The filesystem mounted at / on this server is running out of disk space cPanel

If you are getting the error below while accessing your Cpanel/WHM it means that the / partition of your server is full and the bad-luck is that there is no dynamic way to increase the / partition it can be done by rebuilding server but it is a real costly option at it will result in taking backup and downtime.

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The filesystem mounted at / on this server is running out of disk space. cPanel operations have been temporarily suspended to prevent something bad from happening Please ask your system admin to remove any files not in use on that partition
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To verify the same follow the steps below

SSH server 

Run the command below 
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df -Th
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output of the command will be like.

As you can see / partition is 100% used just need to free-up some space from / partition and your issue will be resolved.

To check the files which are more than 1GB use the command below.

• find / -xdev -type f -size +1024M -exec ls -lh {} \; | awk '{ print $9 ": " $5 }'

1024M is the size in MB, Below is the test example.

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root@server [~]# find / -xdev -type f -size +1024M -exec ls -lh {} \; | awk '{ print $9 ": " $5 }'

/root/10Gb.dat: 1.2G
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Now you have list of files with the size you can choose the unnecessary files and delete them.