Tag: alias

Let’s Make The rm Command A Little Safer

In today’s article, we will discuss a simple trick that will help you make the rm command a little safer. This isn’t something everyone will do, but it might be something a cautious user might do. It might also be something a new user might want to consider doing. After all, you can’t be too safe!

Now, when I say safe, I mean preventing you from accidentally removing files you don’t want to delete. I do not mean safe as in security. I mean safe as in preserving data that is important to you. This isn’t a foolproof method, but it gives you a chance to rethink things.

Obviously, we’ll be using the rm command. Don’t worry, that’s not something you’re going to need to install. It’ll be there with your distro as a part of the standard tools, probably from the nice GNU folks.

For those that don’t know, the rm command is a terminal-based command used to remove files and directories. It does exactly what you tell it to do and sometimes you may tell it to do things you don’t want it to do. Either way, the man page (man rm) describes the rm command succinctly:

rm – remove files or directories

See? Nice and simple.

We’ll also be adding an alias. I intend to write a good article about aliasing things, but this is not that article. Don’t worry, you won’t need to know a whole lot about aliases in order to follow along with this article. I’ll make it nice and simple.

Make The rm Command A Little Safer:

As mentioned in the preamble, the rm command is used in the terminal. So, of course, you’ll need an open terminal for this one. It won’t be too complicated, so press CTRL + ALT + T and your default terminal should open. If it doesn’t, find it in your software menu and open it that way.

NOTE: This article relates to the removal of files over which you the user have control, eg ~/home/<your-username>. If you’re removing files with sudo, root, or as another user, the rm command will function as normal.

Alright, so what’s an alias? An alias is a substitution. You can create an alias that inputs ‘foo’ even though you typed ‘bar’, and that’s the trick we’ll be using to make the rm command a little safer for you. If you don’t do this and you remove important files, all I can say is I told you so! 

I’m going to assume that you have Nano installed. If you do not have Nano installed, you can use a different text editor. For simplicity’s sake, we’ll just go over doing this with Nano.

Let’s Install Nano (With Some Bonus Information)

With Nano installed, your first command is going to be opening up your ~/.bashrc file for editing. You do that with this command:

Yes, the . means that it is a hidden file, but Nano finds it just fine.

Now, you want to use the arrow keys to scroll to the absolute bottom of that file and add the following line:

Next, you’ll save the edited .bashrc file by pressing CTRL + X, then Y, and then ENTER.

With that done, you’ll need to tell the system to reload the .bashrc file. You do that with this command:

Now, when you use the rm command, it will add the -i flag. This will show you the files that the rm command is going to delete and give you a chance to back out of it.

Closure:

See that? You’ve now managed to make the rm command a little safer and you’ve added an alias to the rm command. Pretty neat, I think. This means that you’ve got that second chance when you misfire an rm command. It also means you get to really think about it and that the process doesn’t run without your giving it confirmation to do so.

One of these days I’ll figure out how to write an article about aliases. They’re really handy things to have around and you can use them for all sorts of neat things. I suppose you could just search for that information. Other people have written articles on the subject, probably better than I will. So, there’s always that option… Which is nice…

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Disable Specific Terminal Commands

In today’s article, we’re going to learn how to disable specific terminal commands. It’ll be an interesting article because we get to explore some different tools. It might get a bit verbose, but I’ll do my best! It’s going to be a long article, but I’ll try to keep it at under 1500 words.

It should be noted that this is for people using the bash shell. As I don’t sway too far in that direction, I can’t vouch for it working with something like ZSH or similar. I simply haven’t tested. Feel free to try. I know some of the shell alternatives are compatible so you can check.

Read on to learn how to disable specific terminal commands!

Let’s say you don’t want your computer users (or you yourself)  to run a command in the terminal. Well, you can stop that command from being run easily enough. To do this, we’ll explore some new concepts and tools. One of those topics is ‘aliases’. Let’s just start there…

About Bash Aliases:

In short, bash aliases are alternate ways to enter in a terminal command. You type one thing and the system interprets it as an alias for another command. Let me explain this bit further.

Let’s say you want to run the following command:

Well, if you wanted to, you could assign an alias for those commands. If you wanted, you could even change your aliases so that all you had to type is:

You’ll run the full command when you’ve entered the alias. Aliases are basically little shortcuts to other commands, often used when you want to enter the command quickly and it’s a longer command. You can more or less alias anything with anything if you put enough effort into it.

Getting Ready For Aliases

Still with me? Alright, now you need an open terminal. If you don’t know how to open the terminal, you can do so with your keyboard – just press CTRL + ALT + T and your default terminal should open.

With your terminal now open, let’s check to see if you already have the necessary file. I am aware that you can just add aliases to your ~/.bashrc file, but this way avoids clutter and is more easily portable.

So, we need to check to see if you have ~/.bash_aliases. You can run the following command (from your home directory) to see if you already have the file you need. Simply run:

Now, scan the output from that command. Do you see a .bash_aliases? If so, skip ahead. If not, you will need to create the file yourself. One way to do so is by using the following command:

That command will create a blank file (named .bash_aliases) in your ~/ directory. It is the only file we needed to create and will be the only file we need to edit. You’ll also use nano, which my readers should be familiar with already. Don’t close your terminal yet, we’re still going to need it in the following section.

With just a few tools, we’ll learn how to stop specific terminal commands.

So then…

Disable Specific Terminal Commands:

I had to write that giant intro just to get a newbie up to speed. I’ve been meaning to explain aliases for a while, but I suspect the topic will get its own dedicated article. It’s a pretty broad subject.

For this next session, we’ll use a harmless ‘uptime’ command. Let’s just run that in the terminal just once:

Now, for whatever reason, we will have to pretend that you have decided you want to disable specific terminal commands and uptime is one of those commands. To do that, you’ll start with the following, editing the file you just created:

You will want to start a new line and the command is formatted like so:

For example, you can have an alias like this one:

Save the file with nano. It’s not too daunting a task to save the file. To save a file in nano, all you need to do is press CTRL + X, then Y, and then ENTER

In the above example, if you were to type ‘myip’ into the terminal and run it, it’d almost run the command you told it to run.

You’re almost there. There’d be just another step.

You’ll have to reload the aliases before the system recognizes it as such. I’ll explain how to do that in a second.

Now, if you want to disable specific terminal commands all you need to do is fill the <command> section with a blank space or two. As it is our example, we don’t want the user running this uptime command, it’d look like this:

See? Not all that complicated and we’re almost reaching the end – just one step further and your new alias will work as you’d expect – or not work, as one would expect in this case.

Make Your Alias Permanent:

First, to make that alias stick around you need to have saved the updated ~/.bash_aliases file as was explained above. At this point, the alias will not work. The file you wrote isn’t loaded into memory. It takes a bit more than that.

From here, you could close all your open terminals, log out and back, or reboot – any of those will reload your bash aliases. Alternatively, you can run the following command, which will refresh your terminal’s list of aliases. Like so:

If you’ve done everything properly, you’ll find that this happens when you try to next run the uptime command:

the user is unable to run a specific command - in this case the uptime commnd
That’ll teach ’em from trying to run that pesky uptime command! Catastrophe averted!

But…

If you want to disable specific terminal commands, you might be wanting to do so for security reasons. The ~/.bash_aliases file is owned by the user, so the user can just edit the .bash_aliases file to remove your edit.

So, what can you do? You can make it permanent for everyone. You can add it to /etc/.bashrc, and a user with limited rights won’t be able to edit the file. If they can’t edit the file, they won’t be able to remove the alias. They won’t be able to use the terminal command(s) you’ve aliased to nothing. If you were to simply edit the /etc/bash.bashrc you’d just start a new line at the bottom and then insert the aliases using the same format. 

I haven’t tested it, but I’d wonder if /etc/.bash_aliases might also do the trick in preventing user edits to override your changes. Feel free to test and then let us know. It’d be interesting if you could do something with /etc/skel/ and changing the file permissions – effectively for new users created.

Closure:

There… I think I’ve covered everything. I’ve wanted to write about the bash aliases subject for a while, but it’s just a bit complicated to explain. So, I figured I’d write this article. It’s a long one, but there’s a whole lot to cover. This goes into it pretty heavily, but an aliases-specific article might be nice to have.

Either way, you can now disable specific terminal commands. You can probably temporarily lock yourself out of your own system, so be careful with what aliases you add as system-wide aliases.

If you do lock yourself out, you should be able to boot to a live Linux disk where you’ll mount the drive and just revert your changes. But, anyone with physical access to your computer owns your computer, which is worth keeping in mind.

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