Services and Process Management
- Start/Restart
- Stop
- Monitor
- Enable/Disable at boot
- Locate
Pretty self-explanatory, this command is used for starting linux services such as ssh, ftpd ..etc
We can also make services start on startup with the following command:
D3xt3rM0Rg4IV@htb[/htb]**$** systemctl enable ssh
Synchronizing state of ssh.service with SysV service script with /lib/systemd/systemd-sysv-install. Executing: /lib/systemd/systemd-sysv-install enable ssh
Once we reboot the system, the OpenSSH server will automatically run. We can check this with a tool called ps.
Service and Process Management
We can also use systemctl to list all services.
Service and Process Management
It is quite possible that the services do not start due to an error. To see the problem, we can use the tool journalctl to view the logs.
Service and Process Management
Sometimes it will be necessary to put the scan or process we just started in the background to continue using the current session to interact with the system or start other processes. As we have already seen, we can do this with the shortcut [Ctrl + Z]. As mentioned above, we send the SIGTSTP signal to the kernel, which suspends the process.
Service and Process Management
Now all background processes can be displayed with the following command.
Service and Process Management
The [Ctrl] + Z shortcut suspends the processes, and they will not be executed further. To keep it running in the background, we have to enter the command bg to put the process in the background.
Service and Process Management
Another option is to automatically set the process with an AND sign (&) at the end of the command.
Service and Process Management
Once the process finishes, we will see the results.
Service and Process Management
Task scheduling in Linux automates tasks at specific times or intervals, removing the need for manual execution. Common uses include software updates, script execution, database maintenance, and backups, with options for alerts on certain events. Like a programmed coffee maker, it ensures tasks run reliably and consistently.
For cybersecurity specialists and penetration testers, understanding task scheduling is vital. It’s both a legitimate admin tool and a potential attack vector—malicious cron jobs can maintain persistence or run harmful scripts. Knowing how it works helps identify risks, audit systems, and even simulate attacks in penetration testing.
Systemd is a service used in Linux systems such as Ubuntu, Redhat Linux, and Solaris to start processes and scripts at a specific time. With it, we can set up processes and scripts to run at a specific time or time interval and can also specify specific events and triggers that will trigger a specific task. To do this, we need to take some steps and precautions before our scripts or processes are automatically executed by the system.
- Create a timer (schedules when your mytimer.service should run)
- Create a service (executes the commands or script)
- Activate the timer
To create a timer for systemd, we need to create a directory where the timer script will be stored.
Task Scheduling
Next, we need to create a script that configures the timer. The script must contain the following options: "Unit", "Timer" and "Install". The "Unit" option specifies a description for the timer. The "Timer" option specifies when to start the timer and when to activate it. Finally, the "Install" option specifies where to install the timer.
Code: txt
[Unit]
Description=My Timer
[Timer]
OnBootSec=3min
OnUnitActiveSec=1hour
[Install]
WantedBy=timers.target
Here it depends on how we want to use our script. For example, if we want to run our script only once after the system boot, we should use OnBootSec setting in Timer. However, if we want our script to run regularly, then we should use the OnUnitActiveSec to have the system run the script at regular intervals. Next, we need to create our service.
Task Scheduling
Another way to create automated processes is by using cron.
With Cron, we can also automate tasks, but its setup differs from Systemd. Tasks are stored in a crontab file, where we define when and how they should run. By configuring the Cron daemon with these entries, we can schedule and automate tasks. A Cron job is defined using the following components:
| Time Frame | Description |
| --- | --- |
| Minutes (0-59) | This specifies in which minute the task should be executed. |
| Hours (0-23) | This specifies in which hour the task should be executed. |
| Days of month (1-31) | This specifies on which day of the month the task should be executed. |
| Months (1-12) | This specifies in which month the task should be executed. |
| Days of the week (0-7) | This specifies on which day of the week the task should be executed. |
For example, such a crontab could look like this:
Code: txt
# System Update
0 */6 * * * /path/to/update_software.sh
# Execute Scripts
0 0 1 * * /path/to/scripts/run_scripts.sh
# Cleanup DB
0 0 * * 0 /path/to/scripts/clean_database.sh
# Backups
0 0 * * 7 /path/to/scripts/backup.sh
Systemd and Cron are both tools that can be used in Linux systems to schedule and automate processes. The key difference between these two tools is how they are configured. With Systemd, you need to create a timer and services script that tells the operating system when to run the tasks. On the other hand, with Cron, you need to create a crontab file that tells the cron daemon when to run the tasks.
Network Services (NFS to be thorough)
- Core Technology: Technologies like Docker and Linux Containers (LXC) are central to containerization. They create lightweight, portable environments for applications.
- Containers vs. Virtual Machines (VMs): Unlike VMs, which require a full guest operating system, containers share the host system's kernel. This makes them significantly more lightweight, faster to start, and resource-efficient.
- Benefits:
- Portability: Applications run the same way everywhere, from a developer's laptop to production servers.
- Efficiency: Allows for running many containers on a single host, which is ideal for microservice architectures.
- Scalability: Easy to scale applications up or down by adding or removing containers.
- Security:
- Isolation: Containers provide a security barrier by isolating applications from the host and each other.
- Risks: Despite the isolation, they are not foolproof. Vulnerabilities like privilege escalation or container escapes can pose significant security risks if not managed properly. The level of isolation is generally less than that of a traditional VM.
Installing Docker is relatively straightforward. We can use the following script to install it on a Ubuntu host:
Code: bash
