fcntl refers to a function that provides control over the open file referenced by a file descriptor
fcntl refers to a function that provides control over the open file referenced by a file descriptor.
Questions tagged [fcntl]
234 questions
34
votes
5 answers
How to get hard disk serial number using Python
How can I get the serial number of a hard disk drive using Python on Linux?
I would like to use a Python module to do that instead of running an external program such as hdparm. Perhaps using the fcntl module?
Forge
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26
votes
7 answers
Python fcntl does not lock as expected
On a Debian-based OS (Ubuntu, Debian Squeeze), I'm using Python (2.7, 3.2) fcntl to lock a file. As I understand from what I read, fnctl.flock locks a file in a way, that an exception will be thrown if another client wants to lock the same file.
I…
Wolkenarchitekt
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24
votes
1 answer
Is O_NONBLOCK being set a property of the file descriptor or underlying file?
From what I have been reading on The Open Group website on fcntl, open, read, and write, I get the impression that whether O_NONBLOCK is set on a file descriptor, and hence whether non-blocking I/O is used with the descriptor, should be a property…
Daniel Trebbien
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18
votes
1 answer
python lockf and flock behaviour
I have read enough posts on stackoverflow regarding the difference between flock/lockf/fcntl but I am unable to answer the below observation:
>>> import fcntl
>>> a = open('/tmp/locktest', 'w')
>>> b = open('/tmp/locktest', 'w')
>>> fcntl.lockf(a,…
Jatin Kumar
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16
votes
2 answers
Is it possible (and safe) to make an accepting socket non-blocking?
I'm looking for a way to interrupt an accept() call on a blocking socket. Using signals is not an option, as this is meant to be in a library and I don't want to clutter the user signals. Using select() is another option, buf for various reason it's…
Norswap
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15
votes
2 answers
How to force linkage to older libc `fcntl` instead of `fcntl64`?
It seems GLIBC 2.28 (released August 2018) made a fairly aggressive change to fcntl. The definition was changed in to no longer be an external function, but a #define to fcntl64.
The upshot is that if you compile your code on a system…
HostileFork says dont trust SE
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14
votes
3 answers
How do I atomically create a locked file in Linux?
Scenario: I have many processes running that need to fetch files over the net. If the file is already downloaded, I want it cached on disk. If another process is downloading the file, block until it is finished downloading.
I've been trying to find…
UsAaR33
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12
votes
1 answer
Setting stdout to non-blocking in python
Prior warning: I'm hacking around here out of curiosity. I have no specific reason to do what I'm doing below!
Below is done on Python 2.7.13 on MacOS 10.12.5
I was hacking around with python and I thought it'd be interesting to see what happened if…
Andrew Parker
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12
votes
3 answers
open() doesn't set O_CLOEXEC flag
I try to set O_CLOEXEC flag using open() and have no sucess.
Consider the following microtest:
#include
#include
int main() {
int fd = open("test.c", O_RDONLY | O_CLOEXEC);
int ret = fcntl(fd, F_GETFL);
if(ret & O_CLOEXEC)…
Ivan Efremov
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11
votes
1 answer
How can I make a non-blocking request for an exclusive lock using File#flock?
How Should I Request a Non-Blocking Lock?
Why doesn't Ruby's File#flock work as expected when separate attempts are made to lock a file? Locking the file in a block is not the correct solution for this issue because the point is to show the behavior…
Todd A. Jacobs
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10
votes
1 answer
How to specify a github repo as the source of dependency of a module in Raku?
My module depends on the Fcntl module (https://github.com/manchicken/perl6-Fcntl), which hasn't been updated in a long time and is broken. However, there's a fork (https://github.com/jonathanstowe/perl6-Fcntl) that works for me if I zef install it…
cowbaymoo
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10
votes
3 answers
How to properly convert a C ioctl call to a python fcntl.ioctl call?
Following an example on resetting a serial port in Linux I wanted to translate the following snippet
fd = open(filename, O_WRONLY);
ioctl(fd, USBDEVFS_RESET, 0);
close(fd);
into valid python code. Here is what I have tried so far
file_handler =…
Alex
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9
votes
4 answers
linux fcntl - unsetting flag
How do i unset a already set flag using fcntl?
For e.g. I can set the socket to nonblocking mode using
fcntl(sockfd, F_SETFL, flags | O_NONBLOCK)
Now, i want to unset the O_NONBLOCK flag.
I tried fcntl(sockfd, F_SETFL, flags | ~O_NONBLOCK). It…
chappar
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9
votes
1 answer
How to atomically create "close-on-exec" socket on Mac?
When I create socket on Linux, it's possible to specify the flag O_CLOEXEC on creation time:
auto fd = socket(AF_INET, SOCK_STREAM|SOCK_CLOEXEC, 0);
So there is no way, that some other thread will do fork()+exec() with this socket remaining…
abyss.7
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8
votes
2 answers
c - Usage of F_GETFL and F_SETFL
While trying to use fcntl() with command F_GETFL and F_SETFL, I got some questions:
Why the flag returned by fcntl(fd, F_GETFL) only include a subset of bits of what I set when open file? Does it only show the ones that are modifiable?
When use…
Eric
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