SUSE Linux Enterprise Server for SAP Applications 15
SUSE Linux Enterprise Server 15

In SLES15, all Service Packs, the /etc/issue file is a symlink to /run/issue.
The symlink is created by the systemd "issue-generator" service:

systemctl status issue-generator.service

If changes are made directly to /etc/issue, they will be overwritten on the next system reboot.

The text in /etc/issue:
"Welcome to SUSE Linux Enterprise Server 15 SP3  (x86_64) - Kernel \r (\l)."

comes from: /usr/lib/issue.d/10-SUSE
That file is owned by the "release" RPM: sles-release-15.3-55.4.1

SUSE does not recommend changing that file.

The best way to move forward is to create your own file in:
/etc/issue.d/

Based on the "issue.d" man page, man issue.d:
"Files in /etc/issue.d override files with the same name in /usr/lib/issue.d and /run/issue.d."

If you create the file:
/etc/issue.d/10-SUSE
it will override the default file "/usr/lib/issue.d/10-SUSE".

In addition, new files in /etc/issue.d/ will be appended with "10-SUSE" file and content of the files will be seen in /etc/issue and /run/issue.

In addition to the text mentioned above in the /etc/issue file, this text is also appended:

eth0: \4{eth0} \6{eth0}

This is created by the /usr/sbin/issue-generator script, when it is run by "udev".
When udev is ran it creates the file /run/issue.d/70-<interfacename>.conf

To remove this file and text, the recommended method is to edit the file:
/etc/sysconfig/issue-generator
And make sure that the regex in the variable there does not match any ethernet interface names on the system.

For example change the line to:

NETWORK_INTERFACE_REGEX="^[zz]"

Since there are generally no ethernet interfaces that start with "z" then this line won't match anything on the system and the 70-<interfacename>.conf text file with not be created.

An alternate option to disable the interface info from being added to /etc/issue is to mask the udev rule.
This command will disable the udev rule:

ln -s /dev/null /etc/udev/rules.d/90-issue-generator.rules

 

The RPM "hostinfo" installs a service called "hostinfo.sevice" that creates multiple files in /etc/issue.d that provide various info about the system. 
Examples of those files:

ls -la /etc/issue.d/
total 48
lrwxrwxrwx 1 root root  20 May 11 11:42 00-OS -> 80-hostinfo-00-space
-rw-r--r-- 1 root root 108 Dec  9  2021 10-SUSE
-rw-r--r-- 1 root root   1 May 11 11:42 80-hostinfo-00-space
-rw-r--r-- 1 root root  62 May 11 11:42 80-hostinfo-01-distro
-rw-r--r-- 1 root root  58 May 11 11:42 80-hostinfo-02-date
-rw-r--r-- 1 root root  32 May 11 11:42 80-hostinfo-03-host
-rw-r--r-- 1 root root 184 May 11 11:42 80-hostinfo-04-kernel
-rw-r--r-- 1 root root 145 May 11 11:42 80-hostinfo-05-updates
-rw-r--r-- 1 root root  89 May 11 11:42 80-hostinfo-06-network
-rw-r--r-- 1 root root  84 May 11 11:42 80-hostinfo-07-memory
-rw-r--r-- 1 root root  45 May 11 11:42 80-hostinfo-08-cpuload
lrwxrwxrwx 1 root root  20 May 11 11:42 90-OS -> 80-hostinfo-00-space

Example output of /etc/issue with this info installed:

cat /etc/issue


Welcome to SUSE Linux Enterprise Server 15 SP3  (x86_64) - Kernel \r (\l).

eth0: \4{eth0} \6{eth0}


eth0: \4{eth0} \6{eth0}

Distribution:             SUSE Linux Enterprise Server 15 SP3
Current As Of:            Thu 11 May 2023 11:42:30 AM CDT
Hostname:                 s15s3
Kernel Version:           5.3.18-150300.59.106-default
 Architecture:            x86_64
 Installed:               Tue 03 Jan 2023 02:05:33 PM CST
 Status:                  Not Tainted
Last Installed Package:   Thu 11 May 2023 11:32:53 AM CDT
 Patches Needed:          85
 Security:                55
 3rd Party Packages:      19
Network Interfaces
 eth0:                    192.168.0.74/24 fe80::20c:29ff:fe6b:de26/64
Memory                    83% Available
 Total/Free/Avail:        2.7Gi/435Mi/2.2Gi
CPU Load Average:         0 (0%) with 1 CPUs