s6-linux-init and ttys in lxc containers

s6-linux-init and ttys in lxc containers

[Hoël Bézier]

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Hi,

I’m using s6 and s6-linux-init inside lxc containers.

My /sbin/init (created with s6-linux-init-maker) contains the following:

```
#!/bin/execlineb -S0

s6-linux-init -c "/etc/s6-linux-init/current" -m 0022 -p "/usr/bin:/bin" -C -- "$@"
```

Right after starting my container with `lxc-start -F <container-name>`, I get 
the following warning message:

s6-linux-init: warning: unable to ttyname stdout: No such device

I suspect this is due to the mechanism described on 
https://github.com/lxc/lxd/issues/1724#issuecomment-194412831, although I’m not 
using LXD, only lxc (which does not have a daemon running as root). Note that 
s6-linux-init has been compiled against the musl libc, so the musl ttyname C 
function may have the same issue as the glibc one.

That’s not a really serious issue, but I figured I’d still mention it here.

Hoël

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Re: s6-linux-init and ttys in lxc containers

[Laurent Bercot]

>s6-linux-init: warning: unable to ttyname stdout: No such device
>
>I suspect this is due to the mechanism described on https://github.com/lxc/lxd/issues/1724#issuecomment-194412831, although I’m not using LXD, only lxc (which does not have a daemon running as root).

  You're right, it's the exact same issue. If /proc/1/fd/1 does not
point to a valid pts in the container, then ttyname() will be unable to
resolve it and you will get that warning message - and you also will be
unable to transmit your controlling terminal to stage 2 (which is not a
problem in your case).

  The only solution, I'm afraid, is to make sure your pseudo-filesystems
are correctly prepared before you launch your container, which you may
not be able to do without root privileges. Docker can do it; if you
were running lxd there would probably be a way to do it as well. But if
you have no use for a controlling terminal, you can forget about all 
this
and just ignore the warning.

--
  Laurent