You would probably want to do this if you’re suspecting that there’s an issue where you’re falling short on memory, diagnosing performance issues, etc. It’s much faster than a reboot and if it solves your problem, you’ll know what to do in the future. It’s not likely that you’ll need to do this. Just good to know how.
If you’re interested in more information regarding your memory, you can go look at: https://www.linuxatemyram.com/
Taken from: https://stackoverflow.com/questions/29870068/what-are-pagecache-dentries-inodes
With some oversimplification, let me try to explain in what appears to be the context of your question because there are multiple answers.
It appears you are working with memory caching of directory structures. An inode in your context is a data structure that represents a file. A dentries
is a data structure that represents a directory. These structures could
be used to build a memory cache that represents the file structure on a
disk. To get a directly listing, the OS could go to the dentries–if
the directory is there–list its contents (a series of inodes). If not
there, go to the disk and read it into memory so that it can be used
The page cache could contain any memory
mappings to blocks on disk. That could conceivably be buffered I/O,
memory mapped files, paged areas of executables–anything that the OS
could hold in memory from a file.
The commands flush these buffers.
Every Linux System has three options to clear cache without interrupting any processes or services.
Clear PageCache only.
# sync; echo 1 > /proc/sys/vm/drop_caches
Clear dentries and inodes.
# sync; echo 2 > /proc/sys/vm/drop_caches
Clear PageCache, dentries and inodes.
# sync; echo 3 > /proc/sys/vm/drop_caches
Explanation of above commands. sync will flush the file system buffer. Commands separated by “;” run sequentially. The shell wait for each command to terminate before executing the next command in the sequence. As mentioned in kernel documentation, writing to drop_cache will clean cache without killing any application/service, command echo is doing the job of writing to file. If you have to clear the disk cache, the first command is safest in enterprise and production as “…echo 1 > ….” will clear the PageCache only. It is not recommended to use third option above “…echo 3 >” in production until you know what you are doing, as it will clear PageCache, dentries and inodes. Is it a good idea to free Buffer and Cache in Linux that might be used by Linux Kernel? When you are applying various settings and want to check, if it is actually implemented specially on I/O-extensive benchmark, then you may need to clear buffer cache. You can drop cache as explained above without rebooting the System i.e., no downtime required. Linux is designed in such a way that it looks into disk cache before looking onto the disk. If it finds the resource in the cache, then the request doesn’t reach the disk. If we clean the cache, the disk cache will be less useful as the OS will look for the resource on the disk. Moreover it will also slow the system for a few seconds while the cache is cleaned and every resource required by OS is loaded again in the disk-cache. Now we will be creating a shell script to auto clear RAM cache daily at 2am via a cron scheduler task. Create a shell script clearcache.sh and add the following lines. #!/bin/bash # Note, we are using “echo 3”, but it is not recommended in production instead use “echo 1” echo “echo 3 > /proc/sys/vm/drop_caches” Set execute permission on the clearcache.sh file. # chmod 755 clearcache.sh Now you may call the script whenever you required to clear ram cache. Now set a cron to clear RAM cache everyday at 2am. Open crontab for editing. # crontab -e Append the below line, save and exit to run it at 2am daily. 0 2 * * * /path/to/clearcache.sh For more details on how to cron a job you may like to check our article on 11 Cron Scheduling Jobs. Is it good idea to auto clear RAM cache on production server? No! it is not. Think of a situation when you have scheduled the script to clear ram cache everyday at 2am. Everyday at 2am the script is executed and it flushes your RAM cache. One day for whatsoever reason, may be more than expected users are online on your website and seeking resource from your server. At the same time scheduled script run and clears everything in cache. Now all the user are fetching data from disk. It will result in server crash and corrupt the database. So clear ram-cache only when required,and known your foot steps, else you are a Cargo Cult System Administrator. How to Clear Swap Space in Linux? If you want to clear Swap space, you may like to run the below command. # swapoff -a && swapon -a Also you may add above command to a cron script above, after understanding all the associated risk. Now we will be combining both above commands into one single command to make a proper script to clear RAM Cache and Swap Space. # echo 3 > /proc/sys/vm/drop_caches && swapoff -a && swapon -a && printf ‘\n%s\n’ ‘Ram-cache and Swap Cleared’ OR $ su -c “echo 3 >’/proc/sys/vm/drop_caches’ && swapoff -a && swapon -a && printf ‘\n%s\n’ ‘Ram-cache and Swap Cleared'” root After testing both above command, we will run command “free -h” before and after running the script and will check cache. Clear RAM Cache and Swap Space That’s all for now, if you liked the article, don’t forget to provide us with your valuable feedback in the comments to let us know, what you think is it a good idea to clear ram cache and buffer in production and Enterprise? Sharing is Caring…
Here are a couple of videos that I find profound and very interesting. Unsurprisingly, they’re videos from a couple of my favorite Chinese actresses.
The first one is with Li Yitong 李一桐. I’ve been a fan of hers since seeing her in The Legend of the Condor Heroes. http://www.iqiyi.com/lib/m_208895914.html. In this video, she does a great narrative about breakup. Please watch the video if you could. The gist of it is that you should enjoy what you have. While you’re enjoying it however, you might be too busy enjoying it that you’re not spending the time to cherish it. You also don’t think you’ll ever lose it. Over time, things change and people drift apart. For her, he had known all of her weaknesses, all but one. Her biggest fear however was knowing one day that she wasn’t able to marry the guy. Well, she’s gotten used to not having him. Moving on, she wishes him well, thanks him for the memories and thanks him for allowing her to love her. Basically, be grateful. How profound!
With Athena, this was a quick replay of A Chinese Odyssey Part One: Pandora’s Box 西遊記第壹佰零壹回之月光寶盒, a film that I’ve seen a couple of times and undoubtedly will watch at least couple more. Also about love – interesting that she says that if you’re not in a loving relationship, leave. There’s someone else out there that’s waiting for you. I certainly hope that’s true. I don’t know if it is, but I do think it’s a beautiful story.
I have another blog posting where I talk about how to use 2 ISPs at the same time and the router load balances the outbound connections.
Since then, I’ve upgraded my other Internet connection such that it’s not even worth keeping the other one. I now have one WAN link that’s over 500mbps and another that’s 20mbps. How do we load balance that? Why bother with the 20mbps? For that reason, I just unplugged it for months…
Then I thought about it and turned it back on. It was initially to be used as a backup, in case my primary goes down, which always does and comes back up again, but now, I use them both concurrently. Since I have an older router that was laying around, so it made my decision easy. If I didn’t have the extra router, I may not have gone out to buy another one.
Basically, the way I’m using it is like this:
192.168.0.1 is my primary router. It has my primary WAN link and all of my Internet traffic goes through it, with the exception of some DNS traffic.
192.168.0.6 is my secondary router. This is where my hosts go to get Internet access if my primary goes down. Hopefully, the primary link doesn’t go down for an extended period of time. If it does, this is what I will use. I do need to manually configure my clients. Basically, just change it from automatic DHCP to manual and instead of using 192.168.0.1 as the default gateway, switch it to 192.168.0.6. I use the same DNS servers. I turn off DHCP on this router.
DNS server – I have a separate caching DNS server that runs just to cache DNS requests. On it, I use forwarders to resolve DNS requests to avoid full recursive lookups if possible. To get to those forwarders, I put 1/2 of them through my primary ISP and 1/2 of them through the secondary.
With this configuration, basically I’m just using 1 ISP for everything, with the small exception of DNS. When my primary ISP goes down, I don’t really think about DNS. Maybe I’ll check next time to see if DNS is still working. Usually when it goes down, I look at my router and see that my modem is likely rebooting.
Anyway, when I want to fail over to my 2nd ISP, I do it simply on the device like this:
When configuring manually, you’ll need to configure the DNS as well.
Hope this helps! Please leave any comments or questions below!
Thanks to the Corona virus, the people of San Francisco have been sheltered in. One of the things that I’ve enjoyed doing is watching the Condor Trilogy 射鵰三部曲 series. I got the idea of doing this because of nostalgia. I always enjoyed wuxia as a kid. I don’t know which I watched first – Bruce Lee or Chinese kung fu movies. For that reason, I didn’t even think Crouching Tiger, Hidden Dragon was that awesome when it first came out – thought it was just like another Chinese kung fu movie. Hero though, the film with Jet Li and Donnie Yen, was really awesome! I watched the The Return of the Condor Heroes 神鵰俠侶when I was a kid. My late aunt graciously recorded it for me and I watched while being babysat at my great-grandmother’s house. Only upon watching it for the 3rd time, this time in order without missing any episodes and with subtitles, did I really know how much of the story I missed and how poor my Cantonese is.
When I was a kid, I only cared to see the kungfu action. At least that’s what I thought I cared for. Having watched it very recently, I still enjoyed the kung fu action, but also really enjoyed the story. I also enjoyed seeing the lots of beautiful women cast in the series. It’s almost like watching the UFC actually. Which guy doesn’t like watching violence mixed with beautiful women? With the UFC or boxing, you have ring card girls. I know the movies aren’t real fighting. It’s more of a dance than a fight scene. If I want to watch real fighting, I’ll watch the UFC. That said, this is a series that has a remake every decade. Jin Yong wrote some masterpieces. There’s no other reason they would do a remake every 5-10 years.
So I spent about 30 hours watching the 1983 version of 神鵰俠侶 with Andy Lau and Idy Chan. I enjoyed the series a lot. Andy Lau plays brilliantly and Idy Chan is a goddess. Among them were many other talented and beautiful stars as well. I knew I had to watch it from from the beginning to the end to really understand the film. The moment I started watching the series, I started to notice that I needed to keep track of the characters so that I wouldn’t get lost in remember who was who. I ended up using wikipedia as Cliffs notes. I wish I had known about the fandom link at the time. I would’ve used it as well. I’m not the best at remembering Chinese names. I did my best, but also sadly couldn’t resist reading and finding out what happened prior to seeing it actually happen. It was still entertaining and exciting to see how the directors set up the scenes and how they were executed.
There’s a video below that talks about how they shouldn’t make these series because the ratings seem to be getting lower and lower. I might agree perhaps for the older series e.g. the 1990s and 2008, but would wholeheartedly disagree for the 2017/2019 versions. Also, the guy makes his argument based off of ratings. Well, ratings are based on the time and what was available at the time. If you watch the 1983 神鵰俠侶, you’ll see that the Jinlun Guoshi is wearing a wig that doesn’t match his skin color. You would also see that in a lot of scenes, the backdrops are terrible – totally obvious that it’s done on a set.
Think about it. Why would anyone in their right mind create a remake of a series, spend a shitload of money, and make a series that’s worse than the original? Nobody would. Nobody would invest. Nobody would play the parts. Unless they’re just milking the cow – if they already own something and just want to get as much money out of it as possible before it dies. I don’t think that’s the case with these series. You should expect that every series is better than the next. There are many reasons for that. If a series was successful, people usually would like to replicate that success somehow. With better technology and a bigger budget, they can often produce a better product as well. For example, back in 1984, the best they could do to simulate 小龍女 XiaoLongNu’s bees was to make little lights flash on screen. Technology has gone a long way since then.
At the end of the series, I had a decision to make. Did I want to see the prequel and sequels? Well, it was a resounding yes. Jin Yong can really tell a story! I had no doubt that I wanted to see the other 2 parts of the series. That said, there are about 3-4 different versions I could choose from. My first thought was to try the Amazon prime version. I watched 1 episode of the Legend of the Condor Heroes there and decided immediately that it wasn’t for me. My issue was that the English subtitles get superimposed over the Chinese subtitles and made it hard to read. Another issue was that I think they went overboard with the special effects and computer generated imagery. I guess you’ll never know how far you can go until you have crossed the line. I feel that the 2008 version did just that. I then watched 1 episode of the 2017 version and felt good with it. I’m glad I did.
After watching the The Legend of the Condor Heroes, I proceeded with watching Heavenly Sword and Dragon Slaying Saber. I figured I would go with the 2019 version since it was the latest and it didn’t disappoint. This is available on Amazon Prime video as well, but unfortunately only in Cantonese. Since the movie was filmed in Mandarin and I always prefer to see lips in sync, I opted to watch in Mandarin.
Bambi Zhu Xudan 祝绪丹 is gorgeous, isn’t she? She plays Zhou Zhiruo, a beautiful, sweet, and innocent woman. Does she look like she could kill anyone!? Well, she played a very convincing role when switching over and also deserved the 2 awards she won for her performance.
I do have one complaint about the casting. There’s no shortage of talent in Hong Kong or China. Why do they reuse the same actors for different parts? The only reasons I can think of are budget or directors wanting to work with the same people. Here are some examples of some that look the same. There are more, but since the series are over a decade apart, the actors no longer look the same and they played the parts well. Kathy Chow Hoi-mei 周海媚 played Zhou Zhiruo in the 1994 Legend of the Condor Heroes series and played an awesome evil Abbess Miejue in the 2019 Heavenly Sword and Dragon Slaying Saber. Michael Miu played Yang Kang in the 1983 series and Huang Yaoshi in the 2017 Legend of the Condor Heroes series.
Normally, when watching any drama series, after the whole thing, I feel like I’d wasted my time. After all, it is many hours of my life. After Breaking Bad, arguably one of the most successful series of all time, I felt like I had wasted many hours of my life and wish I hadn’t seen it. I felt the same after watching the IP Man tv series. The Donnie Yen movies were great. The series, not so much. I also watched many episodes of Boardwalk Empire – perhaps 1-2 seasons. At some point, I feel like it’s never going to end and I quit. This is one of the few series that I cannot seem to get enough of. Eventually, I may read the books, but now, I’m content with watching what I can on tv or YouTube and reading on wikipedia and fandom. The reason I feel that I could be critical about the different versions is because I actually went through the different ones that I’ve talked about and found my favorite scenes and watched them in the various versions. You can find almost all of them on Youtube.
My parents recently swapped Internet providers and since they didn’t know that it would take a week for the application to be completed, they were out of Internet service for about a week. The neighbors graciously allowed them to use theirs, but the signal didn’t reach the entire house. To make it reach, we configured the router to rebroadcast their wifi. If you’re going to be doing this, please make sure you get permission first!
The easiest way to do this is to just get one of those wifi extenders. We just didn’t happen to have any at the time. Since the router was Tomato compatible, I first flashed the router with tomato. The screenshots you’re seeing are Tomato by Shibby, just with a custom skin.
To do this, you first need to find out what IP address range you can use. I did this just by connecting a laptop to their wifi. Turned out that the IP address their DHCP server gave me was 192.168.7.x. I tried to ping 192.168.7.253 to make sure it wasn’t taken and sure enough, it wasn’t. I assigned 192.168.7.253 to my router.
Next, I needed to disable DHCP. You don’t want your DHCP competing with the neighbor’s. Lastly, use the default gateway that you get from their DHCP server. In my case, it was 192.168.7.1. You can use the DNS server from them also or you can use others. I like Quad9’s 188.8.131.52 or Cloudflare’s 184.108.40.206 or Google’s 220.127.116.11.
After that, you can match up your wifi settings with theirs’ so that it can connect. Use the exact same SSID, shared key, and use “Wireless Ethernet Bridge” for the Wireless Network Mode.
Lastly, optionally, you can put up any your own wifi settings as virtual wifi settings so that you don’t need to reconfigure any of your own devices.
The virtual setting is the wl0.1. Just add it and that’s it!
That’s all you need to do to make your own Tomato Wireless Extender. This has much better range than a regular wifi extender and was available at the time.
If you’re ever going overseas, you’ll need an adapter converter for any electronics, probably your iphone/ipad/laptop. I would highly recommend a travel adapter converter that includes some USB charging ports. Most hotels nowadays will have these things, but most airports don’t and probably most airbnbs don’t either.
There are other kinds. The ones you want to avoid are the ones with many parts. I was embarrassed when I was in Singapore and had a travel adapter that didn’t fit! One end was literally made to fit in another and it didn’t fit! This one is one piece, so besides the cords, there’s not much that can break. Additionally, there’s a USB-C port. Many tablets and phones now are exclusively usb-c, so this one works great for that use case!
The adapter/charger I got is the Achoro one. I don’t know if there’s a named brand one of these, but this one has served me well for a few uses. I plug this one into the wall where I get a nightlight builtin and charge my iphone/ipad/watch/laptop overnight at the same time with it. https://usgiftgiant.com/achoro-4-usb-ports-travel-adapter/
For just $20, I would say this is a great deal. I would recommend putting one in the suitcase and one in the backpack just in case – these things can easily be lost and unless you’re in Asia, they’re pretty expensive to buy when you need them immediately.