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Re: Invoking ‘init’ from an init.d script (Wheezy)

On Fri, Jun 5, 2015 at 7:39 PM, Konstantin Khomoutov
<flatworm@users.sourceforge.net> wrote:
> On Fri, 5 Jun 2015 16:25:21 +0200
> Alexander Thomas <alexander.thomas+ddml@esaturnus.com> wrote:
> [...]
>> That would be an option, but it might still cause the same problem of
>> apt-get hanging as we currently experience when doing the update
>> before runlevel S.
>> We looked deeper into this and found out that apt-get always hangs
>> while installing a package before the first runlevel switch. An strace
>> reveals an endless loop of SIGCONT and ioctl calls. Running other
>> commands that use ioctl also results in a hang, so the controlling
>> terminal seems to lack certain capabilities at this stage. We have
>> found a workaround: we spawn a new terminal with agetty and run the
>> update script in there, this allows to perform the apt-get
>> dist-upgrade in runlevel S and avoid the init 1 hack.
> I would try running apt-get with </dev/null >somelogfile 2>&1
> redirections: that should ensure it sees no terminal at all on its stdin
> and that should avoid code paths dealing with TTY-related ioctls
> altogether.  (Well, excluding the isatty(3) call which supposedly uses
> fstat(2) and checks to see the device's major number is that of a TTY).

The </dev/null avoids the hang indeed. I haven't looked at the code
but it makes sense that when apt-get starts configuring the packages,
it will probe the terminal or prepare it for user interaction. We
falsely assumed that setting DEBIAN_FRONTEND=noninteractive
APT_LISTCHANGES_FRONTEND=none, and using the -y and --force-yes
options, would never invoke terminal-related code.


Alexander Thomas

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