Can't open file descriptors in /proc/[###]/fd

[aseering]

I'm trying to get bash's process substitution working. It's a few steps shy of working, but, one big one:

The file descriptors under /proc/self/fd aren't openable. They are listed as writeable, but the "open()" libc call is returning -1 when I try to open them.

[aseering]

This was discussed in passing by #91

[aseering]

Here's a gist of a .c file which, if loaded into a Linux (or Windows-Bash) binary, roughly emulates the desired behavior of these file descriptors. It's good enough to get bash process substitution working, anyway.

It's trying to make /dev/fd work, which is what bash process substition uses and which doesn't exist at all in Windows-Bash. If you want /proc/self/fd, modify line 38 accordingly.

[benhillis]

Looks like we're missing the below symlinks in the /dev directory. I just filed an internal bug and will get these added to our dev branch today.

lrwxrwxrwx   1 root root          13 Apr 29  2016 fd -> /proc/self/fd/
lrwxrwxrwx   1 root root          15 Apr 29  2016 stderr -> /proc/self/fd/2
lrwxrwxrwx   1 root root          15 Apr 29  2016 stdin -> /proc/self/fd/0
lrwxrwxrwx   1 root root          15 Apr 29  2016 stdout -> /proc/self/fd/1

Thanks for reporting this!

[aseering]

Thanks for the reply, and the quick action! Those symlinks will be very helpful.

Once you have the symlinks, is there any chance you could run the following one-line bash command real quick, as a test case?:

cat <(echo 'hello world') > >(tee tmp.txt)

It should print "hello world" to the terminal, and write a file "tmp.txt" that contains the same string. Works fine on Ubuntu Linux. Doesn't work on my Windows Bash system, even if I modify bash to use /proc/self/fd rather than /dev/fd (which is in effect what adding those symlinks does).

My workaround (above; link to gist) fixes the issue by aliasing open("/proc/self/fd/NNN") to dup(NNN).

If this is already fixed on your end, great! I await the next build :-) If not, just making sure you know what I'm seeing.

[benhillis]

Something interesting is going on here that I'll need to debug further. I'm getting an error about cat: /dev/fd/63: No such file or directory even though I've verified that the /dev/fd symlink is working correctly. It could be a problem with the tee system call or something else, I'll continue looking into this.

[aseering]

Thanks for looking at this! I'll be curious to hear what you find.

[benhillis]

@aseering - Dug into this a bit more and we're not correctly handling opening pipes by the procfs symlinks correctly (for example open("/dev/fd/1") or open("/proc/self/fd/1"). I've filed a bug internally to track this and we have a good idea of how to fix it.

[benhillis]

This was fixed in our development branch recently and the fix will be making its way to the Windows Insider fast ring.

[aseering]

Thanks!

[pefoley2]

Appears to still be an issue in build 14352.
Hopefully this fix will land in the next release.

[AbhimanyuAryan]

who says this has been fixed @benhillis I am trying to install rvm and I still have this issue on 14352

cat: /dev/fd/63: No such file or directory
cat: /dev/fd/63: No such file or directory
The downloaded package for https://rubies.travis-ci.org/ubuntu/14.04/x86_64/ruby-2.3.1.tar.bz2,
Does not contains single 'bin/ruby' or 'ruby-2.3.1',
Only '' were found instead.

[mcornella]

@AbhimanyuAryan he didn't say it was fixed on 14352, but on their internal dev branch. It's probably not yet released.

[AbhimanyuAryan]

@mcornella my bad so when are we expecting the update? I have un-installed Linux to get Windows and it's still not here. Microsoft said it quite clearly "Ubuntu on Windows" 😥😕

[benhillis]

@AbhimanyuAryan - Sorry for the confusion, the fix will be an insider release soon. We don't have any control over when Insider builds are released so I apologize that I can't give a more firm timeline.

[AbhimanyuAryan]

@benhillis you should explain that to Microsoft Insider team that it's "WindowsOnBash" because of which people are making switch not Windows. So they can set the priorities right😞

Btw you guys are doing great work :)

[stehufntdev]

Insider build 14361 that was just released has the fix for this, and I doubled checked the one line repro above.

[ghost]

Old and closed issue, I know... But we are experiencing the same issue over at https://github.com/ish-app/ish.
@benhillis Is there any possibilities that you could share some details on how this was solved with us?
Thanks in advance!

[ezzuldinSt]

@benhillis could share some details on how did you solve this?
I’m having the same bug on https://github.com/ish-app/ish
Which is :

sysopen:41: can't open file /proc/self/fd/14: no such file or directory