Command Line Archives • Page 46 of 77 • Linux Tips

Let’s Find The Size Of A Directory

Today’s article is one where we’re going to find the size of a directory. Why? Because that sounds like something fun to do. The site has more than 250 articles, most of which are reasonably productive and authored by me. (I do love me some guest articles – so long as they’re from the community. No more paid stuff! That lesson was learned.) They can’t all be winners!

So, why would you want to know the size of a directory? How should I know? Maybe you need to make space? You could want to upload the directories and want to know if you have space at the destination? Perhaps you are going to transfer the files and you want to estimate how long that will take? You do you. I don’t care why you want to find the size of a directory. That sort of thing is between you and your directories!

Anyhow, we’ll be using ‘du’ in this article. If you want a GUI way to find the size of your directories, you can visualize disk usage easily enough. You can also easily find large files. You shouldn’t need to install ‘du’, it should be installed as a part of the standard toolkit (GNU coreutils). To find out if you have ‘du’ installed, you can just try du --v in the terminal, which will spit out some version information.

So this should be a fairly short article – nice and easy. Let’s get on with it!

Find The Size Of A Directory:

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.

We’re going to us ‘du -h‘ for everything, because that -h stands for ‘human readable’ and it’s just easier than seeing byte sizes. You don’t actually have to use the -h, it just makes good sense to do so.

The format for this is largely ‘du -h /directory‘, like so (using the Documents directory as an example):

du -h ~/Documents

1	du -h ~/Documents

You can just add more directories as needed (we’ll add downloads):

du -h ~/Documents ~/Downloads

1	du -h ~/Documents ~/Downloads

That will output the size of both directories. If you are unaware, the ~ (tilde) is a shortcut meaning your home folder. For example, if you’ve navigated away from your desktop, you can cd ~ and get back home. It’s faster than clicking your heels together three times!

By the way, if you’re stringing directories together, you can get the total size of the directories with the following:

du -sh ~/Documents ~/Downloads ~/Pictures

1	du -sh ~/Documents ~/Downloads ~/Pictures

That’s about it. That’s all you really need to know for this exercise. I told you that it’d be quick and easy! Most of my articles involve opening the terminal, and yet so many of them are really quite simple to learn and remember. I strongly urge new Linux users learn a bit about the terminal, not because it’s hard but because it’s often easier and faster than using a graphical tool.

Closure:

I wasn’t kidding about there being more than 250 articles. There are 256 of them at this time, and this will make 257. So far, I haven’t run out of ideas and I’ve been able to get one out to you every other day. I hope you find these articles as useful as I’d like them to be. It does take me longer to come up with ideas, so it might have to slow down at some point. I mean, I can’t keep writing these kind of articles forever, can I? No… No, I don’t think I can.

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.

How To: Convert JPG to PNG

In today’s article, we’re going to learn how to convert JPG to PNG image files. It’s a pretty easy process. In fact, the second part of the article should be fairly brief. Read on to learn more!

I should also mention that we’ll be learning how to convert JPG to PNG in the terminal. There are all sorts of GUI ways to do so, from individually converting files to batch conversions. Well, you can do all that in the terminal and this article will show you how.

Why PNG? Well, it supports lossless compression. PNG also supports transparency. PNG also looks better at higher resolutions, as it is able to display more details. Additionally, PNG not only supports lossless compression, it supports compression better – so you needn’t transfer larger files if you have no reason to do so. Plus, PNG is one of the better formats if you’re going to do things like share the images online.

So, there are a number of reasons why you’d want to convert JPG to PNG. Fortunately, as I mentioned above, it’s really not all that difficult. You have tools to do this right in your default repositories, assuming you’re using a mainstream distro.

Without further ado…

Convert JPG to PNG:

As we’ll be converting in the terminal, you will have to have an open terminal. To do that, just press CTRL + ALT + T and your default terminal should open. See? We’re off to a good start.

Now, the tool we’ll be using is ‘ImageMagick’ and it’s available to install via your normal channels. If you were using a distro that uses apt (Debian/Ubuntu/Mint/etc) then it’s trivial to install with:

sudo apt install imagemagick

1	sudo apt install imagemagick

Otherwise, install it with your default package manager tools. (You just might have installed when we covered how to resize images with ImageMagick. If not, now’s a good time to install it and then read that article!)

So, next you’ll either want to use the /path/to/directory where your JPG files are, or just navigate to the directory where you’ve stored them (the easiest path), and you can convert them all with just one command:

mogrify -format png *.jpg

1	mogrify -format png *.jpg

Congratulations, in just that one command you’ll have converted all the JPG to PNG files. Feel the power of Linux! You’ll retain the originals, just in case something goes awry. If you’re happy with the results, you can always delete the originals with any one of a number of commands.

So, what if you just want to convert one JPG to PNG? Well, that’s easy:

convert <file_name>.jpg <new_file_name>.png

1	convert <file_name>.jpg <new_file_name>.png

See? I told you it was easy. While there’s a whole lot of complexity with ImageMagick, it can be quite simple to use for some very generic day-to-day tasks. Of couse, man imagemagick is always an option to learn more.

Closure:

Yup… It’s really not all that hard to convert JPG to PNG files with ImageMagick. If it’s a large number of files, it could be a bit for you to convert them all, but let it do its thing and it won’t take too long on a modern computer. If you only need to convert one image, that’s fine too.

How To: Reload Your .bash_profile

Today’s article is going to explain how to reload your .bash_profile. It will be just a quick and easy article, one that won’t take up much of your time. It’s not all that complicated, but it’s something folks probably should know.

So, most of you will probably have a .bash_profile. There are other shells, but Bash is the most common. That’s where they store various bash settings. When you make changes to the .bash_profile, the profile needs to be reloaded for the changes to take effect.

I’ve probably covered this elsewhere, though I did write an article to show you how to find out which shell you’re using. If you don’t know, Bash is the name of the shell and stands for Bourne shell. There are many shells, but Bash was the first one ported to Linux. Indeed, it was one of the first applications ported to Linux. It’s still widely used as the default on most distros.

There are times when you’ll want to edit your .bash_profile for additional functionality. It’s where you’d go to change things like terminal output colors and you could even add aliases to the file if you really felt like it. (Those should probably bo in .bash_aliases, for the record.)

With that in mind, I’ll show you how to reload your .bash_profile.

Reload Your .bash_profile:

Like I said, this won’t be a very long article. It’s not terribly complicated.

Let’s say you’ve made a change to your .bash_profile and you want it to take effect immediately. To do that, you enter one of the following two commands:

source .bash_profile

1	source .bash_profile

Alternatively:

source ~/.bash_profile

1	source ~/.bash_profile

You could also close all instances of the terminal and the new .bash_profile changes should take effect the next time you open the terminal. If you really want to have another way, you can reboot and the changes will take effect the next time you open the terminal as that too will reload your .bash_profile.

Closure:

See? I told you this would be a quick and easy article. It’s not all that complicated. You probably don’t need to reload your .bash_profile often, but now you know how to do so when you need to do so. Yup, it’s also another article. There are now more than 250 articles, by the way. Who knew that it’d turn into this?!?

How To: Adjust Swappiness

In today’s article, we’re going to learn how to adjust swappiness. It’s something you might want to do, as many don’t like the initial value set by the developers. It’s relatively easy.

I’ve written about swap before. I think you’ll find the best information in my recent article telling you how to remove a swap file. In that article, I tell you why I still use a swap file – even when I have lots of RAM available.

The reason for that boils down to how a swap file isn’t just some place that the kernel sticks things when you’re out of RAM. It has other uses as well. I figure I’m not smarter than the kernel and evidence tells me that the kernel uses swap even when there’s all sorts of RAM available. So, I use a swap file (not a swap partition these days). You might also want one if you plan on using advanced power management features like hibernation or sleep.

Anyhow, one of the only settings you can change regarding swap is the ‘swappiness’ value. That setting is basically how aggressively the kernel will use swap. The higher the number, the more the kernel will use swap. The lower the number, the less the kernel will use swap. It’s pretty basic in theory.

I don’t actually normally adjust the swappiness value. It works just fine at the default setting, so it doesn’t seem to me like I need to adjust it. Other people adjust it, and that’s fine. Either way, I’m going to tell you how to adjust the swappiness value. You do what you gotta do.

Adjust Swappiness:

With your terminal open, let’s see what value swappiness is set at before we decide to adjust swappiness. Enter the following command:

cat /proc/sys/vm/swappiness

1	cat /proc/sys/vm/swappiness

The default is usually 60, at least in the Ubuntu world, and some folks think that’s too aggressive. That value is easy enough to change. But, what I’d suggest doing is adjusting the value temporarily so that you can see what happens when you adjust swappiness. To set the value temporarily, you can just use this command:

sudo sysctl vm.swappiness=30

1	sudo sysctl vm.swappiness=30

Adjust the ’30’ to any number you want between 0 and 100. Both extremes are likely bad, but I’ve used values as low as 10. You could even set it to 0, which should stop the kernel from swapping anything.

Once you find a swappiness value you like, you can make it a permanent change to your system. That’s pretty easy. You just:

sudo nano /etc/sysctl.conf

1	sudo nano /etc/sysctl.conf

Add the following lines of text:

#set swappiness
vm.swappiness=30

1 2	#set swappiness vm.swappiness=30

Use your own value if it’s not 30 and save the file. To save a file in nano, press CTRL + X, then Y, and then ENTER.

You can then reboot, or just wait until your next reboot, and the new swappiness value will be used. If you don’t feel like rebooting immediately, just adjust it temporarily and reboot when it’s convenient for you.

Closure:

There you have it, another article! This one has you learning how to adjust swappiness to a value that you can work with. I’d encourage folks to read the linked swap file article to see why I use a swap file even when I have gobs of RAM. If nothing else, using one won’t break anything.

Remove A Swap File

In today’s article, we’re going to learn how to remove a swap file. This isn’t something I recommend, for reasons I’ll explain, but I have no ethical qualms about telling you how to do so. After all, it’s your computer. You get to decide what it does!

There are some folks who will tell you that if you have enough RAM you don’t need swap. Well, I am not one of those people. I tend to have swap enabled regardless of how much RAM I have. I have a good reason and I’ll explain it to you as best as I can. I mean, the actual inner workings of the kernel are above my head, but I’ll explain it – or let other people explain it.

See, contrary to popular opinion, swap isn’t just a place the kernel sticks stuff when you’re running low on RAM. For example, check out the picture below:

swap in use with plenty of free RAM — As you can see, swap is used even with plenty of free RAM.

Here’s more information about the free command.

Now, do me a favor and go Google Linux and swap. You’ll find plenty of pages that briefly have this to say (and barely this to say):

Swap space in Linux is used when the amount of physical memory (RAM) is full. If the system needs more memory resources and the RAM is full …

That’s from MIT!

That’s only about half the story… There’s more to it, and that is kinda important.

Some More About Swap:

So, is it really that simple? Of course it isn’t! If it was really that simple, the intro to this would have been so much easier to write. No, it’s slightly more, a bit more, complicated than that. See, let’s quote a more thorough (and accurate) Linux.com:

Swapping is necessary for two important reasons. First, when the system requires more memory than is physically available, the kernel swaps out less used pages and gives memory to the current application (process) that needs the memory immediately. Second, a significant number of the pages used by an application during its startup phase may only be used for initialization and then never used again. The system can swap out those pages and free the memory for other applications or even for the disk cache.

–Emphasis Mine.

What can we take from that? Well, it’s not just a place where the kernel stuffs things when there’s no RAM left – it’s also a place the kernel sticks things to avoid wasting RAM. This is very different than swap is just a place where the kernel stuffs things when RAM is low. It avoids using some RAM that’s best used elsewhere. That seems kinda valuable and important to me. Again, the inner workings of the kernel are pretty much witchcraft to me, but swap seems like a good thing to me.

The kernel is pretty smart about this, from what I’ve observed. It’s good at its job. It’s better at its job than you are. It is better at its job than I am. I highly encourage you to use swap, saving your RAM for more useful things. With disk space as large as it is, you’re not going to miss a couple of gigabytes. Let the kernel do its job, managing RAM as best as it can. They’ve put thousands of hours into making the kernel smartly deal with RAM, there’s no reason to hobble it.

Of course, ain’t nobody gonna listen to me… So, with that said, I might just as well go ahead and tell you how to remove a swap file… You’re gonna do what you want anyhow!

Remove A Swap File:

The first thing we’re going to do is verify that you actually have a swap file…

sudo swapon --show

1	sudo swapon --show

If that mentions a swap file, only calling it a ‘swapfile’ (a single word), then your next step is to turn your swap off.

sudo swapoff -v /swapfile

1	sudo swapoff -v /swapfile

Now, for your next step you will want to remove the swap information from fstab, so let’s go like this to do that:

sudo nano /etc/fstab

1	sudo nano /etc/fstab

Find the line that starts with /swapfile and delete the entire line. All of it. Leave nothing behind. If you screw this up, your next boot may be an interesting exercise. The line is probably longer than it looks unless you’re using a terminal in full screen! Be sure to remove all of it. It should end with a 0, actually a 0 and then a tab and another 0.

Be doubly sure to remove the full line and then save your work. Then save it with nano. To do that, just press CTRL + X, then Y, and then ENTER. That’ll save it.

Finally, remove the swap file itself. That one is nice and easy, you just:

sudo rm /swapfile

1	sudo rm /swapfile

That should do it! If you’ve realized you’ve made a mistake and want to have a swap file, you can always add a swap file. (I’m pretty sure it should be ‘swapfile’, but the rest of the ‘net calls it ‘swap file’, so I’m going with the majority – even though the majority don’t even know what the damned thing does!)

Closure:

There you have it. You now know how to remove a swap file. If that’s what you want to do, you go right ahead and do it. Truth be told, assuming you’ve got enough RAM, it won’t necessarily break anything. You might not even notice it is gone. Still, I figure it’s better safe than sorry – and who am I to judge what the kernel wants?