Debugging: Unix/Linux Process Signals

Developers started noticing "SIGTERM" , "SIGBUS", "SIGHUP" and started panicking ??

Due to many reasons, Unix/Linux processes might throw such error codes, in this short article I have mentioned the most common Unix/Linux process signals that you might notice in the logs/error message, their reason, and possible solutions:

SIGHUP

Reason: Often sent when the terminal or parent process dies.

Solution: Ensure the process can handle SIGHUP, possibly to reload its configuration.

SIGINT

Reason: Interrupt from the keyboard (like pressing Ctrl+C).

Solution: Gracefully terminate the process or handle the interruption in a specific way.

SIGQUIT

Reason: Quit signal from the keyboard

Solution: Similar to SIGINT, but also generates a core dump.

SIGILL

Reason: Illegal Instruction; the program is trying to execute an invalid instruction.

Solution: Debug the program to find the source of the illegal instruction.

SIGTRAP

Reason: Trace/breakpoint trap.

Solution: Used by debuggers, not usually seen in normal operation.

SIGABRT / SIGIOT

Reason: Abort signal, typically from an abort() system call.

Solution: Investigate why the abort was called, often used for critical errors.

SIGBUS

Reason: Bus error due to invalid memory access alignments.

Solution: Debug the program for incorrect memory access.

SIGFPE

Reason: Floating-point exception, like division by zero.

Solution: Check for and handle mathematical errors.

SIGKILL

Reason: Kill signal, forces termination.

Solution: Cannot be caught or ignored; used for unresponsive processes.

SIGUSR1 / SIGUSR2

Reason: User-defined signals.

Solution: Handle as per application requirements.

SIGSEGV

Reason: Invalid memory reference or segmentation fault.

Solution: Debug for invalid memory access or pointer errors.

SIGPIPE

Reason: Writing to a pipe with no reader.

Solution: Handle or ignore the signal, check pipe operations.

SIGALRM

Reason: Timer signal from an alarm system call.

Solution: Used for timeouts; handle as needed.

SIGTERM

Reason: Termination signal, a polite request to terminate.

Solution: Gracefully exit, can be caught and handled.

SIGCHLD

Reason: Child process stopped or terminated.

Solution: Handle to clean up child processes.

SIGCONT

Reason: Continue executing, if stopped.

Solution: Handle if specific action on continue is needed.

SIGSTOP

Reason: Stop executing, cannot be caught or ignored.

Solution: Used for pausing a process.

SIGTSTP

Reason: Terminal stop signal.

Solution: Similar to SIGSTOP but can be caught or ignored.

SIGTTIN / SIGTTOU

Reason: Background process attempting read/write in the terminal.

Solution: Typically stops the process; handle as needed.

SIGURG

Reason: Urgent condition on socket.

Solution: Handle to prioritize urgent data on a socket.

SIGXCPU

Reason: CPU time limit exceeded.

Solution: Optimize the program or increase the CPU limit.

SIGXFSZ

Reason: File size limit exceeded.

Solution: Handle to manage large file operations.

SIGVTALRM

Reason: Virtual alarm clock.

Solution: Used for timers in virtual time.

SIGPROF

Reason: Profiling timer alarm.

Solution: Used in profiling performance of programs.

SIGWINCH

Reason: Window size change.

Solution: Handle if the program needs to respond to terminal resizing.

SIGIO

Reason:I/O now possible on a file descriptor.

Solution: Used for asynchronous I/O notifications; handle as needed.

SIGPWR

Reason: Power failure (System V).

Solution: Handle to save data or perform cleanup in case of power failure.

SIGSYS

Reason: Bad system call (SVr4); not valid for POSIX.1.

Solution: Indicates a system call failure; handle or debug as needed.

SIGLOST

Reason: Resource lost (System V).

Solution: Handle to deal with lost resources, often not used.

SIGRTMIN to SIGRTMAX

Reason: Real-time signals.

Solution: Used for application-specific purposes, handle as per requirements.

Hope next time when you see this in your logs you will not panic and look for the reason and utilize the solutions ??

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