Re: [PATCH] maintenance: specify explicit stdin for crontab

> Hi,
> 
> Derrick Stolee wrote:
>> On 3/30/2021 1:41 AM, Martin Ågren wrote:
>>> On Mon, 29 Mar 2021 at 23:23, Kevin Daudt <me@ikke.info> wrote:
>>>>
>>>> There are multiple crontab implementations that require stdin for
>>>> editing a crontab to be explicitly specified as '-'.
> 
> Amusingly, I wrote the exact same patch 2 weeks ago
> (including not dropping the `argc == 2` which Martin
> mentioned).  That was in response to a report in the Fedora
> bugzilla:
> 
>     https://bugzilla.redhat.com/1939930
> 
> I thought cronie might be rather rare with it's non-POSIX
> handling of crontab without arguments.

> In the end, the cronie folks upstream adjusted things so
> that crontab behaves as defined by POSIX if stdin is not a
> TTY:
> 
>     https://github.com/cronie-crond/cronie/commit/8b0241f
>> That allows cronie to behave more sensibly for interactive
> use without breaking tools like git maintenance.  And it let
> me sidestep proposing a patch to git (or worse, maintaining
> it in the Fedora packages).

> But I didn't dig in to find out whether or how many other
> crontab implemntations had also eschewed the (rather poor)
> POSIX-confirming behavior.  Knowing there are several among
> popular OS's makes it easy to see something like this patch
> being generally useful.
> 
> Though, as Derrick notes below, we would break systems which
> implement crontab strictly per the POSIX spec.  I don't know
> how many crontab's don't accept `-`.
> 
> At the time, I checked on an older OmniOS system I had
> access to (based on Illumos/OpenSolaris) and it did not
> accept `-`.  So my quick sample size of 3 (Fedora, CentOS,
> and OmniOS) I had a 1/3 failure rate.
> 
>> Thank you for reporting this, especially with a patch!
>>
>> However, I'm not sure about this adding of '-' being something that
>> crontab ignores so commonly. My Ubuntu machine reports this:
>>
>> $ crontab -e -
>> crontab: usage error: no arguments permitted after this option
>> usage:  crontab [-u user] file
>>         crontab [ -u user ] [ -i ] { -e | -l | -r }
>>                 (default operation is replace, per 1003.2)
>>         -e      (edit user's crontab)
>>         -l      (list user's crontab)
>>         -r      (delete user's crontab)
>>         -i      (prompt before deleting user's crontab)
>>
>> Is there a way we could attempt writing over stdin, notice the
>> failure, then retry with the '-' option?
> 
> You'd skip the `-e` there, no?  Running `crontab -` in a
> current ubuntu container with the cron package installed
> (what looks like vixie-cron-3.0pl1) works as expected.

> Perhaps a Makefile knob to allow systems with such a crontab
> to adjust the behavior would be an alternative to detecting
> and retrying?
> 
> NEEDS_CRONTAB_STDIN_OPT or something like that, with
> config.mak.uname to override whichever default is chosen.
> Whether that's a better option really depends on how much
> effort it is to add and maintain the detection in the code
> weighed against how many systems would need to have the
> default changed.
> 
> Mildy related, I wonder whether we'll eventually see a patch
> to use systemd timers instead of cron (optionally, of
> course).  Fedora, for example, doesn't install crond by
> default anymore.  (Though, warts and all, I still prefer
> crond myself.)