cannot editor crontab unless I explicitly set the EDITOR

vincix · 06-18-2019, 06:32 AM

Whenever I try to run crontab -e, I get this random code:

Code:

crontab -e
927

?

?

When I press enter, the ? shows up.
It works if I run the command with EDITOR=vim before it, but I'd like to understand what is happening. I know that the EDITOR variable doesn't necessarily need to be set, in order to get a default editor.
update-alternative --config editor doesn't work either. I get these choices:

Code:

  Selection    Path                Priority   Status
------------------------------------------------------------
* 0            /bin/nano            40        auto mode
  1            /bin/ed             -100       manual mode
  2            /bin/nano            40        manual mode
  3            /usr/bin/vim.basic   30        manual mode
  4            /usr/bin/vim.tiny    10        manual mode

I know I could also simply add the EDITOR variable into my .bashrc or whatever, but I'd like to understand the behaviour. Thanks.

I'm running Ubuntu 16.04.4

pan64 · 06-18-2019, 07:58 AM

did you check how is it set (by default?)

vincix · 06-18-2019, 08:02 AM

You mean the EDITOR variable? It's null.

pan64 · 06-18-2019, 08:49 AM

you need to read the man page, you will see either EDITOR or VISUAL is used. And there is also a default (if both of them are unset). But it looks like it depends on the distro, so there is no general answer.

vincix · 06-18-2019, 08:53 AM

Neither EDITOR, nor VISUAL is set. I don't really need a general answer. I'd like a particular answer for my problem

pan64 · 06-18-2019, 09:03 AM

And what do you think who knows how that server was installed/configured exactly?

vincix · 06-18-2019, 09:10 AM

Well, that's why I'm writing on this forum, maybe someone has an idea about what might have led to this. This isn't the first time I've seen this - and it was on a completely different server.

ehartman · 06-18-2019, 11:34 AM

Quote:

Originally Posted by vincix

When I press enter, the ? shows up.

Looks like your version of crontab is using "ed" by default, and as you saw ed is VERY minimal, no prompts, no visual mode, it essentially only supports the commands "sed" does too (in fact sed - the Stream EDitor - is derived FROM ed).
ex, the "command mode" of vim, features an extended set of commands compared to ed (ex stands for EXtended editor, vi then was a later VIsual mode on top of ex and still later there came vim, vi iMproved).

THE thing with ed is, every Unix (and Unix-like O/S like Linux or *BSD) is guaranteed to have a copy around, so it is a reasonable default to compile in when no alternative editor has been set.

scasey · 06-18-2019, 01:55 PM

Quote:

Originally Posted by pan64

you need to read the man page, you will see either EDITOR or VISUAL is used. And there is also a default (if both of them are unset). But it looks like it depends on the distro, so there is no general answer.

Now I'm curious, too.
I'm on CentOS 7. Both EDITOR and VISUAL are unset, but crontab -e works just fine and uses vi, so that's apparently the default, but I'm not finding what manages that default in CentOS. Searches lead to "if you want to change the default, then set EDITOR and VISUAL" without (so far) leading me to where that default happens. I'd appreciate a hint

I see the OP is using Ubuntu, so even if I figure it out, it may not help them.

scasey · 06-18-2019, 02:22 PM

Quote:

Originally Posted by ehartman

Looks like your version of crontab is using "ed" by default, and as you saw ed is VERY minimal, no prompts, no visual mode, it essentially only supports the commands "sed" does too (in fact sed - the Stream EDitor - is derived FROM ed).
ex, the "command mode" of vim, features an extended set of commands compared to ed (ex stands for EXtended editor, vi then was a later VIsual mode on top of ex and still later there came vim, vi iMproved).

THE thing with ed is, every Unix (and Unix-like O/S like Linux or *BSD) is guaranteed to have a copy around, so it is a reasonable default to compile in when no alternative editor has been set.

Aha. You're implying then (if I'm reading you correctly), that the "default" is compiled into something (the kernel?) and it's not, therefore changeable except by setting VISUAL and/or EDITOR (I'm seeing that VISUAL is what crontab looks at first, but I'm also finding lots of places that say set them both the same). That's probably why I can't find where the default is set.

If I've go that right, then the OPs answer (and mine), is to set those environment variables to the desired editor. Yes?

ehartman · 06-18-2019, 04:22 PM

Quote:

Originally Posted by scasey

Aha. You're implying then (if I'm reading you correctly), that the "default" is compiled into something

It is compiled into the "crontab" executable, to have a "sensible default" for the crontab -e command and as there are almost as many different implementations of cron (and thus crontab) as there are (major) distributions (vixieCron, anacron, Dillon cron, etc) and every package builder can specify his own preferred default into the compilation, there is not a single answer for all possible crontab program's.
I.e. in "my" version of crontab there is this string "/usr/bin/vi", so the compiled-in default is "standard vi", not vim.

PS: found with "strings `which crontab`|grep /bin/" (which in MY case had to be as root as the crontab executable is not readable (although executable) by normal users):

Code:

-rws--x--x 1 root root 10096 2012-09-07 22:24 /usr/bin/crontab

BTW: Slackware is using dillon's lightweight cron daemon.
The man page for "crontab" for that package gives:

Quote:

Generally the -e option is used to edit your crontab. crontab will use the editor specified by your EDITOR or VISUAL environment variable (or /usr/bin/vi) to edit the crontab.

so that man page is adjusted to the compiled-in default.

scasey · 06-18-2019, 04:45 PM

Re: #11. Outstanding! Thank you for the through and complete explanation!

pan64 · 06-19-2019, 01:57 AM

based on the man page you find (depends on the version of crontab) it is:
1. compiled into the executable as explained in post #1., but unfortunately it is not all, because
2. sometimes /etc/alternatives/editor is used
3. /usr/bin/editor (or /usr/bin/sensible-editor) is used
4. you can use some tools like update-alternatives or select-editor to configure it
5. whatever else ....
6. if EDITOR and VISUAL are not set.

And finally the garbage was produced because the editor used has no idea about the [type of the] terminal itself and the default term selected by that editor is not compatible with the actual one.

MadeInGermany · 06-25-2019, 12:04 PM

Unfortunately the man page is poor, does not tell what the compiled-in default editor is.
You can try the following hack:

Code:

strings /usr/bin/crontab | grep /bin/

ehartman · 06-25-2019, 04:53 PM

Quote:

Originally Posted by MadeInGermany

Unfortunately the man page is poor, does not tell what the compiled-in default editor is.

That is one of the differences between all of the varying implementations of cron (and crontab) too. Sometimes the "editor" specified in the "configure" part of building the package it is put into the generated man page too, sometimes it isn't.

Code:

strings /usr/bin/crontab | grep /bin/

That's what I used too, although I didn't use the absolute path, but `which crontab`, for distro's that put it somewhere else.