4 ms·

I know this article is for Windows, but if you're wondering if there's a way to do this on Linux, there is: https://strace.io/ https://strace.io/ https://gith

I know this article is for Windows, but if you're wondering if there's a way to do this on Linux, there is: https://strace.io/ https://strace.io/ https://github.com/nelhage/reptyr https://github.com/nelhage/reptyr https://github.com/crigler/dtach https://github.com/crigler/dtach https://github.com/jerome-pouiller/reredirect https://github.com/jerome-pouiller/reredirect https://github.com/pasky/retty https://github.com/pasky/retty

jmclnx 11mo ago
Thanks, links saved. Then there is this method, but I guess that article refers to no redirection output. If in background or via cron, I always redirect. But this is for UN*X type systems with a tail that supports '-f' $ prog > /tmp/log.txt 2>&1 & Then $ tail -f /tmp/log.txt Just so happens, I actually used this the other day for a long running process on OpenBSD :)
- hmng 11mo ago
  Isn't that what tee is for? Like $ prog | tee /tmp/log.txt
  - gosub100 11mo ago
    That's if you start the process with advance knowledge that you'll want to tail the output and log it. Not if you want to view the output of an existing process
    - hmng 11mo ago
      Yes, but I was replying to the above, using redirection and tail -f.
  - jmclnx 11mo ago
    When I submit a process to bg, I mostly use cron and I do not care about seeing output during runtime. So, tail suites my needs in the rare cases something unexpected seems to be happening.
- smcameron 11mo ago
  Can't you just read from /proc/pid/fd/0 ?
  - irishcoffee 11mo ago
    This was my first thought as well. I assume somehow I'm the dummy that doesn't understand the question.
  - jmclnx 11mo ago
    OpenBSD does not have a /proc file system.
glhaynes 11mo ago
I assume roughly the same caveats would apply, though? Buffering might be set wrong (and have no mechanism to be updated because the program never checks again), etc.
maxjohan 11mo ago
Is there a way to read from present tty? In practice: I boot into tty and manually start the graphical session (Wayland/Sway). I occasionally get (non-Sway) warnings when I return to tty (eg close the window manager). But the output is always scuffed, so I can't read the whole log. The lines get printed on top of each other or something. Is there a way to read everything from tty, from within the tty? Neither of the methods below work, because the warnings/errors aren't produced by Sway itself, but some other OS module/component. $ sway |& tee /tmp/sway.log $ tail -f /tmp/sway.log
- yjftsjthsd-h 11mo ago
  It might be useful to try and figure out what's logging the messages. However, if it was me, I'd strongly consider just starting from your shell in the tty, then running tmux, then starting sway, then attaching to tmux from a terminal emulator.
  - maxjohan 11mo ago
    Thanks for your reply! I've thought about that as well. Haven't tried it though. Two thoughts about it: 1. Running graphical from within tmux feels unsafe (?). Introducing another layer can't be the way to go. BUT this comes from a position of limited knowledge, so I might stand corrected on this one. Also, doing it once for debugging won't do any harm. 2. I'm pretty sure the errors are not printed by Sway itself, but some other OS module. Errors that Sway cause for other modules won't be included in the Sway log. So the problem remains, no?
- toast0 11mo ago
  If things are printed on top of each other, try script? https://man.freebsd.org/cgi/man.cgi?query=script&apropos=0&sektion=1&manpath=FreeBSD+15.0-RELEASE+and+Ports&arch=default&format=html https://man.freebsd.org/cgi/man.cgi?query=script&apropos=0&s... But, if you're getting console debugs from the kernel, that wouldn't be captured either... Otoh, debug output from the kernel should also go into logs or dmesg or something? You'll capture everything and maybe be able to figure it out from there?
baobun 11mo ago
This prompted me to ask the crowd about a similar use-case of editing your command line as it's already running your command https://news.ycombinator.com/item?id=46234678 https://news.ycombinator.com/item?id=46234678
zaius 11mo ago
Here's my method using GDB from many years ago: https://gist.github.com/zaius/782263 https://gist.github.com/zaius/782263
mzs 11mo ago
vxworks 6.x: (one login session, say over serial) -> ioTaskStdGet 0, 1 value = 3 = 0x3 -> taskIdSelf value = 13600784 = 0xcf8810 (another session, say over telnet) -> ioTaskStdSet 0xcf8810, 1, 0x9 value = 0 = 0x0 (first session ie SERIAL) -> printf "foo\n" -> taskIdSelf -> i (otherone eg TELNET) -> foo value = 4 = 0x4 value = 13600784 = 0xcf8810 NAME ENTRY TID PRI STATUS PC SP ERRNO DELAY ---------- ------------ -------- --- ---------- -------- -------- ------- ----- ... teeheeheehaw!

jmclnx 11mo ago

Thanks, links saved. Then there is this method, but I guess that article refers to no redirection output. If in background or via cron, I always redirect. But this is for UN*X type systems with a tail that supports '-f' $ prog > /tmp/log.txt 2>&1 & Then $ tail -f /tmp/log.txt Just so happens, I actually used this the other day for a long running process on OpenBSD :)

hmng 11mo ago
Isn't that what tee is for? Like $ prog | tee /tmp/log.txt
- gosub100 11mo ago
  That's if you start the process with advance knowledge that you'll want to tail the output and log it. Not if you want to view the output of an existing process
  - hmng 11mo ago
    Yes, but I was replying to the above, using redirection and tail -f.
- jmclnx 11mo ago
  When I submit a process to bg, I mostly use cron and I do not care about seeing output during runtime. So, tail suites my needs in the rare cases something unexpected seems to be happening.
smcameron 11mo ago
Can't you just read from /proc/pid/fd/0 ?
- irishcoffee 11mo ago
  This was my first thought as well. I assume somehow I'm the dummy that doesn't understand the question.
- jmclnx 11mo ago
  OpenBSD does not have a /proc file system.

glhaynes 11mo ago

I assume roughly the same caveats would apply, though? Buffering might be set wrong (and have no mechanism to be updated because the program never checks again), etc.

maxjohan 11mo ago

Is there a way to read from present tty? In practice: I boot into tty and manually start the graphical session (Wayland/Sway). I occasionally get (non-Sway) warnings when I return to tty (eg close the window manager). But the output is always scuffed, so I can't read the whole log. The lines get printed on top of each other or something. Is there a way to read everything from tty, from within the tty? Neither of the methods below work, because the warnings/errors aren't produced by Sway itself, but some other OS module/component. $ sway |& tee /tmp/sway.log $ tail -f /tmp/sway.log

yjftsjthsd-h 11mo ago
It might be useful to try and figure out what's logging the messages. However, if it was me, I'd strongly consider just starting from your shell in the tty, then running tmux, then starting sway, then attaching to tmux from a terminal emulator.
- maxjohan 11mo ago
  Thanks for your reply! I've thought about that as well. Haven't tried it though. Two thoughts about it: 1. Running graphical from within tmux feels unsafe (?). Introducing another layer can't be the way to go. BUT this comes from a position of limited knowledge, so I might stand corrected on this one. Also, doing it once for debugging won't do any harm. 2. I'm pretty sure the errors are not printed by Sway itself, but some other OS module. Errors that Sway cause for other modules won't be included in the Sway log. So the problem remains, no?
toast0 11mo ago
If things are printed on top of each other, try script? https://man.freebsd.org/cgi/man.cgi?query=script&apropos=0&sektion=1&manpath=FreeBSD+15.0-RELEASE+and+Ports&arch=default&format=html https://man.freebsd.org/cgi/man.cgi?query=script&apropos=0&s... But, if you're getting console debugs from the kernel, that wouldn't be captured either... Otoh, debug output from the kernel should also go into logs or dmesg or something? You'll capture everything and maybe be able to figure it out from there?

baobun 11mo ago

This prompted me to ask the crowd about a similar use-case of editing your command line as it's already running your command https://news.ycombinator.com/item?id=46234678 https://news.ycombinator.com/item?id=46234678

zaius 11mo ago

Here's my method using GDB from many years ago: https://gist.github.com/zaius/782263 https://gist.github.com/zaius/782263

mzs 11mo ago

vxworks 6.x: (one login session, say over serial) -> ioTaskStdGet 0, 1 value = 3 = 0x3 -> taskIdSelf value = 13600784 = 0xcf8810 (another session, say over telnet) -> ioTaskStdSet 0xcf8810, 1, 0x9 value = 0 = 0x0 (first session ie SERIAL) -> printf "foo\n" -> taskIdSelf -> i (otherone eg TELNET) -> foo value = 4 = 0x4 value = 13600784 = 0xcf8810 NAME ENTRY TID PRI STATUS PC SP ERRNO DELAY ---------- ------------ -------- --- ---------- -------- -------- ------- ----- ... teeheeheehaw!