An unresolvable hostname results in cpanel-exim being removed on Ubuntu servers

Symptoms

You will receive an error similar to the following during cPanel updates on Ubuntu servers using an unresolvable hostname.

[2026-01-06 00:44:32 +0000]   hostname: Name or service not known
[2026-01-06 00:44:32 +0000]   dpkg: error processing archive cpanel-exim_4.99-1.cp130~u22_amd64.deb (--install):
[2026-01-06 00:44:32 +0000]    new cpanel-exim package pre-installation script subprocess returned error exit status 1

The script /scripts/check_cpanel_pkgs --fix may also provide output similar to the following:

[2026-01-07 00:40:01 +0000]   Installing new packages: cpanel-exim_4.99-1.cp130~u22_amd64.deb
[2026-01-07 00:40:01 +0000]   Selecting previously unselected package cpanel-exim.
[2026-01-07 00:40:01 +0000]   (Reading database ... 175065 files and directories currently installed.)
[2026-01-07 00:40:01 +0000]   Preparing to unpack cpanel-exim_4.99-1.cp130~u22_amd64.deb ...
[2026-01-07 00:40:01 +0000]   hostname: Name or service not known
[2026-01-07 00:40:01 +0000]   dpkg: error processing archive cpanel-exim_4.99-1.cp130~u22_amd64.deb (--install):
[2026-01-07 00:40:01 +0000]    new cpanel-exim package pre-installation script subprocess returned error exit status 1
[2026-01-07 00:40:01 +0000]   Errors were encountered while processing:
[2026-01-07 00:40:01 +0000]    cpanel-exim_4.99-1.cp130~u22_amd64.deb
[2026-01-07 00:40:01 +0000] W The “/usr/bin/dpkg -i --force-confold --force-confmiss cpanel-exim_4.99-1.cp130~u22_amd64.deb” command (process 13686) reported error number 1 when it ended. Selecting previously unselected package cpanel-exim.
[2026-01-07 00:40:01 +0000] (Reading database ... 175065 files and directories currently installed.)
[2026-01-07 00:40:01 +0000] Preparing to unpack cpanel-exim_4.99-1.cp130~u22_amd64.deb ...
[2026-01-07 00:40:01 +0000] hostname: Name or service not known
[2026-01-07 00:40:01 +0000] dpkg: error processing archive cpanel-exim_4.99-1.cp130~u22_amd64.deb (--install):
[2026-01-07 00:40:01 +0000]  new cpanel-exim package pre-installation script subprocess returned error exit status 1
[2026-01-07 00:40:01 +0000] Errors were encountered while processing:
[2026-01-07 00:40:01 +0000]  cpanel-exim_4.99-1.cp130~u22_amd64.deb

Description

On Ubuntu servers, configuring a hostname that can not be resolved to an IP address will result in cpanel-exim being removed during cPanel updates. 

We've opened an internal case for our development team to investigate this further. For reference, the case number is CPANEL-50916. Follow this article to receive an email notification when a solution is published in the product. 

Workaround

Set a valid and resolvable hostname using "WHM / Change Hostname", then run the following script using SSH or "WHM / Terminal" as root to reinstall cpanel-exim:

/scripts/check_cpanel_pkgs --fix

Additional Resources:

What is an effective hostname?

How to change the server's hostname from WHM