Questions tagged [fifo]
Questions about FIFO - first-in first-out special file, also known named pipe
232
questions
2
votes
2
answers
136
views
Reading from two fifos in Bash
I'm trying to read from two fifos (read from one, if there's no content read from the other, and if there's no content in neither of both try it again later), but it keeps blocking the process (even ...
1
vote
1
answer
65
views
bash IPC using named pipes
Consider the below script
#!/usr/bin/bash
chan=/tmp/pipe.$$
mkfifo $chan
{
for x in a b c d e
do
echo $x > $chan
done
} &
for y in 1 2 3 4 5
do
x=$(cat $chan)
echo &...
- 4,049
2
votes
1
answer
65
views
FIFO and simple bash parallelization on CentOS
I am having problems adapting a bash script to handle a simple parallel execution from Ubuntu 20.04 to CentOS Linux 8.
In the script I spawn multiple "readers" that read a string from a FIFO ...
- 21
0
votes
1
answer
226
views
Writing in the file descriptor of the child process (fd/0)
I'm playing with file descriptors in my CentOS 7 sandbox. In doing so, I noticed an interesting situation. Suppose we've a simple PHP script:
$step = 4 * 1024;
echo "php started\n";
while (!...
- 21
2
votes
1
answer
291
views
Bash named pipes, parallel commands and exit status
I'm trying to use a named pipe so I can keep stdout for status output from a long process. I could use stderr for status output, but I'd like to keep that for errors. Here is an example:
#!/bin/bash
...
- 328
2
votes
1
answer
46
views
Close all readers of a FIFO once all its input is read?
How can I close all readers of a FIFO once all its input is read? Seems I can only get one of them to close, which keeps my program from finishing.
Here's a sample program that works (to test put it ...
- 155
0
votes
0
answers
38
views
parsing concurrent logging from named pipe
I have an application written in C that uses fprintf to stdout/stderr for logging. The output I need is available only through the most verbose setting so the log file quickly becomes huge.
My ...
- 1,433
1
vote
1
answer
105
views
Detecting sound / silence on a sox pipe?
I am trying to keep a sox pipe input from a sound card open and execute a player commend only when there is sound in the pipe (without killing the pipe or using a file).
This could be easily achieved ...
- 11
10
votes
2
answers
3k
views
Linux named pipes: not as FIFO as thought
In short:
mkfifo fifo; (echo a > fifo) &; (echo b > fifo) &; cat fifo
What I expected:
a
b
since the first echo … > fifo should be the first to have opened the file, so I expect ...
- 8,825
-1
votes
1
answer
122
views
named pipe in bash script
I have a C program to experiment with signals (./signal). It processes the standard input, exits when reading a 'q' and reacts to signals.
I would like to test it with a bash script using a named pipe ...
- 415
5
votes
1
answer
404
views
How should I set up a systemd service to auto-start a server and let me pass commands to it?
Goal:
I'm trying to get a Minecraft server to run on computer boot with systemd on Fedora. I have a few self-imposed criteria that I need to meet to be able to properly manage my server(s):
It has to ...
- 55
-1
votes
2
answers
81
views
Do any shells generalize the notion of pipes to multiple parallel pipelines? Would supporting it require changes to the OS kernel?
Quite often, when working on the command line, I find myself specifying the same operation on a bunch of different instances specified by some input stream, and then wanting to recombine their outputs ...
- 369
2
votes
2
answers
264
views
Can we use $PIPESTATUS with the tee (or pee) command?
In my bash scripts, I often use pipes and would like to know which stage of the pipe was causing the problem in case of errors. The basic structure of such snippets is:
#!/bin/bash
ProduceCommand 2&...
- 2,213
1
vote
0
answers
187
views
Write firmware over /dev/ttyUSB0 to embedded device
I'm using the last example in: this post
I keep getting wctx:file length=0 after the sz command. I'm actually opening the serial connection with minicom Minicom is botching the transfer. So, after I ...
- 129
2
votes
1
answer
152
views
Can named pipes/FIFOs be used in a "cyclic" manner together with `tee`?
Why does the last line in this script gets stuck?
#!/usr/bin/env bash
trap 'rm -f numbers' EXIT
mkfifo numbers
decrement() {
while read -r number; do
echo "debug: $number" >&...
- 121
0
votes
0
answers
28
views
Using a ‘permanent’ named pipe as input to a program [duplicate]
I’ll admit I don’t fully understand named pipes. I’ve read everything I can about them, but I’m still not sure how to keep one ‘open’ for repeated use. Basically, I want to use a named pipe as input ...
- 101
1
vote
1
answer
37
views
Bash: Difference between paste command with Command Substiution vs. FIFO FDs
I'm just trying to understand why when I use a couple FIFO FDs in a paste command I get a 'Broken Pipe' but when I use Command Substitution everything is all good.
A little background: I have a need ...
- 21
1
vote
0
answers
45
views
bash script to lazy tar to fifo as files arrive
Here's the hypothetical scenario: I have an archival process where files are showing up and I append them to tar, and then the tar gets zipped. Something like this:
while sleep 1 ; do
new_files=&...
- 965
1
vote
1
answer
85
views
Using named pipe to get process substitution exit codes
I have a script with a fairly complex command with several process substitutions and I need to get the exit codes from the commands in the process substitutions. I'm trying to do so via a named pipe ...
- 2,127
4
votes
1
answer
66
views
What's wrong with this branched data flow using `tee`, fifos, and `paste`?
In the spirit of this question, I want to create a branched data flow from a single source:
cmd1 ──> tee ──────────────> │
├─────> cmd2 ─────> │ cmd4
└─────&...
- 141
0
votes
0
answers
45
views
zsh, zpty: How to read the output of a process after it has exited?
Start some command with zpty:
zpty -d x ; zpty x 'echo hi' ; sleep 1
How do I read its output now that it has exited?
zpty -r x
Returns 2, and this behavior seems expected per the manpage.
- 1,295
0
votes
2
answers
613
views
How can I read from named pipe line by line and exit?
I have the following bash script that I'd like to use as a fuzzy file opener. I create a fifo, spawn a new terminal with fzf running and redirect fzf's output to the fifo. I then call a function that ...
- 347
2
votes
1
answer
2k
views
Can multiple processes open a named pipe?
I'm creating a process that is going to publish data via a named pipe and I envision there being multiple subscribers. Is there some way my process can Tee off the named pipe it is wring too each time ...
- 123
5
votes
2
answers
335
views
coproc and named pipe behaviour under command substitution
I have a requirement to make a function in a zsh shell script, that is called by command substitution, communicate state with subsequent calls to the same command substitution.
Something like C's ...
- 165
-1
votes
1
answer
122
views
Send signal to paused parent process and guarantee that it will arrive AFTER the parent pauses
I have this kind of pseudo-code and i'm wishing to know what I must change in order to guarantee that the signal send to the parent will indeed arrive after that the parent pauses.
int main()
{
...
- 3
0
votes
0
answers
199
views
Program execution hanging when trying to use fgetc() over a file stream returned by fdopen() function
I'm making a program where I'm creating 3 sets of fifos (named pipes) to comunicate over processes, I have found where the execution is hanging but not why, and now I'm stuck.
I have identified that ...
- 3
1
vote
2
answers
505
views
FIFO-based semaphore explanation
I am trying to work on some parallelization of many processes (task send/to be executed on many (let's say hundreds) nodes).
I came across this solution:
https://unix.stackexchange.com/a/216475
# ...
2
votes
1
answer
70
views
Pipes and graphics
When developing a program (in C or Python, say), I often write debug messages to see whether my program behaves as intended. On Linux, such text messages can be handled in varied and flexible ways ...
- 121
1
vote
2
answers
141
views
Ordering output when two subshells write to stdout
I have a command of the below form
input | tee >(subshell) | mainshell
Both subshell and mainshell writes to stdout. So their output is not synchronised. E.g.
echo "Hello\nWorld" | tee &...
- 4,049
1
vote
1
answer
454
views
Redirect script stdin to file in the background
In order to pass my script's stdin to stdin of a command in an alacritty instance it spawns, I'm trying to redirect it to a file in the background (so that the command can start reading it):
t="$(...
- 1,608
1
vote
1
answer
647
views
The memory dump of a process by using GDB inside a bash script - errors, problems
I want to dump some program's memory segment to a file. Because the working time of my program is milliseconds, I use named pipe to stop its execution and dump its memory content by gdb meanwhile. The ...
- 3,730
4
votes
1
answer
1k
views
/proc/[pid]/fd/[0, 1, 2]: No such file or device - even though file exists
I'm trying to access a process' stdio streams from outside its parent process. I've found the /proc/[pid]/fd directory, but when I try
$ cat /proc/[pid]/fd/1
I get a No such file or device error. I ...
- 143
0
votes
0
answers
56
views
FIFO sometimes requires two writes to satisfy read
I found some baffling behavior on Ubuntu 18.04.4 LTS.
In one terminal, I'd like to write a private key to a FIFO.
$ mkfifo /tmp/fifo
$ chmod o-rwx /tmp/fifo
$ chmod g-rwx /tmp/fifo
$ cat id_rsa > /...
3
votes
0
answers
314
views
How to pipe all output streams to another process?
Take the following Bash script 3-output-writer.sh:
echo A >&1
echo B >&2
echo C >&3
Of course when ran as . 3-output-writer.sh it gets the error 3: Bad file descriptor, because ...
1
vote
1
answer
348
views
Trap SIGPIPE upon writing to FIFO
These are the steps to reproduce the problem.
writer:
#!/bin/bash
trap 'echo NoReader!' PIPE
cat > fifo
Open two terminals.
I will denote them by the >T1< and >T2< headers below,
and ...
- 17.4k
1
vote
0
answers
119
views
Is it possible to have SSH display an "active" banner, by running a script to generate the banner each time, rather than read a static file
The sshd_config banner directive reads a file, but I want it to run a script, and ideally personalize the banner to the user... is this possible with ssh, or is there a way I can create a device file ...
- 111
0
votes
2
answers
91
views
how to redirect a pending firefox download to a named pipe?
My router provides a live capture in an fancy web interface full of authentication and JS stuff. So if I capture the traffic firefox download a pcap file til I stop the job. I want to be able to see ...
- 11
1
vote
1
answer
1k
views
mkfifo with all permissions still errors with permissions denied for other user
Ubunbu 20.04
fifo pipe is created via a bash script from user A with: [[ ! -p $fifopath ]] && mkfifo $fifopath -m0777
This creates: prwxrwxrwx 1 A A 0 May 25 00:40 /tmp/somefifo
Then, if ...
- 111
2
votes
0
answers
149
views
Combine mkfifo and cp --reflink to append files without copying data
I have huge files {0..9}.bin which I want concatenate into out.bin. I don't need the original files afterwards. So I was wondering, if this is possible by only modifying the filesystem index without ...
- 165
1
vote
1
answer
307
views
Named pipe stdout redirection instead of numeric file descriptor
So I was fiddling around for hours now. I have the following problem:
I am running a command (node.js script) that writes to stdout via process.stdout.write. It is interactive and at one point it ...
- 113
1
vote
2
answers
60
views
How to read server stdout and continue only after message is outputted
Say I have a simple Node.js server like:
const http = require('http');
const server = http.createServer((req,res) => res.end('foobar'))
server.listen(3000, () => {
console.log(JSON....
user393961
1
vote
0
answers
103
views
Piping two audio FIFOs simultaneously, where one may not have data but takes priority, into a single FIFO output
I have a snapcast audio server, which is configured to have three audio streams (fifos): music, broadcast, and output. My speakers play the audio from the output stream, and my music players pipe ...
- 121
0
votes
1
answer
202
views
Command to create/connect to an I/O stream?
So I'm trying to connect to a (Lua) debugger embedded in a program by redirecting the I/O. Currently I create a pair of FIFOs for the read and write streams and connect to them using cat /tmp/...
- 101
3
votes
0
answers
938
views
Looking at the kernel logs to see if there is something wrong with my machine
My ubuntu machine slowed down, I was following these instructions:
https://askubuntu.com/questions/21632/slow-response-and-system-lag
the slowness I see is pretty uniform, and there's definitely a ...
- 8,308
0
votes
0
answers
64
views
Piping Multiple stdouts to Python program?
I have a program that prints in stdout and I'd like multiple instances of it where each instance's stdout is piped to a sed and then the result(of three such sed) piped to a python program. I'm doing ...
0
votes
1
answer
66
views
What is this code actually doing?
While doing a CTF challenge on a platform, I needed a reverse shell but couldn't get one working so I looked at the processes and found one reverse shell code:
rm /tmp/m;mkfifo /tmp/m;cat /tmp/m|/bin/...
- 301
2
votes
1
answer
3k
views
Why is `BrokenPipeError` dependent on the size of the piped stream?
The following script raises BrokenPipeError: [Errno 32] Broken pipe, when piped to a command like head (unless the number of lines to head exceeds the number of lines printed by the Python script).
...
- 1,749
2
votes
1
answer
48
views
Multiple Tracing Events Readers
Question
Does the tracing pipes in Linux, for tracing events, accepts simultaneous readers?
Context
I am trying to get traces from the RAS subsystem while running some benchmarks.
This subsystem ...
0
votes
1
answer
2k
views
Named pipe buffer after process end
I am creating named pipes in Ubuntu 18 and 16 environments in C language using gcc as compiler (mkfifo() and open()). One of the things I noticed that the named pipes remain in the filesystem after ...
- 101
1
vote
1
answer
231
views
GNU Parallel Python Semaphore
I have a Python script parallelized through GNU parallel which finds a certain result which I would like to output to a file, which I currently do through standard Python file IO. The issue is that I ...
