - ![](/images/linux/admin/image47.png) + ![](images/linux/admin/image47.png) After running the ssh-keygen command successfully, we should see two keys present in the \~/.ssh directory. Id_rsa is the private key and id_rsa.pub is the public key. Do note that the private key can only be read and modified by you. - ![](/images/linux/admin/image7.png) + ![](images/linux/admin/image7.png) 2. Transferring the public key to the remote host @@ -374,23 +374,23 @@ Steps for setting up a passwordless authentication with a remote host: We will look at one of the most common ways of doing it using the ssh-id-copy command. - ![](/images/linux/admin/image11.png) + ![](images/linux/admin/image11.png) Install the openssh-clients package to use ssh-id-copy command. - ![](/images/linux/admin/image46.png) + ![](images/linux/admin/image46.png) Use the ssh-id-copy command to copy your public key to the remote host. - ![](/images/linux/admin/image50.png) + ![](images/linux/admin/image50.png) Now, ssh into the remote host using the password authentication. - ![](/images/linux/admin/image51.png) + ![](images/linux/admin/image51.png) Our public key should be there in \~/.ssh/authorized_keys now. - ![](/images/linux/admin/image4.png) + ![](images/linux/admin/image4.png) \~/.ssh/authorized_key contains a list of public keys. The users associated with these public keys have the ssh access into the remote @@ -401,13 +401,13 @@ Steps for setting up a passwordless authentication with a remote host: General syntax: ssh \@\ \ -![](/images/linux/admin/image14.png) +![](images/linux/admin/image14.png) ### How to transfer files from one host to another host ? General syntax: scp \ \ -![](/images/linux/admin/image32.png) +![](images/linux/admin/image32.png) ## Package Management @@ -435,17 +435,17 @@ the successor to YUM which is now used in Fedora for installing and managing packages. DNF may replace YUM in the future on all RPM based linux distributions. -![](/images/linux/admin/image20.png) +![](images/linux/admin/image20.png) We did find an exact match for the keyword httpd when we searched using yum search command. Let's now install the httpd package. -![](/images/linux/admin/image28.png) +![](images/linux/admin/image28.png) After httpd is installed, we will use the yum remove command to remove httpd package. -![](/images/linux/admin/image43.png) +![](images/linux/admin/image43.png) ## 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. -![](/images/linux/admin/image24.png) +![](images/linux/admin/image24.png) 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) -![](/images/linux/admin/image42.png) +![](images/linux/admin/image42.png) We can use an additional argument with ps command to list the information about the process with a specific process ID. -![](/images/linux/admin/image2.png) +![](images/linux/admin/image2.png) We can use grep in combination with ps command to list only specific processes. -![](/images/linux/admin/image1.png) +![](images/linux/admin/image1.png) ### 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. -![](/images/linux/admin/image53.png) +![](images/linux/admin/image53.png) 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. -![](/images/linux/admin/image22.png) +![](images/linux/admin/image22.png) free command by default shows the memory usage in kilobytes. We can use an additional argument to get the data in human-readable format. -![](/images/linux/admin/image5.png) +![](images/linux/admin/image5.png) ### vmstat The vmstat command can be used to display the memory usage along with additional information about io and cpu usage. -![](/images/linux/admin/image38.png) +![](images/linux/admin/image38.png) ## 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. -![](/images/linux/admin/image36.png) +![](images/linux/admin/image36.png) ### du (disk usage) The du command is used to display disk usage of files and directories on the system. -![](/images/linux/admin/image10.png) +![](images/linux/admin/image10.png) The below command can be used to display the top 5 largest directories in the root directory. -![](/images/linux/admin/image18.png) +![](images/linux/admin/image18.png) ## 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. -![](/images/linux/admin/image16.png) +![](images/linux/admin/image16.png) ### 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. -![](/images/linux/admin/image58.png) +![](images/linux/admin/image58.png) ## Applications in SRE Role