problems with fork

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

dear monks.

I am trying to fetch a big file from a server to another server. I log to my server using ssh.. and I trying to create a script that forks to download, so I can exit my ssh without loosing the download. the code is still waiting for the download. I am not very good with forking, what I want is to be able to run this script, have a forked process download, and safely close my ssh login.
here's what I came up with but it obviously is not working

#!/usr/bin/perl
use LWP::Simple;
if (fork) {
    getstore('ftp://someserver/big640Mbfile', '/myfolder/file');
}
[download]

should I better place a crontab to start the file?

Comment on problems with fork Download Code

Replies are listed 'Best First'.
Re: problems with fork by kappa (Chaplain) on May 15, 2002 at 10:07 UTC
You can use UNX command `nohup` to start any* program you want in the background and be sure that it won't die when you disconnect. Look: $ nohup wget ftp://ftp.server/bigfile appending output to nohup.out $ [download]	[reply] [d/l]
Re: problems with fork by perigeeV (Hermit) on May 15, 2002 at 10:33 UTC
Your `getstore` is being executed by the parent. `fork` returns the PID to the parent, so the truth result of your `if` conditional means you are in the parent. A return value of 0 means you're inside the child. Also check a return of `undef` to make sure fork didn't puke.	[reply] [d/l] [select]
Re: problems with fork by yodabjorn (Monk) on May 15, 2002 at 11:33 UTC
nohup is good, but I would also sugest the most excellent program screen for running your cmds in a remote terminal or wanting to close a term and leave stuff running. Screen is great for coding on remote servers becasue you can detach/reattach to your remote session without loosing anything ( like if you on dialup adn you are writing code on a server and loose connection you can reconnect and re=attach to your screen session) example: ssh foo foo> screen foo> cat /dev/zero& bunches of zeros! foo> screen -d OR close xterm new term: > ssh foo foo> screen -d -RR bunches of zeros! from original session Screen is a virtual Terminal it rocks and It's one othe those programs that after you start using it you wonder how you ever lived without it! ( I sure do! ). Other great thing is mutiple virtual terminals in a single term (C-a c, C-a n) if you are gonna fork then I would reccomend a nice module called Parallel::ForkManager enjoy!	[reply]
Re: problems with fork by perlplexer (Hermit) on May 15, 2002 at 12:26 UTC
You need to daemonize the child process. perlipc has a nice and easy to understand example of doing that : Complete Dissociation of Child from Parent --perlplexer	[reply]
Re: problems with fork by BazB (Priest) on May 15, 2002 at 20:49 UTC
If you want to fork, have a look at BrentDax's ForkBlock, in particular the phork subroutine which does a fork and retries temporary errors, to see how to do it. IIRC, there is similar code in The Camel. Cheers. BazB.	[reply]


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