Usage of negative pid in kill command

Posted on 2011-09-22
Medium Priority
Last Modified: 2012-05-12
I have seen in few example where the negative pid was used with 'kill' command to kill all process of a user. Could someone please let me know how it can be done?

Will kill all your processes, including the shell you're on/your ssh connection 
kill -9 -1 -1

to kill all d process including login shell:
kill -9 0 

Open in new window

Could someone please let me know how does it works? using above example how can I kill all the process of a particular uid/user?
Question by:beer9
  • 2

Accepted Solution

sakman earned 668 total points
ID: 36584569
From the kill man page:

Negative PID values  may  be  used  to  choose  whole process  groups; see the PGID column in ps command output. A PID of -1 is special; it indicates all processes except the kill process  itself  and init.

LVL 21

Assisted Solution

Papertrip earned 668 total points
ID: 36584580
'kill -9 -1'  will kill all processes that the user who issued it is able to.  Check out pkill instead.

Kill all processes with an effective user ID owner of 'bob'
pkill -u bob

Open in new window

Kill all processes with a real user ID of 'bob'
pkill -U bob

Open in new window

You can put the signal after pkill, like pkill -HUP.

man pkill

LVL 38

Assisted Solution

wesly_chen earned 664 total points
ID: 36584599
a regular user can only kill the process owned by that user.
kill -9 -1
   will kill all the user processes with pid larger than 1

If you run this as root, you are pretty much kill everything exit "init" (daemon root) process.

kill -9 0
  0 mean kill all processes in the current process group
LVL 38

Expert Comment

ID: 36584620
Let run some commands so you can get the picture

echo $$    # get your current shell pid , say 1234
pstree -pl -H 1234   # show the process tree, which 1234 branch highlighted.


bash (1234) ----pstree( 1239)
                   |--java (1235)
                   |--perl (1236)

So, the current process goup is root as 1234 and include child processes 1235, 1236, and 1239.

When you issue
kill -9 0
  it kills processes  1239, 1235, 1236 and 1234.

Featured Post

Free Tool: Port Scanner

Check which ports are open to the outside world. Helps make sure that your firewall rules are working as intended.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.

Join & Write a Comment

This article will show you step-by-step instructions to build your own NTP CentOS server.  The network diagram shows the best practice to setup the NTP server farm for redundancy.  This article also serves as your NTP server documentation.
Welcome back to our beginners guide of the popular Unix tool, cron. If you missed part one where we introduced this tool, the link is below. We left off learning how to build a simple script to schedule automatic back ups. Now, we’ll learn how to se…
Learn how to find files with the shell using the find and locate commands. Use locate to find a needle in a haystack.: With locate, check if the file still exists.: Use find to get the actual location of the file.:
Get a first impression of how PRTG looks and learn how it works.   This video is a short introduction to PRTG, as an initial overview or as a quick start for new PRTG users.
Suggested Courses

588 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question