远程运行(通过ssh)时，perl fork无法正常工作 [英] perl fork doesn't work properly when run remotely (via ssh)

问题描述

我有一个perl脚本script.pl，该脚本在运行时会进行派生，父进程将其pid输出到文件，然后退出，而子进程将某些东西输出到STOUT，然后进入while循环.

$pid = fork();

if ( ! defined $pid ) 
{
    die "Failed to fork.";
}
#Parent process
elsif($pid)
{
    if(!open (PID, ">>running_PIDs"))
    {
        warn "Error opening file to append PID";
    }
    print PID "$pid  \n";
    close PID;
}
#child process
else
{
    print "Output started";

    while($loopControl)     
    {
           #Do some stuff
    }
}

当我在本地调用它时效果很好，即:perl script.pl.

该脚本打印出一些内容，然后将控制权返回给Shell. (而子进程在后台进入其循环).

但是，当我通过ssh控件调用它时，它永远不会返回到外壳程序(也从未打印过输出开始"行).

即: $ ssh [e-mail]'perl script.pl'

但是，有趣的是，子进程确实在运行(键入ps时可以看到它).

任何人都可以解释发生了什么事吗?

我在调试下运行它，并得到了它:

###分叉，但不知道如何创建新的TTY.

由于两个调试器争用相同的TTY，因此输入会被严重纠缠.

我知道如何在xterms中将输出切换到其他窗口 和OS/2控制台.对于手动切换，请输入创建的TTY的名称 在$ DB :: fork_TTY中，或定义一个函数DB :: get_fork_TTY()返回此值.

在类似UNIX的系统上，可以获取给定窗口的TTY名称 通过输入tty，并通过睡眠1000000断开外壳与TTY的连接.

解决方案

每当通过非交互式ssh命令启动后台作业时，都需要关闭或以其他方式阻止stdin，stdout和& stderr.否则，ssh将等待后台进程退出. 常见问题解答.. >

这称为与控制终端解除关联或分离，这是编写后台作业(不仅限于SSH)​​时的一般最佳做法.

因此，不会使整个命令静音的最简单的更改是添加:

#close std fds inherited from parent
close STDIN;
close STDOUT;
close STDERR;

就在print "Output started";之后.如果您的子进程需要在运行过程中定期打印输出，那么您将需要重定向到日志文件.

I have a perl script, script.pl which, when run, does a fork, the parent process outputs its pid to a file then exits while the child process outputs something to STOUT and then goes into a while loop.

$pid = fork();

if ( ! defined $pid ) 
{
    die "Failed to fork.";
}
#Parent process
elsif($pid)
{
    if(!open (PID, ">>running_PIDs"))
    {
        warn "Error opening file to append PID";
    }
    print PID "$pid  \n";
    close PID;
}
#child process
else
{
    print "Output started";

    while($loopControl)     
    {
           #Do some stuff
    }
}

This works fine when I call it locally ie: perl script.pl.

The script prints out some things then returns control back to the shell. (while the child process goes off into its loop in the background).

However, when I call this via ssh control is never returned back to the shell (nor is the "Output started" line ever printed.

ie: $ ssh [e-mail] 'perl script.pl'

However, the interesting thing is, the child process does run (I can see it when I type ps).

Can anyone explain whats going on?

EDIT:

I ran it under debug and got this:

### Forked, but do not know how to create a new TTY.

Since two debuggers fight for the same TTY, input is severely entangled.

I know how to switch the output to a different window in xterms and OS/2 consoles only. For a manual switch, put the name of the created TTY in $DB::fork_TTY, or define a function DB::get_fork_TTY() returning this.

On UNIX-like systems one can get the name of a TTY for the given window by typing tty, and disconnect the shell from TTY by sleep 1000000.

解决方案

Whenever you launch background jobs via non-interactive ssh commands, you need to close or otherwise tie off stdin, stdout, & stderr. Otherwise ssh will wait for the backgrounded process to exit. FAQ.

This is called disassociating or detaching from the controlling terminal and is a general best practice when writing background jobs, not just for SSH.

So the simplest change that doesn't mute your entire command is to add:

#close std fds inherited from parent
close STDIN;
close STDOUT;
close STDERR;

right after your print "Output started";. If your child process needs to print output periodically during its run, then you'll need to redirect to a log file instead.

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