How do I find and kill remote processes in Linux?

Question

I am developing a daemon that is acting up and I am now unable to create any new processes (ie. I cannot start a new process to kill the other rogue processes). So, I need to be able to kill the processes from a remote machine. How do I do "kill" remotely without admin privileges? If I cannot kill my own process from a remote machine as a normal user then tell me so I can mark it as the correct answer.

Solution 1

In order to kill a process running on a machine, some local process (or the kernel) has to emit the killing signal. So you need a way to cause a process to emit that signal, and since you can't create a new process, you need to find a way that relies exclusively on already-running processes.

There is no standard daemon that can help you there. They would all process your authentication, then fork a new process (such as a shell) running as you. So if you have no console access and have no existing interaction with the machine, you're out of luck.

---

From your comments, it sounds like you still have a shell on the machine. Then there are things you can do. You can't run any external process, such as ls or ps. But you can run built-in commands such as echo, read, and kill (kill is not a built-in in all shells, but it is one in all shells that support job control, such as bash and zsh).

Each process has an associated directory under /proc: /proc/12345 where 12345 is the process id. Thus you can get some information on exising by exploring /proc. echo with wildcards is helpful here, e.g. cd /proc; echo [0-9]* shows the process ids of all running processes. If the shell is zsh, you can do a lot with glob qualifiers; for instance echo /proc/*(u$UID) shows only the processes running under your user id.

A way to display the contents of a file without forking is

while read -r line; do
  echo "$line"
done </path/to/file

You can kill many processes at once by passing them all to kill. If you've identified a process that belongs to your daemon, try killing its process group with kill -9 -PGID where PGID is the process id of the group leader. You can find the process group id of process 123 with </proc/123/stat read pid tcomm state ppid pgrp sid more; echo $pgrp. (The same information exists in a more readable form in /proc/123/ but you're not in a good condition to read it.) You can also try send a signal to all your processes (including the originating shell) with

trap : NUM
kill -NUM -1

Pick values of NUM other than KILL (9) so that the trap command does cause your shell to ignore the signal (KILL cannot be trapped).

Solution 2

The following information was found at http://www.cyberciti.biz/faq/kill-process-in-linux-or-terminate-a-process-in-unix-or-linux-systems/

Kill process using kill command under Linux/UNIX

kill command works under both Linux and UNIX/BSD like operating systems.

step #1: First, you need to find out process PID (process id)

Use ps command or pidof command to find out process ID (PID). Syntax: ps aux | grep processname pidof processname

For example if process name is lighttpd, you can use any one of the following command to obtain process ID:

ps aux | grep lighttpdOutput

lighttpd  3486  0.0  0.1   4248  1432 ?        S    Jul31   0:00 /usr/sbin/lighttpd -f /etc/lighttpd/lighttpd.conf
lighttpd  3492  0.0  0.5  13752  3936 ?        Ss   Jul31   0:00 /usr/bin/php5-cg

OR use pidof command which is use to find the process ID of a running program:

pidof lighttpd

Output

3486

Step #2: kill process using PID (process id)

Above command tell you PID (3486) of lighttpd process. Now kill process using this PID:

# kill 3486

OR

# kill -9 3486

Where, -9 is special Kill signal, which will kill the process.

killall command examples

DO NOT USE killall command on UNIX system (Linux only command). You can also use killall command. The killall command kill processes by name (no need to find PID):

# killall -9 lighttpd

Kill Firefox process:

# killall -9 firefox-bin

As I said earlier killall on UNIX system does something else. It kills all process and not just specific process. Do not use killall on UNIX system (use kill -9).

Solution 3

As you said in your comment, an admin is the only person who can help you at this point. I suggest you obtain the Perl cookbook and read section 16.19 for the correct method of handling zombies.

Comments

[Joe Phillips]

You don't need process id with pkill. Just the process name

[ewanm89]

pkill grep's the command, kill uses the process ID. Though, what is it stopping the launching of fresh processes, a forkbomb?

[Doug Harris]

I'm not quite following. If you can't create any new processes, how do you expect to connect to the machine and then run pkill or kill? That's at least two new processes which will have to be created.

[stephenmm]

@Doug: My bad, I thought that you could provide pkill a server name as an argument and that it would go to the machine and kill the process. Now that I thin about even if pkill did have that functionality it would probably have to log in as me. So its looking like I cannot do this on my own and that an admin is the only person that can kill these jobs for me, correct?

[stephenmm]

@ewanm: I am not exactly sure what a forkbomb is or why I cannot execute any commands on the machine any more. Whenever I do anything, (ls, pwd, etc...) I get the error: "No more processes." I am getting the impression I am not going to be able to solve this problem on my own.

[stephenmm]

Does anyone have a good resource (best practices, recommendations) for creating your own perl based daemons?

[ewanm89]

Looks like the process table is full, the main way this happens is if someone runs what is called a forkbomb, this is a program that just spawns more and more processes. And then the only way to fix is the magic reboot button as running pkill kill is still a process to run.

[Doug Harris]

You should try kill/killall without -9 before doing it with -9. Well crafted daemons will catch the SIGTERM signal (default for kill) and may do some cleanup before shutting down. Be kind to your system resources and let your daemons release them nicely. If the daemon still doesn't die, then go ahead and send SIGKILL (-9).

[stephenmm]

Wow very thorough! Unfortunately I know how to kill processes what I need to know is how to kill a process when I cannot log on to the machine.

[stephenmm]

@Doug: Thanks, I always wondered why you wouldn't just always do kill -9! Thanks for the enlightenment.