CODEWITHSUNDEEP
bash
nhed
nhed

Reputation: 6001

Why do I end up with two processes?

I wrote a script that has been running as a daemon for quite some time now. If I ever needed to debug it, I would stop the daemon version and rerun manually in current shell. I have never logged anything out of this script, but as I am getting ready to deploy it on a remote server I figured I want to log any errors that the script would get into. For that purpose I followed hints from several SO postings and am doing the following:

if ! tty > /dev/null; then
  exec > >(/bin/logger -p syslog.warning -t mytag -i) 2>&1
fi

This seems to log just fine, I am just surprised to see two instances of my script listed by ps when this feature is enabled. Is there a way to avoid it?

I know I get another process for logger and I assume that it has to do with the >(...), but still hope to avoid it

Upvotes: 0

Views: 112

Answers (2)

Gordon Davisson
Gordon Davisson

Reputation: 125708

bash spawns a subshell to execute the command(s) in >( ... ). In this case, the only thing that subshell does is run /bin/logger, so it's rather pointless. I think you can "fix" this with another exec command:

if ! tty > /dev/null; then
    exec > >(exec /bin/logger -p syslog.warning -t mytag -i) 2>&1
fi

This doesn't prevent the subshell from starting, but then instead of running /bin/logger as a subprocess (of the subshell), the subshell gets replaced with /bin/logger. I haven't tested this with logger, but it worked fine in a quick test I did with cat and it seemed to work fine.

Upvotes: 3

shellter
shellter

Reputation: 37258

Look at the PPID column. (parent process), I think you'll see that the 2 processes are connected to each other.

Generally commands surounded by '( )' pairs indicate 'running-as-a-subprocess', hence 2 listings in ps because there are 2 copies of the process. (I'm not familiar with the bash syntax exec > **${spaceChar}** >( .... ) 2>&1, meaning the '>' seperated by a space from the 2nd '>' )

What is wrong with a crontab entry?

Upvotes: 0

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