SH-22 Add Blog Post naed Life saving commands: nohup & disown

source/posts/2014-05-09-life-saving-commands-nohup-and-disown.md

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+---
+title: 'Life Saving Commands: nohup & disown'
+date: 2014-05-09
+author: baygunm
+tags: linux. macosx, command, nohup, disown
+---
+
+## Why do we need <code>nohup</code> or <code>disown</code> ?
+
+Sometimes while you' re developing, you need a job to continue running in the background even if you close the terminal. Sometimes you need a command running on a remote machine connected with ssh in a terminal window. Sometimes you start the command on the terminal and accidentally close the terminal. So you need to have a look at these commands: <code>nohup</code> and <code>disown</code>. You need these.
+
+## <code>nohup</code>
+
+This is a POSIX command. It's a short for  ' **NO**  **H** ang **UP** '. By using this command you tell the system to ignore the hangup signal for specified command.
+
+### Without nohup
+
+Let's test some commands:
+
+```bash
+% sleep 3600 &
+```
+
+This command will add a background job that waits for 3600 seconds. Why do we need that? We're just putting commands running on background.
+
+You can watch th command running by following command:
+
+```bash
+% ps -e -o pid,command | grep '[s]leep'
+9826 sleep 3600
+```
+
+You can see a similar result with a different process id. Note the process id and close the terminal. When you open a new terminal re-write the command:
+
+```bash
+% ps -e -o pid,command | grep '[s]leep'
+```
+
+So no result? That's correct, your command got a hangup signal when you close the terminal and it's not running now.
+
+### With <code>nohup</code>
+
+When you need a command running in the background even if you close the terminal, you can simply write <code>nohup</code> before the command and go. If you already started the command, don't worry and wait for the <code>disown</code> section.
+
+Let's use <code>nohup</code> now:
+
+```bash
+% nohup sleep 3600 &
+[1] 10325
+appending output to nohup.out
+```
+
+It runs in the background and writes the output to the file nohup.out by default. Check the command still running.
+
+```bash
+% ps -e -o pid,command | grep '[s]leep'
+10325 sleep 3600
+```
+
+Did you note the process id? So let's close the terminal, open a new one and see what happens.
+
+```bash
+% ps -e -o pid,command | grep '[s]leep'
+10325 sleep 3600
+```
+
+So you see it's still there running. So we're done with <code>nohup</code>.
+
+Do not forget to quit the sleep job, because we don't need that now. This is how you can do that:
+
+```bash
+kill -s QUIT $(ps aux | grep '[s]leep' | awk '{print $2}')
+```
+
+This command gets the process ids for all sleep jobs and send them QUIT signal.
+
+## What about <code>disown</code>?
+
+After looking at <code>nohup</code>, let's look at <code>disown</code>. It is used to unbind a job from the current session. Let' s think about this scenario:
+
+* You started a command that's taking too much time,
+* you have to close the terminal,
+* but you forgot to use <code>nohup</code>
+
+It's bad for you, but wait! There's <code>disown</code> suitable for you. Ypu can use it.
+
+Let's run our command:
+
+```bash
+% sleep 3600 &
+% sleep 3600 &
+```
+
+Check them running in the background.
+
+```bash
+% ps -e -o pid,command | grep '[s]leep'
+11661 sleep 3600
+11666 sleep 3600
+```
+
+We already know that if we close terminal we will make them hangup. So take note about the process ids. And this command list the active jobs.
+
+```bash
+% jobs -l -p
+[1]  - 11661 running    sleep 3600
+[2]  + 11666 running    sleep 3600
+```
+
+You see the last command with a plus sign left. Let's use disown and see what happens.
+
+```bash
+% disown
+```
+When you check them you'll see both running on the background:
+
+```bash
+% ps -e -o pid,command | grep '[s]leep'
+11661 sleep 3600
+11666 sleep 3600
+```
+
+Let's see the active jobs again:
+
+```bash
+% jobs -l -p
+[1]  + 11661 running    sleep 3600
+```
+
+You see the latest command is unbound from current session. If we close the terminal now and open a new terminal, we lose only the first command.
+Let's close the terminal and open a new one and check that:
+
+```bash
+% ps -e -o pid,command | grep '[s]leep'
+11666 sleep 3600
+```
+
+If you check the active jobs, you don't see any. Because the previous job is not bound to any sessions and continue working in the background.
+
+```bash
+jobs -l -p
+```
+
+So I wish this commands will be helpful for you, too.