Example: create, increase, or decrease existing swap file size
swapoff -a # turn off swapping
sizeMb=16384 # specify data size of 16GiB
# if file system is NOT ZFS (use df -T to investigate)
# Preempt error: 'swapon: /swapfile: skipping - it appears to have holes.'
sudo dd if=/dev/zero of=/swapfile bs=1M count=$sizeMb # copying zeros to swap with specified file size
sudo chmod 600 /swapfile # set correct permissions
sudo mkswap /swapfile # create swapfile
sudo swapon -a # turn on swapping
sudo swapon /swapfile # direct swap to use /swapfile
# Check contents of fstab
cat /etc/fstab
# If creating new swapfile, create this entry to make /swapfile load on reboots
sudo echo "/swapfile swap swap sw 0 0" >> /etc/fstab
# if file system is ZFS (source: github.com/zfsonlinux/pkg-zfs/wiki/HOWTO-use-a-zvol-as-a-swap-device)
sudo zfs create -V 16G -b $(getconf PAGESIZE) -o compression=zle \
-o logbias=throughput -o sync=standard \
-o primarycache=metadata -o secondarycache=none \
-o com.sun:auto-snapshot=false rpool/swap
sudo mkswap -f /dev/zvol/rpool/swap
sudo echo /dev/zvol/rpool/swap swap swap defaults 0 0 >> /etc/fstab
sudo swapon -a # turn on swapping
sudo swapon /dev/zvol/rpool/swap # direct swap to use /swapfile
# Instead of rebooting the computer for changes to take effect, a more efficient method is to run this command
sudo mount -av # v for verbose
# Check for status of swapping
free -m
Example: adding additional swap file(s)
# Create a new swap2 file 4GB in size
# Option 1: lvm
lvcreate -L 4G -n swap2 /swap2
# Option 2: dd
sudo dd if=/dev/zero of=/swap2 count=4096 bs=1M
# Set permissions
sudo chmod 600 /swap2
# Format it
sudo mkswap /swap2
# Enable it
sudo swapon /swap2
# Set it on as default
sudo echo "/swap2 swap swap sw 0 0" >> /etc/fstab
Example: creating swap partitions
# Create swap volume
ali@kimlinux:/home/ali# lvcreate -L 16G -n swap volumegroup1
Logical volume "swap" created.
# Creating swap file
ali@kimlinux:/home/ali# mkswap /dev/volumegroup1/swap
Setting up swapspace version 1, size = 32 GiB (34359734272 bytes)
no label, UUID=494c818b-c00e-47cd-8937-f7443f218af8
ali@kimlinux:/home/ali# sudo chmod 600 /dev/volumegroup1/swap
# Find disk uuid
ali@kimlinux:~$ ls -l /dev/disk/by-uuid
total 0
lrwxrwxrwx 1 root root 10 Sep 1 20:57 4061-23B6 -> ../../sdb1
lrwxrwxrwx 1 root root 10 Sep 1 20:57 a7e20382-d8f0-4d64-82ad-f161fc45610e -> ../../sdb2
lrwxrwxrwx 1 root root 10 Sep 1 20:59 c7d5f77d-29d6-4ac7-bcf6-cf32b691ce48 -> ../../dm-1
lrwxrwxrwx 1 root root 10 Sep 1 20:57 d7623939-d093-4461-bcd9-deef3e22427c -> ../../dm-0
# set disk variable
ali@kimlinux:~$ swapdisk=/dev/disk/by-uuid/d7623939-d093-4461-bcd9-deef3e22427c
# Enable swap
ali@kimlinux:# sudo su
ali@kimlinux:# swapdisk=/dev/disk/by-uuid/d7623939-d093-4461-bcd9-deef3e22427c
root@kimlinux:# swapon $swapdisk
# Set swap to load on startup
root@kimlinux:/home/kim# echo "$swapdisk swap swap sw 0 0" >> /etc/fstab
# Check results of creating swapfile
ali@kimlinux:/home/ali# free -m
total used free shared buff/cache available
Mem: 32015 4672 24376 1162 2966 25744
Swap: 32767 0 32767
# making some illustrative mistakes of mounting a swap volume as a directory
ali@kimlinux:/home/ali# mkdir /swap
ali@kimlinux:/home/ali# mount /dev/$groupname/swap /swap
mount: /swap: wrong fs type, bad option, bad superblock on /dev/mapper/volumegroup1-swap, missing codepage or helper program, or other error.
ali@kimlinux:/home/ali# lvcreate -L 32015 -n swap /vmstorage1/swap
Volume group name expected (no slash)
Run `lvcreate --help' for more information.
ali@kimlinux:/home/ali# mkdir /vmstorage1/swap
ali@kimlinux:/home/ali# chmod 600 /vmstorage1/swap
ali@kimlinux:/home/ali# mkswap /vmstorage1/swap
mkswap: warning: truncating swap area to 17179869180 KiB
mkswap: cannot open /vmstorage1/swap: Is a directory
ali@kimlinux:/home/ali# sudo dd if=/dev/zero of=/vmstorage1/swap count=32015 bs=1M
dd: failed to open '/vmstorage1/swap': Is a directory
# not able to mount swap filesystem or volume onto a directory
ali@kimlinux:/home/ali# mount /dev/$groupname/swap /swap
mount: /swap: unknown filesystem type 'swap'.
Example: Adding a New Swap Disk
# List disks
sudo lsblk
# Check available disk space
sudo df -h
# Check memory & swap file
free -m
# Set swapfile variable - be certain that a valid value is given here
# In this example: /dev/sda1 has been formatted as swap prior to this
swapdisk=/dev/sda1
# Zero out first 16MB of disk to effectively clear its partitioning table
sudo dd if=/dev/zero of=$swapdisk count=4096 bs=4096
# Set appropriate permissions to secure the directory
chmod 600 $swapdisk
# Create swapfile in the /swapdisk directory
mkswap $swapdisk
#configure system to use $swapfile
swapon $swapdisk
# Check swapdisk settings
swapon -s
# Enable swapfile to persist reboots
sudo echo "$swapdisk swap swap sw 0 0" >> /etc/fstab
# Check fstab
cat /etc/fstab
############## SAMPLE OUTPUT ##############
######### List disks ##############
brucelee@kimlinux:/home/brucelee# lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
loop0 7:0 0 96.6M 1 loop /snap/core/9804
loop1 7:1 0 55.3M 1 loop /snap/core18/1885
loop2 7:2 0 161.4M 1 loop /snap/gnome-3-28-1804/128
loop3 7:3 0 29.9M 1 loop /snap/snapd/8790
loop4 7:4 0 62.1M 1 loop /snap/gtk-common-themes/1506
loop5 7:5 0 39M 1 loop /snap/remmina/4309
sda 8:0 0 14.9G 0 disk
└─sda1 8:1 0 14.9G 0 part
sdb 8:16 0 477G 0 disk
├─sdb1 8:17 0 300M 0 part /boot/efi
└─sdb2 8:18 0 476.7G 0 part /
######### Check Disk Space ##############
brucelee@kimlinux:/home/brucelee# df -h
Filesystem Size Used Avail Use% Mounted on
udev 16G 0 16G 0% /dev
tmpfs 3.2G 1.7M 3.2G 1% /run
/dev/sdb2 469G 7.6G 437G 2% /
tmpfs 16G 401M 16G 3% /dev/shm
tmpfs 5.0M 4.0K 5.0M 1% /run/lock
tmpfs 16G 0 16G 0% /sys/fs/cgroup
tmpfs 16G 0 16G 0% /tmp
/dev/loop1 56M 56M 0 100% /snap/core18/1885
/dev/loop2 162M 162M 0 100% /snap/gnome-3-28-1804/128
/dev/loop3 30M 30M 0 100% /snap/snapd/8790
/dev/loop0 97M 97M 0 100% /snap/core/9804
/dev/loop4 63M 63M 0 100% /snap/gtk-common-themes/1506
/dev/loop5 39M 39M 0 100% /snap/remmina/4309
/dev/sdb1 300M 7.8M 292M 3% /boot/efi
tmpfs 3.2G 12K 3.2G 1% /run/user/1000
brucelee@kimlinux:/home/brucelee# swapdisk=/dev/sda1
brucelee@kimlinux:/home/brucelee# sudo dd if=/dev/zero of=$swapdisk count=4096 bs=4096
4096+0 records in
4096+0 records out
16777216 bytes (17 MB, 16 MiB) copied, 0.072039 s, 233 MB/s
brucelee@kimlinux:/home/brucelee# chmod 600 $swapdisk
brucelee@kimlinux:/home/brucelee# mkswap $swapdisk
Setting up swapspace version 1, size = 14.9 GiB (16012800000 bytes)
no label, UUID=21d57b4a-e385-4d21-a07b-3bee39de57a9
brucelee@kimlinux:/home/brucelee# swapon $swapdisk
brucelee@kimlinux:/home/brucelee# swapon -s
Filename Type Size Used Priority
/dev/sda1 partition 15637500 0 -2
brucelee@kimlinux:/home/brucelee# vim /etc/fstab
brucelee@kimlinux:/home/brucelee# free -m
total used free shared buff/cache available
Mem: 32015 3189 25054 753 3772 27636
Swap: 15270 0 15270
brucelee@kimlinux:/home/brucelee# cat /etc/fstab
# /etc/fstab: static file system information.
#
# Use 'blkid' to print the universally unique identifier for a device; this may
# be used with UUID= as a more robust way to name devices that works even if
# disks are added and removed. See fstab(5).
#
# <file system> <mount point> <type> <options> <dump> <pass>
UUID=4061-23B6 /boot/efi vfat umask=0077 0 2
UUID=a7e20382-d8f0-4d64-82ad-f161fc45610e / ext4 defaults,discard 0 1
tmpfs /tmp tmpfs defaults,noatime,mode=1777 0 0
/dev/sda1 swap swap sw 0 0
More Example: How to Modify the Swap File
# Check for currentl location of swap file
[root@localhost ~]# grep swap /etc/fstab
/dev/mapper/cl-swap swap swap defaults 0 0
# Turn off swap
swapoff /dev/mapper/cl-swap
# Add 4GB to swap
lvextend -L +4G /dev/mapper/cl-swap
# Reset swap file's signature
mkswap /dev/mapper/dev/mapper/cl-swap
# Turn swap back on
swapon -v /dev/mapper/dev/mapper/cl-swap
More Example: another way to modify swap
# First disable it
sudo swapoff /swapfile
# Change its size. This example will append 4GiB of zero bytes at the end of your swap file
sudo dd if=/dev/zero of=/swapfile bs=1M count=4096 oflag=append conv=notrunc
# Reinit swap
sudo mkswap /swapfile
# Re-enable it
sudo swapon /swapfile
Check memory
[root@localhost ~]# free m
total used free shared buff/cache available
Mem: 32667976 669624 30928356 328868 1069996 31274896
Swap: 16482300 0 16482300
Turn off Swap
# Turn off all instances of swap
swapoff -a
# Turn off a specific instance
swapoff /swap2
sed '/swap2/d' /etc/fstab
A quick note on re-purposing old disks
when reusing a disk that has been set as an LVM member previously, there are 2 options: a) recover its data or b) wipe the disk and repartition it for reuse. The follow illustration option (b) without repartitioning it using LVM.
# Scan disks for LVM partitions - although data on this disk has already been decided to be destroyed
root@kim-linux:/home/kim# pvscan
WARNING: Couldn't find device with uuid GzSTjH-GYc0-xdN3-kGhW-UriG-X84G-YcIiv1.
WARNING: VG volumegroup1 is missing PV GzSTjH-GYc0-xdN3-kGhW-UriG-X84G-YcIiv1 (last written to /dev/sdb3).
PV /dev/sda VG volumegroup1 lvm2 [14.91 GiB / 0 free]
PV [unknown] VG volumegroup1 lvm2 [76.64 GiB / 0 free]
Total: 2 [91.55 GiB] / in use: 2 [91.55 GiB] / in no VG: 0 [0 ]
Per best practices, it’s often recommended to adjust the swappiness settings to enhance system performance. Here’s how to view and edit such values:
# View existing configured value
$ sudo sysctl vm.overcommit_memory
vm.overcommit_memory = 0
# optimize swappiness value between 1 and 100, which stands for percentage as a threshold before being triggered
$ sudo sysctl vm.swappiness=1
vm.swappiness = 1
$ sudo sysctl -p # actualize changes without a reboot
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