Questions tagged [fifo]
Questions about FIFO - first-in first-out special file, also known named pipe
246
questions
0
votes
0
answers
33
views
Strange incongruent output for both nc and fifo
I have this exact code:
#!/bin/bash
gtimeout(){
if type -f gtimeout &> /dev/null; then
command gtimeout "$@"
else
timeout "$@"
fi
}
export -f gtimeout;
...
- 9,718
0
votes
0
answers
10
views
Simulating control characters such as "H key" , "UP arrow key" , etc
I have a Device 1 which has debian OS installed on it. I access the serial console of it through other device i.e. Device 2 . I have scripts on the device 2 which will uninstall and install different ...
- 101
0
votes
1
answer
157
views
Continuously polling a named (FIFO) pipe
I am trying to use a named pipe to monitor the activity of a running shell script. That shell script will write to the pipe that it has "Started" processing. When it has completed ...
- 1
0
votes
0
answers
48
views
Simultaneous input from fifo and terminal in bash
I am running ffmpeg inside a script and I want to be able to quit ffmpeg either by pressing 'q' in the terminal it's running in (default behaviour) or by inputting 'q' into a fifo file, whichever I ...
1
vote
1
answer
199
views
send (alsa) audio via network via UDP
This to my understanding records mono in wav format for 300 seconds to a named pipe called "mic_rec"
rec arecord -D hw:4,0 -d 300 -f cd -t wav -c 1 mic_rec
And this sends whatever it finds ...
- 153
1
vote
1
answer
63
views
Allow a sudo sub process to update Zenity running as original user
A script run by user 'staffer' runs zenity --progress.
It then calls sudo -u adminBod adminScript (and the STDOUT and STDERR are collected to logger)
I want adminScript which is running as adminBod to ...
- 2,849
0
votes
1
answer
138
views
Filtering log statements before they're written
I have an application I need to run in verbose mode to get the information I'm interested in. This produces an enormous log file that is <1% interesting for my requirements.I want some way of ...
- 1,968
0
votes
0
answers
29
views
How to implement lossy buffering? [duplicate]
I want to capture log data and analyze it in real time. Specifically the output of mysql's slow query log. However this needs to be minimally invasive.
Pointing the source to a FIFO rather than a ...
- 5,203
2
votes
2
answers
58
views
Process not showing under ps -ef | grep command
I ran a command in shell
cat >my1.fifo &
and when trying to find the PID it is not showing under
ps -ef | grep my1.fifo
- 101
0
votes
0
answers
50
views
Not able to give input to my telnet connection through fifo file if I run it from script
I have a python script which is sending commands to a fifo file through this command.
printf "command" > my1.fifo
An another process (telnet login) is taking input from this my1.fifo ...
- 101
0
votes
1
answer
297
views
Grant Permission to Run Process with FIFO
I am trying to run a program that sets its own scheduler policy to sched_FIFO, but it errors out saying operation not permitted. If I run it with sudo then it succeeds, but I want to reduce the ...
- 73
3
votes
2
answers
843
views
How do I attach a bash shell to a named pipe?
Let’s say I have two containers X and Y (two containers in the same Kubernetes pod, actually) that share a volume. On that volume is a named pipe /foo that I want attached to a bash process on ...
- 163
0
votes
2
answers
250
views
when read buffer size is 2048, it work , but buffer size is 48 or other number, write call will be blocked, why?
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/select.h>
#include <fcntl.h>
#include <unistd.h>
int main(int argc, char* argv[]){
if(...
1
vote
1
answer
639
views
Usage of named pipe as data source for netcat
I want to use netcat as a TCP-server that reads data from a named pipe. For that I did the following:
Step 1. Created a pipe and the server that uses it as a source
mkfifo /tmp/all.pipe
nc -k -l 8080 &...
- 1,235
3
votes
4
answers
157
views
Protect against vanishing output redirection targets
I have a daemon running on an embedded Linux device with its output redirected to the serial console:
my_daemon > /dev/ttyS0
But now if a user exits the shell running on the serial interface then ...
- 5,893
1
vote
1
answer
161
views
Process (mplayer) doesn't read from named pipe when started from webserver (lighttpd)
tl;dr
$ sudo -u www-data mplayer -slave -input file=/srv/mplayer.fifo -playlist /srv/list &
$ lsof /srv/mplayer.fifo | tail +2
mplayer 21059 www-data 4u FIFO 179,2 0t0 2359331 /srv/...
- 121
2
votes
2
answers
809
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 ...
2
votes
1
answer
888
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 &...
- 4,367
2
votes
0
answers
197
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
1k
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
987
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
...
- 583
3
votes
1
answer
596
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 ...
- 165
11
votes
2
answers
5k
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 ...
- 25.1k
-1
votes
1
answer
541
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
1k
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
0
votes
2
answers
125
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 ...
- 482
2
votes
2
answers
964
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&...
- 3,230
1
vote
0
answers
815
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 ...
- 168
2
votes
1
answer
325
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
29
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
62
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
106
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=&...
- 1,045
1
vote
1
answer
193
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 ...
- 2,477
4
votes
1
answer
76
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
234
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.
- 1,533
0
votes
2
answers
2k
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 ...
- 387
2
votes
1
answer
4k
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 ...
- 143
6
votes
2
answers
626
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 ...
- 175
0
votes
1
answer
482
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
354
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
2
votes
2
answers
1k
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
126
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
261
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 &...
- 4,367
1
vote
1
answer
1k
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="$(...
- 1,884
1
vote
1
answer
1k
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 ...
- 4,043
4
votes
1
answer
2k
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 ...
- 155
0
votes
0
answers
172
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
648
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
690
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 ...
- 18.7k
1
vote
0
answers
201
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