Tuesday, June 16, 2026

How to Create, Verify, and Increase Swap Space on Linux

Swap space is disk space that Linux uses as virtual memory when physical RAM is exhausted. Proper swap configuration helps improve system stability and prevents out-of-memory situations.

PURPOSE: All documents are provided on this Blog just for educational purposes only. Please make sure that you run it in your test environment before to move on to production environment.

What is Swap Space?

Swap is a reserved area on disk that acts as an extension of RAM. When memory usage becomes high, inactive pages can be moved from RAM to swap, freeing memory for active processes.

Benefits of Swap

Prevents application crashes due to memory shortages.
Provides additional virtual memory.
Supports system hibernation (when configured appropriately).
Improves system stability during memory spikes.

Check Existing Swap Space

Use any of the following commands to verify current swap configuration and usage.

free -h

Check Active Swap Devices

swapon -s

cat /proc/swaps

swapon --show

Create a New Swap File

This method creates a 2 GB swap file. Adjust the size according to your requirements.

Step 1: Disable Existing Swap (if required)


swapoff -a
Step 2: Create Swap File
sudo fallocate -l 2G /swapfile
Verify file creation:
ls -lh /swapfile

Step 3: Set Correct Permissions
sudo chmod 600 /swapfile
Verify permissions:
ls -l /swapfile
Step 4: Format the File as Swap
sudo mkswap /swapfile

Step 5: Enable Swap
sudo swapon /swapfile

Step 6: Verify Swap Activation
swapon --show
or
free -h

Step 7: Make Swap Persistent After Reboot
Add the following entry to /etc/fstab:
echo "/swapfile none swap sw 0 0" | sudo tee -a /etc/fstab
Verify:
cat /etc/fstab
Expected entry:
/swapfile none swap sw 0 0

Increase Existing Swap Partition
Current swap size: 8GB
Target swap size: 16GB

Step 1: Disable Swap
swapoff -a
Verify:
swapon --show
No output should be displayed.
Step 2: Increase Virtual Disk Size in vCenter
Increate hard disk 1 from 64 to 90 GB
Navigate to VMware vCenter:
VM Settings
→ Hard Disk 1
→ Increase disk size
Example:
64 GB → 90 GB

Step 3: Detect New Disk Size
Check available disk space:
fdisk -l
If the new size is not visible, rescan the disk:
echo 1 > /sys/class/scsi_device/0\:0\:0\:0/device/rescan
Run again:
fdisk -l

Step 4: Modify Partitions
Launch partition manager:
cfdisk
Existing Layout
/dev/sda3  Linux filesystem
/dev/sda4  Linux swap
Delete Existing Swap Partition
Select:
/dev/sda4
Choose:
Delete
Resize Root/Data Partition 
cfdisk
Select:
/ dev/sda3  # This was a root partition which we increased on vCenter.
Choose:
Resize ==> Write

Create New Swap Partition
Use remaining free space:
New
Type → Linux swap

mkswap /dev/sda4
Setting up swapspace version 1, size = 26 GiB (27917262848 bytes)
no label, UUID=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx
# edit the UUID
vi /etc/fstab

mount -a

swapon /dev/sda4
swapon --show
NAME      TYPE      SIZE USED PRIO
/dev/sda4 partition  26G   0B   -2

Tuesday, May 26, 2026

ORA-00800: soft external error, arguments: [Set Priority Failed], [VKTM]

ORA-800_VKTM_Fix

PURPOSE: All documents are provided on this Blog just for educational purposes only. Please make sure that you run it in your test environment before to move on to production environment.

After kernel update on linux system you get ORA-00800 error. In many cases you need to as follow

echo 950000 > /sys/fs/cgroup/cpu,cpuacct/user.slice/cpu.rt_runtime_us

The above command will fix the Issue, and you need to restart the DB. But when you reboot your Server the change will lost. Better to add following line in the rc.local file to persistent after reboot.

vi /etc/rc.local
echo 950000 > /sys/fs/cgroup/cpu,cpuacct/user.slice/cpu.rt_runtime_us

chmod +x /etc/rc.local

That's it

I have script, if you have multiple server to fix the issue via jump host-.

#!/bin/bash

if [ -f $1 ]; then

SERVERLIST=$(cat $1)

else

SERVERLIST=$1

for i in $SERVERLIST; do

echo "Processing $i ..."

ssh -q -T \

-o ConnectTimeout=1 \

-o PreferredAuthentications=publickey \

"$i" /bin/bash --noprofile --norc <<'EOF'

echo 950000 > /sys/fs/cgroup/cpu,cpuacct/user.slice/cpu.rt_runtime_us

cat /sys/fs/cgroup/cpu,cpuacct/user.slice/cpu.rt_runtime_us

touch /etc/rc.local

grep -q "cpu.rt_runtime_us" /etc/rc.local || cat >> /etc/rc.local <<'EORC'

# Set CPU real-time runtime for Oracle VKTM

echo 950000 > /sys/fs/cgroup/cpu,cpuacct/user.slice/cpu.rt_runtime_us

EORC

chmod +x /etc/rc.local

EOF

done

Wednesday, January 21, 2026

SGA resize

How to resize SGA

PURPOSE: All documents are provided on this Blog just for educational purposes only. Please make sure that you run it in your test environment before to move on to production environment.

SQL> show sga

SQL> show parameter pool

SQL> show parameter sga_target;

SQL> select * from v$sgainfo;

SELECT name,value/1024/1024/1024 "SGA (GB)" FROM v$sga;

SELECT sum(value)/1024/1024/1024 "TOTAL SGA (GB)" FROM v$sga;

show parameter sga_max_size

NOTE: create pfile from spfile before do the chanege.

alter system set sga_target=72G scope=spfile sid='*';

---

SQL> alter system set sga_max_size=32G scope=spfile;

SQL> alter system set sga_target=32G scope=spfile;

System altered.

!!! PGA_AGGREGATE_TARGET should be lower than PGA_AGGREGATE_LIMIT.

NOTE: Soll den wert kleiner sein als SGA und grosser als pga_aggregate_target

SQL> alter system set pga_aggregate_limit=16G scope=spfile;

System altered.

NOTE: Soll den wert kleiner sein als pga_aggregate_limit

SQL> alter system set pga_aggregate_target=4G scope=spfile;

System altered.

restart DB:

----

#usefull link with nice example.

http://www.orafaq.com/wiki/SGA_target

Friday, December 5, 2025

Oracle JDBC Connection Test

How to test Oracle connection via JDBC Thin driver.

Oracle JDBC Connection Test

SCOPE: Oracle JDBC Connection Test

PURPOSE: All documents are provided on this Blog just for educational purposes only. Please make sure that you run it in your test environment before to move on to production environment.

STEP 1.

Create a file OracleCon.java with the following code.

vi OracleCon.java

import java.sql.*;

public class OracleCon

{

public static void main(String args[])

throws ClassNotFoundException, SQLException

{

Class.forName("oracle.jdbc.driver.OracleDriver");

String url = "jdbc:oracle:thin:@ ORADBPRD.th.com:1521:KARDBPRD";

Connection conn =

DriverManager.getConnection(url,"user_tst01","pw_xyz");

conn.setAutoCommit(false);

Statement stmt = conn.createStatement();

ResultSet rs=stmt.executeQuery("select user from dual;");

while(rs.next())

{

System.out.println (rs.getString(1));

}

stmt.close();

System.out.println ("Connection succeeded");

}

STEP 2.

Compile the code.

javac OracleCon.java

Execute the program as follow.

java OracleCon

USER_TST01

Connection succeeded

Tuesday, June 10, 2025

April Patch 19c 2025

Oracle Critical Patch Update on 19c - January 2025

Oracle Critical Patch Update (CPU)

19.27.0.0.250415 GI RU Combo:

Patch 37591516 - Combo of OJVM Component Release Update 19.27.0.0.250415 + Grid Infrastructure Apr 2025 Release Update 19.27.0.0.25041

PURPOSE: All documents are provided on this Blog just for educational purposes only. Please make sure that you run it in your test environment before to move on to production environment.

Execute the following commands:

STEP 1

Oracle® Database Patch 37641958 - GI Release Update 19.27.0.0.250415

NOTE: IMPORTANT

GI Home:

You need to update first opatch to the higher or latest version.

You can download latest version from the following link.

For April CPU is required OPatch latest version. It can be downloaded by the following link

Download lest OPatch from "https://updates.oracle.com/download/6880880.html"

Latest OPatch copy files.

p6880880_190000_Linux-x86-64.zip

cd $GRID_HOME

mv OPatch OPatch_old

cd $DOWNLOAD_PATCH/OPatch

cp -r OPatch $GRID_HOME

You Need to do the same on ORACLE_HOME

Oracle ORACLE_HOME

Latest OPatch copy files

cd $ORACLE_HOME

mv OPatch OPatch_old

cd $DOWNLOAD_HOME/OPatch

cp -r OPatch $ORACLE_HOME

Unzip January patch file downloaded.

unzip p37641958_190000_<platform>.zip

Check the conflict:

From Grid_Home

$DOWNLOAD_PATCH is a directory where the patch is located.

$ORACLE_HOME/OPatch/opatch prereq CheckConflictAgainstOHWithDetail -phBaseDir $DOWNLOAD_PATCH/37641958/37642901

$ORACLE_HOME/OPatch/opatch prereq CheckConflictAgainstOHWithDetail -phBaseDir $DOWNLOAD_PATCH/37641958/37654975

$ORACLE_HOME/OPatch/opatch prereq CheckConflictAgainstOHWithDetail -phBaseDir $DOWNLOAD_PATCH/37641958/37643161

$ORACLE_HOME/OPatch/opatch prereq CheckConflictAgainstOHWithDetail -phBaseDir $DOWNLOAD_PATCH/37641958/37762426

$ORACLE_HOME/OPatch/opatch prereq CheckConflictAgainstOHWithDetail -

phBaseDir $DOWNLOAD_PATCH/37641958/36758186

For Database home, as home user

$ORACLE_HOME/OPatch/opatch prereq CheckConflictAgainstOHWithDetail -phBaseDir $DOWNLOAD_PATCH/37641958/37642901

$ORACLE_HOME/OPatch/opatch prereq CheckConflictAgainstOHWithDetail -phBaseDir $DOWNLOAD_PATCH/37641958/37654975

Shut down all instances and listeners associated with the Oracle home that you are updating.

Stop a PDB from Oracle home:

alter pluggable database KARDBPDB close immediate;

srvctl stop database -d KARDBTST

srvctl status database -d KARDBTST

Database is not running.

Stop Listener from GI Home

srvctl stop listener -l LISTENER

srvctl status listener -l LISTENER

Listener LISTENER is enabled

Listener LISTENER is not running

Stop ASM

srvctl stop asm -f

srvctl status asm

ASM is not running.

As root user execute the following command.

You have following options

i) To patch only the GI Home

<GI_HOME>/OPatch/opatchauto apply <UNZIPPED_PATCH_LOCATION>/37641958 - oh <GI_HOME>

ii) To patch oracle_home

opatchauto apply <UNZIPPED_PATCH_LOCATION>/37641958 -oh <oracle_home1_path>

iii) Patching Oracle Home and Grid Home togather:

As root user, execute the following command on each node of the cluster:

# <GI_HOME>/OPatch/opatchauto apply <UNZIPPED_PATCH_LOCATION>/37641958

I am going to apply the path for both grid home and oracle home together.

NOTE: make sure that the Clusterware is running:

crsctl status has

If it is not running, you need to start it as follow.

crsctl start has

export PATH=$PATH:$GRID_HOME/OPatch
$GRID_HOME/OPatch/opatchauto apply $DOWNLOAD_PATCH/37641958

Post-Installation Instructions

Single/Multitenant (CDB/PDB) DB

sqlplus / as sysdba

startup

alter pluggable database all open;

quit

cd $ORACLE_HOME/OPatch

./datapatch -verbose

Any databases that have invalid objects need to execute utlrp.sql run

For example:

cd $ORACLE_HOME/rdbms/admin

sqlplus /nolog

SQL> CONNECT / AS SYSDBA

SQL> @$ORACLE_HOME/rdbms/admin/utlrp.sql

-- You can check valid or invalid objects with the following command.

set pagesize 250;

col STATUS format a20;

col COMP_NAME format a35;

select COMP_NAME, version, status from dba_registry;

STEP 2

Patch 37499406 - Oracle JavaVM Component Release Update 19.27.0.0.250415

For a Non Oracle RAC environment, shut down all databases and listeners associated with the Oracle home that you are updating.

From Oracle_home.

Normally no need to stop ASM. You need to just stop the DB and Listener

alter pluggable database KARDBPDB close immediate;

srvctl stop database -d KARDBTST

srvctl stop listener -l LISTENER

export PATH=$PATH:/usr/ccs/bin

#$ORACLE_HOME/OPatch/opatch apply $DOWNLOAD_PATCH/37499406

Post installation Steps.

startup upgrade

alter pluggable database all open upgrade;

exit

cd $ORACLE_HOME/OPatch

./datapatch -verbose

sqlplus / as sysdba

shutdown

startup

alter pluggable database all open;

cd $ORACLE_HOME/rdbms/admin

SQL> @utlrp.sql

==== DONE ====

Verify the patch Version and Status of the patch:

col ID format a5

col COMMENTS format a20

col VERSION format a12

col BUNDLE format a5

col ACTION_TIME format a30

col ACTION format a10

set linesize 150

select substr(action_time,1,30) action_time, substr(id,1,8) id, substr(action,1,10) action, substr(version,1,8) version, substr(comments,1,20) comments from sys.registry$history ;

set pagesize 20;

set linesize 200;

col ACTION_TIME format a30;

col DESCRIPTION format a50;

select PATCH_ID,ACTION,ACTION_TIME,DESCRIPTION,STATUS from registry$sqlpatch order by ACTION_TIME ;

select PATCH_ID,DESCRIPTION,STATUS from registry$sqlpatch order by ACTION_TIME ;

cd $ORACLE_HOME/OPatch

./opatch lspatches -oh ${ORACLE_HOME}

cd $GRID_HOME/OPatch

./opatch lspatches -oh ${GRID_HOME}

Enjoy !

Your comments are most valuable and it would help me to come up with better posts.

Tags

Tuesday, June 16, 2026

How to create swap file

How to Create, Verify, and Increase Swap Space on Linux

What is Swap Space?

Benefits of Swap

Check Existing Swap Space

Create a New Swap File

Step 1: Disable Existing Swap (if required)

Step 2: Create Swap File

Step 3: Set Correct Permissions

Step 4: Format the File as Swap

Step 5: Enable Swap

Step 6: Verify Swap Activation

Step 7: Make Swap Persistent After Reboot

Increase Existing Swap Partition

Step 1: Disable Swap

Step 2: Increase Virtual Disk Size in vCenter

Step 3: Detect New Disk Size

Step 4: Modify Partitions

Existing Layout

Delete Existing Swap Partition

Resize Root/Data Partition

Create New Swap Partition

Tuesday, May 26, 2026

ORA-800_VKTM

ORA-800_VKTM

ORA-00800: soft external error, arguments: [Set Priority Failed], [VKTM]

ORA-800_VKTM_Fix

Wednesday, January 21, 2026

SGA resize

How to resize SGA

Friday, December 5, 2025

Oracle JDBC Connection Test

How to test Oracle connection via JDBC Thin driver.

Tuesday, June 10, 2025

April Patch 19c 2025

Oracle Critical Patch Update on 19c - January 2025

Oracle Critical Patch Update (CPU)

Patch 37591516 - Combo of OJVM Component Release Update 19.27.0.0.250415 + Grid Infrastructure Apr 2025 Release Update 19.27.0.0.25041

Oracle® Database Patch 37641958 - GI Release Update 19.27.0.0.250415

Download lest OPatch from "https://updates.oracle.com/download/6880880.html"

How to create swap file