[issue40299] os.dup seems broken with execvp (LINUX)

[krsna]

New submission from krsna :

---CODE---
import os
path = "file.txt"
  
fd = os.open(path, os.O_WRONLY) 
  
os.close(1) #STDOUT
os.dup(fd)
pid = os.fork()

if pid == 0:
args = "ls -l".split() 
os.execvp(args[0], args)
else:
os.waitpid(pid, 0)
print('Done from Parent')
--- END CODE ---

Running this with python
```
> python -V
Python 3.8.2
```
I get the following:
```
> echo"" > file.txt && python example.py && cat file.txt 
ls: write error: Bad file descriptor
Done from Parent

```
Running the same with micropython:
```
> echo"">file.txt && micropython me && cat file.txt 
total 76
drwxr-xr-x 2 user user  4096 Apr  5 15:29 Desktop
drwxr-xr-x 2 user user  4096 Apr  5 15:29 Documents
drwxr-xr-x 2 user user  4096 Apr 13 18:22 Downloads
drwxr-xr-x 2 user user  4096 Apr  5 15:29 Music
drwxr-xr-x 2 user user  4096 Apr 12 11:16 Pictures
drwxr-xr-x 2 user user  4096 Apr  5 15:29 Public
drwxr-xr-x 2 user user  4096 Apr  5 15:29 Templates
drwxr-xr-x 2 user user  4096 Apr  5 15:29 Videos
-rw-rw-r-- 1 user user   244 Apr 15 22:02 example.py
Done from Parent
```
With the follow C which is almost a 1:1 to the CODE segment above
```
#include 
#include 
#include 

int main(int argc, const char *argv[])
{
int fd = open("file.txt", O_WRONLY);

close(1);
dup(fd);

if (fork() == 0) {
char *cmd = "ls";
char *argv[3];
argv[0] = "ls";
argv[1] = "-l";
argv[2] = NULL;
execvp(cmd, argv);
} else {
wait(0);
close(fd);

puts("Done from Parent");
}

return 0;
}
```
I get the same output as micropython example above
```
> echo"">file.txt && gcc ccc.c && ./a.out && cat file.txt 
total 76
drwxr-xr-x 2 user user  4096 Apr  5 15:29 Desktop
drwxr-xr-x 2 user user  4096 Apr  5 15:29 Documents
drwxr-xr-x 2 user user  4096 Apr 13 18:22 Downloads
drwxr-xr-x 2 user user  4096 Apr  5 15:29 Music
drwxr-xr-x 2 user user  4096 Apr 12 11:16 Pictures
drwxr-xr-x 2 user user  4096 Apr  5 15:29 Public
drwxr-xr-x 2 user user  4096 Apr  5 15:29 Templates
drwxr-xr-x 2 user user  4096 Apr  5 15:29 Videos
-rwxrwxr-x 1 user user 18904 Apr 15 22:53 a.out
-rw-rw-r-- 1 user user   395 Apr 15 22:50 ccc.c
-rw-rw-r-- 1 user user   244 Apr 15 22:02 example.py
Done from Parent
```
I tried looking around for the code of `dup` in cpython to compare, but could 
only find `dup2.c`.

--
components: Library (Lib)
messages: 366587
nosy: krsna
priority: normal
severity: normal
status: open
title: os.dup seems broken with execvp (LINUX)
type: behavior
versions: Python 3.8

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[issue40299] os.dup seems broken with execvp (LINUX)

[krsna]

krsna  added the comment:

I should read the updated documentation changes to modules more often. Adding 
the inheritable works and yes I tested with `os.dup2` which seemed consistent 
with C's dups2. I still think it is quite odd that the low level `dup` function 
has a different behavior than one would expect.

Thank you for you helpful and quick reply Martin.

This may be closed as it is a documented, imo, misbehavior.

On Thursday, April 16, 2020, 12:13:58 AM HST, Martin Panter 
 wrote: 

Martin Panter  added the comment:

The file descriptor created by "os.dup" is not inherited by child processes by 
default since Python 3.4.
https://docs.python.org/3/library/os.html#os.dup

Does it work if you use "os.set_inheritable" or "os.dup2" (which apparently 
sets it inhertiable by default)?

--
nosy: +martin.panter

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[issue40299] os.dup seems broken with execvp (LINUX)

[krsna]

krsna  added the comment:

Closing has behavior is documented "The file descriptor created by "os.dup" is 
not inherited by child processes by default since Python 3.4.
https://docs.python.org/3/library/os.html#os.dup";

--
resolution:  -> not a bug
stage:  -> resolved
status: open -> closed

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