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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72 views

What signal is sent when you close a bash terminal to the programs it was running

I have a bash script that launches a python program. The bash script handles SIGINT SIGTERM and SIGHUP signals to do a cleanup operation. I noticed that when I close the process in a tab in LXTerminal,...
3
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1answer
153 views

Sending sigaction / sigqueue through shell

I have a c++ program that handles several signals to perform different actions, using signal: signal(SIGHUP, signal_handler); I wanted to extend this signal handling to allow me to send ...
14
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7answers
4k views

Unable to stop a bash script with Ctrl+C

I wrote a simple bash script with a loop for printing the date and ping to a remote machine: #!/bin/bash while true; do # *** DATE: Thu Sep 17 10:17:50 CEST 2015 *** echo -e "\n*** DATE:"...
0
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0answers
38 views

How often is SIGHUP called in this situation?

I have situation where I am connected to my BeagleBone Black over USB cable, and I started my application in Linux terminal and I'm watching its execution, it sends me some data to terminal and it ...
1
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0answers
15 views

How do I terminate Aptitude safely

I have a TMux session with Aptitude open. The Aptitude process has been "killed" several times with STOP/CONT. Now it doesn't react to the Q key. Instead a 'q' is printed on the top-left corner of the ...
6
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1answer
435 views

Difference between closing the terminal using the closing button, and Ctrl-D

When I'm launching a background process and then closes the terminal using the window's closing button, the background process gets killed. However if I close the terminal using Ctrl+D, the background ...
1
vote
2answers
302 views

Cannot rewrite “trap command” for SIGTSTP, SIGTTIN and SIGTTOU

I want to trap the SIGTSTP signal, but I'm not able to. When I call just trap command without arguments, I'm getting this: trap -- '' SIGTSTP trap -- '' SIGTTIN trap -- '' SIGTTOU Obviously, my ...
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3answers
90 views

New signal arrives while execution is in a signal handler, how to decide which is first?

I am working on a tool handling a massive amount of signals (with different signums) with sigaction(). I need to handle the case, if a new signal is coming, while the previous was in a signal handler....
2
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0answers
322 views

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 ...
6
votes
2answers
336 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 ...
9
votes
2answers
2k 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 ...
1
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1answer
48 views

Which process group does my program belong to when started from bash?

If I run a program from bash, then does my program belong to the same process group as the shell, or does it belong to a new process group? As I am making a shell in C, I need to handle the SIGINT ...
0
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1answer
1k 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?
1
vote
2answers
148 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 ...
-1
votes
1answer
76 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
votes
2answers
72 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 ...
2
votes
0answers
32 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 ...
5
votes
1answer
174 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 non-...
1
vote
1answer
141 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 ...
14
votes
1answer
347 views

Update bash history on other terminals when exiting one terminal

I know this question is not obscure, as it is asked here keep updating (and duplicated here). What I'm trying to achieve is a bit different. I don't like the idea of my prompt rewriting a file every ...
3
votes
1answer
92 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 ...
1
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1answer
181 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 ...
2
votes
3answers
12k 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
votes
1answer
105 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 ...
6
votes
2answers
3k 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
votes
1answer
66 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 ...
-1
votes
1answer
70 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
votes
2answers
1k 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
votes
5answers
93 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
vote
1answer
187 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
votes
1answer
140 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 ...
9
votes
2answers
1k 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 ...
6
votes
2answers
2k 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
votes
1answer
60 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 ...
3
votes
2answers
400 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 ...
6
votes
4answers
2k 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 handler?...
0
votes
1answer
293 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
votes
1answer
61 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 ...
7
votes
2answers
784 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 ...
1
vote
1answer
246 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 ...
6
votes
1answer
92 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 ...
3
votes
1answer
2k 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 ...
0
votes
1answer
582 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 I'...
2
votes
2answers
171 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 ...
1
vote
1answer
334 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. ...
2
votes
1answer
90 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 ...
1
vote
2answers
87 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 ...
0
votes
0answers
47 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
320 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
votes
2answers
331 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 ...