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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What happens to a multithreaded Linux process if it gets a signal?

If a Unix (Posix) process receives a signal, a signal handler will run. What will happen to it in a multithreaded process? Which thread receives the signal? On my opinion, the signal API should be ...
5
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2answers
113 views

In zsh, how can I more quickly disown the foreground process?

My method for disowning the foreground process takes too much effort. Suppose I have a process in zsh's foreground. I want to disown it, so I can close the shell without the process being sent a ...
6
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2answers
107 views

Kill a suspended process?

I was slightly confused by: % vim tmp zsh: suspended vim tmp % kill %1 % jobs [1] + suspended vim tmp % kill -SIGINT %1 % jobs [1] + suspended vim tmp % kill -INT %1 % jobs [1] + suspended ...
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1answer
64 views

Disable ctrl c and ctrl z while a script is running

I have a script that takes about 45 seconds to run. How can I disable Ctrl-c and Ctrl-z while a script is running?
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2answers
53 views

Wrong eUID in `/proc/PID/status` when SETUID is used

While doing a wargame challenge, I ran into an issue with permissions. The info given by /proc/PID/status is not in adequation with the permissions that should be given to the processus. I am user ...
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1answer
19 views

Daemon opens a file in RO mode only

I am trying to write a kind of keylogger myself. I don't know if my logic of developing a keylogger is good or not but I have thought of doing it the following way. First a daemon is created, and to ...
2
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2answers
48 views

How to make this loop Ctrl+C-interruptible?

# wait for host to become online while true; do ping host -c 1 -w 3 > /dev/null && break; sleep 1 done When I press Ctrl+C, the ping receives it and exits with exit code 1 (the ...
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0answers
24 views

Data written to /dev/pts/x inside SIGINT (Ctrl+C) handler is randomly discarded [closed]

Have Archlinux64 on VirtualBox. If I declare a SIGINT trap like this: trap 'echo x' INT inside an ssh session (running bash) and press Ctrl+C multiple times, only a few times does something appear ...
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1answer
96 views

Is there a command line tool to manage unix signals?

Is there a command runner like env, nice, nohup, etc., that can run a program with modified signals? In my case, I need something to reset SIGINT to SIG_DFL. Why do I need this? Because ...
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1answer
53 views

Is there a robust way for a child process to signal readyness to its parent? [closed]

I have a (Java) process which is staring a separate process foo. foo takes some number of seconds to start up, then is really running. Control returns back to the parent process as soon as foo is ...
13
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1answer
211 views

Update bash history on others terminals on exit of one

I know this question has a similar interpretation, as its asked here keep updating (and duplicated here). But what I'm trying to achieve is a bit different. I don't like the idea of my prompt ...
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1answer
48 views

Sending signals to long-running processes (AWK, DD)

I'm familiar that DD command doesn't produce output while running. However, if I send a USR1 signal to it, it can print current state. Can I do the same with AWK? Prints its variables, register ...
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1answer
68 views

TTY control characters sent to stdin of sh doesn't work

I tried to develop a remote app that launches sh and resends an incoming data there, and found that some special sequences don't work. So, for testing purposes, I launched on my desktop sh, then ...
3
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3answers
822 views

How to restart (or reset) a running process in linux

I have two Linux systems communicating over sockets (Desktop and ARM-based development board). I want to restart (or reset) my client application (running on a development board) when server sends a ...
7
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1answer
54 views

What happens to requests to a service that is stopped with SIGSTOP

If you run SIGSTOP against a web server, does the kernel just tell the network stack to block/sleep all connections to that socket until it is continued? It seems that the server timeout values don't ...
5
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2answers
393 views

What are pending signals?

When looking at the limits of a running process, I see Max pending signals 15725 What is this? How can I determine a sensible value for a busy service? Generally, I can't seem to find a ...
3
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1answer
46 views

Why does my application die without nohup?

I have a simple system (running on Debian) that works by invoking a script from /etc/init.d/rc.local At the bottom of rc.local I call myScript.sh who sets up some things, and then starts a binary ...
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1answer
36 views

How to make a process wait in the background and be able to be killed by signal other than KILL

I want a script run in the background, take some actions for every hour. It should also quit if receiving a signal. And at last, it should perform some clean-up actions before quitting. Based on the ...
4
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2answers
350 views

Safely exiting while loops in bash

Say I have a bash script that does: while : do foo done I would like to be able to run this script from the console and be able to exit it at an arbitrary time as long as it happens in between ...
2
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5answers
88 views

How to create a script that can't be easily exited

How would I create a script that does not respond to Ctrl-C? This should also prevent any processes launched by the script from being killed (I'm trying to keep apt-get upgrade from being killed). (I ...
1
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1answer
94 views

Ctrl+C process termination without Terminal killing

I started using Sublime Text 3 to compile my FreeFem scripts (interpretator PDEs package solver) under Ubuntu 14.04. To invoke the interpretator I customized the build system as follows "shell_cmd": ...
2
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1answer
59 views

What's the easiest way to detect what signals are being sent to a process?

I'm trying to debug an issue with my shell (specifically, fish) sending signals to my background processes. I'd like to be able to recognize what signals a process is receiving. Ideally, I'd like ...
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2answers
479 views

Why does bash ignore SIGTERM?

Sometimes when I want to logout quickly I do kill -15 -1. I've noticed that bash is ignoring SIGTERM. I wonder what's the rationale for such bash behavior? It's not very UNIX'y to ignore SIGTERM ...
4
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2answers
572 views

On Ctrl+C, kill the current command but continue executing the script

I have a bash script, wherein I execute a line, sleep for sometime and then tail -f my log file to verify a certain pattern is seen, I press ctrl +c to get out of tail -f and then move to the next ...
3
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1answer
49 views

Parent restarted by child doesn't respond to CTRL-C

I wrote a program. It starts a process (call it A) that spawns a child process (call it D) that shutdowns and restarts A. Problem is, now I can't kill A nicely from the terminal (ie. CTRL-C isn't ...
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2answers
226 views

Is there any way to determine the signal that was caught from inside a bash trap function?

I have a bash script, in which I have specified via trap that a function will be called for any (catchable) signal. typeset -i sig=1 while (( sig < 65 )); do trap myfunc $sig let sig=sig+1 ...
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3answers
658 views

Can signal be ignored (lost)?

I have an application which is communicating with workers via signals (particullary SIGUSR1/SIGUSR2/SIGSTOP). Can I trust that whatever happens every signal will be delivered and processed by ...
0
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1answer
98 views

timeout pipeline

I want to execute these two timeout command on the same command but with a different time and instructions. So timeout --signal=SIGINT 5s command timeout --signal=SIGKILL 10s command How to append ...
0
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1answer
50 views

Understanding a signal script

I have the following trap script but the idea about it, is little vague to me. #!/bin/bash for i in {1..64}; do trap "echo 'signal[$$] Caught signal SIG$(kill -l "$i")($i)'" "$i"; done; read -s ...
2
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0answers
212 views

SIGINFO on GNU Linux (Arch Linux) missing

I am developing an application and I would like it to print some runtime stats to the console on demand. kill and signals came to my mind immediately. Reading through Unix signals on Wiki, SIGINFO ...
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1answer
161 views

Why cannot we kill a zombie? [duplicate]

I am editing this question since it was marked duplicate as another question about how to kill a zombie process. I am not looking for an answer to how to kill a zombie process. I do not have zombies ...
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1answer
86 views

HURD: Why is remote process not killed?

On most UNIX systems this will not leave a process running: ssh example.net sleep 1000 <<CTRL-C>> I have tested this behaviour on aix centos debian dragonfly freebsd hpux irix mandriva ...
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1answer
296 views

fork() and how signals are delivered to processes

I program that I wrote in C fork()'s off a child process. Neither process will terminate. If I launch the program from the command line and press control-c which process(es) will receive the interrupt ...
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1answer
198 views

kill parent and child because endless loop

I have a process run by cron every hour. Such process calls another one (not sourced), ie: ./childProc.sh (Not sure if this detail is important) Because of an endless loop in child process (which ...
2
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2answers
137 views

gracefully terminating processes with killall <processname>

I am using several instances (profiles) of Icedove (Thunderbird) and when I need to close all of them, I use: killall icedove According to man killall, if no signal name is specified, SIGTERM is ...
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1answer
88 views

Trying to see default handlers for various signals

I understand that there is a default signal handler, that is a function for each signal , such as SIGKILL etc. In which file it is written? I tried looking at signal.h, but could not find it there. ...
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1answer
54 views

How to suspend a process for a certain period of time?

I have several running processes which is started by a shell, but I don't want them to run during 08:00am - 20:00pm for each day because they are really bandwidth-consuming, so , I have to suspend ...
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2answers
52 views

Give group the right to send kill signals

I have a process that a user1 runs. And I need to grant all the group members the right to send some kill signal to it. So far, I always get this output: myProcess(13919): Operation not permitted ...
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0answers
29 views

Sigstop when trying to run script?

I am trying to list out all commands by users, unfortunately I hit a weird sigstop that I am not sure how to diagnose? #!/bin/ksh echo '[' for USER in `cut -d: -f1 /etc/passwd |sed '/^#/ d'`; do ...
2
votes
1answer
146 views

SIGTERM not working occasionally

We use the regular /etc/init.d/jboss stop to stop the jboss on our machines. But at times, it does not stop the process and we get what is pasted below. When this happens we kill the process with a ...
2
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2answers
140 views

Inheriting Bash signal traps

I'm struggling to find clear, unambiguous information about how the trap command works. In particular, is the effect of trap local to the script where it appears? I had always assumed this to be the ...
1
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1answer
36 views

How to propagate TSTP while running a program as a different user

I'm running a terminal application via "su" in this fashion: su -c "/path/to/app --args" username This is done from a root context, and 'username' is a less privileged user in the system. The ...
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1answer
55 views

On shutdown, do un-mounting drives happen before shutdown signal handling?

So based on my understanding of the Unix/Linux shutdown process (which is highly limited I admit), I think at some point these steps happen: 1. mounted drives get unmounted 2. a termination signal ...
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1answer
107 views

Change to rc.local causing hang on tty1

I added a script execution command to my rc.local but forgot to run it in a separate tty. The script has an infinite loop and has hung my tty1. Ctrl-C does not do anything and I don't have another ...
5
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1answer
198 views

Why different behaviour of trapping EXIT vs INT

Running bash 4.3 on Kubuntu Trusty 64 bit. Please see the following two files: trapping-int.sh #! /bin/bash trap "echo Exiting" INT cat </dev/urandom >/dev/null echo Hello trapping-exit.sh ...
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1answer
1k views

Start a background process from a script and manage it when the script ends

I'd like to run and configure a process similarly to a daemon from a script. My shell is zsh emulated under Cygwin and the daemon is SFK, a basic FTP server. For what matters here, the script ...
4
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3answers
572 views

Control which process gets cancelled by Ctrl+C

I have a live CD that boots into Linux and runs a small Bash script. The script searches for and runs a second program (which is usually a compiled C++ binary). You're supposed to be able to abort ...
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1answer
69 views

What is the meaning of every column when executing psig command?

I try to use psig command to track signal dispositions of a process on Solaris: bash-3.2# psig 3109 3109: bash HUP caught termsig_sighandler 0 ...
2
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1answer
2k views

What does the command pkill -USR1 -n -x dd mean exactly?

I am using dd to do a network transfer of a disk image to an sd card on my BeagleBone. Using pkill -USR1 -n -x dd in an ssh connection to this BeagleBone gives me a status update of the transfer ...
3
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0answers
116 views

Kill a whole process tree regardless different GIDs

I am having issues with process control using the signals available to the process abstraction. In the example below you can see there is a perl script which is the parent of the whole tree with a ...