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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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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2answers
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How can I kill a <defunct> process whose parent is init?

Transmission is intermittently hanging on my NAS. If I send SIGTERM, it doesn't disappear from the process list and a <defunct> label appears next to it. If I send a SIGKILL, it still doesn't ...
38
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3answers
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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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2answers
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What causes various signals to be sent?

I sometimes get a little confused by all of the signals that an application can receive. As I understand it, an application has a default handler for each of these signals, but it can provide its own ...
13
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6answers
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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 ...
6
votes
4answers
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Ctrl+C does not work in gnome-terminal

On my Linux host, Ctrl+C does not seem to work and I do not know how to proceed to make it work. I am using Ubuntu 10.04 with bash 4.1.5(1), and working in Gnome-terminal. When I pressed Ctrl+C while ...
8
votes
3answers
2k views

Process descendants

I'm trying to build a process container. The container will trigger other programs. For example - a bash script that launches running background tasks with '&' usage. The important feature I'm ...
8
votes
2answers
287 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 ...
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2answers
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How to signal the end of stdin input in bash

In Bash, I learned that the ending signal can be changed by here document. But by default how can I signal the end of stdin input? I happened to find that with cat and chardet, their stdin inputs can ...
14
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3answers
11k views

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 ...
15
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6answers
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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?
10
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1answer
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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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4answers
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Why is SIGINT not propagated to childs process when sent to it's parent process?

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: ...
21
votes
2answers
678 views

When you try to terminate a process for good, which option for “kill” should you use?

I am getting a lot of mixed messages from people, and was wondering if it there really is not much of a difference in what you use. kill 'x' killall 'x' kill -9 'x' These are some options I've been ...
9
votes
1answer
1k views

confirmed exit using trap

I am trying to trap the Ctrl+C signal asking a confirmation from the user. The trapping part works fine. But once the signal gets trapped, it does not return to the normal execution. Instead, it quits ...
8
votes
1answer
364 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 ...
11
votes
5answers
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How to soft kill gui applications via terminal?

Is there a way to close a GUI application in friendly "please quit yourself now" way, without graphical access to the applications window? For example, if Gnome/X display crashes to black, I'd like ...
7
votes
3answers
4k views

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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2answers
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how to trap a suspend a resume from a bash script

I have a bash script (on osx) running continuously, it currently traps and handles a terminate like so trap onshutdown TERM how can I make trap also handle suspend/resume like trap onsuspend ? ...
3
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1answer
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Issue with WINCH signal - what am I overlooking?

I am having an issue with the WINCH signal in the following code which is from a tutorial located at developerWorks®: #!/bin/bash trap 'get_window_size' WINCH # trap when a user ...