lxc-attach strange tty behavior (kills command) when stderr is redirected to a file

[Xavier Roche]

On a fresh Ubuntu 16 release, commands started by lxc-attach such as dd are being killed WHEN REDIRECTING stderr (to a file), and lxc-attach return a zero status. Command works fine without the redirection.

This scenario is working on Ubuntu 15 with previous lxc release, but not on new LXC 2.0.0 (same issue on 2.0.1 too)

sudo apt-get -y install lxc
sudo lxc-create -n utest -t ubuntu -- -a amd64 -b $USER
sudo lxc-start -d --name utest

sudo lxc-attach -n utest -- dd if=/dev/zero of=/tmp/foo bs=1M count=10 2>/tmp/bar
sudo lxc-attach -n utest -- ls -lh /tmp/foo
-rw-r--r-- 1 root root 0 May 18 05:46 /tmp/foo

Might be related to bug 1553097 (and/or https://github.com/lxc/lxc/pull/873)

NOTE: Sometimes the "sudo lxc-attach -n utest_bizio_tests -- ls -lh /tmp/foo" ALSO does not return anything (no output)

I'm available for any additional info.

[John Doe (torok-flow)]

"sudo lxc-attach -n utest -- dd if=/dev/zero of=/tmp/foo bs=1M count=10 2>&1" Works

[Xavier Roche (roche)]

Another demonstration:

* This one does not work:

sudo lxc-attach --name utest_generic_tests -- /bin/bash -c "/usr/bin/python -c 'from ctypes import *; memset(0,1,1)'"; echo $?
0

* This one works:

sudo lxc-attach --name utest_generic_tests -- /bin/bash -c "/usr/bin/python -c 'from ctypes import *; memset(0,1,1)' 2>&2"; echo $?
/bin/bash: line 1: 2286 Segmentation fault (core dumped) /usr/bin/python -c 'from ctypes import *; memset(0,1,1)' 2>&2
139