Freeze opening /dev/stdout

Freeze opening /dev/stdout

[João Eiras]

Hi.

On linux now and then I call a program passing "/dev/stdout" as output
file parameter, so the data is output in the terminal.

For instance, something tiny in C.

#include <fcntl.h>
#include <stdio.h>
int main () {
int fd = open("/dev/stdout", O_WRONLY);
printf("Opened stdout: %d\n", fd);
return 0;
}

Unfortunately, this freezes. The problem (I think) is because
/dev/stdout is a pipe, so the open() call waits forever until a
reader() opens /dev/stdout, which in this case should be the terminal.

Interestingly, this does not affect /dev/stderr which is a link to the
console device.

$ ls -la /dev/std*
lrwxrwxrwx 1 user None 15 Sep  6  2017 /dev/stderr -> /proc/self/fd/2
prw------- 1 user None  0 Jun  4 15:54 /dev/stdin
prw------- 1 user None  0 Jun  4 15:54 /dev/stdout

I've just sent another thread about "/dev/stdin" always being a pipe,
so I guess that is related.

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Re: Freeze opening /dev/stdout

[Takashi Yano]

On Fri, 20 Jul 2018 15:35:21 +0200
João Eiras wrote:
> #include <fcntl.h>
> #include <stdio.h>
> int main () {
> int fd = open("/dev/stdout", O_WRONLY);
> printf("Opened stdout: %d\n", fd);
> return 0;
> }
> 
> Unfortunately, this freezes. The problem (I think) is because
> /dev/stdout is a pipe, so the open() call waits forever until a
> reader() opens /dev/stdout, which in this case should be the terminal.

I can't reporduce your problem.

The test case outputs:
Opened stdout: 3

$ ls -la /dev/std*
lrwxrwxrwx 1 yano なし 15 Mar 26  2016 /dev/stderr -> /proc/self/fd/2
lrwxrwxrwx 1 yano なし 15 Mar 26  2016 /dev/stdin -> /proc/self/fd/0
lrwxrwxrwx 1 yano なし 15 Mar 26  2016 /dev/stdout -> /proc/self/fd/1

What happens if you execute:
rm /dev/stdin /dev/stdout
ln -s /proc/self/fd/0 /dev/stdin
ln -s /proc/self/fd/1 /dev/output

-- 
Takashi Yano <takashi.yano@nifty.ne.jp>

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Re: Freeze opening /dev/stdout

[Marco Atzeri]

Am 21.07.2018 um 03:19 schrieb Takashi Yano:
> On Fri, 20 Jul 2018 15:35:21 +0200
> João Eiras wrote:
>> #include <fcntl.h>
>> #include <stdio.h>
>> int main () {
>> int fd = open("/dev/stdout", O_WRONLY);
>> printf("Opened stdout: %d\n", fd);
>> return 0;
>> }
>>
>> Unfortunately, this freezes. The problem (I think) is because
>> /dev/stdout is a pipe, so the open() call waits forever until a
>> reader() opens /dev/stdout, which in this case should be the terminal.
> 
> I can't reporduce your problem.
> 
> The test case outputs:
> Opened stdout: 3
> 

same here.
$ ./prova.exe
Opened stdout: 3

João, what exacly is your enviroment and terminal ?


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Re: Freeze opening /dev/stdout

[Takashi Yano]

On Sat, 21 Jul 2018 10:19:03 +0900
Takashi Yano wrote:
> What happens if you execute:
> rm /dev/stdin /dev/stdout
> ln -s /proc/self/fd/0 /dev/stdin
> ln -s /proc/self/fd/1 /dev/output

This is typo.

s/output/stdout/

-- 
Takashi Yano <takashi.yano@nifty.ne.jp>

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Re: Freeze opening /dev/stdout

[João Eiras]

Thanks everyone.

Turns out it's some problem with my setup that is affecting stdin and
stdout. I had no idea that could happen.

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