A signal is a message which can be sent to a running process. Signals can be initiated by programs, users, or administrators.

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Preventing propagation of SIGINT to Parent Process

Considering a scenario where a Parent program (could be a C++ program or a Shell Script) executes a Child shell script, when we hit Control+C (or whatever character is configured to be the INTR ...
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2answers
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Equivalent of “truss -T” and “truss -U” on Linux?

Is there an equivalent of what the -T and -U option of the truss Solaris utility does on Linux. Those are to specify a system call (-T) or library function (-U) which when called by the traced ...
8
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2answers
393 views

How signals work internally?

In general, to kill processes we generate signals like SIGKILL,SIGTSTP etc. But how is it known who ordered that particular signal, who has sent it to a particular process, and in general how do ...
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1answer
266 views

Keyboard shortcut for SIGTERM in GUI application?

Related to another question, is there a way to send SIGTERM to the currently focused local GUI window application with a keyboard shortcut? Like clicking the [X] button in most WMs or Ctrl-c for the ...
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2answers
216 views

Decode Flags for Kill Command

I am new to Shell Scripting. I saw this Command on a Book for Linux shell Scripting $ kill -HUP 1234 >killout.txt 2>killerr.txt I know what the command does, but i am not able to understand ...
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3answers
233 views

What process is running before I even get a prompt?

When I log in to a specific server I see the following: Note that I get get Last login: ... information but no prompt. I hit Ctrl+C and only then do I get my prompt, thus proving that my username ...
4
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1answer
579 views

A script's background process is still alive after closing the terminal

This is more of a process management/signal handling question than a Bash question. It just uses Bash to explain the issue. I'm running a Bash script in which I run a background process. This is the ...
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2answers
185 views

End process from another SSH window

I forgot to use screen and I have a task that has been running for quite some time, and I do not want to lose the saved data. Basically Ctrlc will end the task and save the data if I am on the same ...
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1answer
765 views

sigaction(7): semantics of siginfo_t's si_code member

I've got a long-running program (becomes a daemon with daemon(3) call) that exits on Signal 11 (Segmentation Violation) every so often. I can't tell why. So, I wrote a SIGSEGV handler, set using the ...
2
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2answers
389 views

Why is `kill -s INT <zsh PID>` behaving differently from `Ctrl-C`?

Starting with: % donothing () { echo $$; sleep 1000000 } % donothing 47139 If at this point I hit Ctrl-C at the same terminal that is controlling the shell, then the function donothing does indeed ...
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1answer
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System sending SIGTERM and SIGKILL during normal work

I have a program (C++) that works with TCP sockets in multithreaded manner. The multithreading is intensive, about 100 threads (POSIX threads). Sometimes, not quite sure when, the program gets ...
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2answers
345 views

Mapping intr to del key

I am in the process of migrating a legacy 4GL application from SCO OpenServer 5.0.7 to CentOS (Red Hat) Linux 5.9. There are a number of screens that prompt the user to press "DEL to ABORT" but is ...
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3answers
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What's the difference between Ctrl-Z and kill -STOP?

When I run a command (make on a large project) from the shell, I can type Ctrl-Z to stop the process and return to the shell. Subsequently, I can run fg to continue the process. I'm trying to write a ...
2
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1answer
102 views

Chain commands with Control + C interrupt

I am trying to execute a program which loops indefinitely, and so must be forcibly interrupted. After executing the program, I want to delete it. I can do it in several steps: ./MyProg Control + C ...
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1answer
1k views

How does systemd survive a kill -9?

Between the recent "Why does 'kill -9 0' end my console session" and "How to get a kernel panic" questions, I got a bur under my saddle and tried kill -9 1 on a mostly up-to-date Arch linux laptop. I ...
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1answer
547 views

What is the difference between exiting a process via Ctrl+C vs issuing a kill -9 command?

I know I can kill any process with kill -9 command . But sometimes i see that even if I have terminated a program with CTRL+C , the process doesn't get killed . So I want to know the difference ...
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3answers
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What happens to suspended jobs in unix?

We can issue CTRL+Z to suspend any jobs in Unix and then later on bring them back to life using fg or bg. I want to understand what happens to those jobs that are suspended like this ? Are they ...
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2answers
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Why does Subversion give a broken pipe error when piped into head?

If I do a svn log | head after the tenth line of output I get an error message: svn: Write error: Broken pipe What's going on here? I haven't seen any other command do this when used with head. ...
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1answer
254 views

What should interactive shells do in orphaned process groups?

(Re-posting in unix per the suggestion in http://stackoverflow.com/questions/13718394/what-should-interactive-shells-do-in-orphaned-process-groups) The short question is, what should a shell do if it ...
6
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1answer
605 views

`kill -s TERM` works, `kill -s ABRT` gets “Operation not permitted”

There is a process that I own whose documentation claims I can send SIGABRT to in order to get some debugging information. However, when I try to send SIGABRT, I get back "Operation not permitted". I ...
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2answers
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“trap … INT TERM EXIT” really necessary?

Many examples for trap use trap ... INT TERM EXIT for cleanup tasks. But is it really necessary to list all the three sigspecs? The manual says: If a SIGNAL_SPEC is EXIT (0) ARG is executed on ...
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2answers
780 views

Why can't I kill a timeout called from a Bash script with a keystroke?

[Edit: This looks similar to some other questions asking how to kill all spawned processes – the answers all seem to be to use pkill. So the core of my question may be: Is there a way to propagate ...
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0answers
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Why does this pipeline get SIGTTIN?

When I run the command for i in *.log; do cat "$i" | sort; done | more, the pipeline gets a SIGTTIN signal and is stopped. bash$ for i in *.log; do cat "$i" | sort; done | more ### (one screenful of ...
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4answers
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How can I kill and wait for background processes to finish in a shell script when I Ctrl+C it?

I'm trying to set up a shell script so that it runs background processes, and when I Ctrlc the shell script, it kills the children, then exits. The best that I've managed to come up with is this. It ...
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3answers
796 views

How Can Terminal Emulators Kill Their Children After Recieving a SIGKILL?

From what I understand, SIGKILL cannot be caught. This would imply that a process does not have time to kill it's children before the OS destroys it. This can be demonstrated with a shell script. ...
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820 views

Why there are only two user defined signals?

In the list of signals defined in a linux system, there are two signals stated as User Defined signals (SIGUSR1 and SIGUSR2). Other signals will be raised or caught in specific situations, but SIGUSRs ...
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How to stop the loop bash script in terminal?

For example, #!/bin/bash while : do sl done How to terminate this bash script?
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1answer
205 views

Control character STTY issue

I am changing control character (e.g- ^C) using stty intr ^_ under root privileges. It changes successfully. But when I am closing terminal and opening terminal again to check whether same ...
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2answers
2k views

Why would Ctrl-C behave differently than kill -2

I have a program which is supposed to handle SIGINT and gracefully shut down. When I run this program from a terminal without backgrounding it I can shut it down just fine using Ctrl-C. Inspecting the ...
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0answers
109 views

Busybox exits instantly printing 'SIGUSR1'

I was tinkering with my router these days. It runs on MIPS core and the OS is based on Linux. But the builtin busybox is very limited. I managed to export a binary of busybox compiled for MIPS through ...
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2answers
340 views

How are signals implemented in Linux?

When one process sends a signal to another process, does receiving process wait until it is rescheduled to run? So if every 1 ms we choose one process to run, does that mean the latency from ...
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327 views

SSH session pauses mid datastream; resumes with a keypress

I've had this problem occur at random, intermittently, across boxes at multiple companies, multiple distros, and multiple kernel revs. I think that I'm just cursed. What happens is that I'll have a ...
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3answers
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Telnet send Ctrl-C

I use telnet to connect to a terminal server, which proxies the traffic to a RS-232 port. Unfortunately when using some of the devices it is not possible to send the CTRL+C character (0x03). Instead ...
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How to make `xargs` ignore child's exit and keep processing further

I sometimes run long xargs jobs overnight and it is really annoying to discover in the morning that xargs died somewhere in the middle, for example because of a segmentation fault in one single ...
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6answers
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Terminating an infinite loop

I have a command that I want to have run again automatically each time it terminates, so I ran something like this: while [ 1 ]; do COMMAND; done; but if I can't stop the loop with Ctrl-c as that ...
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2answers
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difference between signalfd and sigwaitinfo?

I went through examples and man page but couldn't figure out difference between signalfd and sigwaitinfo Apart from syntax both are doing same thing i.e. waiting for signal storing it details into ...
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2answers
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Get ssh to forward signals

I want to be able to send signals (SIGINT is the most important) through ssh. This command: ssh server "sleep 1000;echo f" > foo will start sleep on server and after 1000 seconds it will put ...
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1answer
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Why does SIGUSR1 cause process to be terminated?

I was surprised with this comment in other question: Sending dd the USR1 signal too soon after it has started (i.e. in a bash script, the line after you started it) will in fact terminate it Can ...
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1answer
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Why is my C++ program killed by OS

I've compiled small C++ application for school project on my virtual ubuntu 11.04. However when I attempt to run it over some larger data set after ~20 sec the program is killed by OS. Killed ...
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920 views

Killing other user processes

There are certain user environments in which we have to login during certain performance testing and and kill all the process running in that environment. The environment names are like rswrk01, … up ...
3
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1answer
901 views

Issue with WINCH signal - what am I overlooking?

I am having an issue with the WINCH signal in the following code which is from a tutorial located at developerWorks®: #!/bin/bash trap 'get_window_size' WINCH # trap when a user ...
21
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2answers
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When you try to terminate a process for good, which option for “kill” should you use?

I am getting a lot of mixed messages from people, and was wondering if it there really is not much of a difference in what you use. kill 'x' killall 'x' kill -9 'x' These are some options I've been ...
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1answer
271 views

Why doesn't an orphan process receive signals?

I have two shell scripts: launch_job.sh and sub_job.sh. If launch_job.sh uses the following method to run sub_job.sh: nohup sub_job.sh & sub_job.sh becomes an orphan, i.e. with PPID 1. I ...
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1answer
932 views

Crash and exit code 721035

Where can I find what this exit code means? I have process (A) that calls program (B) using clib system(). Sometimes program (B) returns with exit code 721035 and AIX kills process A. This is random ...
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2answers
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How can I trap a program that returns 139 (segmentation fault) in bash?

I have a bash script that tests some programs and one of the program returns Segmentation fault so I tried to add a trap in the head of my script: trap "echo 'segfault occured!'" SIGSEGV That ...
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2answers
713 views

Wrapper program that sets signal handler

I would like to have a wrapper program that runs a given command and sets a signal handler so that it gets run when the command receives a specified signal. The question is this: Is there an ...
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1answer
771 views

What does “trace trap” mean when reported by zsh?

I am trying to run a set UID root program in UNIX using the zsh shell. But I keep getting this message $ ./progExe zsh: trace trap ./progExe Can anyone please tell what does “zsh: trace trap” mean? ...
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How to soft kill gui applications via terminal?

Is there a way to close a GUI application in friendly "please quit yourself now" way, without graphical access to the applications window? For example, if Gnome/X display crashes to black, I'd like ...
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2answers
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why would typing Ctrl+c twice stop a running process in Linux?

There are Linux programs, for example vlc, that recommend typing ctrl+c twice to kill their execution from a terminal if the program didn't stop after the first one. Why would typing ctrl+c twice ...
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4answers
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Ctrl+C does not work in gnome-terminal

On my Linux host, Ctrl+C does not seem to work and I do not know how to proceed to make it work. I am using Ubuntu 10.04 with bash 4.1.5(1), and working in Gnome-terminal. When I pressed Ctrl+C while ...