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broken image path in linux basics
This commit is contained in:
Kalyanasundaram Somasundaram
@@ -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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We did find an exact match for the keyword httpd when we searched using
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yum search command. Let's now install the httpd package.
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After httpd is installed, we will use the yum remove command to remove
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httpd package.
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## Process Management
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@@ -457,7 +457,7 @@ used to monitor the processes on linux systems.
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The ps command is used to know the information of a process or list of
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processes.
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If you get an error "ps command not found" while running ps command, do
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install **procps** package.
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@@ -468,17 +468,17 @@ processes on the system by using the below command.
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Reference:
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[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)
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We can use an additional argument with ps command to list the
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information about the process with a specific process ID.
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We can use grep in combination with ps command to list only specific
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processes.
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### top
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@@ -486,7 +486,7 @@ The top command is used to show information about linux processes
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running on the system in real time. It also shows a summary of the
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system information.
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For each process, top lists down the process ID, owner, priority, state,
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cpu utilization, memory utilization and much more information. It also
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@@ -504,19 +504,19 @@ The free command is used to display the memory usage of the system. The
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command displays the total free and used space available in the RAM
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along with space occupied by the caches/buffers.
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free command by default shows the memory usage in kilobytes. We can use
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an additional argument to get the data in human-readable format.
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### vmstat
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The vmstat command can be used to display the memory usage along with
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additional information about io and cpu usage.
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## Checking Disk Space in Linux
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@@ -528,19 +528,19 @@ used to view disk space on linux.
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The df command is used to display the free and available space for each
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mounted file system.
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### du (disk usage)
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The du command is used to display disk usage of files and directories on
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the system.
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The below command can be used to display the top 5 largest directories
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in the root directory.
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## Daemons
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@@ -562,7 +562,7 @@ The below examples shows the unit configuration files available at
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We are more interested in the configuration file that ends with service
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as these are service units.
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### Managing System Services
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@@ -584,7 +584,7 @@ which can be very useful for viewing system logs and applications logs
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in linux. These logs can be very useful when you are troubleshooting on
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the system.
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## Applications in SRE Role
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Reference in New Issue
Block a user