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 “trace trap” mean when reported by zsh?

I am trying to run a set UID root program in UNIX using the zsh shell. But I keep getting this message $ ./progExe zsh: trace trap ./progExe Can anyone please tell what does “zsh: trace trap” mean? ...
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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 ...
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why would typing Ctrl+c twice stop a running process in Linux?

There are Linux programs, for example vlc, that recommend typing ctrl+c twice to kill their execution from a terminal if the program didn't stop after the first one. Why would typing ctrl+c twice ...
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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 ...
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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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Interruption of system calls when a signal is caught

From reading the man pages on the read() and write() calls it appears that these calls get interrupted by signals regardless of whether they have to block or not. In particular, assume a process ...
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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 ...
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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 ...
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Program behavior when kill -HUP is recieved?

Is there a way to find out what will program do when it receives kill signal HUP? Without simply running the command ofc :D For example, killall -HUP pppd will restart pppd killall -HUP firefox ...
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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 ...
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Can you specify a separate trap in a subshell created with ()?

I'm writing a script that starts a subshell to go off and do some work. In a special case, the script needs to tell the subshell to cleanly stop what it's doing and exit early. However, my ...
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What's the difference between the ^S and ^Z control characters inside a terminal?

When using a terminal emulator, one can stop the currently running program with either CTRL-Z or CTRL-S. What's the difference between these signals?
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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 ? ...
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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 ...
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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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when does the system send a SIGTERM to a process?

My server program received a SIGTERM and stopped (with exit code 0). I am surprised by this, as I am pretty sure that there was plenty of memory for it. Under what conditions does linux (busybox) send ...
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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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What documentation shows the associated numbers for linux signals like SIGTERM and SIGKILL?

I can look around the internet and find that the associated number for SIGKILL is 9, but is there linux documentation (such as, a man page) showing the complete list of signals and their numbers?
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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 ...
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Is nohup indefinite?

If I run a program with an infinite loop with nohup, will the program run indefinitely (until the machine is reset or until I manually terminate it)?