DEV Community: Aasik

What is a Cronjob and understanding syntax

Aasik — Sat, 04 Oct 2025 04:47:41 +0000

A cron job is a task automated using cron, a scheduler tool on a Unix System like Linux. Common cron jobs include running scheduled backups, updating software, clearing the cache, and monitoring the disk space, deleting files periodically which are no longer required and running system maintenance tasks etc.

Creating cron jobs helps reducing human error and save time as you don't need to repeatedly perform the same tasks.

Cronjob Syntax

The cronjob syntax consists of five fields with the following possible values:

1.Minute - minute of the hour the command will run, ranging from 0-59.

Hour - hour the command will run, ranging from 0-23 in a 24-hour notation
Day of the month - date of the month the user wants the command to run, ranging from 1-31.
Month - month the user wants the command to run. It ranges from 1-12, representing January until December.
Day of the week - day of the week for a command to run, ranging from 1-7.

If you want the cron daemon to run the root/backup.sh script every Saturday at 8.27 pm, here's what the cron command should look like:

 27 20  6 root/backups.sh

To specify multiple values in a fields

asterisk (*) -> Specifies all possible values for a field.
comma (,) -> specifies a list of values
dash(-) -> specifies a range of values
Seperator(/) -> divides a value. If you want to run a script every twelve hours, write */12 in the Hour field.
Last(L) -> Users can use this operator in the day-of-the month and day-of-week fields. Writing 3L in the day-of-week field means the last Wednesday of the month.

Cron is commonly pre-installed by default in all Linux distributions. Otherwise, run the below command to install cron

sudo apt install cron

There are two configuration files you need to consider regarding cronjob, system crontab and user crontab. System crontab is used to schedule system-wide essential jobs that are only editable by those with root privileges. Meanwhile, we can use user crontab to create and edit jobs that only apply at the user level.

To create a crontab file

crontab -e

To display a list of active scheduled tasks

crontab -l

If the system has multiple users, you can view their crontab files by entering the command below as a superuser

crontab -u username -l

To delete scheduled tasks

crontab -r

crontab -i is similar to crontab -r, except you will get a confirmation before deleting the tasks.

To run a cron job, connect to your Linux system using terminal with root permissions. Then create a crontab file and add the script using text editors like vim or Nano.

Zero Trust Architecture: The Future of Cybersecurity

Aasik — Sun, 31 Aug 2025 12:51:07 +0000

“Never trust, always verify.” This phrase sums up the core of Zero Trust Architecture (ZTA), a modern security model designed for today’s borderless, cloud-driven world.

As cyberattacks become more sophisticated and organizations move beyond traditional perimeters, the need for a security approach that assumes no user or device can be trusted by default has never been greater.

What is Zero Trust?
Traditional security models operate on the principle of trust but verify, granting users access based on their location within the network (e.g., inside the corporate firewall). Zero Trust flips this concept.

It requires every user and device—whether inside or outside the organization—to be authenticated, authorized, and continuously validated before they can access applications or data.

Zero Trust assumes there is no traditional network edge. Whether resources are on-premises, in the cloud, or across hybrid environments, the same strict security policies apply everywhere.

Why Zero Trust?
• Rising threats: Ransomware, phishing, and supply chain attacks are increasing.
• Remote work & BYOD: Users now access corporate resources from personal devices and multiple locations.
• Cloud adoption: Data and applications are no longer confined to a single corporate network.

Zero Trust is designed to meet these challenges by removing implicit trust and replacing it with continuous verification.

Key Principles of Zero Trust

Default Deny: Assume every request is untrusted until verified.
Verify Every Time: Authenticate users and devices on every access attempt.
Monitor Everything: Log and analyze all activity to detect anomalies.
Least Privilege: Grant only the minimum access necessary for a user’s role.

How to build a Zero Trust Architecture

Zero Trust isn’t a single product—it’s a framework and strategy. Building it requires planning, policies, and the right tools.

Here’s a simplified roadmap:

Assess Your Organization
• Identify sensitive data, applications, and critical assets.
• Audit all user accounts, including service and privileged accounts.
• Review authentication policies and eliminate weak or outdated protocols.
Map Your Assets and Data Flows
• Create an inventory of all devices, applications, and data locations.
• Understand how users interact with these resources.
• Segment identities and enforce strict access controls.
Apply Preventative Measures

• Multi-Factor Authentication (MFA): Add extra layers of security for all logins.
• Least Privilege Access: Give users only the permissions they need.
• Identity Segmentation: Use micro-perimeters to contain lateral movement.

Monitor and Respond

• Continuously inspect and log all network traffic.
• Detect and contain suspicious activity quickly.
• Implement automated responses to high-risk behaviors.

Benefits of Zero Trust Architecture
• Improved Visibility: Know who is accessing what, and when.
• Reduced Risk: Harder for attackers to move laterally within the network.
• Better User Experience: Seamless access with Single Sign-On (SSO) and adaptive MFA.
• Cloud-Ready: Works across local, cloud, and hybrid environments.
• Supports BYOD: Security doesn’t depend on who owns the device, only on verification.

Fixing User Input Issue in VS Code (Java)

Aasik — Sun, 31 Aug 2025 09:49:17 +0000

Last week, during the Java practical session, some students had trouble entering user input while running their code in VS Code. This happens because Code Runner (the extension used to run code) runs programs in the Output window, which does not support interactive input by default.

Here’s how to fix it:

go to file menu --> preferences --> Settings

Search for code runner in the search bar

Scroll down and tick the checkbox for “Run in Terminal”

That’s it! Now your Java program will run in the terminal, and you’ll be able to enter input without any issues.