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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1answer
65 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 ...
1
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1answer
42 views

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

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
169 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 ...
3
votes
1answer
37 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
39 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
votes
3answers
86 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
44 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
votes
2answers
121 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
39 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
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1answer
27 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
184 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
84 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
69 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
46 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 ...
8
votes
2answers
360 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
votes
2answers
327 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
45 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
207 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
3answers
531 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
votes
1answer
79 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
44 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 ...
1
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0answers
123 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
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1answer
138 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
83 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 ...
1
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1answer
188 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
150 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
votes
2answers
129 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 ...
0
votes
1answer
52 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
50 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
43 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
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0answers
24 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
105 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
115 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 ...
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1answer
33 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 ...
1
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1answer
51 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 ...
1
vote
1answer
91 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
votes
1answer
162 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 ...
1
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1answer
851 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
votes
3answers
358 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 ...
1
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1answer
60 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
votes
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
votes
0answers
108 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 ...
3
votes
1answer
87 views

Terminating SSH called from a script (SIGPIPE handling?)

so I was wondering why there are some hanging SSH connection left from some of my automated scripts and I came to a weird issue - SSH, if used without PTY, doesn't terminate when the output pipe gets ...
3
votes
1answer
97 views

How to restore the default signal processing behavior on Solaris?

I have found the signal processing behavior on my Solaris 10 is changed. For example, when I Ctrl+C, the program can't exit. Use psig to check the signal processing behavior: HUP default INT ...
2
votes
1answer
384 views

Prevent SIGINT from interrupting function call and child process(es) within

Consider the following script: #!/bin/bash set -o pipefail set -o history trapper() { func="$1" ; shift for sig ; do trap "$func $sig" "$sig" done } err_handler () { case $2 in ...
15
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2answers
2k views

Why does `kill -l` not list signal numbers of 32 and 33?

Executing kill -l on linux gives: 1) SIGHUP 2) SIGINT 3) SIGQUIT 4) SIGILL 5) SIGTRAP 6) SIGABRT 7) SIGBUS 8) SIGFPE 9) SIGKILL 10) SIGUSR1 11) SIGSEGV ...
1
vote
1answer
104 views

Send specific signal number with specific key

I want to set a specific key like F12 to send me a specific signal number that out of linux signals range that I can handle this signal with trap command. How can I do that? NOTE: I'm working with ...
4
votes
1answer
184 views

How to catch a signal in command line?

I asked this question. SIGPIPE signal is generated to stop the execution of the command as told in the answer. But how do I capture this signal and gracefully terminate the command? The command exits ...
1
vote
1answer
52 views

PID of process causing error

I have this script: #!/bin/bash # -> dump.$pid ulimit -c unlimited # trap ERR set -o errexit # also trap error in the middle of a pipe (1) # otherwise it will only trap the error on (2) set -o ...
2
votes
0answers
35 views

unbuffer/expect swallows the rcode when its child is signaled

unbuffer is able to pass along the return code of a process under normal circumstance, but if the process you are unbuffering is killed, for instance with a segfault, I see $? as 0 while I expect 139. ...