Unix Signals
Below is a MRR and PLR article in category Computers Technology -> subcategory Other.
Understanding Unix Signals
Unix signals are essential messages sent to running processes, acting as an important mechanism for communication within Unix-based systems.
What Are Unix Signals?
Signals can be initiated by running programs, administrators, or operators. For example, the SIGHUP signal instructs the Internet Daemon (inetd) to re-read its configuration file. To trigger this, use the command: `kill -SIGHUP [PID]`.
Using Signals to Control Processes
You can terminate a running process with signals. To stop the inetd process, execute: `kill [PID]`. By default, this sends a SIGTERM signal. If it fails, use SIGKILL: `kill -9 [PID]`. However, SIGKILL should be used cautiously as it forcefully stops a process without allowing it to clean up.
Managing Unix Signals
When a Unix program receives a signal, it triggers a default set of actions. Programmers can customize how signals are handled by writing signal handlers. These are pieces of code that define how a process should respond to specific signals.
However, certain signals cannot be redefined. SIGKILL always terminates a process, and SIGSTOP sends a running application to the background when it is in the foreground.
Understanding and managing Unix signals is crucial for effective system administration and software development within a Unix environment.
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