Category: Command Line

Create A New User

Today’s article is going to be quick and easy as we simply discuss how you create a new user. This is a fairly basic task and shouldn’t take too long to cover. If you want to create a new user, read on!

If it’s not obvious,  you have a user account. You use this information even if you don’t realize it. Indeed, you use this information when you log into your computer to begin with. When you log in, you’re logging into your user account.

There are other users. You may have a root account or an account for MySQL. If you want to know how many different users are on your system, you can follow along with the following article:

How To: List All Users In Linux

One of the things that helps keep Linux secure is that it’s a true multi-user environment. You can only perform operations on the files you have access to. This is why you use sudo or root.

Managing users is a fundamental task in Linux. This article is going to cover how to create a new user and we’ll be doing so in the terminal. This should be fairly universal and you won’t need to install anything as user management tools will be included by default.

We will use a couple of tools, however. The first among them is:

useradd:

The useradd command is basic and, as the name implies, is used to add new users. There’s nothing complicated about it in today’s article and you can be certain that this is already a tool available to you.

If you’re curious about the command, check the man page:

If you do so, you’ll see that it’s described as this:

useradd – create a new user or update default new user information

So, that’s the correct tool for this job.

passwd:

The other tool we’ll be using is the passwd command. You can again tell by the name what the tool is going to do. Simply, it’s used as a password management tool. This too isn’t all that complicated and you can check the man page with this command:

If you do so, you’ll see that I wasn’t kidding and that this tool does what you think it does. It’s described like so:

passwd – change user password

This is the correct tool for the job. After we create a new user, we’ll assign them a password. If the user wishes, they can change that password on their own.

Create A New User:

As mentioned above, we’ll create a new user with terminal-based tools. This is a nice and universal way to do things. Sure, there are GUI tools out there but this is going to work on any Linux system you’re likely to engage with. You can crack open your favorite terminal, often by just pressing CTRL + ALT + T on your keyboard.

First, we’ll create a new user with the useradd command. The syntax is very simple:

For example:

Now, we’ll add a password. This is also a simple command:

For example:

You’ll be asked to enter the password a couple of times. This is to help ensure that you’ve not made any typographical errors while entering the password. It’s all basic stuff.

Next, you can verify that the new user account has been created. For this next step, we’ll simply use cat and grep.

Again, here’s an example:

The output should look a little something like this:

If you find your user, you’ve done this properly and you’ve learned how to create a new user. I told you that it wouldn’t be too complicated!

Closure:

So… This is an article about how to create a new user. It’s a pretty basic task but one you might just want to know about. You never know when you’ll need to create a new user but now you know where to look if you do need to. User management can be a pretty important task, especially for a server admin.

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Let’s Learn About Grep

I’ve used the grep command many times but haven’t written an article to learn about grep. It seems like a good idea to do so so I can reference this article. That’s something that’s considered a good thing.

The thing is, I’ve tried to write this article before and it just came out terrible. That article never got published. It just wasn’t good enough. As you’ve seen the quality of some of these articles, tells you how bad that attempt went. 

You won’t need to install anything for this article. If you’re using a desktop or a server, you have grep. I’d expect to find grep in embedded systems because it’s just a useful tool. I suppose some companies might have ripped it out of their devices to save space and stop you from rooting around and messing with things.

So, I decided I’d do what I’d done before. I reached out to my buddy ChatGPT and asked them to write an article. Sure enough, ChatGPT did a fine job at it. This doesn’t save me much time. I still need to do all the formatting and that takes more time than you might expect.

So then, let’s get into the article…

About Grep:

The grep command in Linux is a powerful tool used for searching and manipulating text within files or standard input streams. It stands for “global regular expression print” and is primarily used to match patterns in text and display the lines that contain those patterns. grep is highly versatile and widely used in various scenarios, ranging from simple text searches to complex pattern matching and filtering tasks.

Basic Syntax:

The basic syntax for grep is as follows:

  • pattern: The pattern to search for. It can be a simple string or a complex regular expression.
  • file: Optional. The file(s) to search. If not specified, grep reads from standard input.
Common Options:
  • -i or --ignore-case: Ignore case distinctions.
  • -v or --invert-match: Invert the sense of matching, displaying non-matching lines.
  • -r or --recursive: Recursively search subdirectories.
  • -n or --line-number: Prefix each line of output with its line number.
  • -l or --files-with-matches: Display only the names of files containing matches.
  • -E or --extended-regexp: Interpret pattern as an extended regular expression (ERE).
  • -F or --fixed-strings: Interpret pattern as a list of fixed strings (not regular expressions).
Examples:

Basic Text Search:

This command searches for the occurrence of “keyword” in the file file.txt and displays all lines containing that keyword.

Case Insensitive Search:

This command performs a case-insensitive search for the pattern “pattern” in the file file.txt.

Invert Match:

This command displays all lines in file.txt that do not contain the word “exclude”.

Search in Multiple Files:

This command searches for the pattern in both file1.txt and file2.txt.

Recursive Search:

This command recursively searches for the pattern in all files within the specified directory and its subdirectories.

Display Line Numbers:

This command displays the line numbers along with the lines containing the pattern in file.txt.

Regular Expressions:

grep supports regular expressions, allowing for more advanced pattern matching. Regular expressions enable users to define complex search patterns, such as matching specific character sequences, ranges, or repetitions.

For example:

  • . matches any single character.
  • ^ matches the beginning of a line.
  • $ matches the end of a line.
  • [ ] specifies a character class.
  • * matches zero or more occurrences of the preceding element.
  • \ is used to escape special characters.
Additional Information:

The grep command is an essential tool for text processing and manipulation in the Linux terminal. Its versatility, combined with regular expressions, allows users to perform a wide range of tasks, including simple text searches, pattern matching, filtering, and data extraction. Whether it’s analyzing log files, searching for specific information in codebases, or performing system administration tasks, grep remains an indispensable utility for Linux users. Understanding its capabilities and various options can greatly enhance productivity and efficiency when working with text data in the terminal.

Closure:

So, there you have it. You have an AI-generated article about grep. It’s formatted quite differently than I’d normally format it, but it works. I dare say that AI did the job better than I had when I tried in the past.

People worry about AI but it’s just a tool. I am slowly learning when to make it useful to me. I’m not sure how many jobs AI is going to replace, but I can see lots of ways to use AI to make life easier. I can see ways to make AI more educational, such as in this article. It’s a nice overview, I think.

Thanks for reading! If you want to help, or if the site has helped you, you can donate, register to help, write an article, or buy inexpensive hosting to start your site. If you scroll down, you can sign up for the newsletter, vote for the article, and comment.

Find Files Created On A Specific Date

We sure do have a lot of file management articles and this is another one that will help you find files created on a specific date. This is a relatively easy task and you won’t even have to install anything new. If you want to find files created on a specific date, you might as well use this method!

Here’s a similar article.

Find Files Modified On A Specific Day

So, what is file management? To me, it’s manipulating files on your file system. It’s gathering information about the files on your file system. That’s what I mean when I say ‘file management’. I’ve covered a lot of articles with this as a subject.

Seriously… I tag articles with various terms. There are pages and pages of articles that have been tagged with file management.

Articles Tagged With File Management

Yup, that’s a lot of articles. Managing your files is something you do on a daily basis. You’re creating, editing, and moving your files around your file system. That’s file management and that’s okay!

Because this is something you do on a daily basis, even if you don’t pay attention to it, it’s something covered often. Even if you’re just browsing the internet, you’re adding files such as cached files. If you’re emailing with an email client, you have added and deleted files – if not more. File management is a pretty big thing.

Today, we’ll be using two basic commands – ls and grep. Let’s learn more!

The ls Command:

The ls command is an application that lets you list files. There are flags you can use, but it’s a basic application that, at its core, just lists files. You don’t need to install anything. You can verify that ls is available with this command:

The output should look like this:

Check the ls man page with this command:

If you do that, you’ll see that we’re on the right path if we want to find files created on a specific date. The ls command is briefly described as this:

ls – list directory contents

We’ll be using the ls command to output a list of files and we’ll then use the pipe operator to process that output with grep.

The grep Command:

The grep command is one of those commands that’s used in conjunction with another command. By itself, it’s not that useful. It is when you use grep with other commands that you realize how powerful it is.

The grep command is usually used with the | “pipe” operator. The pipe operator takes the output from one command and processes it with another application. I’ve not yet covered this in an article, nor have  I done an article about the grep command. I should do both.

Again, you won’t need to install anything. You can verify this with this command:

The output should match this:

Next, you can check the man page with this command:

grep, egrep, fgrep, rgrep – print lines that match patterns

You can see that there are options. We’ll be using just plain grep. And, as you can deduce, this is yet another process that will help us find files created on a specific date. We’ll take the output from one command and use it with the grep command. This should appear obvious shortly if you have not yet realized how we’ll be proceeding in this article.

Find Files Created On A Specific Date:

Both ls and grep are tools used in the terminal. As such, you can be sure that you’ll need an open terminal. Either open a terminal from your application menu or open a terminal by pressing CTRL + ALT + T on your keyboard. This article assumes that you don’t have year numbers in your file names, as you’ll see…

With your terminal open, we can begin to find files created on a specific date. Further, let’s stay right there in the ~/home/user directory. We’ll keep it simple.

Let’s start with this command:

That will list all your files. Now, let’s add hidden files – with the -a (all) flag with the following command:

Next up, let’s get more information from the ls command with the -l (long listing format) flag. That looks like this:

You should now see that there’s a time listed. We’re going through this just so that the example commands work. This isn’t strictly necessary, it’s just how it is being explained in this article.

If you want, you can sort that output by time. The following example command will show you the time the files were created, starting with the most recent example.

Again, that’s not strictly necessary.

Pay attention to the date section, because that’s what we’ll be using. 

More specifically, we’ll be piping the output from the ls command to the grep command. That’s done like this:

NOTE: You’ll be grepping a pattern. So, if you look carefully, the dates from 1 to 9 have two spaces! You’ll need to grep accordingly!

So, if you wanted to list articles created on the day this will be published, the command would look like this:

Notice that there are two spaces.

If you wanted to find files created on the 10th of February, your command would be different. You don’t add a 2nd space, as there is no second space in the pattern you’re looking for:

That will show you all the files (including the hidden files) that were created on the 10th of February. It does not care about the year and doesn’t show the year field. You’re simply finding files created on a specific date (ignoring the year, of course).

This is still useful.

This is also only true for files created within the past year. The ls command will happily show the date on files older than a year.

Here’s an example where the files are older than a year:

So, to find files including the year, your command now has more spaces to contend with. For this command, you would now add two spaces between the day and the year. Like so:

See the two spaces? That’s essential.

Again, don’t forget that you need two spaces when you’re working with days that are a single digit. If I wanted to find files from the 4th of November in 2022, that command would be this:

REMEMBER: The grep command is used to find patterns and will only find the specified patterns. It’s very specific! It is also very powerful when used properly.

You can do even more with this. If you want to find files older than a year and by the specific year of their creation, you could simply run a command that looks like this:

Of course, you can substitute ‘2020’ with any year you’d like and get results – so long as you have files that were created in that year.

Also, of course, that command is ONLY useful if you do not have year numbers or numbers similar to years in file names. After all, 2022 is 2022 and grep is going to find them all. That’s what grep does – it finds patterns. As such, it’s up to you to pick the patterns you’ve used and this does have a limited functionality if you’ve gone ahead and added dates to your file names.

If you do have numbers in your file names and you don’t have spaces, you can still grep for a pattern. For example, this might work assuming no space in your file name is in front of the year field – which there generally shouldn’t be:

I can’t be too specific because I don’t know if you’ve put numbers/years in your file names. If you have, grep will equally find those. This whole article assumes that you’ve done nothing of the sort.

This can be even handier and here’s a little bit of some bonus information.

Let’s say you have a directory where you’ve stored files for years. Further, you want to know how many files you created in the year 2022. This directory contains files containing many years and you don’t want to just count them.

Well, you can do something about that!

That command lists the files. The grep command then finds files created in 2022. You then pipe that output to the ‘wc’ command to count the lines.

Here’s an example output:

That means I added 8 files to that directory in the year 2023.

It’s pretty complicated. If you have years and spaces in your file names, this isn’t going to work that well for you. If you use patterns that match the output from the ls command, grep will find them. That’s what grep does.

While this does have a bit of a limited use case, it’s more of an exploration of what you can do with two simple commands. Unless you use matching patterns in your file names, this should work just famously for you. Otherwise, not so much – but you can have both fun trying AND you can look for other patterns that you can pass to grep.

Closure:

Well, that was kind of fun. We used the ls and grep commands to find files created on a specific date. There are always so many fun things to do with Linux. Many of these fun things can be done in the terminal. I like to think we both learn and have fun here on this site.

This can also be a handy tool. Let’s say you made some changes and then had some trouble later. You know you added files, but you can’t remember which files those were. Before restoring from a backup, you decide you want to troubleshoot. To do so, you start by finding files you created on the same day that you last changed your system.

Of course, this can be useful in a business setting. If you need to account for a problem, you can find the files created that day. Should there be something amiss, you can find files created on a specific date. If, for example, files were created on a date when no files should have been created… Well, you get the idea.

Perhaps more importantly, this shows what you can do with just two basic Linux commands. You’ll find ls and grep on every single desktop Linux (or server Linux) you touch. There’s no need for you to install something. You don’t have to worry about which package manager you use or building software from scratch because the developers didn’t release a package for your distro. You just use the commands that are already available.

Anyhow, this article is already too long. Sorry about that…

I kid. If I was sorry, I wouldn’t have done it in the first place! Ha! Take that!

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Short: Show File Creation, Modification, and Access Times

Today’s article is short because there’s no reason to make it longer and we’ll just show file creation, modification, and access times. This is just a simple process and won’t take all that much to learn. It shouldn’t take too long to explain.

Files contain metadata. This can be everything from the GPS location of an image file to the kind of camera used. You can even add your metadata fields with audio files, for example.

For example, we’ve previously covered metadata in these articles:

How To: Sanitize Exif Data From Your Digital Images For Privacy Sake
Review: MetaClean (Clean Exif/meta Data From Email Attachments Automatically)

Well, your files contain other metadata. This information includes things like file creation, modification, and access times. You can easily find out when a file was created. It’s easy to show when the file was modified and just as easy to see when the file was last accessed.

Nice and simple, right?

Well, we’ll be using the stat command.

The stat Command:

You won’t need to install anything. You’ll find that the stat application is already available. You can verify this with:

The outcome should match:

You can check the man page with this command:

Doing so will show you that stat is described like:

Which is exactly what we need to show creation, modification, and access times. This will be the correct tool for the job.

Show File Creation, Modification, and Access Times:

This is a terminal-based process and you can usually access your default terminal by pressing CTRL + ALT + T. If that doesn’t work, find the terminal in your application menu.

With your terminal open, list the files:

Now, pick a file…

When you’ve picked a file, use the stat command. The syntax is easy:

When you opened your default terminal, you probably opened it in your home directory. Most of you will have a ~/.bashrc  file, so we’ll use that. An example of this stat command would be:

Here’s an example output:

As you can see, there’s the ‘birth’ (file creation time), an access time, and a changed time. There’s a lot of other information, but that’s outside the scope of this article.

Be sure to read the man page:

You can use several flags to extract just the information you want. If you wanted to, this would be useful for scripting or other programming. You don’t have to have the full output. For this simple and short article, the information isn’t that overwhelming. I see no reason to cover any particular flags unless I intended to cover a half dozen of them. You can find those just fine on your own.

Closure:

This has just been a short article. I wanted to cover the stat command and there’s not much to it – for the average user. File management is a pretty advanced topic and we cover that often. This time around, it’s just file creation, modification, and access times. Nothing too advanced.

I don’t do many of these short articles. I probably should, as they’re quick and get straight to the point. They’re quick articles that should be plenty easy to process and you don’t have to wade through a lot of text to get to the point of the article. If you like them, let me know.

Thanks for reading! If you want to help, or if the site has helped you, you can donate, register to help, write an article, or buy inexpensive hosting to start your site. If you scroll down, you can sign up for the newsletter, vote for the article, and comment.

How To: Crack A PDF Password

I don’t know how handy today’s article is going to be in reality but it’s sort of possible to crack a PDF password. Once you read the article, you’ll see why I said “sort of possible”. The odds of success will vary greatly.

Everybody knows what a PDF file is. It’s a Portable Document Format. This is actually a standard (ISO 32000). You don’t need Adobe products to create, edit, or read PDF-formatted documents. Odds are good that your distro comes with tools for manipulating PDF documents.

It’s possible to password-protect a PDF document. You can have an owner’s password (allowing editing) or you can have a user’s password (allowing you to read the document). This may be something you’ve encountered in the past.

Well, like all things password-protected, it’s possible to crack the password.

What do I mean by crack? I mean it will reveal the password to you in plain text. This will allow you to access the document in one form or another, depending on which password you crack.

This is gonna take some time…

Also, I’ll assume you’re using something based on Debian because I’ve not tested this with other distros. I’ve only tested this on my systems.

The tool we’ll be using is a ‘brute-force’ password cracker. That means it starts from the letter a and works its way up, adding new letters after the rest of the letters have been tried. So, you’ll see aa, ab, ac, ad, and progression along those lines. You can immediately see why this is going to take a while.

The tool we’ll be using is helpfully called ‘pdfcrack’.

pdfcrack:

This pdfcrack is a terminal-based PDF password-cracking tool. You can use brute force or lists of words such as common passwords. You can also specify the character list, though the default is to just use the regular alphabet in both uppercase and lowercase formats.

The pdfcrack application is helpfully described as such:

pdfcrack – Password recovery tool for PDF-files

I’ll assume that you’re only trying to recover passwords on documents you should legally have access to. I assume that you won’t use this to access content that does not belong to you. That seems like a safe assumption!

As you can see, this is the correct tool if you want to crack a PDF password.

Crack A PDF Password:

As mentioned above, you’ll crack passwords in the terminal. That requires an open terminal, so we might as well install pdfcrack in the terminal. Just press CTRL + ALT + T and that will usually open up a terminal for you.

With your terminal now open, install pdfcrack:

With that installed, check the man page:

Download:

Example PDF File

Now, crack it…

As it’s a download, it’s probably in your ~/Downloads directory, but mine is stored in my ~/Documents directory because it’s a document. So, my example:

That uses a very simple password that should be cracked in a few seconds. On my older and slower computer, I was able to do more than 20,000 words per second. This short password should crack almost instantly.

Leave a comment telling me what the password is!

By default, pdfcrack will crack the user password. You can specify which password you wish to crack. Though the syntax is a little wonky. In this case, the syntax is as follows:

Which translates into the following…

For the owner:

For the user:

If you want to pause this, you can! 

To pause a running pdfcrack instance just press CTRL + C. This will save the progress as savedstate.sav. The program will automatically resume when you run the command again. Pretty neat!

There’s a lot you can do with this command. Let’s say you recall the password was between 8 and 12 characters and want to just search in that area.

You can also specify the character set. If you want to use uppercase, lowercase, and numbers you can do that. You just add them to the command with the -c flag, making sure to put them in quotes. That’d look like this:

You can specify a wordlist like so:

The format for that file appears to require one word per line and there are collections of common passwords you can download to help you crack a PDF password.

As you can imagine, and as you were warned near the start, this process can take a while. Assuming you have the right characters loaded and enough time, it’s certain to work eventually.

Go ahead and crack my example file above. That one won’t take you very long, even on a slow computer. It won’t be instantaneous, but it’ll be pretty quick.

If you want, you can also run a benchmark to see how fast your computer is. The command to do that is quite simply this:

I ran this on the slowest computer I use. I didn’t run it on anything faster because I don’t care that much. I’m sure you’ll do better on your computers, though you can share the results as a way to compare your rig with others.

Anyhow, my output was this:

Be sure to check out the man page. It’s a simple application but there are many options available for pdfcrack and you might as well learn about them now. You never know when you’ll find an old PDF document with a forgotten password. It can (and does) happen!

Also, be sure to check the pdfcrack project page.

Closure:

So, you might wonder why I’d include an article like this. After all, isn’t cracking passwords a potential legal mess? Isn’t it immoral to crack passwords? Is it even legal to crack passwords?

The answer is simple enough. It’s a tool you can use to recover your lost passwords. You can use this tool to access things that you shouldn’t be accessing, just like you can use a screwdriver to poke things you shouldn’t be poking. I’m just giving information.

I am also not a lawyer. I permit you to crack the password of the included file. For other files, don’t do anything illegal in your jurisdiction. If it’s a crime, don’t do it. I’m decidedly not your lawyer. If you think this requires asking a lawyer, go ahead and do so.

That and it’s not a great secret. If you’re relying on a password to protect PDF files from anyone serious, you’re probably doing your security wrong. It’s well known that this is possible and that the tools are easily installed. PDF passwords aren’t very good for security, though you can make complicated passwords.

The distro you’re using may very well have pdfcrack available, even if it isn’t one of the Debian-based distros. Just search and you can find it. With some work, you can even mostly install it with PIP. Just click the link above to the project page for more information about that.

As always…

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