Category: Command Line

How To: Clear Swap

Today’s article is just going to be a quick and easy article, where we learn how to clear swap. I figured I’d do this article while swap was still fresh in my memory so that I’d not forget to write it down the road. If you use swap and want to learn how to clear swap, read on!

Again, this article is only useful for those that use a swap. There are different opinions about using swap and this article is for those who do. I just wrote an article about how to monitor swap, so we might as well learn to clear it.

What do I mean by clearing swap? I mean emptying it. I mean removing all the data held in swap, allowing for data to be written to swap again. It’s not something I worry about, but I know folks have asked about it in the past. I might just as well cover it, though it really won’t take much time.

Clear Swap:

This article requires an open terminal, like many other articles on this site. 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, you can clear swap with the following command, by turning swap off:

You then turn swap back on with:

Tada! You’re all done. If you want, you can do it all with just a one-liner:

That’s really all there is to it. It’s not terribly complicated and it’s something you might as well know if you’re going to use swap and are concerned with monitoring and clearing it.

Closure:

There you have it. I told you that it’d be short and easy. You now know how to clear swap, should you actually want to do so. You might as well know how. It’s bound to come in handy for someone.

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A Couple Of Ways To Monitor Swap Usage

Today’s article will be nice and easy, as we cover just a couple of ways to monitor swap usage. There are several ways to monitor swap usage, so we’ll just cover a couple of them. One of ’em is bound to work.

So, this only applies to those people who use swap. If you use the search feature, you’ll see that I’ve addressed this before and that I tend to use swap – because it’s more than just a place the kernel sticks stuff when you’ve run out of RAM.

swap is still used with plenty of RAM
See? The system happily uses swap with plenty of free rams.

As you can see, on a system with plenty of RAM – and plenty of free RAM – the system still uses swap. I figure that the kernel is smarter than I am. You do you, but I will continue using swap.

But, enough about that. If you don’t use swap, just accept that this article isn’t meant for you and move along. Tomorrow’s article might just have something useful for you. You never know!

So then, I will assume readers know enough about what swap is and will have made their own choices. This article is for those who want to monitor swap usage.

Let’s Monitor Swap Usage:

You guessed it. You’re going to need an open terminal. So, open your favorite terminal emulator. 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, you can try the following command:

(You can just use ‘free‘ but the -m flag makes it easier to read. You can also use ‘free -h‘ if you prefer that output.)

That command should be fairly universal. You can also use the following command if you’d prefer. It’s just:

That command is pretty handy and pretty much is the same as you’d get if you just run’cat /proc/swaps‘ which is, I suppose, yet another way for you to monitor swap usage. Think of it as a bonus way to check swap usage. After all, you can’t have too many ways and one of ’em is bound to stick with you if you use it often enough.

Closure:

And there you have it. You have another article. This time, we’ve discussed how to monitor swap usage (in the terminal, of course). It’s a handy tool for those who do use swap (be it partition or swapfile). If you don’t use swap, you probably won’t get much use from this article. Maybe tomorrow will be more interesting for you?

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Let’s Make An Animated GIF (With ImageMagick)

Today’s article is just for fun, where we learn how to make an animated gif in the terminal – with ImageMagick. It’s just for fun and not something you’ll likely need unless you’re some sort of content creator. (We don’t know any of those, do we?) Anyhow, let’s go ahead and make an animated .gif in the terminal.

Today, we’ll be using ‘ImageMagick’. As far as I know, imagemagick has one of the longest and most complicated man pages. It’s huge and a capable tool in the right hands. ImageMagick has all sorts of capabilities but a new user isn’t likely to use them because of the complexity involved.

And, ImageMagick is complex… In fact, it defines itself as:

ImageMagick – is a free software suite for the creation, modification and display of bitmap images.

That’s an accurate description, I think… Except, well, it does a whole lot more than that. We’ll be using the .gif format, while the man page description only mentions bitmap. So, there’s a lot to the application.

Thus, without further ado, we make an animated gif in the terminal…

How To Make An Animated GIF:

The ImageMagick application is terminal-based. So, you’re going to need an open terminal. If you want, you can just press CTRL + ALT + T and your default terminal should open.

If you don’t have ImageMagick installed, you’ll need to install it. If you’re using a mainstream distro, it’s possibly installed already. Otherwise, it’ll certainly be in your default repositories as it’s a pretty major tool. For example, an apt user would just use a command like this (adjust for your package manager):

With your terminal now open and imagemagick properly installed, let’s just see how long that man page is:

See? I wasn’t kidding!

Now, here’s what you need to make an animated gif:

  1. A dedicated folder, perhaps in your ~/Pictures directory.
  2. A few images of the same format, we’ll use .jpg in our example.
  3. A terminal opened in the above-mentioned dedicated folder.

The first thing to learn is that this command is going to take those images and turn them into an animated file with the .gif extension. It is going to organize them alphanumerically. So, you should rename the  .jpg files in the order you wish to see them (assuming the order matters to you).

All set? Have you done all those things? Are you 100% prepared? Good!

The command we’re looking for would be:

Alright, so the ‘delay 100’ is how long each image will be shown – in hundredths of a second. The ‘-loop 0’ tells it to loop infinitely, or you can pick your own number of times. The ‘*.jpg’ means use all the .jpg files in that directory. The ‘file_name’ is the name of the file you want to have as your output.

See? Pretty simple. An example command might be something like:

Let the command run, and it is a pretty speedy process unless you have a whole lot of images, and you’ll get an animated gif as a result. As these tend to have smaller file sizes, it’s sometimes a better option than sharing a larger video file. It depends on your circumstances, I suppose.

NOTE: This article has been edited to correct the time delay, the delay between changing images. Thanks @wizardfromoz!

Closure:

There you have it. You have an article that tells you how to make an animated gif with ImageMagick. The ImageMagick application has a ton of options, making it daunting for a new Linux user. So, this is just a tiny bite. This is just one of many ways to use ImageMagick. Instead of learning the whole application at once, you can do so in chunks – learning only what you need.

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Let’s Play With Touch And Time

Today’s article is just a fun article where we get the chance to play with touch and time. This article won’t necessarily be something you rely on daily, but it should at least be informative. That and there’s surely a subset of users who use these commands. There’s bound to be! Otherwise, why would they make touch flags for adjusting the time?!?

We’ve used the ‘touch’ command before.

Some Useful Ways To Use The Touch Command In Linux

I’m pretty sure we’ve also used the touch command in at least another article. There are a lot of search results for the word and it’s not important enough to go looking. The key point is that touch is a command you use in the terminal and it describes itself as:

touch – change file timestamps

See, we (and perhaps most other sites) have used the touch command to *make* files, but it’s useful (and intended for) changing file timestamps. Like oh so many commands, there are all sorts of ways to use it and so many folks do things in their own way. The great thing about Linux is that we have so many choices.

This is why I figure I’ll cover touch and time in this article. It’s just a few commands that we’ll be using, so it’s not all that advanced. A beginner probably won’t need to know this sort of information, but it’s information worth sharing.

Playing With Touch And Time:

As we use touch in the terminal, you’re going to need to have an open terminal to play with touch and time. If you don’t know how to open a terminal, press CTRL + ALT + T and your default terminal should open.

With your terminal now open, let’s start by creating a file:

That command will create a file with a created timestamp from the time you ran the command. If you want, you can change the access time, that is the time stored with the file that says when it was last accessed. Run the following command with the -a flag:

That’ll change the ‘foo file’s access time to the time when you ran the command. All well and good? Alright… Let’s remove that file with:

Now, we’re going to create the foo file again, but we’re going to give it a specific timestamp. The format you want is:

Or, something like this:

That will give the file a timestamp from March 3rd at one minute and one second past midnight. Note the period denoting seconds as that’s the only modifier you need for this command.

NOTE: If you use a different time format, that command might be different for you. I don’t think it is, but I’m not set up to test that. If it does matter, please let us know in a comment, thanks!

Finally, let’s say you have a file named ‘bar’ and you want ‘foo’ to have the same timestamp that bar has. You can do that with the touch command. It’s relatively easy to do with the -r flag:

That command will give foo the same timestamp that bar has, should you be inclined to do so. It’s pretty easy to use the touch command to change a timestamp on files, which is why you might not want to rely too much on timestamps. They can be useful, but they are not immutable. 

You can run the command above to delete the foo file when you’re done playing around with the touch command:

Closure:

There you go, another article. This time, we’ve had an article about using touch and time, which is kinda why the touch command exists in the first place. It’s far more useful than just creating files. Be sure to run man touch (no inappropriate jokes) in the terminal to learn more about the touch command. There are other touch commands that you may find yourself interested in, I’ve just covered a few of them.

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How To: Restart SSH

Today’s article will be a very short and easy article, where we learn how to restart SSH. This involves restarting the SSH service. It may not even require a second section, it’s that easy. No, it probably will, just to keep things uniform. So, to learn how to restart SSH read on!

This one is drawn from my own frustration. I recently have had to deal with this a couple of times and I’m not sure why. I’ll root through the logs to figure it out at some point, but the obvious issue here is that I had issues with SSH stopping. More specifically, the SSH daemon/service stopped running.

In my case, I was able to just use another remote connection to the device. I suppose I could have just walked across the house, but it was easier to just use TeamViewer.

Oddly, I’ve had TeamViewer cause problems before. I even have an article detailing how to restart TeamViewer from the terminal (via SSH, I suppose).

So, rather than rebooting the system, I just connected via an alternative method and restarted SSH. It’s easily done.

Restart SSH:

You’ll first need some way of connecting to the device with the stopped SSH service. In the opening section, I mentioned doing so with TeamViewer. It pays to have a backup method to connect to your servers, so you could use VNC or something else that works for you.

If you physically go to the device, or remotely connect to the device, you’ll need a terminal to work with. So, open a terminal. Depending on how you’re connected, you might have to find the terminal in the menu as not all keyboard shortcuts will be passed to the remote computer.

So, once you have a terminal open on the remote computer, try this command:

If that doesn’t work, try this command:

One of those should work for you. Make note of which one works and you, if you think you’ll be doing it often. You can also ‘stop‘ and ‘start‘ services, easily enough, but just a restart should do the trick.

Closure:

See? I told you that it’d be quick and easy. I could use a quick and easy article right now, and this subject just happens to be something I’m currently thinking of. So, you get this as an article, an article about how you restart SSH. Simple and easy…

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 own site. If you scroll down, you can sign up for the newsletter, vote for the article, and comment.

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