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      How To Add Swap Space on Debian 8


      Introduction

      One of the easiest way of guarding against out-of-memory errors in applications is to add some swap space to your server. In this guide, we will cover how to add a swap file to a Debian 8 server.

      Warning: Although swap is generally recommended for systems using traditional spinning hard drives, using swap with SSDs can cause issues with hardware degradation over time. Due to this consideration, we do not recommend enabling swap on DigitalOcean or any other provider that utilizes SSD storage. Doing so can impact the reliability of the underlying hardware for you and your neighbors. This guide is provided as reference for users who may have spinning disk systems elsewhere.

      If you need to improve the performance of your server on DigitalOcean, we recommend upgrading your Droplet. This will lead to better results in general and will decrease the likelihood of contributing to hardware issues that can affect your service.

      What is Swap?

      Swap is an area on a hard drive that has been designated as a place where the operating system can temporarily store data that it can no longer hold in RAM. Basically, this gives you the ability to increase the amount of information that your server can keep in its working “memory”, with some caveats. The swap space on the hard drive will be used mainly when there is no longer sufficient space in RAM to hold in-use application data.

      The information written to disk will be significantly slower than information kept in RAM, but the operating system will prefer to keep running application data in memory and use swap for the older data. Overall, having swap space as a fallback for when your system’s RAM is depleted can be a good safety net against out-of-memory exceptions on systems with non-SSD storage available.

      Step 1 – Checking the System for Swap Information

      Before we begin, we can check if the system already has some swap space available. It is possible to have multiple swap files or swap partitions, but generally one should be enough.

      We can see if the system has any configured swap by typing:

      If you don't get back any output, this means your system does not have swap space available currently.

      You can verify that there is no active swap using the free utility:

      Output

      total used free shared buffers cached Mem: 1.0G 331M 668M 4.3M 11M 276M -/+ buffers/cache: 44M 955M Swap: 0B 0B 0B

      As you can see in the Swap row of the output, no swap is active on the system.

      Step 2 – Checking Available Space on the Hard Drive Partition

      Before we create our swap file, we'll check our current disk usage to make sure we have enough space. Do this by entering:

      Output

      Filesystem Size Used Avail Use% Mounted on /dev/vda1 25G 946M 23G 4% / udev 10M 0 10M 0% /dev tmpfs 201M 4.3M 196M 3% /run tmpfs 501M 0 501M 0% /dev/shm tmpfs 5.0M 0 5.0M 0% /run/lock tmpfs 501M 0 501M 0% /sys/fs/cgroup tmpfs 101M 0 101M 0% /run/user/1001

      The device with / in the Mounted on column is our disk in this case. We have plenty of space available in this example (only 946M used). Your usage will probably be different.

      Although there are many opinions about the appropriate size of a swap space, it really depends on your personal preferences and your application requirements. Generally, an amount equal to or double the amount of RAM on your system is a good starting point. Another good rule of thumb is that anything over 4G of swap is probably unnecessary if you are just using it as a RAM fallback.

      Step 3 – Creating a Swap File

      Now that we know our available hard drive space, we can go about creating a swap file within our filesystem.

      We will create a file called swapfile in our root (/) directory. The file must allocate the amount of space we want for our swap file. There are two main ways of doing this:

      The Traditional, Slow Way

      Traditionally, we would create a file with preallocated space by using the dd command. This versatile disk utility writes from one location to another location.

      We can use this to write zeros to the file from a special device in Linux systems located at /dev/zero that just spits out as many zeros as requested.

      We specify the file size by using a combination of bs for block size and count for the number of blocks. What we assign to each parameter is almost entirely arbitrary. What matters is what the product of multiplying them turns out to be.

      For instance, in our example, we're looking to create a 1 Gigabyte file. We can do this by specifying a block size of 1 megabyte and a count of 1024:

      • sudo dd if=/dev/zero of=/swapfile bs=1M count=1024

      Output

      1024+0 records in 1024+0 records out 1073741824 bytes (1.1 GB) copied, 1.36622 s, 786 MB/s

      Check your command before pressing ENTER because this has the potential to destroy data if you point the of (which stands for output file) to the wrong location.

      We can see that 1 Gigabyte has been allocated by typing:

      Output

      -rw-r--r-- 1 root root 1.0G May 30 15:07 /swapfile

      If you've completed the command above, you may notice that it took a few seconds. Only 1.3 seconds for this small swapfile, but that could increase significantly for larger files on slower hard drives.

      If you want to learn how to create the file faster, remove the file swapfile using sudo rm /swapfile, then follow along below:

      The Faster Way

      The quicker way of getting the same file is by using the fallocate program. Note that this command only works with more modern filesystems, so if you're using an ext3 system, for instance, this option is not available to you.

      The fallocate command creates a file of a preallocated size instantly, without actually having to write dummy contents.

      We can create a 1 Gigabyte file by typing:

      sudo fallocate -l 1G /swapfile
      

      The prompt will be returned to you almost immediately. We can verify that the correct amount of space was reserved by typing:

      Output

      -rw-r--r-- 1 root root 1.0G May 30 15:07 /swapfile

      As you can see, our file is created with the correct amount of space set aside.

      Step 4 – Enabling the Swap File

      Now that we have a file of the correct size available, we need to actually turn this into swap space.

      First, we need to lock down the permissions of the file so that only the users with root privileges can read the contents. This prevents normal users from being able to access the file, which would have significant security implications.

      Make the file only accessible to root by typing:

      Verify the permissions change by typing:

      Output

      -rw------- 1 root root 1.0G May 29 17:34 /swapfile

      As you can see, only the root user has the read and write flags enabled.

      We can now mark the file as swap space by typing:

      Output

      Setting up swapspace version 1, size = 1048572 KiB no label, UUID=757ee0b7-db04-46bd-aafb-adf6954ea077

      After marking the file, we can enable the swap file, allowing our system to start utilizing it:

      Verify that the swap is available by typing:

      Output

      NAME TYPE SIZE USED PRIO /swapfile file 1024M 0B -1

      We can check the output of the free utility again to corroborate our findings:

      Output

      total used free shared buffers cached Mem: 1.0G 925M 74M 4.3M 13M 848M -/+ buffers/cache: 63M 936M Swap: 1.0G 0B 1.0G

      Our swap has been set up successfully and our operating system will begin to use it as necessary.

      Step 5 – Making the Swap File Permanent

      Our recent changes have enabled the swap file for the current session. However, if we reboot, the server will not retain the swap settings automatically. We can change this by adding the swap file to our /etc/fstab file.

      Back up the /etc/fstab file in case anything goes wrong:

      • sudo cp /etc/fstab /etc/fstab.bak

      Add the swap file information to the end of your /etc/fstab file by typing:

      • echo '/swapfile none swap sw 0 0' | sudo tee -a /etc/fstab

      Next we'll review some settings we can update to tune our swap space.

      Step 6 – Tuning your Swap Settings

      There are a few options that you can configure that will have an impact on your system's performance when dealing with swap.

      Adjusting the Swappiness Property

      The swappiness parameter configures how often your system swaps data out of RAM to the swap space. This is a value between 0 and 100 that represents a percentage.

      With values close to zero, the kernel will not swap data to the disk unless absolutely necessary. Remember, interactions with the swap file are "expensive" in that they take a lot longer than interactions with RAM and they can cause a significant reduction in performance. Telling the system not to rely on the swap much will generally make your system faster.

      Values that are closer to 100 will try to put more data into swap in an effort to keep more RAM space free. Depending on your applications' memory profile or what you are using your server for, this might be better in some cases.

      We can see the current swappiness value by typing:

      • cat /proc/sys/vm/swappiness

      Output

      60

      For a Desktop, a swappiness setting of 60 is not a bad value. For a server, you might want to move it closer to 0.

      We can set the swappiness to a different value by using the sysctl command.

      For instance, to set the swappiness to 10, we could type:

      • sudo sysctl vm.swappiness=10

      Output

      vm.swappiness = 10

      This setting will persist until the next reboot. We can set this value automatically at restart by adding the line to our /etc/sysctl.conf file:

      • sudo nano /etc/sysctl.conf

      At the bottom, you can add:

      /etc/sysctl.conf

      vm.swappiness=10
      

      Save and close the file when you are finished.

      Adjusting the Cache Pressure Setting

      Another related value that you might want to modify is the vfs_cache_pressure. This setting configures how much the system will choose to cache inode and dentry information over other data.

      Basically, this is access data about the filesystem. This is generally very costly to look up and very frequently requested, so it's an excellent thing for your system to cache. You can see the current value by querying the proc filesystem again:

      • cat /proc/sys/vm/vfs_cache_pressure

      Output

      100

      As it is currently configured, our system removes inode information from the cache too quickly. We can set this to a more conservative setting like 50 by typing:

      • sudo sysctl vm.vfs_cache_pressure=50

      Output

      vm.vfs_cache_pressure = 50

      Again, this is only valid for our current session. We can change that by adding it to our configuration file like we did with our swappiness setting:

      • sudo nano /etc/sysctl.conf

      At the bottom, add the line that specifies your new value:

      /etc/sysctl.conf

      vm.vfs_cache_pressure=50
      

      Save and close the file when you are finished.

      Conclusion

      Following the steps in this guide will give you some breathing room in cases that would otherwise lead to out-of-memory exceptions. Swap space can be incredibly useful in avoiding some of these common problems.

      If you are running into OOM (out of memory) errors, or if you find that your system is unable to use the applications you need, the best solution is to optimize your application configurations or upgrade your server.



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      How To Add Swap Space on Debian 9


      Introduction

      One of the easiest way of guarding against out-of-memory errors in applications is to add some swap space to your server. In this guide, we will cover how to add a swap file to a Debian 9 server.

      Warning: Although swap is generally recommended for systems using traditional spinning hard drives, using swap with SSDs can cause issues with hardware degradation over time. Due to this consideration, we do not recommend enabling swap on DigitalOcean or any other provider that utilizes SSD storage. Doing so can impact the reliability of the underlying hardware for you and your neighbors. This guide is provided as reference for users who may have spinning disk systems elsewhere.

      If you need to improve the performance of your server on DigitalOcean, we recommend upgrading your Droplet. This will lead to better results in general and will decrease the likelihood of contributing to hardware issues that can affect your service.

      What is Swap?

      Swap is an area on a hard drive that has been designated as a place where the operating system can temporarily store data that it can no longer hold in RAM. Basically, this gives you the ability to increase the amount of information that your server can keep in its working “memory”, with some caveats. The swap space on the hard drive will be used mainly when there is no longer sufficient space in RAM to hold in-use application data.

      The information written to disk will be significantly slower than information kept in RAM, but the operating system will prefer to keep running application data in memory and use swap for the older data. Overall, having swap space as a fallback for when your system’s RAM is depleted can be a good safety net against out-of-memory exceptions on systems with non-SSD storage available.

      Step 1 – Checking the System for Swap Information

      Before we begin, we can check if the system already has some swap space available. It is possible to have multiple swap files or swap partitions, but generally one should be enough.

      We can see if the system has any configured swap by typing:

      If you don't get back any output, this means your system does not have swap space available currently.

      You can verify that there is no active swap using the free utility:

      Output

      total used free shared buff/cache available Mem: 996M 44M 639M 4.5M 312M 812M Swap: 0B 0B 0B

      As you can see in the Swap row of the output, no swap is active on the system.

      Step 2 – Checking Available Space on the Hard Drive Partition

      Before we create our swap file, we'll check our current disk usage to make sure we have enough space. Do this by entering:

      Output

      Filesystem Size Used Avail Use% Mounted on udev 488M 0 488M 0% /dev tmpfs 100M 4.5M 96M 5% /run /dev/vda1 25G 989M 23G 5% / tmpfs 499M 0 499M 0% /dev/shm tmpfs 5.0M 0 5.0M 0% /run/lock tmpfs 499M 0 499M 0% /sys/fs/cgroup tmpfs 100M 0 100M 0% /run/user/1001

      The device with / in the Mounted on column is our disk in this case. We have plenty of space available in this example (only 1.4G used). Your usage will probably be different.

      Although there are many opinions about the appropriate size of a swap space, it really depends on your personal preferences and your application requirements. Generally, an amount equal to or double the amount of RAM on your system is a good starting point. Another good rule of thumb is that anything over 4G of swap is probably unnecessary if you are just using it as a RAM fallback.

      Step 3 – Creating a Swap File

      Now that we know our available hard drive space, we can create a swap file on our filesystem. We will allocate a file of the swap size that we want called swapfile in our root (/) directory.

      The best way of creating a swap file is with the fallocate program. This command instantly creates a file of the specified size.

      Since the server in our example has 1G of RAM, we will create a 1G file in this guide. Adjust this to meet the needs of your own server:

      • sudo fallocate -l 1G /swapfile

      We can verify that the correct amount of space was reserved by typing:

      Output

      -rw-r--r-- 1 root root 1.0G May 29 17:34 /swapfile

      Our file has been created with the correct amount of space set aside.

      Step 4 – Enabling the Swap File

      Now that we have a file of the correct size available, we need to actually turn this into swap space.

      First, we need to lock down the permissions of the file so that only the users with root privileges can read the contents. This prevents normal users from being able to access the file, which would have significant security implications.

      Make the file only accessible to root by typing:

      Verify the permissions change by typing:

      Output

      -rw------- 1 root root 1.0G May 29 17:34 /swapfile

      As you can see, only the root user has the read and write flags enabled.

      We can now mark the file as swap space by typing:

      Output

      Setting up swapspace version 1, size = 1024 MiB (1073737728 bytes) no label, UUID=b591444e-c12b-45a6-90fc-e8b24c67c006f

      After marking the file, we can enable the swap file, allowing our system to start utilizing it:

      Verify that the swap is available by typing:

      Output

      NAME TYPE SIZE USED PRIO /swapfile file 1024M 0B -1

      We can check the output of the free utility again to corroborate our findings:

      Output

      total used free shared buff/cache available Mem: 996M 44M 637M 4.5M 314M 811M Swap: 1.0G 0B 1.0G

      Our swap has been set up successfully and our operating system will begin to use it as necessary.

      Step 5 – Making the Swap File Permanent

      Our recent changes have enabled the swap file for the current session. However, if we reboot, the server will not retain the swap settings automatically. We can change this by adding the swap file to our /etc/fstab file.

      Back up the /etc/fstab file in case anything goes wrong:

      • sudo cp /etc/fstab /etc/fstab.bak

      Add the swap file information to the end of your /etc/fstab file by typing:

      • echo '/swapfile none swap sw 0 0' | sudo tee -a /etc/fstab

      Next we'll review some settings we can update to tune our swap space.

      Step 6 – Tuning your Swap Settings

      There are a few options that you can configure that will have an impact on your system's performance when dealing with swap.

      Adjusting the Swappiness Property

      The swappiness parameter configures how often your system swaps data out of RAM to the swap space. This is a value between 0 and 100 that represents a percentage.

      With values close to zero, the kernel will not swap data to the disk unless absolutely necessary. Remember, interactions with the swap file are "expensive" in that they take a lot longer than interactions with RAM and they can cause a significant reduction in performance. Telling the system not to rely on the swap much will generally make your system faster.

      Values that are closer to 100 will try to put more data into swap in an effort to keep more RAM space free. Depending on your applications' memory profile or what you are using your server for, this might be better in some cases.

      We can see the current swappiness value by typing:

      • cat /proc/sys/vm/swappiness

      Output

      60

      For a Desktop, a swappiness setting of 60 is not a bad value. For a server, you might want to move it closer to 0.

      We can set the swappiness to a different value by using the sysctl command.

      For instance, to set the swappiness to 10, we could type:

      • sudo sysctl vm.swappiness=10

      Output

      vm.swappiness = 10

      This setting will persist until the next reboot. We can set this value automatically at restart by adding the line to our /etc/sysctl.conf file:

      • sudo nano /etc/sysctl.conf

      At the bottom, you can add:

      /etc/sysctl.conf

      vm.swappiness=10
      

      Save and close the file when you are finished.

      Adjusting the Cache Pressure Setting

      Another related value that you might want to modify is the vfs_cache_pressure. This setting configures how much the system will choose to cache inode and dentry information over other data.

      Basically, this is access data about the filesystem. This is generally very costly to look up and very frequently requested, so it's an excellent thing for your system to cache. You can see the current value by querying the proc filesystem again:

      • cat /proc/sys/vm/vfs_cache_pressure

      Output

      100

      As it is currently configured, our system removes inode information from the cache too quickly. We can set this to a more conservative setting like 50 by typing:

      • sudo sysctl vm.vfs_cache_pressure=50

      Output

      vm.vfs_cache_pressure = 50

      Again, this is only valid for our current session. We can change that by adding it to our configuration file like we did with our swappiness setting:

      • sudo nano /etc/sysctl.conf

      At the bottom, add the line that specifies your new value:

      /etc/sysctl.conf

      vm.vfs_cache_pressure=50
      

      Save and close the file when you are finished.

      Conclusion

      Following the steps in this guide will give you some breathing room in cases that would otherwise lead to out-of-memory exceptions. Swap space can be incredibly useful in avoiding some of these common problems.

      If you are running into OOM (out of memory) errors, or if you find that your system is unable to use the applications you need, the best solution is to optimize your application configurations or upgrade your server.



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      Como criar um Space e uma API Key na DigitalOcean


      Introdução

      DigitalOcean Spaces é um serviço de armazenamento de objetos que torna mais fácil e econômico armazenar e fornecer grandes quantidades de dados. Spaces individuais podem ser criados e colocados em uso rapidamete, sem necessidade de configuração adicional.

      Neste tutorial, iremos utilizar o Painel de Controle da DigitalOcean para criar um novo Space. Em seguida, iremos recuperar uma Chave de API ou API Key e um secret que podem ser utilizados para conceder acesso ao Space para quaisquer clientes ou bibliotecas compatíveis com S3.

      Pré-requisitos

      Para completar este tutorial, você vai precisar de uma conta na DigitalOcean. Se você já não tiver uma, você pode registrar uma nova na página de inscrição.

      Faça o login no Painel de Controle da DigitalOcean para começar.

      Criando um Space

      Para criar um novo Space, utilize o botão Create no canto superior direito do Painel de Controle. Clique no botão, em seguida escolha Spaces na lista suspensa:

      Se você nunca criou um Space antes, você também pode criar um diretamente da página do Spaces. Para fazer isso, clique Spaces na navegação principal do Painel de Controle, e então clique em Create a space. Qualquer uma das opções o levarão à tela Create a Space:

      Primeiro, escolha um nome para o seu Space. Esse nome deve ser único entre todos os Spaces (ou seja, nenhum outro usuário do Spaces pode ter o mesmo nome em qualquer região), deve ter de 3 a 63 caracteres, e pode conter apenas letras minúsculas, números e traços.

      Em seguida, escolha a região do datacenter onde você gostaria que seu Space estivesse. No momento em que esta captura de tela foi feita, nyc3 e ams3 eram as escolhas possíveis. Outras se tornarão dsponíveis ao longo do tempo.

      Finalmente, escolha se deseja que os usuários não autenticados possam listar todos os arquivos em seu Space. Isso não afeta o acesso a arquivos individuais (que é definido em uma base por aquivo), mas apenas a capacidade de obter uma lista de todos os arquivos. A escolha padrão de Private é segura, a menos que você tenha alguns scripts ou clientes que precisem buscar listagens de arquivos sem uma chave de acesso ou access key.

      Quando seu nome e as opções estiverem todos definidos, desça e clique no botão Create a Space. Seu Space será criado, e você será levado para a interface do navegador de arquivos:

      Se este é o seu primeiro Space, você terá um arquivo welcome.html, do contrário, o Space estará vazio.

      Tome nota da URL do seu Space. Está disponível logo abaixo do nome do Space na visualização do navegador de arquivos. Nesse caso de exemplo, a URL completa é https://example-name.nyc3.digitaloceanspaces.com. O nome do Space aqui (geralmente chamado de nome do bucket) é example-name. A URL do servidor (ou endereço) é a parte restante, consistindo do nome do datacenter seguido por .digitaloceanspaces.com: https://nyc3.digitaloceanspaces.com.

      Existem algumas maneiras diferentes pelas quais os clientes e bibliotecas solicitarão essas informações. Alguns vão querer no mesmo formato dado no Painel de Controle. Alguns exigem que o nome do bucket siga a URL do servidor, como em https://nyc3.digitaloceanspaces.com/example-name. Outros ainda pedirão para você inserir o endereço do servidor e o nome do bucket ou Space separadamente. Consulte a documentação do seu cliente ou biblioteca para mais orientações nesse item.

      A seguir, criaremos a chave que precisamos para acessar nossos Spaces a partir de clientes de terceiros.

      Criando uma Access Key

      Para acessar seus arquivos de fora do Painel de Controle da DigitalOcean, precisamos gerar uma chave de acesso ou access key e um secret. Estes são um par de tokens aleatórios que servem como nome de usuário e senha para conceder acesso ao seu Space.

      Primeiro, clique no link da API na navegação principal do Painel de Controle. A página resultante lista seus tokens de API da DigitalOcean e as chaves de acesso do Spaces. Role para baixo até a parte do Spaces:

      Se este é o seu primeiro Space, você não pode ter nenhuma chave listada. Clique no botão Generate New Key. A caixa de diálogo New Spaces key será exibida:

      Digite um nome para a chave. Você pode criar quantas chaves quiser, portanto, lembre-se de que a única maneira de revogar o acesso a uma chave é excluí-la. Desse modo, você pode querer particionar as chaves por pessoa, por equipe ou pelo software cliente no qual você as estiver utilizando.

      Neste caso, estamos criando uma chave chamada example-token. Clique no botão Generate Key para completar o processo. Você retornará à tela da API listando todas as suas chaves. Observe que a nova chave tem dois tokens longos exibidos:

      O primeiro é a sua access key. Isso não é secreto e continuará visível no Painel de Controle. A segunda string é o seu secret ou secret key. Isso só será exibido uma vez. Registre-a em um local seguro para uso posterior. Na próxima vez que você visitar a página da API, esse valor será eliminado e não há como recuperá-lo.

      Diferentes clientes compatíveis com S3 podem ter nomes sutilmente diferentes para access key e secret. A terminologia usada é normalmente próxima o suficiente para deixar claro qual token deve ir para onde. Caso contrário, consulte a documentação do seu cliente ou biblioteca para obter mais informações.

      Conclusão

      Neste tutorial criamos um novo Space na DigitalOcean e uma nova access key e secret. Agora sabemos nossa URL de servidor, nome do bucket (ou nome do Space), access key, e secret. Com essas informações você pode conectar praticamente qualquer cliente ou biblioteca compatível com S3 ao seu novo Space na DigitalOcean!

      Por Brian Boucheron



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