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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service killed at ssh hangup [duplicate]

If I use ssh to run some command in background, that command gets killed as soon an ssh hangs up: ssh localhost -t "bash -c '(for i in 1 2 3 4 5; do sleep \$i;done)&'"; ps x|grep sleep This ...
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Processes do not respond to my signals

I have a strange behavior on my system. When I invoke a command in the shell (bash version 4.2.45(1)-release), say top or cat, the running program (the process) does not respond to Ctrl+C. I even ...
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6answers
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Does pressing ctrl-c several times make the running program close more quickly?

I often start to read a huge file and then want to quit after a while, but there is a lag from pressing Ctrl+C to the program stops. Is there a chance of shortening the lag by pressing the Ctrl+C key ...
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4answers
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Ctrl-C with two simultaneous commands in bash

I want to run two commands simultaneously in bash on a Linux machine. Therefore in my ./execute.sh bash script I put: command 1 & command 2 echo "done" However when I want to stop the bash ...
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2answers
431 views

What does this logrotate nginx config do?

In my /etc/logrotate.d/nginx I saw, /var/log/nginx/*.log { daily missingok rotate 52 compress delaycompress notifempty create 640 nginx adm ...
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2answers
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Ctrl-C handling in SSH session

When I start an SSH session that executes a long-running command, what happens with Ctrl+C (SIGINT) handling? I can see that the SSH session is closed, but I am not sure who gets the SIGINT first: is ...
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2answers
386 views

Pipe command to tail: when is the first command aborted?

In this example: $ for i in {1..3}; do sleep 1; echo $i; done | head -n 2 why is the first command (for loop) killed only just before the 3 is displayed ? I expected it to be killed right after ...
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3answers
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Default exit code when process is terminated?

When a process is killed with a handle-able signal like SIGINT or SIGTERM but it does not handle the signal, what will be the exit code of the process? What about for unhandle-able signals like ...
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1answer
419 views

Suppress “Alarm clock: 14” from ping

I've made a simple script for rebooting my router and afterwards showing a progress bar until my computer has an internet connection again. When running the script I get the following output: The ...
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1answer
96 views

Do not set $? to non-zero on Control+C

My $PS1 in Zsh includes this expression: %(?. %?.) It means «if exit code of previous command ($?) is true, show $?, else show nothing». This is generally useful, but one thing annoys me: shells set ...
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1answer
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child process does not inherit the pending signals from the parent after a fork system call, why?

Could anybody please tell me the reason to why pending signals are not inherited by the child process? On the other hand, the child process inherits the signal handlers and signal mask from the ...
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Cancel completion, but only completion, in zsh

When a completion function takes a long time, I can interrupt it by pressing Ctrl+C (terminal interrupt key, sends SIGINT) or Ctrl+G (bound to send-break). I am then left with the uncompleted word. ...
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1answer
47 views

Does Control+C delete the files that you were downloading and installing? [closed]

If you are installing a package in the terminal and you use Control+C to stop it, does it also undo all the changes and remove the files that it downloaded?
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2answers
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How to generate signal interrupt on a file descriptor in Linux?

How can I generate a signal interrupt on a file descriptor in Linux? Motivation is to generate a interrupt in userland as we have in microcontrollers. I'll have file descriptor for I/O, and want to ...
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1answer
113 views

How to list killable tasks?

As manpage of ps states A process with STATUS with the value "D" means "uninterruptible sleep (usually IO)" Also, I've read: You should use TASK_INTERRUPTIBLE here, otherwise your kernel thread ...
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2answers
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How can I check what signals a process is listening to?

How can I verify whether a running process will catch a signal, or ignore it, or block it? Ideally I'd like to see a list of signals, or at least not have to actually send the signal to check.
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In which cases is SIGHUP not sent to a job when you log out?

I read an answer from a user who claimed that running foo 2>&1 >& output.log & would result in foo continuing to run even when they log out. According to this user, this even ...
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1answer
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How do I find out what process is consuming pending signals?

A user is getting the following message when they try to run a particular program. timer_create: Resource temporarily unavailable From this StackOverflow Q&A titled: timer_create() : -1 ...
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3answers
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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 ...
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2answers
580 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
326 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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244 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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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 ...
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1answer
699 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
198 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
937 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 ...
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2answers
470 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
2k views

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
425 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 ...
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1answer
108 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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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
636 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
296 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
662 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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“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
977 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
929 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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2answers
1k 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
233 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
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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
411 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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1answer
356 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 ...