BusyBox cron container example

Dockerfile

FROM gliderlabs/alpine:3.3
COPY myawesomescript /bin/myawesomescript
COPY root /var/spool/cron/crontabs/root
RUN chmod +x /bin/myawesomescript
CMD crond -l 2 -f

myawesomescript

#!/bin/sh
echo "Hi Andy" >> /dev/stdout

root

*	*	*	*	*	/bin/myawesomescript

Just mount your own file over the top of /var/spool/cron/crontabs/root (be VERY careful with file permissions here - must be owned by root and chmod 600 on your HOST) and replace e.g. run-parts /etc/periodic/15min with run-parts --lsbsysinit /etc/periodic/15min

@jsarenik I believe the "no . in your file name" logic is part of run-parts, not crond or docker.

Ah yes, totally in run-parts. Here is a patch:

diff --git a/debianutils/run_parts.c b/debianutils/run_parts.c
index 585a4b58f..7677ab894 100644
--- a/debianutils/run_parts.c
+++ b/debianutils/run_parts.c
@@ -119,7 +119,10 @@ static bool invalid_name(const char *c)
 {
 	c = bb_basename(c);
 
-	while (*c && (isalnum(*c) || *c == '_' || *c == '-'))
+	if (*c == '.')
+		return *c;
+
+	while (*c && (isalnum(*c) || *c == '_' || *c == '-' || *c == '.'))
 		c++;
 
 	return *c; /* TRUE (!0) if terminating NUL is not reached */

To test:

mkdir /tmp/testrp
printf "#!/bin/sh\necho test\n" > /tmp/testrp/test.sh
chmod a+x /tmp/testrp/*
busybox run-parts /tmp/testrp
# "test\n" on stdout
mv /tmp/testrp/test.sh /tmp/testrp/.test.sh
busybox run-parts /tmp/testrp
# no output

Planning to send it upstream as soon as I refresh memories of how things are properly done on the mailing list.

UPDATE: Patch sent to the busybox mailing-list and I used exactly this original git documentation.

UPDATE: Patch merged in 8c1f8aa01.

This patch is tested (with busybox@7de0ab21d) and works.

Lol wow. Wonder how many people's workflows are going to break because of this 😂

Lol wow. Wonder how many people's workflows are going to break because of this

Haha :) Should be pretty backward-compatible since the hidden files are still ignored (though were not in my originally proposed patch, but luckily we have peer-review :-)

But I assume lots of people's workflows are based on the fact that files with a . in the filename are not executed 😅 Whether they know that or not

But I assume lots of people's workflows are based on the fact that files with a . in the filename are not executed Whether they know that or not

Yes. And with the patch it works exactly like you say. Just that also file.sh gets executed now (despite the dot).

Yeah bud, file.sh is exactly what I was talking about

Yeah bud, file.sh is exactly what I was talking about

Do you really think people know file.sh will not be executed ? Moreover not executed on Alpine but executed on Debian ?
I'm unfortunately for me - and the time I spent - not part of these people.

Try crond --help:

/ # crond --help
BusyBox v1.24.2 (2016-06-22 17:51:28 GMT) multi-call binary.

Usage: crond -fbS -l N -d N -L LOGFILE -c DIR

    -f  Foreground
    -b  Background (default)
    -S  Log to syslog (default)
    -l N    Set log level. Most verbose:0, default:8
    -d N    Set log level, log to stderr
    -L FILE Log to FILE
    -c DIR  Cron dir. Default:/var/spool/cron/crontabs

I've been looking & this is the most information I can find about this...

for the crond -fbS -l N -d N -L LOGFILE -c DIR it says -l has options from 0 to at least 8 with 0 giving the most detail, it then has -d that maybe has the same scale, but is it -d=log to stderr? so, for example if I ran cron -fbS -l 2 -d 0 -L /var/log/cron.log would it log to the foreground, background, & syslog with level 2 & log to STDERR with verbose log (0) while logging what to /var/log/cron.log? Would it be the level set as -l?

Whoa... You mean this thread, my comment, spawned a patch upstream to BusyBox?! Niiiiiiice. Thanks @jsarenik !

@eduncan911 My pleasure :)