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 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 ...
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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 ...
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2answers
788 views

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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1answer
28 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 ...
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1answer
50 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 ...
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1answer
55 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 ...
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5answers
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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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2answers
469 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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936 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 ...
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1answer
45 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 ...
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1answer
82 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 ...
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2answers
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What is signal 0 in a trap command?

I'm following this guide on how to set up passwordless SSH authentication with ssh-agent. To start up ssh-agent the author recommends the following code in .bash_profile: SSHAGENT=/usr/bin/ssh-agent ...
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29 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 ...
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0answers
19 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. ...
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2answers
44 views

What happens to the signals requested recursively?

People often hit Ctrl + c or Ctrl + z to cancel or abandon the job if the process gets sluggish, in this case which of these signals get processed, the first one or the last one? is each signal ...
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23 views

Show signals received by processes [duplicate]

Is there a command or file that stores what signals each process receives? I know if I open one from a terminal and kill -9 PID it'll tell me, but what about something like firefox that is opened ...
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2answers
59 views

Why is my trap not printing any log message?

What I'm doing is, trap 'rm -f /path/of/file/fileName.running; echo "TRAPPED & READY";' 1 2 9 15 >> trap.log I didn't get anything in log & the file which should have been deleted ...
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4answers
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Send SIGINT to child process of shell, simulating CTRL+C (Linux)

Given a shell process (e.g. sh) and it's child process (e.g. cat), how to simulate the behavior of CTRL+C using the shell's process ID? This is what I've tried: Running sh and then cat: ...
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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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1answer
40 views

Can Linux programs be sent a SIGXXX command they can respond to in the UI?

I am trying out the timeout command and would like to know if there is a kill signal that a GUI program, whether a graphics desktop or a terminal program will treat as the user terminating the program ...
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1answer
20 views

Multiple processes reporting signals received

If I run multiple programs with program & in one terminal, and then from another one start sending SIGKILL SIGINT or any other signal, will the terminal running all the processes tell me what ...
2
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1answer
186 views

Forward SIGTERM to child in Bash

I have a Bash script, which looks similar to this: #!/bin/bash echo "Doing some initial work...."; /bin/start/main/server --nodaemon Now if the bash shell running the script receives a SIGTERM ...
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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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Trap not trapping SIGTSTP

I have a script that keeps displaying the login prompt: #!/bin/bash trap '' 2 20 while true; do login done This is part of a bigger project so please don't tell me to just use the system login ...
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2answers
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How to programatically detect when a device raises an interrupt?

How to programatically detect when a device raises an interrupt? This can be when a device is connected or disconnected. And also this case: for example: when a finger is held over a fingerprint ...
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44 views

Idiomatic way to kill -9 only if “graceful” way doesn't work?

Is there a common way or existing utility to do the following? kill a process Give it a few seconds to shut down gracefully kill -9 it if it hasn't stopped
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63 views

Does this dispatcher produce zombie process?

I have such a dispatcher shell script. while read line do java TestProg $line & done < $tasklist On the zombie process Wikipedia page, it says if a parent fails to call wait, the ...
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1answer
6k views

How to suspend and resume processes like bash does

this question is a follow-up to: How to suspend and resume processes I have started firefox from a bash session in gnome-terminal. The process tree looks like this: $ ps -e -o pid,ppid,cmd -H 1828 ...
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1answer
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Ctrl-C is ignored by pppd when put in a shell script

I'm trying to connect to GPRS network through a serial port connected GSM modem. When I call /usr/sbin/pppd call <peer_name> from the command line, it correctly receives and handles Ctrl+C from ...
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3answers
6k views

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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1answer
879 views

ctrl c vs. ctrl z with foreground job

Ctrl+Z stops the job whereas Ctrl+C kills the job. Why is that? Wouldn't the other way make more sense? z@z-lap:~$ sleep 100& [1] 4458 z@z-lap:~$ sleep 200& [2] 4459 z@z-lap:~$ jobs [1]- ...
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1answer
27 views

How do I obtain the kill signal / message / reason within a script?

I am using the following trap: trap OnExit EXIT And in my OnExit function I would like to capture all the info I can on what happened so I can write it to a log file. Id like to know who, why, how, ...
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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
46 views

What signal does X send to its clients when it receives SIGINT?

If I terminate the Xorg server with a SIGINT signal (eg. when I press Ctrl+C), what signal does it send to its clients?
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1answer
91 views

SIGKILLing after a grace period

I've seen a lot of process managers that try to do this. It was my understanding that you should only use SIGTERM to kill a process. The process could take an unknown amount of time to clean up after ...
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0answers
34 views

Execute snippet of code when key is pressed [duplicate]

I want to create a process in Linux which waits for some particular keys to be pressed and executes a snippet of code and goes back to sleep. How can I achieve this? Initially a process will be in ...
7
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1answer
253 views

stderr over ssh -t

This sends output to STDERR, but does not propagate Ctrl+C (i.e. Ctrl+C will kill ssh but not the remote sleep): $ ssh localhost 'sleep 100;echo foo ">&2"' This propagates Ctrl+C (i.e. ...
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2answers
791 views

How to terminate remotely called “tail -f” when connection is closed?

I just noticed that if I execute ssh user@remote_host tail -f /some/file , then tail -f /some/file keeps running on the remote_host even if ssh connection is closed! So, after several connects and ...
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0answers
181 views

Archive (Compress) giant folder in Linux using command line without termination

Well, I'm just trying to compress a whole directory (infact giant!) under Linux using a terminal. The entire folder size is about 7 GB. I've used below command to create the archive. tar -zcvf ...
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3answers
140 views

CTRL C behavior in hierarchy of shells

First of all sorry about terminology errors, I'd try to be clear. I open a shell (like sbt or node debug from my bash). Then inside this shell, I open another one (using scala or node repl ...
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5answers
929 views

Getting pid of bash script from itself

I have a bash script with doing lot of things called script.sh: #!/bin/bash #It #Is #Doing #Things Is there a way that I be able to get the proccess of script and then kill it after 5 minutes? ...
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321 views

Disable the display of “terminated xxx” info of bash

For example, when I kill a background process, then bash weil display terminated xxx, How to disable this info? $ ping g.cn >/dev/null & [1] 25123 $ pkill ping [1] + 25123 terminated ping ...
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1answer
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calling sigprocmask from bash

I have a process that spawn a bash command with system() while the signal mask has all the signals blocked. This cannot be fixed easily. The bash command eventually execs into a process. The all ...
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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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Does time window still exist when the signal is not blocked

Many books say that a time window exists between the generation and delivery of the signal when the signal is not blocked. So I wonder whether the time window still exists when the signal is not ...
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2answers
160 views

Bash script to signal a concurrently running instance (same script) about a condition and increment counter

Background Here's what I want to achieve. I have a (potentially) long-running process. Now I have locking in place just fine and all is generally in order. However, since this is a scheduled job, ...
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Timing out in a shell script

I have a shell script that's reading from standard input. In rare circumstances, there will be no one ready to provide input, and the script must time out. In case of timeout, the script must execute ...
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1answer
181 views

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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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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2answers
412 views

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 ...