kill - Send a specified signal to a process or process group.

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235
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9answers
103k views

When should I not kill -9 a process?

I am always very hesitant to run kill -9, but I see other admins do it almost routinely. I figure there is probably a sensible middle ground, so: When and why should kill -9 be used? When and why ...
167
votes
12answers
130k views

What if 'kill -9' does not work?

I have a process I can't kill with kill -9 <pid>. What's the problem in such a case, especially since I am the owner of that process. I thought nothing could evade that kill option.
95
votes
7answers
11k views

How to kill a runaway cat?

Many times I accidentally run the cat command on files have contents up to few thousand lines. I try to kill the cat command with Ctrl+ C or Ctrl+Z, but both only take effect after the total output ...
73
votes
2answers
8k views

How does Linux “kill” a process?

It often baffles me that, although I have been working professionally with computers for several decades and Linux for a decade, I actually treat most of the OS' functionality as a black box, not ...
37
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 ...
33
votes
2answers
3k views

What does `kill -0` do?

I recently came across this in a shell script. if ! kill -0 $(cat /path/to/file.pid); then ... do something ... fi What does kill -0 ... do?
32
votes
1answer
4k views

Why is the UNIX system call kill named 'kill'?

I'm curious about the history of the name, it seems to me that the 'kill' system call could have been named 'signal', and the 'signal' system call could have been named 'handle'. I was wondering ...
28
votes
2answers
3k views

Will Linux start killing my processes without asking me if memory gets short?

I was running a shell script with commands to run several memory-intensive programs (2-5 GB) back-to-back. When I went back to check on the progress of my script I was surprised to discover that some ...
21
votes
9answers
2k views

How can I kill a process and be sure the PID hasn't been reused

Suppose, for example, you have a shell script similar to: longrunningthing & p=$! echo Killing longrunningthing on PID $p in 24 hours sleep 86400 echo Time up! kill $p Should do the trick, ...
21
votes
2answers
653 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 ...
21
votes
1answer
2k 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 ...
20
votes
2answers
2k views

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 ...
18
votes
5answers
52k views

How to stop a background process?

I have started a wget on remote machine in background using &. Suddenly it stops downloading. I want to stop its process, then start it again. How can I stop it? I haven't close its shell window. ...
18
votes
3answers
17k views

Where can I see a list of kernel killed processes?

Is there some way I can check which of my processes the kernel has killed? Sometimes I log onto my server and find that something that should've run all night just stopped 8 hours in and I'm unsure if ...
16
votes
5answers
9k views

How can I close a terminal without killing its children (without running `screen` first)?

sometimes I run an app in the gnome-terminal, but then I suddenly have to restart gnome or something. I guess the answer to the question is also useful then I want to disconnect from SSH where ...
16
votes
2answers
1k 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 ...
16
votes
2answers
24k 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 ...
15
votes
8answers
9k views

pgrep and pkill alternatives on mac os x?

Are there alternatives to pgrep and pkill commands on Mac OS X or should I just create aliases for them using other commands available for me?
14
votes
5answers
4k views

Any way to restart a Linux machine via SSH if the root filesystem is not working?

Just as a curiosity; something went wrong with a Linux machine, making the root file system show up as "64Z". A few commands work, like top, df, and kill, but others like reboot come up with "command ...
14
votes
3answers
5k views

How to kill a process with a single command?

I want to kill a process, after finding the id in a single step. I currently use these two commands: pidof <name> kill <#number_which_is_result_of_command> How can I write a single ...
13
votes
3answers
8k 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 ...
13
votes
2answers
3k views

Why does bash show 'Terminated' after killing a process?

Here is the behaviour I want to understand: $ ps PID TTY TIME CMD 392 ttys000 0:00.20 -bash 4268 ttys000 0:00.00 xargs $ kill 4268 $ ps PID TTY TIME CMD 392 ttys000 ...
13
votes
3answers
4k views

Linux: Kill process based on arguments

How can I kill a process based on its command line arguments? killall, pgrep, and pkill seem to only work based on the process name. I need this to be able to differentiate between a number of ...
12
votes
5answers
4k 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 ...
12
votes
2answers
2k views

Is '-9' a flag to kill command?

What does -9 do? It does not show up in the syntax: $ kill kill: usage: kill [-s sigspec | -n signum | -sigspec] pid | jobspec ... or kill -l [sigspec] $
12
votes
3answers
1k views

How Can Terminal Emulators Kill Their Children After Recieving a SIGKILL?

From what I understand, SIGKILL cannot be caught. This would imply that a process does not have time to kill it's children before the OS destroys it. This can be demonstrated with a shell script. ...
12
votes
2answers
1k views

Is there an upper limit to the number of zombie processes you can have?

I used to work with an HP-UX system and the old admin told me there is an upper limit on the number of zombie processes you can have on the system, I believe 1024. Is this a hard fact ceiling? I ...
11
votes
2answers
2k views

Does `kill -p` really work?

In the man page of kill it is written as following SYNOPSIS kill [ -s signal | -p ] [ -a ] [ -- ] pid ... kill -l [ signal ] -p Specify that kill should only print the process id ...
11
votes
1answer
713 views

Why does running `killall init` as user log me out?

On multiple computers running Ubuntu 14.XX, I ran the command "killall init" as user, and was immediately logged out. I could log back in again without a problem. Why is this? What's going on behind ...
11
votes
5answers
4k 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 ...
10
votes
6answers
12k views

Kill many instances of a running process with one command

This is one of the questions that has troubled me often. Suppose I have thousand or more instances of any process(for e.g. say the process vi) running. How do I kill them all in one single shot/one ...
10
votes
3answers
3k views

What's the difference between pkill and killall?

I know that pkill has more filtering rules than killall. My question is, what is the difference between: pkill [signal] name and killall [signal] name I've read that killall is more effective ...
9
votes
5answers
12k views

Kill all descendant processes [duplicate]

I'm writing an application. It has the ability to spawn various external processes. When the application closes, I want any processes it has spawned to be killed. Sounds easy enough, right? Look up ...
9
votes
2answers
721 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 ...
9
votes
4answers
533 views

Terminate every background process

I have a few Stopped background processes. kill $(jobs -p) and kill `jobs -p` have no effect kill %1, kill %2, etc. successfully terminate individual processes How can I kill every background ...
9
votes
4answers
6k 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 ...
8
votes
1answer
708 views

Why does “kill -9 0” end my console session?

I just wonder why kill -9 0 ends my tty console session? What exactly is PID 0, it is not listed on a ps aux?
8
votes
2answers
392 views

How can I create a hard to kill process

I want to create a program that will be difficult to stop (even for the administrator) once it is started (with root privileges). Once started the process should continue to start itself at startup ...
8
votes
2answers
3k views

How to kill both process and subprocess?

I asked a question to know how to get multiple lines of message from Python's subprocess module. The problem is that in the course of testing, I had to kill the python process that runs gnuchess ...
7
votes
4answers
799 views

How to find source of spawning process?

I have a Java process running on a RedHat Linux instance. The problem is it keeps reappearing after I kill it. I am not sure where to look. I've already went to crontab, but no luck. I've looked at ...
7
votes
4answers
7k views

'kill java' doesn't kill java

I am running debian right now and sometimes I need to kill java manually from the terminal, but when I try kill #pid# or pkill java nothing happens. No console output (ok, that's normal) and java is ...
7
votes
3answers
1k views

How to stop a bunch of processes on unix fast?

How to stop a bunch of processes on unix fast. I can use ps/top, kill. If the number of processes is very large, I use shell script. Are there other ways, only one or two unix commands can do it ...
7
votes
3answers
14k views

How to kill a daemon with its name gracefully?

I usually kill a process with killall. killall markdoc But I am not sure if this command terminates the process gracefully. Does this command achieve graceful termination? If it does not, how can ...
7
votes
2answers
619 views

Kill user processess on logout

I have a Ubuntu server that handles remote X sessions from users. However, I don't want to allow users to run any kind of background processes - so here is my question: How do I prevent users from ...
7
votes
1answer
1k views

Interrupt sequence CTRL+C does not work for user

In any terminal operating under GNOME, if I press Ctrl+C, I only see a question mark. Same goes for Ctrl+Z. The output of stty -a | grep intr is: intr = ^C; quit = ^\; erase = ^?; kill = ^U; eof = ...
6
votes
2answers
9k views

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 ...
6
votes
4answers
6k views

Finding the ID of a process and killing it

When ever I need to kill a background process I do ps -e | grep <process_name> Which prints something like this 1766 ? 00:00:13 conky , Then I use the process ID to kill it like so kill 1766 . ...
6
votes
3answers
4k views

killall gives me `no process found ` but ps

Could somebody explain to me the difference between kill and killall? Why doesn't killall see what ps shows? # ps aux |grep db2 root 1123 0.0 0.8 841300 33956 pts/1 Sl 11:48 0:00 ...
6
votes
3answers
13k views

Terminating a bash shell script running in the background

I often use bash shell scripts to run simple commands for many different files. For example, suppose that I have the following bash shell script, called script.sh, that runs the program/command foo ...
6
votes
4answers
3k views

Exit Google Chrome from terminal

Is there a way to cause google-chrome to quit, from the terminal, besides using killall google-chrome? I would like to be able to close it from a script without killing it.