How to create a swapfile?

Question

I have a 500Gib hard disk and 2Gib of RAM. I have ubuntu 12.04

When I originally particioned the disk, I had unallocated space because I had another disk with Windows in it. This disk died, so I had to install Windows in this disk and had to erase Swap Partition.

Now, as I work with lot of pictures, videos and so on, computer is turning slow and I think it is because I haven't swapfile.

A friend of mine gave me the command below, but the count number give me 2Gib of swapfile and I want to have 4 Gib of swapfile.

Please can you tell me which number to put in count?

sudo dd if=/dev/zero of=/swapfile.swap bs=4096 count=1048576

Answer 1

To create 4GB of swapfile, you can run:

sudo dd if=/dev/zero of=swapfile bs=1K count=4M

so by using multiplicative suffixes it's easier to count (1K * 4M = 4 GiB).

Then you need to convert that file into swap space, and enable it, so:

sudo mkswap swapfile
sudo swapon swapfile

For more details, check: How do I add a swap?

Answer 2

The basic steps of how to create a swap file are described in Arch Wiki article on swap. I took the liberty of condensing all those steps into a script。 Basic usage:

Usage is very simple:

sudo ./addswap.sh INTEGER LETTER

For adding 1 gigabyte you would do sudo ./addswap.sh 1 G. For adding 1 megabyte do sudo ./addswap.sh 1 M.

Script

This script is also available on my personal GitHub repository.

#!/bin/bash
set -e  # bail if anything goes wrong

is_root(){
   if [ "$( id -u )" -ne 0  ] ; then
      return 1
   fi
   return 0
}

get_swap_amount(){
    # Obtain amount of swap in Gigabytes
    awk '/SwapTotal/{printf "%.2f",($2/1048576)}' /proc/meminfo
}

make_swap_file(){ 
   # This is the function that does the job of creatig swap file
   # and enabling it.  All files are timestamped
   printf "Current swap ammount: %f\n" "$(get_swap_amount)"
   printf "Working on creating swap file\n"
   DATE=$(date +%s) # append date of creation to filename
   filename="/swapfile.""$DATE" # File will be /swapfile.$DATE
   dd if=/dev/zero  of="$filename" bs=1"$2" count="$1"
   chmod 600 "$filename"
   mkswap "$filename" && 
   swapon "$filename" && 
   printf "\nCreated and turned on %s\n"  "$filename"
   printf "Current swap ammount: %f" "$(get_swap_amount)"
}


ask_to_enable_on_boot(){
   # Prompt user to enable this new swap file on boot. If user
   # enters y, the swap file will be added to /etc/fstab
   printf "Do you want to turn on this file at boot?[y/n]\n"
   read ANSWER
   case "$ANSWER" in
    [Yy]) printf "\n%s none swap defaults 0 0\n" "$filename"  >> /etc/fstab &&
       printf "\n %s added to /etc/fstab successfuly\n" "$filename"
       exit 0 ;;
    [Nn]) printf "Exiting\n" && exit 0 ;;
    *) printf "Wrong input: %s . Exiting. /etc/fstab not altered\n" "$ANSWER" && exit 1 ;;
   esac

}

bad_arguments(){
     # check if second argument is a character 
     case "$2" in 
         [A-Z]) return 1;;
         *) return 0;;
     esac

    # Check if first argument is a digit. 
    # https://stackoverflow.com/a/3951175/3701431
    case "$1" in
        ''|*[!0-9]*) return 0;;
        *) return 1 ;;
    esac 

}

main(){

    # Check if we're root and if args are OK. If everything is ok, do stuff

    if is_root 
    then
        if [ $# -ne 2   ] ||  bad_arguments "$@"
        then
            printf "%s\n" ">>> ERR: $0: bad or insufficient arguments" > /dev/stderr
            printf "%s\n" ">>> Usage: $0 INTEGER LETTER" > /dev/stderr
            exit 2
        fi
        make_swap_file "$@" && ask_to_enable_on_boot
    else
        printf ">>> ERR: $0 must run as root\n" > /dev/stderr
        exit 1
    fi
}

main "$@"

Test run

$ sudo ./addswap.sh 1 G                                                                                                                                                                 
[sudo] password for xieerqi: 
Current swap ammount: 4.000000
Working on creating swap file
1+0 records in
1+0 records out
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 6.83322 s, 157 MB/s
Setting up swapspace version 1, size = 1024 MiB (1073737728 bytes)
no label, UUID=8bf1d78d-0a8a-478b-a783-38c5935c362f

Created and turned on /swapfile.1498976162
Current swap ammount: 5.000000Do you want to turn on this file at boot?[y/n]
Y

 /swapfile.1498976162 added to /etc/fstab successfuly
 $ 

Answer 3

Multiply your count by 2.

If
  1048576 blocks with a size of 4086bytes each = 2GB
then,
  2097152 blocks with a size of 4086bytes each = 4GB

For anyone else reading this, the above values are not accurate. They're based off the values given by the OP