Tag Archives: linux

Understanding cron environment variables


I wanted to automate a certain task on a CentOS server, so I wrote a bash script to perform this task, with the intention of using cron to provide the scheduling.

The script worked beautifully when invoked from the SSH bash shell. However, when cron calls the script, the task failed.

Looking at the error logs, it seems like some line of commands failed with “command not found” error. This usually means that the program called in those lines are nowhere to be found in the current $PATH environment variable.

I have always assumed that when a cron job executes, it inherits the same environment variables as when you log in directly to the shell via SSH. The above error proves that this is not the case.

Finding the difference

In order to modify the script so that it will work with cron, I needed to know what the environment looks like when cron calls a script. Thankfully, a quick Google search revealed this post on stackoverflow.

First, we add the following line to the crontab. This will save the output of the env command, which is the list of all current environment variables, into a file once every minute. We just need it to run once, therefore remove the line from crontab once the first minute mark has passed.

* * * * * env > ~/env.out

The contents of this output file reveal that the environment variables loaded when cron runs a script is a very small subset of the environment variables loaded when you get to the shell prompt via SSH login.

Load the environment and test

Now we can use this output file to load the same environment variables as when cron executes a script, and modify the script we wish to run via cron until it works.

# env - `cat ~/env.out` /bin/sh
# ./script.sh

Install Oracle Enterprise Manager Cloud Control 12c Release 3 on Oracle Linux 6


This post is intended to document the process of installing Oracle Enterprise Manager Cloud Control 12c Release 3 on Oracle Linux 6.


OEM Cloud Control is used as a centralised management point for Oracle Database installations in your environment.

You can install this for free and use the base functionalities for free as long as you have an active support subscription with Oracle for any targets (database, hosts, etc.) you want to manage.

The list of the base functionalities you can use for free can be reviewed on the OEM Cloud Control Licensing Guide.

Server setup

First, we start with a minimal installation of Oracle Linux 6 with 8GB of RAM and 100GB hard disk.  A swap space of 8GB is configured.

Install Oracle Database

OEM Cloud Control will use an Oracle Database to store OEM data, and this database will have to have been installed when you run the OEM Cloud Control installer.  The OEM Cloud Control installer will not install the Oracle Database as part of the installation.

You may use an existing Oracle Database for this purpose or you can install a separate database specifically for it.

From the Licensing Guide:

Enterprise Manager includes a restricted-use license of the Oracle Database for use only with the Oracle Management Repository or other complementary repositories included with Enterprise Manager (such as, Ops Center, Real User Experience Insight, Load Testing, and Test Manager).

Additional database options or additional servers for disaster recovery require separate licensing. Customers receive one single-instance database with the Cloud Control, or RMAN, repository. To protect the repository with Data Guard, customers need to purchase a license for the standby site. To protect the repository with Oracle Real Application Clusters, customers must license the second node for the database, and both nodes require an Oracle Real Application Clusters license.

As long as you use a single-instance installation of Oracle Database and do not use this database for anything other than OEM, the database is considered properly licensed.

Prep the server for Oracle Database installation

Funnily enough, at the time of writing, the highest version of Oracle Database certified to be used as the OEM repository is 11gR2.  12c is not certified.

You can check the certifications via My Oracle Support by following the steps in the Installation Guide.

Now we install the 11gR2 pre-requisite RPM to prepare the server for Oracle Database installation.

[root@server ~]# yum install oracle-rdbms-server-11gR2-preinstall

The preinstall RPM will have added the oracle OS user, as well as the oinstall and dba OS groups.

Next, we create the directory structure to hold the Oracle Database files.

[root@server ~]# mkdir -p /u01/app/oracle
[root@server ~]# chown -R oracle:oinstall /u01

Get the Oracle Database installer from OTN, and copy the files into the server.  Finally, unzip the installation files.

Perform Oracle Database Installation

Set up X forwarding, and run the installer as the oracle user.

[oracle@server ~]$ cd database
[oracle@server database]$ ./runInstaller

Choose to configure a database during installation.

Choose to configure database during installation.

Choose a server class installation.

Choose server class

Choose single instance installation.

Choose single-instance installation.

Choose Enterprise Edition, and de-select all options except Partitioning, which is required by OEM Cloud Control 12c.  We remove all unnecessary options to avoid future trouble with Oracle Licensing.

Choose Enterprise EditionDe-select all options except Partitioning.

Proceed with the rest of the installation as usual.  Just accept all the defaults for the database configuration, as we will remove this database later and create a new one.

Create repository instance

After the installation has completed, run the Database Configuration Assistant (DBCA) and remove the instance configured during the database installation.

Then use DBCA to create a new instance from scratch.  Using any of the seed databases supplied by Oracle will not do as the database for the OEM repository should not have the SYSMAN schema present.

The settings for the new database should match your expected deployment size.  Refer to the Advanced Installation and Configuration Guide for sizing guide.  For this article, I will be using the SMALL deployment size, which have the following settings for the repository database:

Parameter Minimum Value
processes 300
pga_aggregate_target* 1024 MB
sga_target* 2 GB
redo log file size 300 MB
shared_pool_size 600 MB
*memory_target of 3 GB can be used in place of sga_target and pga_aggregate_target

We can now begin creating the database using DBCA.

Choose to create a database.

Choose Create a Database

Choose to create a custom database.

Choose Custom Database

Uncheck the Configure Enterprise Manager and Enable automatic maintenance tasks checkboxes.

Uncheck Configure Enterprise ManagerUncheck enable automatic maintenance tasks

Remove all the optional database components

Remove all optional componentsRemove all optional components

Check the Use Automatic Memory Management checkbox and make sure the memory size is more than 3 GB.

Enable Automatic Memory Management

Set processes to 300.

Set processes to 300

Change all three redo log file sizes to 300 MB.

Set redo log file size to 300 MB.

Complete the database creation.

Install Oracle Enterprise Manager Cloud Control 12c Release 3

With the repository database ready, it is time to install the OEM proper.

Review package requirements.

First, review the operating system package requirements from the Installation Guide.

For my installation, since the oracle-rdbms-server-11gR2-preinstall package was already installed, the only missing package is the glibc-devel 32-bit package.  So, that will now be installed using yum.

[root@server ~]# yum install glibc-devel.i686

Next, get the installer from OTN.

Unzip the files, and run the installer as the oracle user.

[oracle@server oem]$ ./runInstaller

Configure the email and software updates if you want to, and click Next.

The pre-requisite checks will be performed, and in my case, all the tests were successful.

Pre-requisite checks

Choose to create a new Advanced Enterprise Manager System.

Choose Advanced Installation

Next, specify the location to install the Middleware and Agent components of OEM Cloud Control.  I chose to use the ORACLE_BASE of the database installation as the base directory, with directories for the Middleware and Agent components located in this base.

Specify middleware and agent directories

The next page we will be able to choose which management plugins we wish to install.  For my install, I will only use OEM Cloud Control to manage Oracle Databases.  Therefore, I will not install any additional plugins.

Choose plugins to install.

Next, provide passwords WebLogic and Node Manager, and specify installation directory for OMS.  Again, I used the same directory structure as the Oracle Database installation.

Provide passwords and specify OMS installation directory.

Step 8: Provide the details of the repository database.  Here we insert the details of the repository database which we have installed earlier, and select the corresponding deployment size.

Insert database details and deployment size.

When I clicked Next, an error popped out saying that a CBO statistics collection job must be disabled.  The installer offered to fix this automatically, and I accept.

Click Yes to disable CBO stats gathering job.

After clicking Yes, the installer presented me with several warnings regarding database parameter mis-matches that will affect the performance of the OEM Cloud Control.  I can choose to fix them now, or proceed with the installation and fix them later.

Database parameter mis-match warnings.

The first warning is about the memory_target parameter.  However, checking the parameter shows that the parameter is set up correctly for the SMALL deployment size.

SQL> show parameter memory_target

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
memory_target                        big integer 3200M

The second warning is for the session_cached_cursors parameter.  Change this to the recommended value.  This parameter is not changeable online, so a database restart is required.

SQL> show parameter session_cached_cursors

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
session_cached_cursors               integer     50

SQL> alter system set session_cached_cursors=500 scope=SPFILE;

System altered.

SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup
ORACLE instance started.

Total System Global Area 3340451840 bytes
Fixed Size                  2257840 bytes
Variable Size            1811942480 bytes
Database Buffers         1509949440 bytes
Redo Buffers               16302080 bytes
Database mounted.
Database opened.
SQL> show parameter session_cached_cursors;

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
session_cached_cursors               integer     500

The third and final change is to the shared_pool_size parameter.

SQL> show parameter shared_pool_size

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
shared_pool_size                     big integer 0
SQL> alter system set shared_pool_size=600M scope=both;

System altered.

SQL> show parameter shared_pool_size

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
shared_pool_size                     big integer 608M

Now, we return to the installer and click Cancel and re-run the database check.  Now, only one warning appears, which I guess is an installer glitch in reading the memory parameter.  Click Ok to resume with the installation.

The remaining database parameter mis-match warning.

Step 9: On this page of the installer, we specify the passwords for SYSMAN and registration.  This SYSMAN password will be used in the initial login to the OEM Cloud Control.  You can change the default locations of the tablespaces to be created, and also the location of the software library to be used by OEM Cloud Control.

Provide passwords and tablespace locations.

Step 10: Review the port assignments for OEM Cloud Control, or change them if you wish.

Review port assignments.

Step 11: Finally, we get to the review page.  Click Install to begin OEM Cloud Control installation.

Review Page.

The installer will prompt for execution of root scripts.  Run the script.

[root@server ~]# /u01/app/oracle/middleware/oms/allroot.sh

Starting to execute allroot.sh .........

Starting to execute /u01/app/oracle/middleware/oms/root.sh ......
Running Oracle 11g root.sh script...

The following environment variables are set as:
    ORACLE_OWNER= oracle
    ORACLE_HOME=  /u01/app/oracle/middleware/oms

Enter the full pathname of the local bin directory: [/usr/local/bin]: <Press Enter>
The file "dbhome" already exists in /usr/local/bin.  Overwrite it? (y/n)
[n]:<Press Enter>
The file "oraenv" already exists in /usr/local/bin.  Overwrite it? (y/n)
[n]:<Press Enter>
The file "coraenv" already exists in /usr/local/bin.  Overwrite it? (y/n)
[n]:<Press Enter>

Entries will be added to the /etc/oratab file as needed by
Database Configuration Assistant when a database is created
Finished running generic part of root.sh script.
Now product-specific root actions will be performed.
/etc exist

Creating /etc/oragchomelist file...
Finished execution of  /u01/app/oracle/middleware/oms/root.sh ......

Starting to execute /u01/app/oracle/agent/core/ ......
Finished product-specific root actions.
/etc exist
Finished execution of  /u01/app/oracle/agent/core/ ......

The installation is now completed.

Configure firewall for OEM Cloud Control

Now we we will need to configure the firewall to enable OEM Cloud Control to work properly.  Of course, you can disable the firewall instead should you choose to.

Check the Port List

First, check the list of ports used by your installation.  This list can be located inside your middleware installation directory <path_to_middleware>/oms/install/portlist.ini.

[root@server ~]# cat /u01/app/oracle/middleware/oms/install/portlist.ini
Enterprise Manager Upload Http Port=4889
Enterprise Manager Upload Http SSL Port=4903
Enterprise Manager Central Console Http SSL Port=7802
Node Manager Http SSL Port=7403
Managed Server Http Port=7202
Enterprise Manager Central Console Http Port=7788
Oracle Management Agent Port=3872
Admin Server Http SSL Port=7102
Managed Server Http SSL Port=7301

Configure Firewall

Next, configure the firewall to allow incoming connections from all the ports listed above.

[root@server ~]# iptables -I INPUT 5 -m state --state NEW -p tcp --dport 4889 -j ACCEPT
[root@server ~]# iptables -I INPUT 6 -m state --state NEW -p tcp --dport 4903 -j ACCEPT
[root@server ~]# iptables -I INPUT 7 -m state --state NEW -p tcp --dport 7802 -j ACCEPT
[root@server ~]# iptables -I INPUT 8 -m state --state NEW -p tcp --dport 7403 -j ACCEPT
[root@server ~]# iptables -I INPUT 9 -m state --state NEW -p tcp --dport 7202 -j ACCEPT
[root@server ~]# iptables -I INPUT 10 -m state --state NEW -p tcp --dport 7788 -j ACCEPT
[root@server ~]# iptables -I INPUT 11 -m state --state NEW -p tcp --dport 3872 -j ACCEPT
[root@server ~]# iptables -I INPUT 12 -m state --state NEW -p tcp --dport 7102 -j ACCEPT
[root@server ~]# iptables -I INPUT 13 -m state --state NEW -p tcp --dport 7301 -j ACCEPT
[root@server ~]# service iptables save
iptables: Saving firewall rules to /etc/sysconfig/iptables:[  OK  ]

Login to OEM Cloud Control

Now, we are ready to login for the first time to the OEM Cloud Control installation.  Open up a browser and go to the following URL:


The port should be the port listed for Enterprise Manager Central Console Http SSL Port in the portlist.ini file that we checked earlier.

Login Page

Login with username SYSMAN and the password for SYSMAN that was set during the OEM Cloud Control installation earlier.

You will be presented with a License Agreement Page.

License Agreement Page

Read the license agreement and click I Accept.

You will now be presented with the Welcome Page.  You can now start using OEM Cloud Control 12c.

Adding Oracle Linux 6.4 Installation DVD as a yum repository

First, make sure the install DVD is mounted properly and take note of the mount point.  For the purpose of this post, the DVD is mounted at /mnt.

Next, create a repository file at the yum repository directory.

# vi /etc/yum.repos.d/dvd.repo

Insert the following lines inside the file, and save.

name=Oracle Linux 6.4 Installation DVD $basearch

name=Oracle Linux 6.4 Installation DVD $basearch - UEK

Now, the yum command will use the DVD as a repository.  Don’t forget to disable other repositories in the folder if you do not want newer packages to be installed.

Local mirror of Oracle public yum – UPDATED

Updating Oracle Linux installations via the Oracle public yum server has been cumbersome because the download speeds I have been getting are quite terrible.

Having quite a number of Oracle Linux installations compounds the issue as each server will have to endure the same slow download speeds for the same packages.  One way to stop this from happening is having a local mirror of the public yum server.  This local mirror will perform the download of the packages from the public yum server, and all other Oracle Linux installations will then grab the packages from the local mirror, saving lots of time.

I have been scouring the internet for days looking for the best way to do this, and I think the best guide so far comes from this post by Martin Nash.

I hope to setup my own mirror soon.

Update 19 August 2013

Below are the steps to setup yum mirror from a fresh CentOS 6.4 Minimal Install.

Create the directory to put the repository in.

# mkdir -p /repos/x86_64

Install the yum-utils and createrepo packages that provide the reposync and createrepo commands.

# yum install yum-utils createrepo

Set up the repository to mirror as per the instruction at Oracle.  Open the repo file and disable all repos by making sure enabled=0 for all repos.

# vi /etc/yum.repos.d/public-yum-ol6.repo

Run reposync.  This will take quite a long time, especially with the slow speeds from the Oracle public yum server.

# reposync --repoid=ol6-latest --repoid=ol6-UEK-latest -p /repos/ol6

After the reposync command finished downloading all the packages from the source repo, run createrepo to create the repository metadata.

# createrepo /repos/ol6/ol6_UEK_latest/getPackage/
# createrepo /repos/ol6/ol6_latest/getPackage/

Create a script to re-run the above as often as required (I am going to run it once a day).

LOG_FILE=/repos/logs/orayum-update_$(date +%Y.%m.%d).log
/usr/bin/reposync --repoid=ol6_latest --repoid=ol6_UEK_latest -p /repos/ol6 >> $LOG_FILE 2>&1
/usr/bin/createrepo /repos/ol6/ol6_UEK_latest/getPackage/ >> $LOG_FILE 2>&1
/usr/bin/createrepo /repos/ol6/ol6_latest/getPackage/ >> $LOG_FILE 2>&1

Create the directories to store the script and logs, and move the script inside the directory

# mkdir -p /repos/logs
# mkdir -p /repos/scripts
# mv orayum-update.sh /repos/scripts

Make the script executable

# chmod +x /repos/scripts/orayum-update.sh

Add the script to crontab, and run once every day.

# crontab -e
0 0 * * * /repos/scripts/orayum-update.sh

# crontab -l
0 0 * * * /repos/scripts/orayum-update.sh

Install and configure Apache webserver.

# yum install httpd
# chkconfig httpd on
# service httpd start

Now configure Apache to serve the repository.

# mkdir -p /var/www/html/repo/OracleLinux/OL6/latest
# mkdir -p /var/www/html/repo/OracleLinux/OL6/UEK/latest
# ln -s /repos/ol6/ol6_latest/getPackage/ /var/www/html/repo/OracleLinux/OL6/latest/x86_64
# ln -s /repos/ol6/ol6_UEK_latest/getPackage/ /var/www/html/repo/OracleLinux/OL6/UEK/latest/x86_64

Open up the firewall for Apache.

# iptables -I INPUT 5 -p tcp --dport 80 -m state --state NEW -j ACCEPT
# service iptables save

Now we need to fix the SELinux contexts for the repository files, so that the repository, which is soft-linked from the /var/www/html sub-folders, can be served by Apache.

# yum install policycoreutils-python
# semanage fcontext -a -t httpd_sys_content_t "/repos/ol6/ol6_latest/getPackage(/.*)?"
# semanage fcontext -a -t httpd_sys_content_t "/repos/ol6/ol6_UEK_latest/getPackage(/.*)?"
# restorecon -R -v /repos/ol6/

Get the repository GPG key as well, and put it into the root Apache directory.

# cd /var/www/html
# wget http://public-yum.oracle.com/RPM-GPG-KEY-oracle-ol6

Now the local yum mirror is fully setup!  Local Oracle Linux 6 installations can now use this repository by creating a repo file in /etc/yum.repos.d/ folder.

# cd /etc/yum.repos.d
# vi public-yum-ol6-local.repo

The repo file looks something like this:

name=Oracle Linux $releasever Latest ($basearch)

name=Latest Unbreakable Enterprise Kernel for Oracle Linux $releasever ($basearch)