Fixing “The filesystem mounted at /tmp on this server is running out of disk space. (Free space is 0 MB)” on a cPanel Server

If you're encountering the error:

Sorry for the inconvenience,
The filesystem mounted at /tmp on this server is running out of disk space. (Free space is 0 MB)
Please check the server space and try again.

…it means the /tmp partition on your server is full. This is common on servers using a loopback-mounted /tmp device, such as /dev/loop0, typically around 3.2 GB by default.

This issue can cause PHP sessions to break, webmail to stop working, and cPanel services to behave unpredictably.

In this guide, we’ll walk through how we fixed this issue by safely resizing /tmp on a cPanel server.

Step 1: Confirm the Issue

Run the following command:

df -h /tmp

Example output:

Filesystem      Size  Used Avail Use% Mounted on
/dev/loop0      3.2G  3.0G   32K 100% /tmp

If Use% is at 100%, the partition is full and needs to be resized.

Step 2: Stop Services That May Use /tmp

To avoid file locks or corruption, stop major services temporarily:

systemctl stop httpd
systemctl stop exim
systemctl stop clamd
systemctl stop mysql

Step 3: Unmount and Remove the Old /tmp Loop Device

Unmount /tmp and /var/tmp:

umount -fl /tmp
umount -fl /var/tmp

Remove the existing loopback file:

rm -f /usr/tmpDSK

Step 4: Create a New, Larger /tmp (e.g., 6GB)

Use the following commands to create a new loop file:

dd if=/dev/zero of=/usr/tmpDSK bs=1M count=6144
mkfs.ext4 /usr/tmpDSK

Mount the new /tmp:

mount -o loop,noexec,nosuid,rw /usr/tmpDSK /tmp
chmod 1777 /tmp

Bind it to /var/tmp:

mount --bind /tmp /var/tmp
chmod 1777 /var/tmp

Step 5: Update /etc/fstab for Persistence

Open /etc/fstab:

nano /etc/fstab

Make sure the following lines are present (remove noauto if it's there):

/usr/tmpDSK   /tmp      ext4   loop,noexec,nosuid,rw  0 0
/tmp          /var/tmp  none   bind                   0 0

Save and exit.

Step 6: Apply and Reboot

Apply system changes and reboot:

systemctl daemon-reexec
systemctl daemon-reload
reboot

Step 7: Verify the Fix

After the system reboots:

df -h /tmp

Expected output:

Filesystem      Size  Used Avail Use% Mounted on
/dev/loop0      6.0G  200M  5.8G   4% /tmp

Bonus: Auto-Cleanup /tmp with tmpwatch

Install and configure tmpwatch to clean up stale files regularly:

yum install tmpwatch -y

Add this to your crontab:

echo "0 */6 * * * root /usr/sbin/tmpwatch --mtime --all 12 /tmp" >> /etc/crontab

This process restores stability to services relying on /tmp, including PHP sessions, cPanel operations, and webmail.

Let us know if you need a script to automate this solution.

Still need help?

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