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Full Discussion: Send Foreground job to background redirecting output
Top Forums Shell Programming and Scripting Send Foreground job to background redirecting output Post 302403081 by Corona688 on Thursday 11th of March 2010 10:41:10 AM
Old 03-11-2010
Quote:
Originally Posted by jhullbuzz
@corona688 ok so it creates the output at the initial process call. what if i were to start it in the background with a logfile...is there a way to bring it into the FG?
I repeat: The shell cannot redirect output for a process that already exists. You can't just reach in and change a completely different process' file table for it.

The shell has to do all redirection for a new process before the new process is run -- it does this by creating a subshell, which does all redirection, then replaces itself with the new program but keeping I/O redirections intact. Once that's done, the new process controls its own output like any other program.

If you want to view the logfile as its written to, try 'tail -f logfile'. This will watch logfile for new lines and print them to standard output.

There's also the screen terminal/utility/shell/thing, which uses network sockets to do something similar to you want. It keeps sessions that you can connect and disconnect to without killing or halting them.
 

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LEARN ABOUT LINUX

bootlogd

BOOTLOGD(8)						Linux System Administrator's Manual					       BOOTLOGD(8)

NAME

       bootlogd - record boot messages

SYNOPSIS

       /sbin/bootlogd [-c] [-d] [-r] [-s] [-v] [ -l logfile ] [ -p pidfile ]

DESCRIPTION

       Bootlogd  runs in the background and copies all strings sent to the /dev/console device to a logfile. If the logfile is not accessible, the
       messages will be kept in memory until it is.

OPTIONS

       -d     Do not fork and run in the background.

       -c     Attempt to write to the logfile even if it does not yet exist.  Without this option, bootlogd will wait for the  logfile	to  appear
	      before attempting to write to it.  This behavior prevents bootlogd from creating logfiles under mount points.

       -r     If there is an existing logfile called logfile rename it to logfile~ unless logfile~ already exists.

       -s     Ensure  that the data is written to the file after each line by calling fdatasync(3).  This will slow down a fsck(8) process running
	      in parallel.

       -v     Show version.

       -l logfile
	      Log to this logfile. The default is /var/log/boot.

       -p pidfile
	      Put process-id in this file. The default is no pidfile.

BUGS

       Bootlogd works by redirecting the console output from the console device.  (Consequently bootlogd requires PTY support in the  kernel  con-
       figuration.)   It  copies that output to the real console device and to a log file.  There is no standard way of ascertaining the real con-
       sole device if you have a new-style /dev/console device (major 5, minor 1) so bootlogd parses the kernel  command  line	looking  for  con-
       sole=... lines and deduces the real console device from that.  If that syntax is ever changed by the kernel, or a console type is used that
       bootlogd does not know about then bootlogd will not work.

AUTHOR

       Miquel van Smoorenburg, miquels@cistron.nl

SEE ALSO

       dmesg(8),fdatasync(3).

								   Jul 21, 2003 						       BOOTLOGD(8)
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