Linux: Enable Kdump

July 3, 2025 Leave a comment

Some systems may have Kernel crash dumps (kdump) disabled due to performance concerns. When encountering a kernel panic and contacting RHEL support, they might request a kdump. You are advised to enable kdump and either wait for the incident to occur or manually trigger it to observe the kernel panic. Kdump must be enabled in order for the incident to generate the dump files.

1. If kernel-tools package is removed from the system, install it:

# yum install kexec-tools -y

2. To reserve memory for Crashkernel, add the crashkernel option to the current kernel:

# grubby --update-kernel=/boot/vmlinuz-$(uname -r) --args="crashkernel=1G"

3. Reboot the System

# reboot

4. Enable and start Kdump service

# systemctl enable --now kdump.service

5. Verify Kdump is running

# systemctl status kdump.service

● kdump.service - Crash recovery kernel arming
   Loaded: loaded (/usr/lib/systemd/system/kdump.service; enabled; vendor prese>
   Active: active (exited) since Tue 2025-06-24 20:29:58 UTC; 7min ago
 Main PID: 1169 (code=exited, status=0/SUCCESS)
    Tasks: 0 (limit: 196884)
   Memory: 0B
   CGroup: /system.slice/kdump.service

⚠️ Testing: Trigger a Kernel Panic

Please note that I will show you a command that can trigger a kernel panic. This will allow you to check if a dump is generated. This is meant for testing purposes only and should not be executed on a production system during working hours. 🙂

Are you sure you want to cause a kernel panic right now? – If yes, then here is the command:

# echo c > /proc/sysrq-trigger

At this point, the node/VM has crashed and rebooted. When you relog in, you can check /var/crash/ directory to see if crash data was generated.

# ll /var/crash/
...
drwxr-xr-x 2 root root 67 Jun 24 20:15 127.0.0.1-2025-06-24-20:15:51

# cd /var/crash/
# ll
..
drwxr-xr-x 2 root root 67 Jun 24 20:15 127.0.0.1-2025-06-24-20:15:51

# cd 127.0.0.1-2025-06-24-20\:15\:51/

# ll
...
-rw------- 1 root root     45904 Jun 24 20:15 kexec-dmesg.log
-rw------- 1 root root 242941092 Jun 24 20:15 vmcore
-rw------- 1 root root     43877 Jun 24 20:15 vmcore-dmesg.txt
⚠️ Be sure to monitor disk space in /var/crash, as vmcore files can be large.

Filed under Linux, Oracle Enterprise Linux, OS Tagged with , , , , , , ,

Azure CLI install ssh extension

June 5, 2023 Leave a comment

Problem:

To enable AD authentication on a Linux OS Azure VM, you must install Azure CLI and have the SSH extension. However, the SSH extension is not installed automatically after installing Azure CLI.

I can guide you through the simple steps to add this extension.

Solution:

Ensure that the extension is not present:

~ az version
{
  "azure-cli": "2.49.0",
  "azure-cli-core": "2.49.0",
  "azure-cli-telemetry": "1.0.8",
  "extensions": {}
}

List available extensions:

~ az extension list-available --output table

Name    Version    Summary  Preview  Experimental  Installed
------- --------   -------  -------  ------------  --------------------------
...
ssh     1.1.6      SSH...   False    False         False
...

Add extension:

~ az extension add --name ssh

Ensure that the extension has been added:

~ az version
{
  "azure-cli": "2.49.0",
  "azure-cli-core": "2.49.0",
  "azure-cli-telemetry": "1.0.8",
  "extensions": {
    "ssh": "1.1.6"
  }
}

Filed under Azure, Linux Tagged with , , , , , , ,

This system has no repositories available through subscriptions.

December 29, 2022 Leave a comment

Problem:

Enabling repos fails:

[root@app1 mari_scripts]# subscription-manager repos --enable rhel-7-server-optional-rpms \
>     --enable rhel-server-rhscl-7-rpms \
>     --enable rhel-7-server-devtools-rpms
This system has no repositories available through subscriptions.

Solution:

Run the following:

[root@app1 mari_scripts]# subscription-manager attach --auto

Installed Product Current Status:
Product Name: Red Hat Enterprise Linux Server
Status:       Subscribed

Reenable repositories:

[root@app1 mari_scripts]# subscription-manager repos --enable rhel-7-server-optional-rpms     --enable rhel-server-rhscl-7-rpms     --enable rhel-7-server-devtools-rpms
Repository 'rhel-7-server-optional-rpms' is enabled for this system.
Repository 'rhel-7-server-devtools-rpms' is enabled for this system.
Repository 'rhel-server-rhscl-7-rpms' is enabled for this system.

Filed under Linux, OS Tagged with , , , ,

Database Express Setup: This site can not be reached

April 21, 2022 Leave a comment

Note: These steps are for TEST non-production databases only.

Configuring/enabling EM express on HTTPS should be simple, by running only:

SQL> exec DBMS_XDB_CONFIG.SETHTTPSPORT(5500);

But after configuring it you may still not be able to access the web page and show the error “This site can’t be reached”

The reason for this can be permissions on the wallet files:

[grid@rac1 ~]$ ll /u01/app/oracle/product/19.3.0/dbhome_1/admin/orcl/xdb_wallet
total 8
-rw------- 1 oracle asmadmin 3864 Apr 15 17:40 cwallet.sso
-rw------- 1 oracle asmadmin 3819 Apr 15 17:40 ewallet.p12

The correct permission is 600, but when database is on top of ASM with role separation, then group should also have read permission on these files:

[root@rac1 ~]# chmod 640 /u01/app/oracle/product/19.3.0/dbhome_1/admin/orcl/xdb_wallet/*

After changing it, the web page is displayed.

Filed under DB, EM Tagged with , , , ,