Select the TWO statements that are true about SIGKILL and SIGSTOP.
LPIC-1 Exam 101-500, objective 103. GNU and Unix commands medium
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The options
Choose 2.
Correct SIGKILL cannot be caught, blocked or ignored by the target process.
True. The kernel enforces this, which is why kill -9 is the last resort that always works on a live process.
Correct SIGSTOP cannot be caught, blocked or ignored by the target process.
True. SIGSTOP is the unconditional stop; the catchable variant is SIGTSTP, which is what Ctrl+Z sends.
Not correct SIGKILL lets the process flush its buffers and remove its temporary files before it exits.
False. That orderly shutdown is what a handler for SIGTERM is for. SIGKILL gives the process no chance to run any code at all.
Not correct A process stopped by SIGSTOP resumes when it is sent SIGTERM.
False. The signal that resumes a stopped process is SIGCONT. SIGTERM sent to a stopped process is delivered only once it continues.
Not correct SIGSTOP is the signal that Ctrl+Z sends to the foreground job.
False. Ctrl+Z sends SIGTSTP, which a program may catch in order to tidy up its terminal settings before suspending.
Why
Every signal except SIGKILL (9) and SIGSTOP (19 on x86) may be caught by a handler, blocked in the process signal mask, or ignored. That is the reason kill defaults to SIGTERM (15): it is the polite request a well-written program answers by shutting down cleanly, and SIGKILL is reserved for programs that refuse. The stop and continue pair is SIGSTOP or SIGTSTP to suspend and SIGCONT to resume.
Where this comes from
- Cited
- manual page signal(7)
Practise this
Reading one question is not practice. The trainer will draw a short set from objective 103 and space the ones you get wrong.
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