Re: how to use nohup with gnu parallel

[Benjamin R. Haskell]

On Wed, 2 Feb 2011, Ole Tange wrote:

> On Tue, Feb 1, 2011 at 7:59 PM, Shantanu Unknown wrote:
> > Hi,
> > I could not find any info on how to use nohup with gnu parallel?
> > is the correct usage
> > nohup cat filename|parallel <runjob> {}
> > or is it
> > cat filename|parallel  nohup <runjob> {}
> > or something else?
>
> This works for me:
>
> nohup cat filename|parallel <runjob> {} &

I would think the important part to make immune to HUP would be 
`parallel` itself.  Plus `nohup` the command (rather than the shell 
builtin, which is rare, I think) operates on a single portion of a 
pipeline.

Also eliminating "useless use of cat"[1]:

nohup parallel <runjob> {} < filename &


Some simple test commands bear this out:

$ seq 1 5 > filename

$ nohup cat filename | parallel -j1 'sleep 10 ; echo {}' &
(close shell ; in another shell `ps -ef | grep parall` shows nothing)

$ cat filename | nohup parallel -j1 'sleep 10 ; echo {}' &
(close shell ; in another shell `ps -ef | grep parall` shows something)


If `cat` isn't really cat(1), and it generates enough data that parallel 
wouldn't read it instantly, it might need protection, too:

nohup complex command | nohup parallel <runjob> {} &


> I am curious why you use nohup and not GNU Screen?
> http://www.gnu.org/software/screen/

Sometimes `screen` is overkill, especially if the goal is really to just 
have something that survives a HUP from a crashed terminal.  Sometimes 
it's not installed (`nohup` is sometimes even a shell builtin).

--
Best,
Ben

[1] http://en.wikipedia.org/wiki/Cat_(Unix)#Useless_use_of_cat