Ilmar Kerm

Oracle, databases, Linux and maybe more

Tag: linux

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Oracle Rest Data Services (ORDS) is a HTTP frontend for various Oracle Database related tasks – database admin APIs, SQL Developer web and most famously ofcourse APEX. It is a java program and for a few years now it comes with a built in Jetty web server that is recommended to use for production workloads – without Tomcat, Weblogic or any other Java servlet container.

All the setup guides for ORDS in the Internet start ORDS usually on port 8443, or any other high port. But the default port for HTTPS is 443. If ORDS should be used without any additional web server/proxy, then wouldn’t it be nice to use the default HTTPS port already directly for ORDS?

This brings a little problem – Linux does not allow non-privileged users to open ports lower than 1024 and I really do not think it is a good idea to run ORDS as root.

The easiest way to achieve this I’ve found is to just use FirewallD to create an internal port-forward. I’ve tested this on Oracle Linux 8.

As an one-time operation, as root, configure FirewallD to allow incoming port 443 and then forward all traffic from 443 to 8443.

firewall-cmd --add-port=443/tcp --permanent
firewall-cmd --add-forward-port=port=443:proto=tcp:toport=8443 --permanent
firewall-cmd --reload

Then, start ORDS normally on port 8443, using non-privileged user.

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I noticed that the latest Oracle Linux 8 U7 Cloud Image from https://yum.oracle.com/oracle-linux-templates.html comes with UEKr7 kernel by default (5.15.0). But this is not yet supported by Oracle Database 19c and it is also missing for example ceph filesystem kernel module.

So here are instructions how to downgrade kernel on OEL8.

First enable UEKr6 tum repository and disable UEKr7 respository. I’m not going to write these instructions, since the copy I have uses our own internal repositories and not public ones.

After that execute:

update file /etc/sysconfig/kernel and set
DEFAULTKERNEL=kernel-uek

# Install old UEKr6 kernel
dnf install kernel-uek
# Remove the new UEKr7 kernel
rpm -e kernel-uek-core
# Regenerate GRUB config
grub2-mkconfig -o /boot/grub2/grub.cfg

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To continue my previous post abiout ADR log mining, another monitoring agent that I created was just a very simple (initially) Linux monitoring agent. System metrics.

I know there are plenty of existing software products already doing exactly that, but I don’t really like the one that was chosen by my employer – other people maintaining it for different goals. Also I wanted to have much richer metadata (and Oracle specific – like cluster name) added to the monitoring data.

Here is the code:

https://github.com/ilmarkerm/monitoring/blob/main/linux/system-monitor.py

Cheap to run and just uses regular expressions to parse information returned by standard Linux monitoring command. Data is again sent to InfluxDB backend intended to be used in Grafana dashboards.

I push it out using Ansible, so I left in some Ansible tags in the configuration section… and so pleople would not just blindly take the code and try to run it without understanding it 🙂

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I have quite many different databases and would like to log in to them from my linux box using my AD username and password. Creating tnsnames.ora aliases for all of them is too much work, I’d like to just specify hostname and service from command line.

Bash aliases to the rescue, but simple alias is not enough in this case, so just take it as an example how can more complex aliases be created in Bash.

Just copy these functions to $HOME/.bashrc, modify them according to your needs and done 🙂

This creates two “aliases” – sqls for secure database connection and sql for insecure. I also need to use instantclient driver for database connection (Radius authentication).

Usage:

sqls rac-scan.example.com myapplicationservice.prod
sqls rac-scan.example.com myapplicationservice.prod dbauser
SQLS_OPTS="-verbose" sqls rac-scan.example.com myapplicationservice.prod

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Before storage device can be removed (or unassigned) from server, it must first be removed from Linux. This is even more necessary if the server is running Oracle ASMLib, because if there are any removed or read-only storage devices present when running service oracleasm scandisks, the command will just hang and server load will start to increase (maximum I’ve seen was 3500).

Here you find RedHat instructions on how to cleanly remove storage devices in RHEL6. A lot of steps, especially when running multipath and having multiple paths to each device.

Since we do database replication and cloning to test using storage replication, then assigning and unassigning storage devices from test servers is quite frequent and if not done properly and cleanly, we have to reboot the server. Here is a little script to help with that task. It takes ASMLib disk names to be removed as an argument, finds all paths to the device and removes them from Linux.

Tested in OEL5 (using RHEL kernel) and OEL6 (using UEK2 kernel). This script only deals with dm-* and sd* devices, so before using please check and modify the script for your environment. Before removing the storage devices from Linux, make sure that the disk groups are dismounted from ASM and they are not used.

Ilmar Kerm