Check the oradism permission in $ORACLE_HOME/bin. It should be owned by root and sticky bit set. Oradism should be owned by root:oinstall with permission of 4750.

$ cd $ORACLE_HOME/bin
$ ls -lrt oradism
-rwsr-x--- 1 root oinstall 147848 Apr 17 2019 oradism

You can change the permission as below:

chown root $ORACLE_HOME/bin/oradism
chmod 4750 $ORACLE_HOME/bin/oradism

Oracle Database 19c Enterprise Edition Release 19.0.0.0.0 - Production
Version 19.28.0.0.0
SQL> set lines 200 pages 20
SQL> col parameter for a30
col "Session Value" for a15
SQL> SQL> col "Instance Value" for a15
SQL> col "Description" for a40
SQL> select a.ksppinm "Parameter", b.ksppstvl "Session Value", c.ksppstvl "Instance Value", a.KSPPDESC "Description" from x$ksppi a, x$ksppcv b, x$ksppsv c where a.indx = b.indx and a.indx = c.indx and a.ksppinm like '_%' and a.ksppinm like '_highest_priority_process%';

Parameter                      Session Value   Instance Value  Description
------------------------------ --------------- --------------- ----------------------------------------
_highest_priority_processes    VKTM|CTWR       VKTM|CTWR       Highest Priority Process Name Mask

If not "VKTM" is not prioritized, please elevate the priority using below SQL

SQL> alter system set "_high_priority_processes"'VKTM' scope=spfile;=

Restart the Database and verify VKTM is elevated or not.

After setting the above, still you have error for vktm then we need to verify the cgroup configuration.

Note: The above looks good or configured proper and it still fails. In which case, the instance might be running in some other cgroup.

You can find PID of VKTM of database which has problem :

The instance might be running in some other cgroup. Check the VKTMs cpu cgroups.

cat /proc/<vktm pid>/cgroup | grep cpu

If it shows some other path ( other than root such as 7:cpu,cpuacct:/ ), then make sure that the required cgroup is having the correct settings.

Try for VKTM :

-bash-4.1$ ps -eaf|grep -i vktm |grep -v grep
oracle 15722 1 29 Sep05 ? 06:49:05 ora_vktm_orcl12102
oracle 18110 1 0 13:33 ? 00:00:01 ora_vktm_orcl12201

If it shows some other path ( other than root such as 7:cpu,cpuacct:/ ), then make sure that the required cgroup is having the correct settings

If customer has below settings, For the vtkm process

SID= > cat /proc/60698/cgroup | grep cpu

6:cpuset:/
2:cpuacct,cpu:/user.slice

Kindly do the following settings

1. echo 0 > /sys/fs/cgroup/cpu,cpuacct/system.slice/cpu.rt_runtime_us
2. echo 950000 > /sys/fs/cgroup/cpu,cpuacct/user.slice/cpu.rt_runtime_us

Execute the below commands and then retry alter system set "_high_priority_processes"'VKTM' scope=spfile;=

Restart the database and check ORA-800 resolved or not.

Still ORA-800 occurs then you can use following commands to check priority and runtime[RR]

#ps -eLo 'pid tid cls pri cmd comm cgroup' | egrep 'TID|vktm' |grep -v grep [ from oracle user]

For example :

-bash-4.2$ ps -eLo 'pid tid cls pri cmd comm cgroup' | egrep 'TID|vktm' |grep -v grep

PID TID CLS PRI CMD COMMAND CGROUP
8902 8902 TS 19 ora_vktm_db193cdb ora_vktm_db193c 6:devices:/system.slice/oracle-database.service,5:cpu,cpuacct:/system.slice,1:name=systemd:/system.slice/oracle-database.service
9332 9332 TS 19 ora_vktm_orcl19c ora_vktm_orcl19 6:devices:/system.slice/oracle-database.service,5:cpu,cpuacct:/system.slice,1:name=systemd:/system.slice/oracle-database.service

Here CLS and PRI is having incorrect value (TS and 19) but the correct value is RR and 41.

To the know the value please use

cgget system.slice or cgget user.slice [ based on customer environment cpu,cpuacct:/system.slic OR cpu,cpuacct:/user.slice]

Run the below command to set the correct value

A)  If it is user.slice:
echo 0 > /sys/fs/cgroup/cpu,cpuacct/system.slice/cpu.rt_runtime_us
echo 950000 > /sys/fs/cgroup/cpu,cpuacct/user.slice/cpu.rt_runtime_us

Or

cgset -r cpu.rt_runtime_us=950000 user.slice  >> root user command
B) if it is system.slice :
echo 0 > /sys/fs/cgroup/cpu,cpuacct/user.slice/cpu.rt_runtime_us
echo 950000 > /sys/fs/cgroup/cpu,cpuacct/system.slice/cpu.rt_runtime_us

or

cgset -r cpu.rt_runtime_us=950000 system.slice

• stop and start the database to pick the changes by vktm

check the CLS and PRI, [ CLS is RR (realtime) and priority is 41 ]

-bash-4.2$ ps -eLo 'pid tid cls pri cmd comm cgroup' | egrep 'TID|vktm' |grep -v grep

PID TID CLS PRI CMD COMMAND CGROUP
18876 18876 RR 41 ora_vktm_db193cdb ora_vktm_db193c 6:devices:/system.slice/oracle-database.service,5:cpu,cpuacct:/system.slice,1:name=systemd:/system.slice/oracle-database.service
19287 19287 RR 41 ora_vktm_orcl19c ora_vktm_orcl19 6:devices:/system.slice/oracle-database.service,5:cpu,cpuacct:/system.slice,1:name=systemd:/system.slice/oracle-database.service

Please check the mount having the oradism binary is having "nosuid" option set. If having "nosuid" option, please unset this option.
Even if the permissions are proper and kernel configurations are fine, the oradism execution as root user will not be honored by root.
Check the mount option for this case.

Sometimes oradism and oracle binary will have different permissions (see bug31909951).
For example, the oracle and oradism will have permissions as below
e5pod-2vzxt1: -rwsr-s–x 1 oracle asmadmin 450717448 Sep 20 22:16 oracle
e5pod-2vzxt1: -rwsr-x— 1 root oinstall 147752 Aug 26 17:13 oradism
Since oracle binary group does not match oradism it fails with error [dism:16]
As a solution, you need to fix oradism to be in the same group as oracle binary.

After setting the above changes, still you are getting ORA-800 then you may be hitting the following bugs.

ORA-00800: soft external error, arguments: [Set Priority Failed], [VKTM], [Check traces and OS configuration], [Check Oracle document and MOS notes], []

======= Dump for incident 763248 (ORA 800) ====== [TOC00003] –— Beginning of Customized Incident Dump(s) –— ksesethighpri: (ksb.c:9896) Failed to elevate VKTM's priority from 0 to 1, policy 3 >>>>>>>>>>>>>>>>>>>>>> Error Info: Category(-2), Opname(skgdism_send), Loc(sp.c:setpr:0), ErrMsg(Operation not permitted) Dism(128) –— End of Customized Incident Dump(s) –—

ORA-00800: soft external error, arguments: [Set Priority Failed], [VKTM],[Check traces and OS configuration], [Check Oracle document and MOS notes],

======= Dump for incident 1041281 (ORA 800) ====== –— Beginning of Customized Incident Dump(s) –— ksesethighpri: (ksb.c:9893) Failed to elevate VKTM's priority from 0 to 1, policy 3

Error Info: Category(-2), Opname(skgdism_create), Loc(sp.c:setpr:1), ErrMsg(Error 0) Dism(16)