A process can be terminated in ways other than signals, normal exits (exit()), or unhandled exceptions. Here are some additional mechanisms:
✅ 1. Killed by the Kernel (OOM Killer)
If the system runs out of memory, the Out-Of-Memory (OOM) killer may forcibly terminate a process: No signal from user space is sent manually.
The process is terminated by the kernel to free up memory.
💡 Detectable in logs via dmesg or system logs.
✅ 2. Killed by Parent Process Using ptrace or process_vm_writev
A parent or debugger can manipulate or terminate a child using ptrace:
Inject code or overwrite memory.
Can simulate a crash or exit by corrupting the instruction pointer.
✅ 3. Segmentation Fault or Illegal Instruction
If a process accesses invalid memory or executes an illegal instruction, it will terminate.
Although this results in a signal (e.g., SIGSEGV, SIGILL), it’s not from an external source—it's due to internal program behavior.
✅ 4. abort() or assert() Failures
abort() triggers abnormal termination and generates a core dump.
Common in libraries when internal errors are unrecoverable.
✅ 5. Kernel Panic or Hardware Failure
A system crash, hardware fault (e.g., CPU, memory failure), or disk corruption could kill processes without going through the usual exit routines.
✅ 6. Container or CGroup Restrictions
If a process exceeds CPU, memory, or I/O quotas in a container or control group, it may be killed.
These terminations are managed by the kernel or container runtime (e.g., Docker, Kubernetes).
✅ 7. Filesystem or I/O Errors
A blocked I/O operation, unmounted filesystem, or disk error might cause a process to be forcibly terminated by the kernel.
✅ 8. Dynamic Library Failures (e.g., dlopen/dlsym)
Failure in shared library loading or mislinked symbols during dynamic loading might crash the process.
✅ 9. Overwriting the Stack or Heap (Undefined Behavior)
A bug like buffer overflow may corrupt memory, leading to an unpredictable crash without an explicit signal or exit.
✅ 10. System Calls Returning Irrecoverable Errors
Some system calls (e.g., execve, fork) may result in fatal errors if misused or constrained by resource limits.
Conclusion:
Even when not terminated by an explicit exit(), signal, or exception, a process can still be terminated via:
Kernel interventions
Resource limits
Internal bugs or memory corruption
Debugger or parent manipulation