Manage Linux Services with systemctl

What is systemctl?
`systemctl` is the command-line interface to **systemd**, the modern init system used by most major Linux distributions (like Ubuntu, CentOS, RHEL, Debian, Arch, Fedora).

You use `systemctl` to:
- Start and stop services
- Enable services to run at boot
- Check service status
- View logs
- Troubleshoot failures
- Manage dependencies

Real-World Example: Creating a Custom Service
Let’s say you have a Python web application that you want to run as a systemd service.
Create Your Application Directory
sudo mkdir -p /opt/mywebapp
sudo chown $USER:$USER /opt/mywebapp
Add your app file (for example, app.py) inside /opt/mywebapp/.
Create the systemd Service File
sudo nano /etc/systemd/system/mywebapp.service

Paste this configuration:
[Unit]
Description=My Python Web Application
After=network.target

[Service]
ExecStart=/usr/bin/python3 /opt/mywebapp/app.py
WorkingDirectory=/opt/mywebapp
Restart=always
RestartSec=20
User=webuser
Group=webgroup
Environment="ENV=production"

[Install]
WantedBy=multi-user.target

Explanation:
    After=network.target ensures the network is up before starting.
    Restart=always and RestartSec=20 ensures the app auto-recovers on failure.
    User and Group ensure minimal privileges.
    WantedBy=multi-user.target ensures the service starts at system boot.

Reload systemd
sudo systemctl daemon-reload

Complete systemctl Command Reference
Action    Command
Start    sudo systemctl start <service>
Stop    sudo systemctl stop <service>
Restart    sudo systemctl restart <service>
Reload    sudo systemctl reload <service>
Status    sudo systemctl status <service>
Enable/Disable Services at Boot
Action    Command
Enable    sudo systemctl enable <service>
Disable    sudo systemctl disable <service>
Check Enabled    systemctl is-enabled <service>
Masking Services
Action    Command
Mask    sudo systemctl mask <service>
Unmask    sudo systemctl unmask <service>
Editing Services Safely
Action    Command
Edit    sudo systemctl edit <service>
Revert    sudo systemctl revert <service>
List Services and Units
Action    Command
Running Services    systemctl list-units --type=service
All Unit Files    systemctl list-unit-files
Enabled Units    systemctl list-unit-files --state=enabled
View Logs (journalctl)
Action    Command
View Logs    journalctl -u <service>
Follow Logs    journalctl -fu <service>
Today’s Logs    journalctl -u <service> --since today

ValueError: cannot set a frame with no defined index and a scalar

This error message typically occurs when trying to assign a scalar value to a DataFrame without specifying the index or columns. Here's an example:

python

import pandas as pd

df = pd.DataFrame({'A': [1, 2, 3], 'B': [4, 5, 6]})

# This line will raise the ValueError
df.loc[0] = 7
 

In this example, we have a DataFrame with two columns 'A' and 'B' and three rows. The df.loc[0] = 7 line is trying to set the first row of the DataFrame to the value 7. However, since we haven't specified which columns to update, Pandas is trying to set all columns to the scalar value 7, which isn't possible.

To fix this error, we need to specify which columns we want to update. For example:

python

df.loc[0, 'A'] = 7
 

This will set the value of the 'A' column in the first row to 7. Alternatively, we can specify the columns to update using a list:

python

df.loc[0, ['A', 'B']] = [7, 8]
 

This will set the values of both the 'A' and 'B' columns in the first row to 7 and 8, respectively.

Default ports for major products and services

Web Services
    HTTP: 80
    HTTPS: 443
    HTTP/3 (QUIC): 443

Database Systems
    MySQL: 3306
    PostgreSQL: 5432
    MongoDB: 27017
    Redis: 6379
    Microsoft SQL Server: 1433
    Oracle Database: 1521
    Cassandra: 9042
    CouchDB: 5984
    InfluxDB: 8086
    Elasticsearch: 9200

Message Brokers & Queues
    Apache Kafka: 9092
    RabbitMQ: 5672 (AMQP), 15672 (Management UI)
    Apache ActiveMQ: 61616
    Amazon SQS: 443 (HTTPS)

Application Servers & Frameworks
    Apache Tomcat: 8080
    Jetty: 8080
    Node.js (Express): 3000 (common default)
    Django: 8000
    Flask: 5000
    Spring Boot: 8080
    Ruby on Rails: 3000

Email Services
    SMTP: 25 (unencrypted), 587 (TLS), 465 (SSL)
    POP3: 110 (unencrypted), 995 (SSL)
    IMAP: 143 (unencrypted), 993 (SSL)
    
File Transfer & Remote Access
    FTP: 21
    SFTP/SSH: 22
    Telnet: 23
    RDP (Remote Desktop): 3389
    VNC: 5900

DNS & Network Services
    DNS: 53
    DHCP: 67/68
    SNMP: 161
    NTP: 123
    LDAP: 389 (unencrypted), 636 (SSL)

Cloud & Container Services
    Docker: 2376 (secure), 2375 (insecure)
    Kubernetes API: 6443
    etcd: 2379 (client), 2380 (peer)
    Consul: 8500
    Vault: 8200

Monitoring & Observability
    Prometheus: 9090
    Grafana: 3000
    Jaeger: 16686 (UI), 14268 (collector)
    Zipkin: 9411
    New Relic: 443

Development Tools
    Jenkins: 8080
    GitLab: 80/443
    SonarQube: 9000
    Nexus Repository: 8081
    JFrog Artifactory: 8081

Gaming & Entertainment
    Minecraft: 25565
    Steam: 27015
    Discord: 443

IoT & Smart Home
    MQTT: 1883 (unencrypted), 8883 (SSL)
    CoAP: 5683

Linux basic commands

Here are some basic Linux commands along with their full forms and brief descriptions:

1. ls (List): Lists files and directories in the current working directory. Example: ls -l (long format listing), ls -a (include hidden files), ls -h (human-readable sizes).
2. cd (Change Directory): Changes the current working directory. Example: cd /path/to/directory.
3. pwd (Print Working Directory): Displays the current working directory. Example: pwd.
4. cp (Copy): Copies files and directories. Example: cp file.txt destination/.
   copy file with same  timestamp
   cp -p oldfile newfile
   
5. mv (Move): Moves or renames files and directories. Example: mv file.txt new_location/, mv old_name.txt new_name.txt.
6. rm (Remove): Deletes files and directories. Example: rm file.txt, rm -r directory/ (recursively delete a directory).
7. mkdir (Make Directory): Creates a new directory. Example: mkdir new_directory.
8. rmdir (Remove Directory): Deletes an empty directory. Example: rmdir empty_directory.
9. cat (Concatenate): Displays the contents of a file. Example: cat file.txt.
10. more or less: Pager commands to view text files page by page. Example: more file.txt, less file.txt.
11. head and tail: Display the first or last part of a file. Example: head file.txt (displays the first few lines), tail file.txt (displays the last few lines).
12. grep (Global Regular Expression Print): Searches for a pattern in a file or input. Example: grep "keyword" file.txt.
13. find: Searches for files and directories based on different criteria. Example: find /path/to/search -name "filename".
14. chmod (Change Mode): Modifies file permissions. Example: chmod +x script.sh (adds execute permission), chmod 644 file.txt (sets read-write permissions for owner, read-only for group and others).
15. chown (Change Ownership): Changes the owner of a file or directory. Example: chown user:group file.txt.
16. ps (Process Status): Displays information about currently running processes. 

Example: ps aux (lists all processes), ps -ef | grep process_name (search for a specific process).

17. kill: Sends a signal to terminate a process. Example: kill PID (PID is the process ID).
18. df (Disk Free): Shows disk space usage on file systems. Example: df -h ,df -g(displays sizes in human-readable format).
19. free: Shows system memory usage. Example: free -h,free-g (displays sizes in human-readable format).
20. top and htop: Displays real-time system resource usage and processes. Example: top, htop (htop is an improved version of top).
21. ifconfig : Interface Configuration: Displays and configures network interfaces (deprecated on modern systems).
22. ip - IP: A modern alternative to ifconfig for network configuration.
23. ping : Sends an ICMP echo request to a host to check network connectivity.
24. ssh - Secure Shell: Allows secure remote login to another machine over a network.
25. scp - Secure Copy: Securely copies files between hosts over a network.
26. tar - Tape Archive: Used to archive multiple files into a single tarball file.
27. gzip - GNU Zip: Compresses files to reduce their size.
28. unzip - Unzip: Extracts files from a zip archive.
29. who - Who: Displays a list of currently logged-in users.
30. history - History: Shows a list of previously executed commands.
     

 

Move a Database to an Oracle Home with a different patch level( 19.8 to 19.12) Using dbaascli in Exacs

This post covers detailed steps to move a database to an Oracle Home with a different patch level( 19.8 to 19.12) Using dbaascli in Exacs.

High Level Steps:
 --> Verify present db version and components list from registry
 --> Gather invalid objects details and try to compile
 --> Run Prechecks for db home move
 --> Move db to different oracle home with different patch level
 --> Verify db present version and components list from registry , Invalid objects
 
Verify Present db Version:
SQL> select INSTANCE_NAME,host_name,status,logins,version,VERSION_FULL,to_char(STARTUP_TIME,'DD/MM/YYYY HH24:MI:SS') "STARTUP_TIME" from gv$instance;
INSTANCE_NAME      HOST_NAME           STATUS       LOGINS     VERSION           VERSION_FULL      STARTUP_TIME
---------------- -------------------  ------------ ---------- ----------------- ----------------- -------------------
stgdb011           ociexacs-node1       OPEN         ALLOWED    19.0.0.0.0        19.8.0.0.0        22/08/2022 04:04:03
stgdb012           ociexacs-node2       OPEN         ALLOWED    19.0.0.0.0        19.8.0.0.0        22/08/2022 04:04:03

Verify installed components and component version:
SQL> select COMP_ID,COMP_NAME,VERSION,VERSION_FULL,STATUS from dba_registry;
COMP_ID         COMP_NAME                            VERSION         VERSION_FULL                   STATUS
-------------- ------------------------------------ ---------------- ------------------------------ --------
CATALOG         Oracle Database Catalog Views        19.0.0.0.0      19.8.0.0.0                     VALID
CATPROC         Oracle Database Packages and Types   19.0.0.0.0      19.8.0.0.0                     VALID
RAC             Oracle Real Application Clusters     19.0.0.0.0      19.8.0.0.0                     VALID
JAVAVM          JServer JAVA Virtual Machine         19.0.0.0.0      19.8.0.0.0                     VALID
XML             Oracle XDK                           19.0.0.0.0      19.8.0.0.0                     VALID
CATJAVA         Oracle Database Java Packages        19.0.0.0.0      19.8.0.0.0                     VALID
APS             OLAP Analytic Workspace              19.0.0.0.0      19.8.0.0.0                     VALID
XDB             Oracle XML Database                  19.0.0.0.0      19.8.0.0.0                     VALID
OWM             Oracle Workspace Manager             19.0.0.0.0      19.8.0.0.0                     VALID
CONTEXT         Oracle Text                          19.0.0.0.0      19.8.0.0.0                     VALID
ORDIM           Oracle Multimedia                    19.0.0.0.0      19.8.0.0.0                     VALID
SDO             Spatial                              19.0.0.0.0      19.8.0.0.0                     VALID
XOQ             Oracle OLAP API                      19.0.0.0.0      19.8.0.0.0                     VALID
OLS             Oracle Label Security                19.0.0.0.0      19.8.0.0.0                     VALID
DV              Oracle Database Vault                19.0.0.0.0      19.8.0.0.0                     VALID

15 rows selected.

Check Invalid objects:
SQL> select OWNER,OBJECT_NAME,OBJECT_TYPE from dba_objects where STATUS='INVALID';
no rows selected

Check installed DB Home details on Exacs nodes:
[root@ociexacs-node1 ~]# dbaascli system getDBHomes
DBAAS CLI version 22.3.1.1.0
Executing command system getDBHomes
Job id:
{
  "OraHome3" : {
    "id" : "",
    "homePath" : "/u02/app/oracle/product/19.0.0.0/dbhome_1",
    "homeName" : "OraHome3",
    "version" : "19.12.0.0.0",
    "createTime" : 1664597038000,
    "updateTime" : 1664597038000,
    "ohNodeLevelDetails" : {
      "ociexacs-node2" : {
        "nodeName" : "ociexacs-node2",
        "version" : "19.12.0.0.0"
      },
      "ociexacs-node1" : {
        "nodeName" : "ociexacs-node1",
        "version" : "19.12.0.0.0"
      }
    },
    "messages" : [ ]
  },
  "OraHome100" : {
    "id" : "",
    "homePath" : "/u02/app/oracle/product/19.0.0.0/dbhome_2",
    "homeName" : "OraHome100",
    "version" : "19.8.0.0.0",
    "createTime" : 1664596819000,
    "updateTime" : 1664596819000,
    "ohNodeLevelDetails" : {
      "ociexacs-node2" : {
        "nodeName" : "ociexacs-node2",
        "version" : "19.8.0.0.0"
      },
      "ociexacs-node1" : {
        "nodeName" : "ociexacs-node1",
        "version" : "19.8.0.0.0"
      }
    },
    "messages" : [ ]
  }
}
dbaascli execution completed

19.12 version already installed on Exacs nodes, if target version not installed follow steps in https://www.dbops-tech.com/2021/08/install-oracle-rdbms-on-oracle-cloud.html  to installed required db version.

Execute Pre-checks for db move:
[root@ociexacs-node1 ~]# dbaascli database move --dbname stgdb01 --ohome /u02/app/oracle/product/19.0.0.0/dbhome_1 --executePrereqs

DBAAS CLI version 22.3.1.1.0
Executing command database move --ohome /u02/app/oracle/product/19.0.0.0/dbhome_1 --executePrereqs
Job id: cf0a124f-6131-4a11-86af-767175292a27
Loading PILOT...
Session ID of the current execution is: 4
Log file location: /var/opt/oracle/log/stgdb01/database/move/pilot_2022-09-28_09-12-02-PM_90184
-----------------
Running initialization job
Completed initialization job
-----------------
Running validate_user_input job
Completed validate_user_input job
-----------------
Running validate_database job
Completed validate_database job
-----------------
Running validate_creg_file_existence job
Completed validate_creg_file_existence job
-----------------
Running validate_source_home job
Completed validate_source_home job
-----------------
Running validate_major_version job
Completed validate_major_version job
-----------------
Running validate_oracle_home_type job
Completed validate_oracle_home_type job
-----------------
Running check_target_source_home_not_same job
Completed check_target_source_home_not_same job
-----------------
Running validate_home_existence job
Completed validate_home_existence job
-----------------
Running validate_home_consistency job
Completed validate_home_consistency job
-----------------
Running validate_home_options job
Completed validate_home_options job
-----------------
Running validate_disk_space job
Completed validate_disk_space job
dbaascli execution completed
[root@ociexacs-node1 ~]#

Move db to different home using dbaascli:
[root@ociexacs-node1 ~]# dbaascli database move --dbname stgdb01 --ohome /u02/app/oracle/product/19.0.0.0/dbhome_1

DBAAS CLI version 22.3.1.1.0
Executing command database move --ohome /u02/app/oracle/product/19.0.0.0/dbhome_1
Job id: 5bd5403b-0bb4-4db3-8bee-aeca7eebf327
Loading PILOT...
Session ID of the current execution is: 5
Log file location: /var/opt/oracle/log/stgdb01/database/move/pilot_2022-09-28_09-17-09-PM_156886
-----------------
Running initialization job
Completed initialization job
-----------------
Running validate_user_input job
Completed validate_user_input job
-----------------
Running validate_database job
Completed validate_database job
-----------------
Running validate_creg_file_existence job
Completed validate_creg_file_existence job
-----------------
Running validate_source_home job
Completed validate_source_home job
-----------------
Running validate_major_version job
Completed validate_major_version job
-----------------
Running validate_oracle_home_type job
Completed validate_oracle_home_type job
-----------------
Running check_target_source_home_not_same job
Completed check_target_source_home_not_same job
-----------------
Running validate_home_existence job
Completed validate_home_existence job
-----------------
Running validate_home_consistency job
Completed validate_home_consistency job
-----------------
Running validate_home_options job
Completed validate_home_options job
-----------------
Running validate_disk_space job
Completed validate_disk_space job
-----------------
Running acquire_lock job
Completed acquire_lock job
-----------------
Running copy_config_files job
Completed copy_config_files job
-----------------
Running stop_database_instance-ociexacs-node1 job
Completed stop_database_instance-ociexacs-node1 job
-----------------
Running update_database_resource-ociexacs-node1 job
Completed update_database_resource-ociexacs-node1 job
-----------------
Running start_database_instance-ociexacs-node1 job
Completed start_database_instance-ociexacs-node1 job
-----------------
Running stop_database_instance-ociexacs-node2 job
Completed stop_database_instance-ociexacs-node2 job
-----------------
Running update_database_resource-ociexacs-node2 job
Completed update_database_resource-ociexacs-node2 job
-----------------
Running start_database_instance-ociexacs-node2 job
Completed start_database_instance-ociexacs-node2 job
-----------------
Running exacs_post_patch_node_updation job
Completed exacs_post_patch_node_updation job
-----------------
Running update_dba_directories job
Completed update_dba_directories job
-----------------
Running datapatch_and_recompile_invalid_objects job
Datapatch execution on database 'stgdb01' is in progress
Datapatch execution on database 'stgdb01' is complete
Recompilation of invalid objects on database 'stgdb01' is in progress
Recompilation of invalid objects on database 'stgdb01' is complete
Completed datapatch_and_recompile_invalid_objects job
-----------------
Running release_lock job
Completed release_lock job
-----------------
Running invoke_backup_asst job
Completed invoke_backup_asst job
-----------------
Running post_move_validation job
Completed post_move_validation job
-----------------
Running generate_dbsystem_details job
Completed generate_dbsystem_details job
dbaascli execution completed


Post validations:
SQL> select INSTANCE_NAME,host_name,status,logins,version,VERSION_FULL,to_char(STARTUP_TIME,'DD/MM/YYYY HH24:MI:SS') "STARTUP_TIME" from gv$instance;
INSTANCE_NAME      HOST_NAME          STATUS       LOGINS     VERSION           VERSION_FULL      STARTUP_TIME
---------------- ------------------  ------------ ---------- ----------------- ----------------- -------------------
stgdb011           ociexacs-node1      OPEN         ALLOWED    19.0.0.0.0         19.12.0.0.0       28/09/2022 21:18:18
stgdb012           ociexacs-node1      OPEN         ALLOWED    19.0.0.0.0         19.12.0.0.0       28/09/2022 21:20:22

SQL> select COMP_ID,COMP_NAME,VERSION,VERSION_FULL,STATUS from dba_registry;
COMP_ID         COMP_NAME                            VERSION         VERSION_FULL                   STATUS
-------------- ------------------------------------ ---------------- ------------------------------ --------
CATALOG         Oracle Database Catalog Views        19.0.0.0.0      19.12.0.0.0                     VALID
CATPROC         Oracle Database Packages and Types   19.0.0.0.0      19.12.0.0.0                     VALID
RAC             Oracle Real Application Clusters     19.0.0.0.0      19.12.0.0.0                     VALID
JAVAVM          JServer JAVA Virtual Machine         19.0.0.0.0      19.12.0.0.0                     VALID
XML             Oracle XDK                           19.0.0.0.0      19.12.0.0.0                     VALID
CATJAVA         Oracle Database Java Packages        19.0.0.0.0      19.12.0.0.0                     VALID
APS             OLAP Analytic Workspace              19.0.0.0.0      19.12.0.0.0                     VALID
XDB             Oracle XML Database                  19.0.0.0.0      19.12.0.0.0                     VALID
OWM             Oracle Workspace Manager             19.0.0.0.0      19.12.0.0.0                     VALID
CONTEXT         Oracle Text                          19.0.0.0.0      19.12.0.0.0                     VALID
ORDIM           Oracle Multimedia                    19.0.0.0.0      19.12.0.0.0                     VALID
SDO             Spatial                              19.0.0.0.0      19.12.0.0.0                     VALID
XOQ             Oracle OLAP API                      19.0.0.0.0      19.12.0.0.0                     VALID
OLS             Oracle Label Security                19.0.0.0.0      19.12.0.0.0                     VALID
DV              Oracle Database Vault                19.0.0.0.0      19.12.0.0.0                     VALID
15 rows selected.

SQL> select OWNER,OBJECT_NAME,OBJECT_TYPE from dba_objects where STATUS='INVALID';
no rows selected

Layers of the OSI Model

OSI (Open Systems Interconnection) model is a conceptual framework that standardizes how different network protocols communicate across a computer network. It was developed by the International Organization for Standardization (ISO) in 1984 to provide a universal set of rules for network communication.

7 Layers of the OSI Model
The OSI model is organized into 7 distinct layers, each with specific responsibilities. Data flows from the top layer (Application) down to the bottom layer (Physical) when sending, and from bottom to top when receiving.
🔝 Layer 7: Application Layer
What it does: Interface between user applications and the network
    Examples: HTTP/HTTPS, FTP, SMTP, DNS, DHCP
    Function: Provides network services directly to applications
    Real-world example: When you browse a website, your browser uses HTTP/HTTPS protocols

📋 Layer 6: Presentation Layer
What it does: Data translation, encryption, and compression
    Examples: SSL/TLS, JPEG, GIF, ASCII, EBCDIC
    Function: Ensures data is readable by the receiving system
    Real-world example: Encrypting your password when logging into a website

🔗 Layer 5: Session Layer
What it does: Manages communication sessions between applications
    Examples: NetBIOS, RPC, SQL sessions
    Function: Establishes, maintains, and terminates connections
    Real-world example: Maintaining your login session on a website

🚚 Layer 4: Transport Layer
What it does: Reliable data transfer and error correction
    Examples: TCP, UDP
    Function: Ensures complete data transfer with error checking
    Real-world example: TCP ensures all parts of a file download arrive correctly

🗺️ Layer 3: Network Layer
What it does: Routing and logical addressing
    Examples: IP (IPv4/IPv6), ICMP, OSPF, BGP
    Function: Determines the best path for data across multiple networks
    Real-world example: Routers use IP addresses to forward data packets

🔌 Layer 2: Data Link Layer
What it does: Node-to-node delivery and error detection
    Examples: Ethernet, Wi-Fi (802.11), PPP
    Function: Handles communication between directly connected devices
    Real-world example: Your computer communicating with your router via Ethernet or Wi-Fi

⚡ Layer 1: Physical Layer
What it does: Raw data transmission over physical medium
    Examples: Cables, fiber optics, radio waves, electrical signals
    Function: Transmits raw bits over the physical medium
    Real-world example: Electrical signals traveling through an Ethernet cable

🔄 How Data Flows Through the OSI Model
Sending Data (Top to Bottom)
    Application → User creates data (email, web request)
    Presentation → Data is encrypted/compressed
    Session → Session is established
    Transport → Data is segmented and prepared for reliable delivery
    Network → Routing information is added
    Data Link → Frame headers are added for local delivery
    Physical → Data becomes electrical/optical signals

zsh: no matches found

"zsh: no matches found" typically occurs in the Zsh shell when you use wildcard characters (such as *, ?, or []) in a command, and there are no files or directories that match the specified pattern in the current directory.

Here are a few common scenarios where you might encounter this error:
Using a command with a wildcard pattern that doesn't match any files:
$ ls *.xyz
zsh: no matches found: *.xyz

In this example, Zsh couldn't find any files in the current directory with the ".xyz" extension.
Using a command with a wildcard pattern, but the pattern itself doesn't match anything:

$ echo [a-z]
zsh: no matches found: [a-z]

If there are no lowercase letters in the current directory, the [a-z] pattern won't match anything.

To resolve this issue, you can do the following:
1.Double-check your command or wildcard pattern to ensure it matches existing files or directories in the current directory.
2.Use proper escaping or quoting if necessary. For example, if you want to list files with a literal asterisk in their names, you can use single or double quotes to prevent globbing:

$ ls '*.*'

If you want to use a wildcard pattern to match files in subdirectories as well, consider enabling the globstar option in Zsh:

$ setopt globstar
$ ls **/*.txt

The ** pattern will match files in subdirectories.

How to Delete a Primary Key Index in Oracle

Deleting a primary key index can be a complex task, as it involves modifying the structure of the database table. Here are the steps you can follow to delete a primary key index:

Identify the name of the primary key index: 

SELECT index_name FROM dba_constraints WHERE table_name = 'table_name' AND constraint_type = 'P';

Drop the primary key constraint: Before you can drop the primary key index, you must first drop the primary key constraint. 
ALTER TABLE table_name DROP PRIMARY KEY;

Drop the primary key index: Once the primary key constraint has been dropped, you can then drop the primary key index

DROP INDEX index_name ON table_name;

It's important to note that deleting a primary key index will also remove the associated primary key constraint, which can have implications for data integrity and referential integrity in your database. Be sure to fully understand the implications of removing a primary key index before proceeding.

How to Increase the max_map_count Kernel Parameter in Linux to Optimize Vector Server Performance

If you're running a Vector Server or any application that relies heavily on memory-mapped areas, you might encounter issues related to running out of map areas. This problem often stems from a default kernel parameter setting that limits the number of map areas available. Fortunately, you can address this issue by increasing the max_map_count kernel parameter. 

How to Increase max_map_count:
1. Edit the sysctl.conf File

vi /etc/sysctl.conf
Add the following line to the file:
vm.max_map_count=map_count

Replace map_count with an appropriate value based on your system’s memory. As a general guideline, set map_count to approximately 1 per 128 KB of system memory. For instance, on a system with 256 GB of RAM, you might set:

vm.max_map_count=2097152

2. Reload the Configuration
After updating the sysctl.conf file, apply the new settings by reloading the configuration:
sudo sysctl -p

3. Verify the New Setting
cat /proc/sys/vm/max_map_count

This command should display the updated value you set in the sysctl.conf file.
4. Restart Vector
sudo systemctl restart vector

or whatever service management command is appropriate for your setup.

How to Remove Exited Docker Containers

Docker containers can sometimes exit unexpectedly or remain in an "exited" state, taking up valuable system resources. In this guide, we'll explore different methods to identify and remove these exited containers.
Identifying Exited Containers
First, let's see how to identify exited containers. You can use the following command to list all containers, including exited ones:
docker ps -a
To specifically filter for exited containers, use:
docker ps -a | grep "Exited"
CONTAINER ID        IMAGE                      COMMAND                  CREATED             STATUS                     PORTS                                        NAMES
9b65cedfc4b3        d0eadfcacdc2               "/bin/sh -c 'apt-get…"   10 months ago       Exited (1) 10 months ago                                                stupefied_kirch
c3edc0a8c3c6        7aa9bc2b797e               "/bin/bash"              10 months ago       Exited (0) 10 months ago                                                wonderful_mirzakhani
7f20f353fa7b        7aa9bc2b797e               "/bin/sh -c 'apt-get…"   10 months ago       Exited (1) 10 months ago                                                zen_payne

Methods to Remove Exited Containers
Using docker container prune:
simplest way to remove all stopped containers is using the docker container prune command:
docker container prune -f
Deleted Containers:
9b65cedfc4b37b5754e0a16709b387a2c5c39999412908be0a4f6c23da72c29d
c3edc0a8c3c6c2d46712637c58be22e801f46a140608c89fb0ff38d968837a06
7f20f353fa7b7a7c3ae3b6780bfc96021792a9761d99aff88f4503f30df53c95
Total reclaimed space: 310.1MB

The -f flag forces the removal without asking for confirmation. This command will:
1.Remove all stopped containers
Show you which containers were deleted
Display the total space reclaimed

2. Removing Specific Containers
If you want to remove a specific exited container, you can use its container ID:
docker rm <container_id>

3. Removing All Exited Containers
To remove all containers that are not running, use:
docker rm $(docker ps -a -q -f status=exited)

Verifying the Cleanup
After removing the containers, you can verify that all exited containers have been removed:
docker ps -a | grep "Exited"

Troubleshooting Dispatcher Issues in Oracle Database

Troubleshooting Oracle Dispatchers involves diagnosing issues related to performance, connectivity, or server processes. Dispatchers are crucial for routing client requests to shared server processes, and any issues with Dispatcher config  can affect overall database performance and client access. Below is a detailed guide on how to troubleshoot Oracle Dispatchers, including common issues and solutions.
1. Dispatcher Process Not Starting
Symptoms:
    The Dispatcher process does not appear to be running.
    Errors in the log files related to the Dispatcher process (e.g., ORA-12500: TNS:listener failed to start a dedicated server process).
Where to Look:
    Listener Logs: Check the Oracle Listener log (listener.log) for errors related to Dispatcher processes.
    Database Alert Log: Check the database alert log for any errors related to process startup or configuration.
    V$DISPATCHER View: Query the V$DISPATCHER view to check if the Dispatchers are registered with the database.
Common Causes and Solutions: Listener Configuration Issue: Ensure that the listener.ora file is correctly configured and the listener is running.
Incorrect DISPATCHERS Parameter: Double-check the DISPATCHERS parameter in spfile.ora or init.ora for any syntax errors or incorrect configurations.
Example of a correct entry:
     DISPATCHERS = '(PROTOCOL=TCP)(SERVICE=orcl)(DISPATCHERS=4)'
     
2. Dispatcher is Overloaded or Not Handling Requests Efficiently
Symptoms:
    High CPU usage by Dispatcher processes.
    Slow client responses or timeout issues.
    Clients experience delays in receiving responses due to Dispatcher bottlenecks.
Where to Look:
SELECT * FROM V$DISPATCHER;  To monitor the number of active Dispatcher processes and their load.
SELECT * FROM V$SHARED_SERVER;Check for an imbalance between Dispatchers and shared servers.
Check if sessions are waiting for Dispatchers to process requests.
SELECT SID, SERIAL#, STATUS, EVENT FROM V$SESSION WHERE EVENT LIKE 'dispatcher%';
Common Causes and Solutions:
Insufficient Dispatchers: If there are more requests than available Dispatchers, they will queue up, causing delays. Increase the number of Dispatchers using the ALTER SYSTEM command.
ALTER SYSTEM SET DISPATCHERS = '(PROTOCOL=TCP)(SERVICE=orcl)(DISPATCHERS=6)' SCOPE=BOTH;
Imbalance Between Dispatchers and Shared Servers: Check if there are enough shared server processes to handle the incoming requests. Adjust the SHARED_SERVERS parameter accordingly.
ALTER SYSTEM SET SHARED_SERVERS=10 SCOPE=BOTH;

3. Clients Cannot Connect to the Database (ORA-12500, ORA-12545, ORA-12514 Errors)
Symptoms:Clients cannot establish a connection to the database.
    Errors like:
        ORA-12500: TNS:listener failed to start a dedicated server process
        ORA-12545: Connect failed because target host or object does not exist
        ORA-12514: TNS:listener does not currently know of service requested in connect descriptor.
Check Listener Log: Look for any connection or listener-related errors in the listener log & Alert Log
Common Causes and Solutions: Listener Not Running or Misconfigured: Ensure the listener is up and properly configured. Restart the listener and ensure the correct service is registered.
Incorrect SERVICE_NAME or SID: Verify that the SERVICE_NAME or SID specified in the tnsnames.ora file or connection string is correct.
Listener Unable to Start Shared Server: Ensure that the listener is correctly configured to handle shared server processes. In the listener.ora file, ensure the SID_LIST includes the shared server configurations.

4. Dispatcher Hanging or Not Responding to Client Requests (ORA-12535)
Symptoms:
    Clients experience long delays or timeouts while waiting for responses from the Dispatcher.
    Errors like ORA-12535: TNS:operation timed out or client hangs.
Common Causes and Solutions:
    Network Issues: Check for network latency or firewalls blocking communication between clients and Dispatchers. Use network diagnostic tools like ping or traceroute to verify the path.
    Increase Timeout: Increase the timeout values for client connections and Dispatchers to allow more time for processing.
        Adjust the SQLNET.INBOUND_CONNECT_TIMEOUT parameter if necessary.
    ALTER SYSTEM SET SQLNET.INBOUND_CONNECT_TIMEOUT=180;
    Dispatcher Load: Check if Dispatchers are overloaded and adjust the number of Dispatchers or shared servers as needed.

5. Poor Performance or Latency in Dispatcher Handling
Symptoms:
    Slower performance during peak usage times.
    Latency in query processing or client response time.
Common Causes and Solutions:
    Increase Dispatcher or Shared Server Processes: Increase the number of Dispatchers if the load is high.
    ALTER SYSTEM SET DISPATCHERS = '(PROTOCOL=TCP)(SERVICE=orcl)(DISPATCHERS=8)' SCOPE=BOTH;
    Review System Resources: Ensure the system has enough CPU, memory, and disk space for the expected load. Overutilization of system resources can cause slow response times.
    Review Execution Plans: Slow queries can cause delays in processing. Use SQL Trace and Explain Plan to identify and optimize slow queries.

6. General Connection Issues (ORA-12170, ORA-12541)
Symptoms:
    Clients fail to connect and report network-related errors like ORA-12170: TNS:Connect timeout occurred or ORA-12541: TNS:no listener.
Common Causes and Solutions: Listener Configuration: Ensure that the listener is properly configured and the required services are registered. Restart the listener to fix any issues.
Network Configuration: Ensure there are no firewall or network configuration issues preventing the client from reaching the database server.

Database Releases and Support Timelines