ORA-27125: unable to create shared memory segment during startup

Problem

After reboot, unable to startup Oracle 12c database instance (Red Hat Enterprise Server 7.6)

ORA-27125: unable to create shared memory segment
Linux-x86_64 Error: 28: No space left on device
Additional information: 3822
Additional information: 6157238272

Solution

Verify OS kernel.shmall memory setting.

1. Get current value 

cat /proc/sys/kernel/shmall

1677722

This seems to be too high..

2. Determine page size

getconf PAGE_SIZE

4096

3. Calculate recommended value for shmall

shmall = <total size of SGA>/<page size>

In our case, we have 16GB RAM, so, shmall = 16 * 1024 * 1024 * 1024 / 4096 = 4194304

4. Update /etc/sysctl.conf

vi /etc/sysctl.conf

kernel.shmall=4194304

sudo sysctl -p

5. Verify  kernel.shmall again

cat /proc/sys/kernel/shmall

4194304

6. Start Oracle instance

sudo su - oracle

sqlplus / as sysdba

startup;

This of course leads to another error..

References

https://support.oracle.com/knowledge/Oracle%20Database%20Products/301830_1.html

http://www.nazmulhuda.info/ora-27102-out-of-memory-linux-x86_64-error-28-no-space-left-on-device

https://it.toolbox.com/blogs/surachartopun/shared-memory-startup-database-ora-27102-out-of-memory-linux-x86-64-error-28-no-space-left-on-device-102409

https://jameshuangsj.wordpress.com/2018/06/07/ora-27125-unable-to-create-shared-memory-segment-linux-x86_64-error-28-no-space-left-on-device/

Formula to set proper values for max processes, sessions and transactions in Oracle

Problem

Need to adjust max number of sessions in Oracle DB.

Solution

Standard formula looks like:

PROCESSES = Operating System Dependant
SESSIONS = (1.1 * PROCESSES) + 5
TRANSACTIONS = 1.1 * SESSIONS

alter system set sessions=1000 scope=spfile;

alter system set processes=905 scope=spfile;

alter system set transactions=1100 scope=spfile;

shutdown immediate;

startup;

How to get external IP for Linux VMs on Azure

Problem

How to get external IP for Linux VMs on Azure

Solution

dig +short myip.opendns.com @resolver1.opendns.com 

Change mount point for /mnt folder in Ubuntu Linux on Azure

Problem

When provisioning Linux VMs on Azure, /mnt folder is automatically created and pointed to Resource Disk. In some case, we need to have more fine-grained control over /mnt folder (for instance for backward compatibility) and map Resource Disk to its sub-folder, e.g. /mnt/tmp

Solution

Azure provides fantastic support for Linux VMs called Microsoft Azure Linux Agent.

sudo service waagent restart

vi /etc/waagent.conf 
# Mount point for the resource disk
ResourceDisk.MountPoint=/mnt/resources 

 Restart waagent service

 sudo service waagent restart

Install telnet client from command line on Windows Server

Problem

Need to install telnet client on Windows Server 2012, 2016

Solution

pkgmgr /iu:”TelnetClient”

Rhino.Mocks WhenCalled() throws exception "Method requires a return value or an exception to throw"

When using of WhenCalled, you should also specify Return statement at the end. More details here.

Copy maven dependencies to WEB-INF/lib

Use Case

Configure Dynamic Web Project in Eclipse to copy maven dependencies (jars) to WEB-INF/lib.

Solution

1. Update eclipse.ini, specify -vm option

-vm
C:\Program Files\Java\jdk1.6.0_25\bin\

2. Convert project to MAVEN backed, set packaging to WAR.

3. Configure JRE

Go to Project > Properties > Java Build Path > Libraries. Choose JRE System Library and click 'Edit'. Choose Execution Environment from list of available environments, use the same vm as eclipse.ini has.

4. Configure Deployment Assembly

Go to Project > Properties > Deployment Assembly. Click Add button, then choose Java Build Path Entries. Choose Maven Dependencies from the list and click OK.