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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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 ...
7
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6answers
4k views

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 ...
2
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2answers
32 views

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 ...
2
votes
2answers
49 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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5answers
4k views

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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vote
1answer
60 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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vote
1answer
310 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 ...
8
votes
4answers
3k views

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 ...
5
votes
2answers
129 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 ...
32
votes
6answers
4k views

Does pressing ctrl-c several times make the running program close more quickly?

I often start to read a huge file and then want to quit after a while, but there is a lag from pressing Ctrl+C to the program stops. Is there a chance of shortening the lag by pressing the Ctrl+C key ...
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4answers
310 views

Ctrl-C with two simultaneous commands in bash

I want to run two commands simultaneously in bash on a Linux machine. Therefore in my ./execute.sh bash script I put: command 1 & command 2 echo "done" However when I want to stop the bash ...
9
votes
5answers
2k views

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 ...
0
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2answers
70 views

What does this logrotate nginx config do?

In my /etc/logrotate.d/nginx I saw, /var/log/nginx/*.log { daily missingok rotate 52 compress delaycompress notifempty create 640 nginx adm ...
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2answers
15k views

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 ...
7
votes
4answers
2k views

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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4answers
9k views

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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2answers
99 views

Pipe command to tail: when is the first command aborted?

In this example: $ for i in {1..3}; do sleep 1; echo $i; done | head -n 2 why is the first command (for loop) killed only just before the 3 is displayed ? I expected it to be killed right after ...
7
votes
3answers
1k 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 ...
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votes
2answers
1k views

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 ...
2
votes
1answer
175 views

Suppress “Alarm clock: 14” from ping

I've made a simple script for rebooting my router and afterwards showing a progress bar until my computer has an internet connection again. When running the script I get the following output: The ...
5
votes
1answer
67 views

Do not set $? to non-zero on Control+C

My $PS1 in Zsh includes this expression: %(?. %?.) It means «if exit code of previous command ($?) is true, show $?, else show nothing». This is generally useful, but one thing annoys me: shells set ...
10
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2answers
96 views

Cancel completion, but only completion, in zsh

When a completion function takes a long time, I can interrupt it by pressing Ctrl+C (terminal interrupt key, sends SIGINT) or Ctrl+G (bound to send-break). I am then left with the uncompleted word. ...
2
votes
1answer
490 views

child process does not inherit the pending signals from the parent after a fork system call, why?

Could anybody please tell me the reason to why pending signals are not inherited by the child process? On the other hand, the child process inherits the signal handlers and signal mask from the ...
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1answer
44 views

Does Control+C delete the files that you were downloading and installing? [closed]

If you are installing a package in the terminal and you use Control+C to stop it, does it also undo all the changes and remove the files that it downloaded?
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vote
2answers
462 views

How to generate signal interrupt on a file descriptor in Linux?

How can I generate a signal interrupt on a file descriptor in Linux? Motivation is to generate a interrupt in userland as we have in microcontrollers. I'll have file descriptor for I/O, and want to ...
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2answers
264 views

How are signals implemented in Linux?

When one process sends a signal to another process, does receiving process wait until it is rescheduled to run? So if every 1 ms we choose one process to run, does that mean the latency from ...
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vote
1answer
69 views

How to list killable tasks?

As manpage of ps states A process with STATUS with the value "D" means "uninterruptible sleep (usually IO)" Also, I've read: You should use TASK_INTERRUPTIBLE here, otherwise your kernel thread ...
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2answers
639 views

Equivalent of “truss -T” and “truss -U” on Linux?

Is there an equivalent of what the -T and -U option of the truss Solaris utility does on Linux. Those are to specify a system call (-T) or library function (-U) which when called by the traced ...
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2answers
855 views

difference between signalfd and sigwaitinfo?

I went through examples and man page but couldn't figure out difference between signalfd and sigwaitinfo Apart from syntax both are doing same thing i.e. waiting for signal storing it details into ...
32
votes
2answers
864 views

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.
6
votes
1answer
487 views

In which cases is SIGHUP not sent to a job when you log out?

I read an answer from a user who claimed that running foo 2>&1 >& output.log & would result in foo continuing to run even when they log out. According to this user, this even ...
4
votes
1answer
551 views

How do I find out what process is consuming pending signals?

A user is getting the following message when they try to run a particular program. timer_create: Resource temporarily unavailable From this StackOverflow Q&A titled: timer_create() : -1 ...
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votes
2answers
277 views

Why is `kill -s INT <zsh PID>` behaving differently from `Ctrl-C`?

Starting with: % donothing () { echo $$; sleep 1000000 } % donothing 47139 If at this point I hit Ctrl-C at the same terminal that is controlling the shell, then the function donothing does indeed ...
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votes
3answers
717 views

Preventing propagation of SIGINT to Parent Process

Considering a scenario where a Parent program (could be a C++ program or a Shell Script) executes a Child shell script, when we hit Control+C (or whatever character is configured to be the INTR ...
7
votes
1answer
196 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 ...
2
votes
1answer
184 views

Keyboard shortcut for SIGTERM in GUI application?

Related to another question, is there a way to send SIGTERM to the currently focused local GUI window application with a keyboard shortcut? Like clicking the [X] button in most WMs or Ctrl-c for the ...
2
votes
2answers
398 views

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)?
6
votes
2answers
184 views

Decode Flags for Kill Command

I am new to Shell Scripting. I saw this Command on a Book for Linux shell Scripting $ kill -HUP 1234 >killout.txt 2>killerr.txt I know what the command does, but i am not able to understand ...
9
votes
1answer
4k views

How to suspend and resume proccesses like bash does

this question is a follow-up to: How to suspend and resume proccesses I have started firefox from a bash session in gnome-terminal. The proccess tree looks like this: $ ps -e -o pid,ppid,cmd -H ...
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votes
3answers
197 views

What process is running before I even get a prompt?

When I log in to a specific server I see the following: Note that I get get Last login: ... information but no prompt. I hit Ctrl+C and only then do I get my prompt, thus proving that my username ...
4
votes
1answer
340 views

A script's background process is still alive after closing the terminal

This is more of a process management/signal handling question than a Bash question. It just uses Bash to explain the issue. I'm running a Bash script in which I run a background process. This is the ...
3
votes
1answer
542 views

sigaction(7): semantics of siginfo_t's si_code member

I've got a long-running program (becomes a daemon with daemon(3) call) that exits on Signal 11 (Segmentation Violation) every so often. I can't tell why. So, I wrote a SIGSEGV handler, set using the ...
2
votes
2answers
158 views

End process from another SSH window

I forgot to use screen and I have a task that has been running for quite some time, and I do not want to lose the saved data. Basically Ctrlc will end the task and save the data if I am on the same ...
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vote
1answer
1k views

System sending SIGTERM and SIGKILL during normal work

I have a program (C++) that works with TCP sockets in multithreaded manner. The multithreading is intensive, about 100 threads (POSIX threads). Sometimes, not quite sure when, the program gets ...
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vote
2answers
244 views

Mapping intr to del key

I am in the process of migrating a legacy 4GL application from SCO OpenServer 5.0.7 to CentOS (Red Hat) Linux 5.9. There are a number of screens that prompt the user to press "DEL to ABORT" but is ...
6
votes
3answers
1k views

What's the difference between Ctrl-Z and kill -STOP?

When I run a command (make on a large project) from the shell, I can type Ctrl-Z to stop the process and return to the shell. Subsequently, I can run fg to continue the process. I'm trying to write a ...
7
votes
1answer
212 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 ...
2
votes
1answer
91 views

Chain commands with Control + C interrupt

I am trying to execute a program which loops indefinitely, and so must be forcibly interrupted. After executing the program, I want to delete it. I can do it in several steps: ./MyProg Control + C ...
19
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1answer
898 views

How does systemd survive a kill -9?

Between the recent "Why does 'kill -9 0' end my console session" and "How to get a kernel panic" questions, I got a bur under my saddle and tried kill -9 1 on a mostly up-to-date Arch linux laptop. I ...
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1answer
433 views

What is the difference between exiting a process via Ctrl+C vs issuing a kill -9 command?

I know I can kill any process with kill -9 command . But sometimes i see that even if I have terminated a program with CTRL+C , the process doesn't get killed . So I want to know the difference ...