dpkg and rpm

saumya043

"Like RPM, it is not designed to directly retrieve packages in day-to-day use, but to install and remove them locally."
i am not able to understand what this line state.

luisviveropena

Hi @saumya043 ,

That means that 'rpm' and 'dpkg' commands are not intended to install packages from repositories, but they can install and remove packages that are present locally on the system. For installing packages we use 'yum/dnf' and 'apt', tools that resolve dependencies.

I hope that's clear enough

Note: next time please provide the Chapter and topic you are referring to, so it's easier to find the information.

Regards,
Luis.

saumya043

@luisviveropena thank you .

luisviveropena

@saumya043 it's a pleasure!

Regards,
Luis.

saumya043

hi luis ,
while doing lab 18.2 in chapter 18 ,I am not able to make changes on /etc/fstab file.how can i do that.

luisviveropena

Hi @saumya043 ,

You need to use 'sudo' or become root in order to edit the /etc/fstab file.

Regards,
Luis.

saumya043

hi luis
thank you....
in chapter 24 while creating raid disk ,we are writing "$ sudo bash -c "mdadm --detail --scan >> /etc/mdadm.conf" a commnad line. can u please explain this command to me

nicolasmendoza

Hi @saumya043 , you need to know the different ways to get information about commands. Using man, help, info, apropos, etc. Are your friends.

sudo bash -c "mdadm --detail --scan >> /etc/mdadm.conf"

1. I see a command "bash" with a -c parameter followed an expression (command) between ", the parameter -c indicates to bash to interprete the expression between " " as a command.

2. I can see the command between " " is using redirection, specifically, append ">>" (if you don't understand the concept of append, pipe, or redirection, please find information about that, this is an essential and important concept in Bash. Basically, this will take the output of the "mdadm --detail --scan" and APPEND (>>) it into the file /etc/mdadm.conf

3. See the man (man is your friend!!) page for mdadm to understand "--detail" and "--scan" option.

man mdadm | less -p ' --detail' (press N to move between results)

     -D, --detail
          Print details of one or more md devices.

man mdadm | less -p ' --scan' (press N to move between results)

  -s, --scan
          Scan config file or /proc/mdstat for...

So, Do you need to know what's the mdadm.conf ?,

ok ...our friend "man" is here

man mdadm.conf

I like to see mdadm.confg like an extra "fstab" for RAID , but the man page explains this better.

---

I recommend you master the basics about redirection, pipe, vars, alias in bash. You will find interesting things. Also if you understand the different ways to find information in Linux, for example,** man -k** is very helpful when you don't have an idea how to do something, also exists apropos but I prefer use man -k.

coop

the sudo bash -c ... is beacuse you cannot do something like "sudo echo something > /etc/file" because the sudo will apply to the echo but not the redirection.

luisviveropena

Hi @saumya043 ,

I think that nicolasmendoza and coop already answered your question

In case you are not sure what the command does, you always can read the documentation for the command, and then run it for testing purposes. Just be sure to try it in a virtual machine, so you don't mess your main system, hehehe.

Many regards,
Luis.