Questions tagged [fifo]
Questions about FIFO - first-in first-out special file, also known named pipe
38
questions
16
votes
3
answers
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A virtual file containing the concatenation of other files
Is there a way of creating a filesystem object akin to this:
mknod files p
cat file1 file2 ... fileN > files
but such that it can be seeked in, as if it were a regular file?
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11
votes
3
answers
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What characterizes a file in Linux/Unix?
What characterizes a file in Linux/Unix?
A file can have many types: regular file, directory, symlink, device file, socket, pipe, fifo, and more that I miss. For example, a symlink:
$ sudo file /...
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21
votes
3
answers
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continuous reading from named pipe (cat or tail -f)
I have configured rsyslog to log certain log events to /dev/xconsole:
*.*;cron.!=info;mail.!=info |/dev/xconsole
/dev/xconsole is a named pipe (fifo). If I want to see what is being logged, I ...
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3
votes
1
answer
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views
What is the purpose of using a FIFO vs a temporary file or a pipe?
From APUE
FIFOs can be used to duplicate an output stream in a series of shell
commands. This prevents writing the data to an intermediate disk
file (similar to using pipes to avoid intermediate ...
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2
votes
1
answer
327
views
Can FIFO or other thing not block on writer's access, and instead just drop data?
FIFO is problematic in use because both reader and writer have to open it – if one of them is being late, the other one is blocked inside the operating system.
I have to implement a publishing ...
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24
votes
3
answers
10k
views
Prevent automatic EOFs to a named pipe, and send an EOF when I want it
I have a program that exits automatically upon reading an EOF in a given stream ( in the following case, stdin ).
Now I want to make a shell script, which creates a named pipe and connect the program'...
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15
votes
1
answer
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views
How do I use inotify or named pipes over SSHFS?
Thanks sshfs magic, I can mount my home dir from a remote server with
sshfs user@server:/home/user ~/remote
Optimistically, I thought I'd set a local inotify-hook on ~/remote/logFile (in the sshfs ...
- 4,516
12
votes
3
answers
6k
views
Named pipes, file descriptors and EOF
Two windows, same user, with bash prompts. In window-1 type:
$ mkfifo f; exec <f
So bash is now attempting to read from file descriptor 0, which is mapped to named pipe f. In window-2 type:
$ ...
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5
votes
1
answer
174
views
Joined pipelines
Considering a routine such as this one:
alpha() { echo a b c |tr ' ' '\n'; }
which outputs a stream, I would like to take the output stream, transform it, and paste it with the original output ...
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55
votes
5
answers
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views
Are FIFO, pipe & Unix domain socket the same thing in Linux kernel?
I heard that FIFOs are named pipes. And they have exactly the same semantics. On the other hand, I think Unix domain socket is quite similar to pipe (although I've never made use of it). So I wonder ...
- 713
15
votes
2
answers
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How does a FIFO (named pipe) differs from a regular pipe (unnamed pipe)? [duplicate]
How does a FIFO (named pipe) differs from a regular pipe (|)? As I understand from Wikipedia, unlike a regular pipe, a FIFO pipe "keeps living" after the process has ended and can be deleted sometime ...
15
votes
2
answers
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Under what conditions exactly does SIGPIPE happen?
Say we have a named pipe called fifo, and we're reading and writing to it from two different shells. Consider these two examples:
shell 1$ echo foo > fifo
<hangs>
shell 2$ cat fifo
foo
shell ...
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8
votes
2
answers
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views
How to cat named pipe without waiting
If there is nothing in a named pipe and I do:
cat my_named_pipe
it will wait until data arrives. Is there a flag I can use to exit immediately if there is no data to be read? Or perhaps a command ...
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8
votes
2
answers
7k
views
Reading a named pipe: tail or cat?
I made a file descriptor using
mkfifo fifo
As soon as something is written to this pipe, I want to reuse it immediately. Should I use
tail -f fifo
or
while true; do cat fifo; done
?
They seem ...
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4
votes
1
answer
4k
views
Write to FIFO only if it exists
Most of the examples that I see about writing to a FIFO say to use the echo or cat commands and redirect stdout to the file. E.g.,
echo 'a' > /tmp/my_fifo
However, this will create a regular file ...
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0
votes
1
answer
311
views
How to Pipe Segment of Heredoc Output to Local File
I am issuing a command to a remote device in order to run a tcpdump on one of it's interfaces, but capture the output to a local .pcap file on my Ubuntu VM. The command that I'm issuing is as follows:
...
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12
votes
3
answers
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views
Buffering (named) pipe in GNU OS
In the GNU OS a process can only write data to a pipe if another process reads the same data (from the same pipe) at the same time.
Is there something like a pipe which lets the 1st process write and ...
- 557
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 ...
- 25k
9
votes
2
answers
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views
Send EOF to named pipe - cleaning up / drying up fifo
If I have some random processes reading from a named pipe:
tail -f MYNAMEDPIPED
cat MYNAMEDPIPE | someOtherProc
Elsewhere, I have a handle on MYNAMEDPIPED by name.
is there a safe and clean way to ...
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9
votes
2
answers
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views
Why does this script with a FIFO pipe not terminate?
This script:
#!/bin/bash
tmppipe=/tmp/temppipe
mkfifo $tmppipe
echo "test" > $tmppipe
cat $tmppipe
exit
does not terminate. I assume that the cat command is waiting for an EOF from the ...
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8
votes
2
answers
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Does named pipe modify the filesystem?
If I create a named pipe and then read/write on it, is the filesystem where the named pipe resides affected? I.e. is the data buffered on the filesystem until read, or does it reside in memory only?
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8
votes
1
answer
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Increase FIFO size limit
Thanks to the answers to my other question, I now understand that FIFO on Linux, i.e. /dev/xconsole has a buffer limit of 64 KB.
How can I increase this limit to 128 KB?
Apparently, I will need to ...
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7
votes
4
answers
4k
views
How do I make systemd sockets close when service is stopped?
I'm currently trying to make a systemd service with two Fifo sockets. These sockets map to stdout and stdin of the application. I'm currently using the following configuration files.
foo.service
[...
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6
votes
1
answer
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views
Print current number of bytes in a pipe
I can create a pipe to transfer information between two programs. I can even use a utility like pv to view progress of total data passing through the pipe. In my case I am using a named pipe. When ...
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5
votes
2
answers
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views
Writing on a FIFO with multiple processes
I need to make a named pipe with mkfifo. For instance:
mkfifo mypipe
I'm going to have a systemd service (a simple shell script) that read from the pipe and I will write on the same pipe calling ...
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4
votes
1
answer
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views
How to read a webcam that is already used by a background capture?
A ffmpeg webcam capture is running in the background.
ffmpeg -f video4linux2 -s vga -i /dev/video0 capture.mp4 (1)
I am therefore unable to read it with ffplay since the device /dev/video0 is ...
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4
votes
2
answers
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How can I pipe commands to any terminal?
I often use more than one terminal (or terminal emulator) at a time; and while in X I can copy-paste commands, besides not being very practical, it obviously does not work on the real TTY. The first ...
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4
votes
1
answer
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/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 ...
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3
votes
0
answers
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views
Write to stdin of running process on occasion
From time to time I want to send some text to the input of netcat. Netcat will send it then to another netcat process (either on my machine or a local network), but now I am only concerned with the ...
- 269
3
votes
1
answer
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How make service reading from FIFO socket
So before I take my axe and destroy my Desktop I will try asking here :-)
I have a socket activated service named commander.service.
Because of simplicity I just want to push bare strings or chars to ...
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2
votes
1
answer
2k
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Why stdout won't flush when redirecting input from a fifo?
I have a program that displays a prompt message and waits for the user to input some text.
$ program
Input a line of text: <aaaa>
Some more output.
$
Now, I also want to be able to provide ...
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2
votes
2
answers
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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
1k
views
create several /dev/xconsole files automatically upon boot
I understand from my previous question that the /dev/xconsole file can be created using mkfifo.
On my system (Debian Wheezy), /dev/xconsole gets created automatically. I am wondering who creates it (...
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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="$(...
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1
vote
2
answers
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Cheapest way to find the oldest file (recursively) from a directory under heavy load
What is the least expensive way to find the oldest file in a directory, including all directories underneath. Assume directory is backed by SAN and under heavy load.
There is concern that "ls" could ...
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1
vote
1
answer
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How does a temporary file differs from a pipe? [duplicate]
When one sends data (say stdout) to a temporary file, it is likely that something would be done with that data (the temporary file will be used as stdin for some process), then the temporary file will ...
0
votes
0
answers
33
views
Strange incongruent output for both nc and fifo
I have this exact code:
#!/bin/bash
gtimeout(){
if type -f gtimeout &> /dev/null; then
command gtimeout "$@"
else
timeout "$@"
fi
}
export -f gtimeout;
...
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0
votes
0
answers
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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.
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