For example, I started some process that works and produces quite a lot of text in stdout. I understand that I don’t have time to read the whole flow of text, but I know how to filter what I need.

Is it possible to redirect an already running process from stdout, for example to | grep somefilter | grep somefilter or | less | less ? How to do it?

(It is clear that you can stop and restart, but in some cases this is unacceptable.)

  • one
    So go? Those. redirect to a file, and then tailf on it and do what we need. Maybe you can immediately shove the team, but this is not to me) - BOPOH
  • stackoverflow.com/questions/593724/… - fghj
  • @ user1034749 thanks, I'll test it tomorrow, I didn't have time today. - Nick Volynkin ♦

1 answer 1

translation of the answer Redirect STDERR / STDOUT of a process AFTER it's been started, using the command line? :

  • connect to the process with the gdb program and execute commands in it ( /dev/null here as an example; substitute the name of the real file):
    • p dup2 (open ("/ dev / null", 0), 1)
    • p dup2 (open ("/ dev / null", 0), 2)
    • detach
    • quit

example:

 $ tail -f /var/log/lastlog & [1] 5636 $ ls -l /proc/5636/fd total 0 lrwx------ 1 myuser myuser 64 Feb 27 07:36 0 -> /dev/pts/0 lrwx------ 1 myuser myuser 64 Feb 27 07:36 1 -> /dev/pts/0 lrwx------ 1 myuser myuser 64 Feb 27 07:36 2 -> /dev/pts/0 lr-x------ 1 myuser myuser 64 Feb 27 07:36 3 -> /var/log/lastlog $ gdb -p 5636 GNU gdb 6.8-debian Copyright (C) 2008 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html> This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. Type "show copying" and "show warranty" for details. This GDB was configured as "x86_64-linux-gnu". Attaching to process 5636 Reading symbols from /usr/bin/tail...(no debugging symbols found)...done. Reading symbols from /lib/librt.so.1...(no debugging symbols found)...done. Loaded symbols for /lib/librt.so.1 Reading symbols from /lib/libc.so.6...(no debugging symbols found)...done. Loaded symbols for /lib/libc.so.6 Reading symbols from /lib/libpthread.so.0...(no debugging symbols found)...done. [Thread debugging using libthread_db enabled] [New Thread 0x7f3c8f5a66e0 (LWP 5636)] Loaded symbols for /lib/libpthread.so.0 Reading symbols from /lib/ld-linux-x86-64.so.2...(no debugging symbols found)...done. Loaded symbols for /lib64/ld-linux-x86-64.so.2 (no debugging symbols found) 0x00007f3c8eec7b50 in nanosleep () from /lib/libc.so.6 (gdb) p dup2(open("/dev/null",0),1) [Switching to Thread 0x7f3c8f5a66e0 (LWP 5636)] $1 = 1 (gdb) p dup2(open("/dev/null",0),2) $2 = 2 (gdb) detach Detaching from program: /usr/bin/tail, process 5636 (gdb) quit $ ls -l /proc/5636/fd total 0 lrwx------ 1 myuser myuser 64 Feb 27 07:36 0 -> /dev/pts/0 lrwx------ 1 myuser myuser 64 Feb 27 07:36 1 -> /dev/null lrwx------ 1 myuser myuser 64 Feb 27 07:36 2 -> /dev/null lr-x------ 1 myuser myuser 64 Feb 27 07:36 3 -> /var/log/lastlog lr-x------ 1 myuser myuser 64 Feb 27 07:36 4 -> /dev/null lr-x------ 1 myuser myuser 64 Feb 27 07:36 5 -> /dev/null
  • Cool! And instead of /dev/null you can advise opening a fifo with a command previously connected to it in the background (for example, grep ) - avp