How to quit `tail -f` mode without using `Ctrl+c`?

Question

When I do tail -f filename, how to quit the mode without use Ctrl+c to kill the process?

What I want is a normal way to quit, like q in top.

I am just curious about the question, because I feel that killing the process is not a good way to quit something.

Answer 1

As said in the comments, Ctrl-C does not kill the tail process, which is done by sending either a SIGTERM or SIGKILL signal (the infamous -9...); it merely sends a SIGINT which tells tail to end the forward mode and exit.

FYI, these's a better tool:

less +F filename

In less, you can press Ctrl-C to end forward mode and scroll through the file, then press F to go back to forward mode again.

Note that less +F is advocated by many as a better alternative to tail -f. For difference and caveats between the two tools, read this answer: Is `tail -f` more efficient than `less +F`?

Answer 2

What I want is a normal way to quit, like q in top.

That's ControlC :)

I am just curious about the question, because I feel that killing the process is not a good way to quit something.

^C (ControlC) sends a SIGINT to the process, which is defined as:

The SIGINT signal is sent to a process by its controlling terminal when a user wishes to interrupt the process

That's exactly what you want to do here, is interrupt tail. There's no other way to accomplish what you're trying to do ("nicely" quit tail) and while other answers provide a means to stop tail in other ways, they're no better.

Pressing ^C will attempt to interrupt a task in Linux -- this is perfectly normal, and it's only "not good" if that process is in the middle of something and you're not letting it finish, and then the only "not good" side effect is leftover things from that process. As an example, ^C in the middle of a make command leaves partially-compiled software, but that's fine: a further run of make will clean that up / resume where it left off.

Answer 3

tail -f filename, how to quit the mode without use Ctrl c to kill the process

You can't do that. Perhaps you wanted to run tail -f somefile | less

The Ctrl c is interpreted by the tty subsystem (and by your shell) and sends a SIGINT signal (see signal(7) and pty(7)...). See tty demystified.

Answer 4

This would work and answers your question, but is not a particularly satisfactory solution.

timeout 15s tail -f /var/log/messages

This will run the command for 15 seconds and then kill it for you, without having to press ^C

Answer 5

Assuming you have a function

function prll(){
..... 
pkill -9 -x tail
}

Assuming you run tail along your function

tail -n 1 -f file | 
pv -l > /dev/null | 
prll file

echo !!done!!

Conclusion, the answer is:

pkill -9 -x tail

Answer 6

Answers differ based on context. To quit tail -f elegantly, you will need a trigger. Assume you are trying to monitor output of a task that will finish at some point in time - that can become your trigger.

task >& filename.log &
task_pid=$!
tail -f filename.log &
tail_pid=$!
while [ 1 ]
do
    # -0 is a special "poke" signal - "are you around?"
    kill -0 $task_pid
    if [ $? -eq 0 ]
    then
        # Original task is still alive.
        sleep 2
        continue
    fi
    kill -TERM $tail_pid
    break
done

I have used similar ideas in the past.

Enjoy.

Answer 7

I think another good approach is using the old ps + kill in another session.

ps -fea | grep tail

The above command would identify any tail running by any user, and after finding the right PID, just run kill. For example:

kill 999999

Hope this can help someone as an alternative approach.

Answer 8

Issuing

echo tail -n 1 -f <filename>

works for me though I'm not 100% sure it terminates the tail process.