I have read quite a few posts on this, but I am still unsure about the correct approach, assuming:
1. I have a default Ubuntu 14.04 LTS VM created by and running on Azure, which doesn't come with a swap
2. I would like to create a swap using existing VM storage, instead of create a new disk using additional storage
I was also in need for this (actually 16.04 instead of 14.04, but my answer will apply to both I think).
Posts I have read:
But when I saw I had to read so long essays that you point out, I was going to give up... But suddenly I remembered a very straightforward article in DigitalOcean's blog:
How To Add Swap On Ubuntu 14.04
It's so simple that I've even written a script for it (at least for the best part, not yet the swappiness settings and other advanced stuff):
#!/usr/bin/env fsharpi
open System
open System.IO
open System.Net
open System.Diagnostics
#load "InfraTools.fs"
open Gatecoin.Infrastructure
// automation of https://www.digitalocean.com/community/tutorials/how-to-add-swap-on-ubuntu-14-04
let NUMBER_OF_GB_FOR_SWAP = 1
let isThereSwapMemoryInTheSystem (): bool =
let _,output,_ = Tools.SafeHiddenExec("swapon", "-s")
(output.Trim().Length > 0)
if (isThereSwapMemoryInTheSystem()) then
Console.WriteLine("Swap already setup")
Environment.Exit(0)
let swapFile = new FileInfo(Path.Combine("/", "swapfile"))
if not (swapFile.Exists) then
Tools.BailIfNotSudoer("Need to use 'fallocate' to create swap file")
Console.WriteLine("Creating swap file...")
Tools.SafeExec("fallocate", String.Format("-l {0}G {1}", NUMBER_OF_GB_FOR_SWAP, swapFile.FullName), true)
let permissionsForSwapFile = 600
if not (Tools.OctalPermissions(swapFile) = permissionsForSwapFile) then
Tools.BailIfNotSudoer("Need to adjust permissions of the swap file")
Tools.SafeExec("chmod", String.Format("{0} {1}", permissionsForSwapFile, swapFile.FullName), true)
Tools.BailIfNotSudoer("Enable swap memory")
Tools.SafeExec("mkswap", swapFile.FullName, true)
Tools.SafeExec("swapon", swapFile.FullName, true)
if not (isThereSwapMemoryInTheSystem()) then
Console.WriteLine("Something went wrong while enabling the swap file")
Environment.Exit(1)
Tools.BailIfNotSudoer("Writing into /etc/fstab")
Tools.SafeHiddenExecBashCommand(String.Format("echo \"{0} none swap sw 0 0\" >> /etc/fstab", swapFile.FullName))
For the above to work, you need to sudo apt install fsharp first (at least Ubuntu 16.04 has fsharp in the repositories, not sure about 14.04).
Also you need this InfraTools.fs file:
open System
open System.IO
open System.Net
namespace Gatecoin.Infrastructure
module Tools =
let HiddenExec (command: string, arguments: string) =
let startInfo = new System.Diagnostics.ProcessStartInfo(command)
startInfo.Arguments <- arguments
startInfo.UseShellExecute <- false
// equivalent to `>/dev/null 2>&1` in unix
startInfo.RedirectStandardError <- true
startInfo.RedirectStandardOutput <- true
use proc = System.Diagnostics.Process.Start(startInfo)
proc.WaitForExit()
(proc.ExitCode,proc.StandardOutput.ReadToEnd(),proc.StandardError.ReadToEnd())
let HiddenExecBashCommand (commandWithArguments: string) =
let args = String.Format("-c \"{0}\"", commandWithArguments.Replace("\"", "\\\""))
HiddenExec("bash", args)
let SafeHiddenExecBashCommand (commandWithArguments: string) =
let exitCode,stdOut,stdErr = HiddenExecBashCommand commandWithArguments
if not (exitCode = 0) then
Console.Error.WriteLine(stdErr)
Console.Error.WriteLine()
Console.Error.WriteLine("Bash command '{0}' failed with exit code {1}.", commandWithArguments, exitCode.ToString())
Environment.Exit(1)
exitCode,stdOut,stdErr
let Exec (command: string, arguments: string, echo: bool) =
let psi = new System.Diagnostics.ProcessStartInfo(command)
psi.Arguments <- arguments
psi.UseShellExecute <- false
if (echo) then
Console.WriteLine("{0} {1}", command, arguments)
let p = System.Diagnostics.Process.Start(psi)
p.WaitForExit()
p.ExitCode
let ExecBashCommand (commandWithArguments: string, echo: bool) =
let args = String.Format("-c \"{0}\"", commandWithArguments.Replace("\"", "\\\""))
if (echo) then
Console.WriteLine(commandWithArguments)
Exec("bash", args, false)
let SafeHiddenExec (command: string, arguments: string) =
let exitCode,stdOut,stdErr = HiddenExec(command, arguments)
if not (exitCode = 0) then
Console.Error.WriteLine(stdErr)
Console.Error.WriteLine()
Console.Error.WriteLine("Command '{0}' failed with exit code {1}. Arguments supplied: '{2}'", command, exitCode.ToString(), arguments)
Environment.Exit(1)
exitCode,stdOut,stdErr
let SafeExec (command: string, arguments: string, echo: bool) =
let exitCode = Exec(command, arguments, echo)
if not (exitCode = 0) then
Console.Error.WriteLine("Command '{0}' failed with exit code {1}. Arguments supplied: '{2}'", command, exitCode.ToString(), arguments)
Environment.Exit(1)
failwith "unreached"
()
let SafeExecBashCommand (commandWithArguments: string, echo: bool) =
let args = String.Format("-c \"{0}\"", commandWithArguments.Replace("\"", "\\\""))
if (echo) then
Console.WriteLine(commandWithArguments)
SafeExec("bash", args, false)
let FirstElementOf3Tuple (a, _, _) = a
let SecondElementOf3Tuple (_, b, _) = b
let SimpleStringSplit (str: string, separator: string): string list =
List.ofSeq(str.Split([|separator|], StringSplitOptions.RemoveEmptyEntries))
let SplitStringInLines (str: string): string list =
SimpleStringSplit(str,Environment.NewLine)
let CommandWorksInShell (command: string): bool =
let exitCode =
try
Some(FirstElementOf3Tuple(HiddenExec(command,String.Empty))
with
| :? System.ComponentModel.Win32Exception -> (); None
if exitCode.IsNone then
false
else
true
let BailIfNotSudoer(reason: string): unit =
if not (CommandWorksInShell "id") then
Console.WriteLine ("'id' unix command is needed for this script to work")
Environment.Exit(2)
()
let _,idOutput,_ = HiddenExec("id","-u")
if not (idOutput.Trim() = "0") then
Console.Error.WriteLine ("Error: needs sudo privilege. Reason: {0}", reason)
Environment.Exit(3)
()
()
let OctalPermissions (file: FileInfo): int =
let output = SecondElementOf3Tuple(SafeHiddenExec("stat", String.Format("-c \"%a\" {0}", file.FullName)))
Int32.Parse(output.Trim())
Many solutions were discussed but I can't seem to find one that will persists across server reboots
The part that makes my answer work through server reboots is the writing to /etc/fstab file.
The good thing about this solution is that it should work in Azure, DigitalOcean, YouNameIt, ...
Enjoy!
