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    <p>Although you are sending the <code>ssh</code> process to the background via <code>&amp;</code>, its file descriptors are still "attached" to your terminal. A demonstration:</p> <pre><code># Terminal 1 $ ssh $host sleep 600 &amp; [3] 14340 # Terminal 2 $ ls -l /proc/14340/fd lrwx------ 1 iscfrc iscfrc 64 Oct 3 10:30 0 -&gt; /dev/pts/1 lrwx------ 1 iscfrc iscfrc 64 Oct 3 10:30 1 -&gt; /dev/pts/1 lrwx------ 1 iscfrc iscfrc 64 Oct 3 10:30 2 -&gt; /dev/pts/1 lr-x------ 1 iscfrc iscfrc 64 Oct 3 10:30 3 -&gt; socket:[125941180] lrwx------ 1 iscfrc iscfrc 64 Oct 3 10:31 4 -&gt; /dev/pts/1 lrwx------ 1 iscfrc iscfrc 64 Oct 3 10:31 5 -&gt; /dev/pts/1 lrwx------ 1 iscfrc iscfrc 64 Oct 3 10:31 6 -&gt; /dev/pts/1 </code></pre> <p>Note how all the FDs (Minus the TCP socket) are attached to <code>/dev/pts/1</code>.</p> <p>So what happens when your script runs <code>ssh</code>, puts it in to the background, but the <code>ssh</code> process continues to poll the terminal for input?</p> <pre><code># Terminal 2 $ sudo strace -p 14340 Process 14340 attached - interrupt to quit select(7, [3 4], [], NULL, NULL # Terminal 1 $ read # Terminal 2, output select(7, [3 4], [], NULL, NULL) = 1 (in [4]) read(4, 0xbff1dbbc, 16384) = ? ERESTARTSYS (To be restarted) --- SIGTTIN (Stopped (tty input)) @ 0 (0) --- --- SIGTTIN (Stopped (tty input)) @ 0 (0) --- # (infinite loop of the previous three lines) </code></pre> <p>It goes in to panic when attempting to <code>read()</code> input from file descriptor <code>4</code>, which you can see above is the terminal. (<code>4 -&gt; /dev/pts/1</code>)</p> <p>The solution is to disconnect <code>ssh</code> from the terminal's input; I recommend using <code>nohup</code>:</p> <pre><code>nohup ssh -q sc-2 tail -f /home/logs/oam-2.log &gt; /root/logs/file.log &amp; </code></pre> <p>Additional suggestions for consideration:</p> <ol> <li>Add the <code>-T</code> argument to your <code>ssh</code> command to disable TTY allocation on the remote host. Since you don't need to interact with the <code>tail</code> command a TTY is unnecessary.</li> <li>Store the PID of the <code>ssh</code> command in to a variable via <code>$!</code> in order to save yourself needing to parse the output of <code>ps</code>.</li> <li>And to be even more spartan, you can save yourself an <code>echo</code> by using <code>read</code>'s <code>-p</code> option. (<code>p</code> is for <em>prompt</em>)</li> </ol> <p>Combining all of the above:</p> <pre><code>nohup ssh -qT sc-2 tail -f /home/logs/oam-2.log &gt;/root/logs/file.log &amp; sshpid=$! read -p $'press return to stop the trace\n' kill $sshpid </code></pre> <p>I tested the above (With my own host/files paths filled in) and it ran for >10 minutes without stopping.</p>
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    1. POHow to use tail -f in a shell script?
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    1. POHow to use tail -f in a shell script?
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    1. COthis solution is very close to what i want, however this script is only responsible to start the tail command and put the output in the log file. I need to write another function called print_stop where it will kill the command when the invoked
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    2. COthe only concern i have is even with nohup tail is still not running in the background.
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    3. COYou used both the terms script and function - are you saying that you need to write two scripts, one to start the `ssh` process and another to kill it later? If so, you'll need to use `nohup` to start that script instead of using it inside the script itself. If that's not the case, I'm not sure why it wouldn't be going in to the background - as long as the `&` is at the end of the `nohup` line it should.
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