I am getting this message on the console of my AlmaLinux 9 host: [31178.107847] (NULL device *): port 1 already used(dev 6/1/4 stat 2 I've tried to google pieces of the message but getting no where. What is this message trying to tell me? It repeats every 10 seconds so I assume its important

In this context, an 'exception' is an undesirable scenario, which could be: a code-level signal (like SIGSEGV), incorrect ways of launching an app (like launching a command-line app as a daemon) etc. For a command-line app, the way to report exceptions to the user is by outputting to stderr - no doubts here. For a GUI app using GTK, an error window displayed using GTK's [MessageDialog](https://docs.gtk.org/gtk3/class.MessageDialog.html) can be used. But what if the MessageDialog fails, either due to unstable state of the app (SIGSEGV or SIGBUS may not have any recovery) or the API itself failed... in that case, how can a GUI app inform the user? Finally, a daemon... A daemon needs to inform user either due to a code-level exception (signals) or an external exception - user could launch a command-line app as a daemon, which is not a desirable way of launch, since a command-line app would've exited after its task is completed, but a daemon is expected to run for a long time. The command-line app could detect it was launched as a daemon and inform the user that it was launched incorrectly, but output to stderr does nothing here... how can a command-line app launched as daemon inform user that it was launched incorrectly? The main question is, how can each of these apps communicate with the user in the above mentioned scenarios? What is Linux's recommendation? PS: I'm new to Linux and app development in Linux.

Using either docker logs foo | less or docker logs foo 2>&1 | less produces readable text, but only with the stderr redirect can one scroll or type /somepattern and obtain matches. Without it, searching gives "Nothing to search (press RETURN)" and a column of ~'s. Given that stderr and stdout aren't the same, why does less show them the same until I start doing something in less? This may be some weird multi-window vim thing that I just don't understand. Thoughts?

I run a Windows command line program (that I can not make accessible) with wine. It apparently writes something to stdout and I'm trying to capture that output, but I can't redirect it. No matter if I redirect stdout or stderr to a file, the program output is still printed on the console and is not written to the file. When I redirect stderr, the wine output goes away, but the program's output is stilled printed on screen. wine program.exe > out # File is empty, program output printed on screen wine program.exe 2> out # Wine output gets redirected to file, program output still printed on screen If I redirect both, the output is neither printed on screen nor written to the file. **Edit:** On Windows, behavior is similar, but when redirecting both, everything is still printed on screen. Here are some examples with the complete output. $ wine program.exe fixme:winediag:start_process Wine Staging 1.9.23 is a testing version containing experimental patches. fixme:winediag:start_process Please mention your exact version when filing bug reports on winehq.org. output by program.exe fixme:msvcrt:__clean_type_info_names_internal (0x100aaa54) stub When I try to redirect the output, this happens: $ wine program.exe > out 2>&1 $ cat out fixme:winediag:start_process Wine Staging 1.9.23 is a testing version containing experimental patches. fixme:winediag:start_process Please mention your exact version when filing bug reports on winehq.org. fixme:msvcrt:__clean_type_info_names_internal (0x100aaa54) stub I.e., the program's console output is completely missing. The program still works fine and writes some files it's supposed to write. As a check, I did the same with pngcrush, and I get what I'd expect. Without redirection: $ wine pngcrush_1_8_10_w32.exe test.png out.png fixme:winediag:start_process Wine Staging 1.9.23 is a testing version containing experimental patches. fixme:winediag:start_process Please mention your exact version when filing bug reports on winehq.org. | pngcrush-1.8.10 | Copyright (C) 1998-2002, 2006-2016 Glenn Randers-Pehrson | Portions Copyright (C) 2005 Greg Roelofs | This is a free, open-source program. Permission is irrevocably | granted to everyone to use this version of pngcrush without | payment of any fee. | Executable name is pngcrush_1_8_10_w32.exe | It was built with bundled libpng-1.6.26 | and is running with bundled libpng-1.6.26 | Copyright (C) 1998-2004, 2006-2016 Glenn Randers-Pehrson, | Copyright (C) 1996, 1997 Andreas Dilger, | Copyright (C) 1995, Guy Eric Schalnat, Group 42 Inc., | and bundled zlib-1.2.8.1-motley, Copyright (C) 1995 (or later), | Jean-loup Gailly and Mark Adler, | and using "clock()". | It was compiled with gcc version 4.8.0 20121015 (experimental). Recompressing IDAT chunks in test.png to out.png Total length of data found in critical chunks = 431830 Critical chunk length, method 1 (ws 15 fm 0 zl 4 zs 0) = 495979 Critical chunk length, method 2 (ws 15 fm 1 zl 4 zs 0) > 495979 Critical chunk length, method 3 (ws 15 fm 5 zl 4 zs 1) = 495354 Critical chunk length, method 6 (ws 15 fm 5 zl 9 zs 0) = 457709 Critical chunk length, method 9 (ws 15 fm 5 zl 2 zs 2) > 457709 Critical chunk length, method 10 (ws 15 fm 5 zl 9 zs 1) = 451813 Best pngcrush method = 10 (ws 15 fm 5 zl 9 zs 1) = 451813 (4.63% critical chunk increase) (4.63% filesize increase) CPU time decode 4.407583, encode 17.094248, other 4294967296.000000, total 17.180143 sec With redirection: $ wine pngcrush_1_8_10_w32.exe test.png out.png > out 2>&1 $ cat out fixme:winediag:start_process Wine Staging 1.9.23 is a testing version containing experimental patches. fixme:winediag:start_process Please mention your exact version when filing bug reports on winehq.org. | pngcrush-1.8.10 | Copyright (C) 1998-2002, 2006-2016 Glenn Randers-Pehrson | Portions Copyright (C) 2005 Greg Roelofs | This is a free, open-source program. Permission is irrevocably | granted to everyone to use this version of pngcrush without | payment of any fee. | Executable name is pngcrush_1_8_10_w32.exe | It was built with bundled libpng-1.6.26 | and is running with bundled libpng-1.6.26 | Copyright (C) 1998-2004, 2006-2016 Glenn Randers-Pehrson, | Copyright (C) 1996, 1997 Andreas Dilger, | Copyright (C) 1995, Guy Eric Schalnat, Group 42 Inc., | and bundled zlib-1.2.8.1-motley, Copyright (C) 1995 (or later), | Jean-loup Gailly and Mark Adler, | and using "clock()". | It was compiled with gcc version 4.8.0 20121015 (experimental). Recompressing IDAT chunks in test.png to out.png Total length of data found in critical chunks = 431830 Critical chunk length, method 1 (ws 15 fm 0 zl 4 zs 0) = 495979 Critical chunk length, method 2 (ws 15 fm 1 zl 4 zs 0) > 495979 Critical chunk length, method 3 (ws 15 fm 5 zl 4 zs 1) = 495354 Critical chunk length, method 6 (ws 15 fm 5 zl 9 zs 0) = 457709 Critical chunk length, method 9 (ws 15 fm 5 zl 2 zs 2) > 457709 Critical chunk length, method 10 (ws 15 fm 5 zl 9 zs 1) = 451813 Best pngcrush method = 10 (ws 15 fm 5 zl 9 zs 1) = 451813 (4.63% critical chunk increase) (4.63% filesize increase) CPU time decode 4.339310, encode 17.137527, other 4.294083, total 17.182100 sec What could be the cause of that not working for the other program? wine stdout stderr io-redirection

I want to do a simple grep on dumpe2fs output but I keep seeing dumpe2fs 1.46.5 (30-Dec-2021) showing up after my grep:

$ sudo dumpe2fs -h /dev/sdb2 | grep 'Block count:'
dumpe2fs 1.46.5 (30-Dec-2021)
Block count:              1247300

But if I redirect stderr of dumpe2fs to stdout using |& then it will just work fine as expected:

$ sudo dumpe2fs -h /dev/sdb2 |& grep 'Block count:'
Block count:              1247300

The question is why dumpe2fs is writing version number dumpe2fs 1.46.5 (30-Dec-2021) to stderr?!

Is there an official POSIX, GNU, or other guideline on where progress reports and logging information (things like "Doing foo; foo done") should be printed? Personally, I tend to write them to stderr so I can redirect stdout and get only the program's actual output. I was recently told that this is not good practice since progress reports aren't actually errors and only error messages should be printed to stderr. Both positions make sense, and of course you can choose one or the other depending on the details of what you are doing, but I would like to know if there's a commonly accepted standard for this. I haven't been able to find any specific rules in POSIX, the GNU coding standards, or any other such widely accepted lists of best practices. We have a few similar questions, but they don't address this exact issue: * https://unix.stackexchange.com/q/79315/22222 : The accepted answer suggests what I tend to do, keep the program's final output on stdout and anything else to stderr. However, this is just presented as a user's opinion, albeit supported by arguments. * https://unix.stackexchange.com/q/8813/22222 : This is specific to help messages but cites the GNU coding standard. This is the sort of thing I'm looking for, just not restricted to help messages only. So, are there any official rules on where progress reports and other informative messages (which aren't part of the program's actual output) should be printed?

Consider the following: command1 | command2 | command3 As I understand pipelines every command is run regardless of any errors which may occur. When a command returns stderr, it is not piped to the next command, but the next one is still run (unless you use |&). I want any error which may occur to terminate the rest of the pipeline. I thought set -o pipefail would accomplish this, but it simply terminates anything which may come after the pipeline if anything in the pipeline failed, ie: (set -o pipefail; cmd1 | cmd2 && echo "I won't run if any of the previous commands fail") So, What is the most succinct way terminate the **rest** of the pipeline if any of its commands fail? I also need it to exit with the proper stderr of the command which failed. I'm doing this from a command-line context, not a shell script, hence why I'm looking for brevity. Thoughts?

I want to set my terminal up so stderr is printed in a different color than stdout; maybe red. This would make it easier to tell the two apart. Is there a way to configure this in .bashrc? If not, is this even possible? - - - **Note**: This question was merged with [another](https://unix.stackexchange.com/q/53563/22565) that asked for stderr, stdout *and the user input echo* to be output in *3 different colours*. Answers may be addressing either question.

I'm writing some application code that is used to execute Linux shell commands, and it then logs the command details into an SQL database. This includes the output of STDOUT + STDERR (separately). After the command has been executed, and assuming the process didn't output anything... could there be any reason to leave the STDOUT/STDERR fields as NULL -vs- setting them to be empty strings? To put the question another way: is there technically any difference between these two things? - A process that doesn't output anything to STDOUT - A process that outputs an empty string to STDOUT (and nothing else) And to put the question another way again... does it make sense to make these columns NOT NULL in SQL?

I'm redirecting stdout and stderr to the same file by using > and >> respectively:

rsync -a --exclude cache/ src_folder/ target_folder/ 1>out_err.log 2>>out_err.log

However the stderror is not logged in the file. What happens to the stderror when using >> instead of > to redirect both to the same file? My intention was to write stdout to a new file and then append stderr to that same file.

In zsh, how can I annotate each line in a file to which both stdout and stderr have been redirected with the line's source (stdout or stderr)? I want output with the source name prepended to the line, like:

stdout: 
stderr:

Having a bash script that essential only doing:

mbuffer --md5 -i dummy.tar -o /dev/null

A user of this script wants to use tee and store the output messages in a log file.

./script.sh 2>&1 | tee log.txt

Everything is visible on terminal but nothing is written to log.txt. How can I do to get output on both terminal and in file? Just running in a terminal winds up the same, nothing in log.txt:

mbuffer --md5 -i dummy.tar -o /dev/null 2>&1 | tee log.txt

Tried on Ubuntu and Rocky Linux. Also tried

stdbuf -e 0 -o 0 mbuffer --md5 -i dummy.tar -o /dev/null 2>&1 | tee log.txt

I want to extend question [How to store standard error in a variable](https://stackoverflow.com/q/962255/1455694) and get general solution (bash function or functions) to extract from the called function/command together with standard error also all other possible outcomes. The function should capture and return as vars for the called function/command the following: - stderr - stdout - result string out var - return code API for the function should be convenient to use. --- Example of test function that produces all different output results:

func_to_test_all_outs() {
    local param="${1:?}"; shift
    local -n out_result=${1:?}; shift

    echo "test error output" >&2
    echo "test normal output"

    out_result=""
    if [[ "$param" = "return_string_result" ]]; then
        out_result="result string"
    fi

    return 3
}

More comprehensive/general example of test function that produces all different output results including spawning background processes to produce stout and stderro, interleaving stdout/stderr output, and including leading/trailing/mid white space plus potential command injection, variable expansion, and globbing chars in output streams and does redirection of FD3 in case the calling script relies on that:

func_to_test_all_outs() {
    local param="${1:?}"; shift
    local -n out_result=${1:?}; shift

    ( sleep 2; printf '\n   first  \n$RANDOM *\nerror output\n' >&2; ) &
    exec 3>&1
    printf ' first  \n$(date)\n*\nnormal output\n\n' >&3

    exec 3>&2
    printf '\nsecond $RANDOM *\nerror output\n\n\n' >&3
    ( sleep 2; printf 'second\ntest\n$(date)\n*\nnormal output\n\n' ) &

    ( printf 'third\n$(date)\n*\nnormal output\n\n' ) &

    out_result=""
    if [[ "$param" = "return_string_result" ]]; then
        printf -v out_result '\n\nresult\t\n\nstring\n\n\n'
    fi

    return 127
}

I have a bash script like this: #!/bin/bash while read -r -a line do ... parse $line in some way done This script is executed by piping the command from another program: some-random-program | myscript.sh This works as long as some-random-program sends its output to stdout. However, if the script sends output to stderr, then my script sees no output. I know I can do this: some-random-program 2>&1 | myscript.sh **My question is this:** is there a way to get myscript.sh to read from stderr so that the "2>&1" (or any variation of it) *is not necessary*? I thought I could do this: while read -r -a line do ... parse $line in some way done < /dev/stderr But that didn't work. The script never sees any input.

Where are stdin, stdout, and stderr (the fds) **first** opened? Is it the kernel that does it? And when and where are the symlinks /dev/std{in,out,err} made? Where is the code that does it? I assume it is in the linux kernel source code but I wasn't able to find where it happens even after a search in the archlinux 6.5.3-arch1-1 linux kernel github repo. edit: please, if you are downvoting this question can you explain why so I can make it better? I would really like to know about this question. It is not easy to find the answer.

I'm writing a program that needs to pull in the clang include paths. Thanks to Dump include paths from g++ I'm half-way there. The command I'm using is: clang++ -E -x c++ - -v stdout.txt clang++ -E -x c++ - -v stderr.txt So where is the output being redirected to and what command do I need to execute to properly store off the information that is printed to console?