How to terminate a background process?

Question

I have started a wget on remote machine in background using &. Suddenly it stops downloading. I want to terminate its process, then re-run the command. How can I terminate it?

I haven't closed its shell window. But as you know it doesn't stop using Ctrl+C and Ctrl+Z.

Solution 1

There are many ways to go about this.

Method #1 - ps

You can use the ps command to find the process ID for this process and then use the PID to kill the process.

Example

$ ps -eaf | grep [w]get 
saml      1713  1709  0 Dec10 pts/0    00:00:00 wget ...

$ kill 1713

Method #2 - pgrep

You can also find the process ID using pgrep.

Example

$ pgrep wget
1234

$ kill 1234

Method #3 - pkill

If you're sure it's the only wget you've run you can use the command pkill to kill the job by name.

Example

$ pkill wget

Method #4 - jobs

If you're in the same shell from where you ran the job that's now backgrounded. You can check if it's running still using the jobs command, and also kill it by its job number.

Example

My fake job, sleep.

$ sleep 100 &
[1] 4542

Find it's job number. NOTE: the number 4542 is the process ID.

$ jobs
[1]+  Running                 sleep 100 &

$ kill %1
[1]+  Terminated              sleep 100

Method #5 - fg

You can bring a backgrounded job back to the foreground using the fg command.

Example

Fake job, sleep.

$ sleep 100 &
[1] 4650

Get the job's number.

$ jobs
[1]+  Running                 sleep 100 &

Bring job #1 back to the foreground, and then use Ctrl+C.

$ fg 1
sleep 100
^C
$

Solution 2

In bash you can use fg to get the job to the foreground and then use Ctrl+C

Or list the process in the background with jobs and then do

kill %1

(with 1 replaced by the number jobs gave you)

Solution 3

You can equally use kill $! to kill the most recently backgrounded job.

Solution 4

EDIT: Once in the foreground, you can Ctrl+C, or as @Zelda mentions, kill with the '%x' where 'x' is the job number will send the default signal (most likely SIGTERM in the case of Linux).

just type fg to bring it to the foreground, if it was the last process you backgrounded (with '&').

If it was not the last one, type: jobs and find the 'job number', represented in '[]'. Then just type:

fg 2

..where '2' is the job number, for example:

foo@bar:~/junk/books$ jobs
[1]+  Running                 okular how_to_cook_a_turkey.pdf &
foo@bar:~/junk/books$ fg 1
okular how_to_cook_a_turkey.pdf            <- this is now in the foreground.

Solution 5

One thing I don't see here, which I've found very useful especially when testing out commands, is pidof. You can use pidof [command] to find the process id of a process that is currently running. I like it because it allows me to quickly find the id of the command I want, which is usually something I just invoked.

Once you have the pid, you can simply kill the process. It allows for creating simple scripts for killing a process only if it's currently running.

View more solutions

Comments

[Mohammad Etemaddar]

The jobs has no output and fg sais: -bash: fg: 1: no such job. But typing fg works well and also pkill wget works well. but ps -eaf|grep wget and then kill <process number> dose not stop the job. ps: I use the third number as process number.

[slm]

@MohammadEtemaddar - use the 2nd number from the output of ps. The 3rd # is the parent's process id.

[Mohammad Etemaddar]

When I use the second number, It sais: No such process and then when I check the process number again using ps -eaf|grep wget I find that the process number has changed.

[Mohammad Etemaddar]

The command ps -eaf|grep wget gives the grep wget process. ps -efa|grep <my user id> gives this.

[slm]

@MohammadEtemaddar - ah, the ps is finding the grep. Do it like this: ps -eaef| grep [w]get.

[slm]

@MohammadEtemaddar - you can also use pgrep instead, pgrep wget.

[Mohammad Etemaddar]

Would you please tell a little about the functionality of option eaef?

[slm]

@MohammadEtemaddar - sorry the extra e is a typo. Should read ps -eaf | grep [w]get. The options are are in the ps man page. man ps.

[John_West]

Suddenly, on RHEL5 my job was not killed by Ctrl-C after fg (method 5 did not work.). Method 4 seems to be the fastest and the shortest to type.

[mejdev]

Ah this helped me! kill %1 wasn't working for some reason, "kill: failed to parse argument: '%1'" and Ctrl+C wasn't working; couldn't find process in ps or anything because it was root (I forgot I used sudo with it)

[Jack Chi]

It's fg %1 to bring the job back into foreground.

[slm]

@JackChi - the fg 1 notation works as well. Try it.

[Alex]

I did the first, second and third steps, it didnt work, so I just closed the current open tag where I opened the programs, and problem solved

[Nate Ritter]

If it's used as a command like an alias in a bash profile, be sure to wrap in single quotes.

[Ronny Sherer]

kill %% kills the last background process. Repeating it will kill the one before and so on. kill %1 kills the first background process.

[Fox]

This adds nothing to the currently-accepted answer, and moreover won't work in this case. Using kill %1 (as suggested by others) will, but Ctrl+C is meaningless against programs that ignore the keyboard interrupt as mentioned in this question

[avm]

what does [ ] do in grep [w]get?

[slm]

@avm - it basically tricks grep into not showing the actual grep command in the output. The grep command shows up as grep [w]get but the command grep is looking for the string wget. The [...] is a set of characters, in this case a set of 1 character, w.

[Admin]

But if you launched this process yourself, you should already have the pid of this background process.