view output of already running processes in linux

There is already an program that uses ptrace(2) in linux to do this, retty:

http://pasky.or.cz/dev/retty/

It works if your running program is already attached to a tty, I do not know if it will work if you run your program in background.

At least it may give some good hints. :)

You can probably retreive the exit code from the program using ptrace(2), otherwise just attach to the process using gdb -p <pid>, and it will be printed when the program dies.

You can also manipulate file descriptors using gdb:

(gdb) p close(1)$1 = 0(gdb) p creat("/tmp/stdout", 0600)$2 = 1

http://etbe.coker.com.au/2008/02/27/redirecting-output-from-a-running-process/

You could try to hook into the /proc/[pid]/fd/[012] triple, but likely that won't work.

Next idea that pops to my mind is strace -p [pid], but you'll get "prittified" output. The possible solution is to strace yourself by writing a tiny program using ptrace(2) to hook into write(2) and writing the data somewhere. It will work but is not done in just a few seconds, especially if you're not used to C programming.

Unfortunately I can't think of a program that does precisely what you want, which is why I give you a hint of how to write it yourself. Good luck!