On 3/30/2021 1:43 PM, Todd Zullinger wrote: > 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@xxxxxxxxx> 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. Thanks for this link! I appreciate the context. > 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). Nice! > 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. Yes, this is my mistake. My machine supports "crontab -". > 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.) Perhaps the best way to approach this is to try adding '-' by default, and remove it and try again on a failure. If the usage is actually a problem, that first command should fail quickly. I'm not sure if we could rely upon a specific category of error codes or if we should just say "non-zero exit means retry". Thanks! -Stolee
