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How to Add Swap Space/file on CentOS 7 and CentOS 8

Before You Begin

check if your CentOS installation already has swap enabled by typing:

swapon –show

Empty output means that your system does not have swap enabled. Otherwise, swap enabled. Note that you may have multiple swap partitions and/or files.

Creating a Swap Partition

Creating a Swap File

 

First, create a file which will be used as swap space 1GB:

fallocate -l 1G /swapfile

If the fallocate utility is not available

sudo dd if=/dev/zero of=/swapfile bs=1024 count=1048576

Ensure that only the root user can read and write the swap file

chmod 600 /swapfile

Next, set up a Linux swap area on the file:

mkswap /swapfile

Run the following command to activate the swap:

swapon /swapfile

Make the change permanent by opening the /etc/fstab file:

vi /etc/fstab

and pasting the following line:

/swapfile swap swap defaults 0 0

Verify that the swap is active

swapon –show

or

free -h

Adjusting the Swappiness Value

Swappiness can have a value between 0 and 100. A low value will make the kernel to try to avoid swapping

cat /proc/sys/vm/swappiness

To set the swappiness value to 10

sysctl vm.swappiness=10

To make this parameter persistent across reboots append the following line to the /etc/sysctl.conf file:

vm.swappiness=10

Removing a Swap File #

Start by deactivating the swap space by typing:

sudo swapoff -v /swapfile

Next, remove the swap file entry /swapfile swap swap defaults 0 0 from the /etc/fstab file.

Finally, delete the actual swapfile file with rm :

sudo rm /swapfile

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How to Create Swap Partition in CentOS 7 & CentOS 8

Swap Partition Size

RedHat

RedHat distributions should have a swap partition size of 20% of the available RAM. The minimum amount of RAM is 4GB.
CentOS

CentOS provides the following guidelines:

The swap partition should be twice the amount of RAM if the total RAM amount is below 2GB.
If you have more than 2GB of RAM, then the swap partition should be the size of RAM + 2 GB. For example, use 8GB of swap for 6GB of RAM.

Ubuntu/Debian

Ubuntu has based its swap size recommendations on the use of hibernation.

If you use hibernation, the swap partition should be the same as the amount of RAM plus the square root of the RAM amount.

If you don’t use hibernation:

For less than 1GB of RAM, the swap partition size should be at least the same as the amount of RAM and, at most, double the amount of RAM.
For more than 1GB of RAM, create a swap partition at least equal to the square root of the RAM amount and, at most, double the RAM amount.

 

swapon Command

swapon –show

Check /proc/swaps File

cat /proc/swaps

Comman to check your swap

free -h

How to Create a Swap Partition

1. Run the fdisk command for the disk you want to partition:

sudo fdisk [disk_path]

Replace [disk_path] with your disk identifier.

2. Type p and press Enter for an overview of the disk.

The output provides information about the available disk space for a new partition. If the last partition ends before the last sector of the hard drive, there is enough space to create a new partition. The output above shows the entire disk space is available for creating a new partition.

3. Type n and press Enter to create a new partition. For partition type, enter p and press Enter.

4. Set the partition number (or keep the default number 1) and press Enter to confirm.

5. Enter the first available sector for the new partition and press Enter. You can also keep the default one offered.

6. Set the last available sector for the partition. You can specify the partition size in KiB, MiB, or GiB units. We will create a swap partition of 1GiB, so the command is:

+1G

7. Press p to verify the partition creation and confirm with Enter.

8. By default, the partition type is 83, while 82 is a partition type identifier for swap space.

Type t and press Enter to change the partition type. Change the value to 82 and press Enter.

9. Verify the change with p and confirm with Enter.

10. fdisk doesn’t make any changes to the disk before confirmation. To proceed with the changes, type w, and press Enter.

12. Update the partition table using the following syntax:

sudo partprobe [disk_path]

13. Use the mkswap command to format the partition for swap space. The command writes a swap signature in the partition, leaving the rest unformatted. The unformatted space stores the memory pages.

Use the following syntax to format the partition and create a swap space:

sudo mkswap [disk_path]

After formatting, the swap partition is created and ready to use.

How to Initialize/Enable a Swap Partition

3. Make Swap Persistent (Optional)

Include the partition in the /etc/fstab file to ensure the swap partition activates on boot.

vi /etc/fstab

Add the following line at the end:

/dev/sdb none swap sw 0 0

Replace /dev/sdb with the path to your swap partition.

How to Change the Size of a Swap Partition

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How To Move Home Directory To New Partition Or Disk In Linux

Get Partition Information

To get the block device information using the lsblk command, run:

lsblk

As stated earlier, we can also use the fdisk command to get the block device information.

sudo fdisk -l

To check under which partition the home directory is mounted, use the df command. In my case, it is mounted under /.

df -h /home

Create New Partition

Let’s create a new partition from the new drive where the home partition will be mounted. I will be using the fdisk utility to create a partition. In my case, I will add partition on /dev/sda disk.

sudo fdisk /dev/sda

Type “n” to create a new partition.

It will prompt you to choose the partition type, partition number, first sector, and last sector.

Type “w” and it will write the changes to the partition table.

Now verify if the new partition (i.e. sdb1 -> 10G) is created by listing the block device information with the lsblk command:

lsblk /dev/sda

Format and mount the Partition

sudo mkfs.ext4 /dev/sdb1

Now the partition can be mounted to any directory as you wish. Since we are going to mount this directory temporarily, I am choosing /mnt directory.

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Disk Usage Check | CWP | CWPpro

In most cases, full disk space usage on a server is caused by backups or logs but it can be also many other things.
Lets find out the cause and fix it.
List partitions and usage

df -h

Check Disk Usage per User

repquota -a -s

Show only accounts with usage in Gbytes

repquota -a -s | grep G

Check Disk Usage per Partition ignoring links
* You can replace /home with the parition or folder you want to check
Let’s check /home partition

du -hx --max-depth 1 /home

Show only folders with usage in Gbytes

du -hx --max-depth 1 /home | grep G

Check /var partition

du -hx --max-depth 1 /var

Show only folders with usage in Gbytes

du -hx --max-depth 1 /var | grep G

Check Mail folder /var/vmail

du -hx --max-depth 1 /var/vmail

Show only folders with usage in Gbytes

du -hx --max-depth 1 /var/vmail | grep G

Check MySQL folder /var/lib/mysql

du -hx --max-depth 1 /var/lib/mysql

Show only folders with usage in Gbytes

du -hx --max-depth 1 /var/lib/mysql | grep G

Check Backups

du -hx --max-depth 1 /backup

Show only folders with usage in Gbytes

du -hx --max-depth 1 /backup | grep G

Show only daily backup folder with usage in Gbytes

du -hx --max-depth 1 /backup/daily | grep G

Now when you know how to check the partitions and folders here are some useful commands to check files in the folder sorted by size:

ls -lahS /folder/location

Example for MySQL folder /var/lib/mysql/

ls -lahS /var/lib/mysql/

Some useful scripts we already have are checking the most frequent folders:
/var/log/
/usr/local/apache/logs/
/usr/local/apache/domlogs/
/usr/local/cwpsrv/logs/
/tmp
/root
/var/lib/mysql/

/scripts/disk_check

Delete Files
Now when you know how to check, the question is how can you delete or empty files.
Note that you shouldn’t delete files other than logs or backups as all others can crash your server.

Log files are in use by the programs so in case you want to clean big active log files you can’t just delete them as they will remain invisible until you restart the service.
The solution is to empty the file, example:

:> /usr/local/apache/logs/access_log

However all other logs files you can simply delete, examples

rm -f  filename

An example case when you have active log files and logrotated which are not active and are renamed with -DATE

Delete single log file NOT currently in use by service

rm -f /var/log/maillog-20211108

Delete all maillog files NOT currently in use by service

rm -f /var/log/maillog-*

Empty active log file which is in use by the service

:> /var/log/maillog

* If you are not sure it’s better to grab a support service and have the experienced sysadmin to check this for you.

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How to clean all log files in CWP or CWP Pro | Control Web Panel

CWP – Delete All Log Files

First create a file in /root dir :

cd /root
vi clearlog.sh

Then paste this Bash script and save it by press ctrl+x:

#!/bin/bash

truncate -s 0 /usr/local/apache/logs/*bytes
truncate -s 0 /usr/local/apache/logs/*log
truncate -s 0 /usr/local/apache/domlogs/*bytes
truncate -s 0 /usr/local/apache/domlogs/*log
truncate -s 0 /var/log/messages
truncate -s 0 /var/log/maillog
truncate -s 0 /var/log/*log
truncate -s 0 /opt/alt/*/usr/var/log/php-fpm.log
truncate -s 0 /usr/local/cwpsrv/logs/access_log
truncate -s 0 /usr/local/cwpsrv/logs/error_log
truncate -s 0 /var/log/cron
truncate -s 0 /var/log/secure
truncate -s 0 /var/log/cwp/services_action.log
truncate -s 0 /var/log/cwp/cwp_sslmod.log
truncate -s 0 /var/log/cwp/cwp_cron.log
truncate -s 0 /var/log/cwp/cwp_backup.log
truncate -s 0 /var/log/cwp/activity.log
rm -rf /var/log/maillog-*
rm -rf /var/log/monit.log-*
rm -rf /var/log/spooler-*
rm -rf /var/log/messages-*
rm -rf /var/log/secure-*
rm -rf /var/log/pureftpd.log-*
rm -rf /var/log/yum.log-*
rm -rf /var/log/monit.log-*
rm -rf /var/log/cron-*

Change the permission :

chmod 755 /root/clearlog.sh

Now run this command to run the clear log script:

sh /root/clearlog.sh

Thats it the logs will be cleared you can go and check to the respected locations of the log.

Cron Job :

You can also create cron job like below by following solution 2 and create this cron job task according to your needs :

TO run DAILY :

0 0 * * * /usr/bin/sh /root/clearlog.sh

TO run Weekly :

0 0 * * 0 /usr/bin/sh /root/clearlog.sh

TO run Monthly:

0 0 1 * * /usr/bin/sh /root/clearlog.sh

That’s All!
It will save lot’s of space.