[SOLVED] is cron daemon crond is running when there is no cronjob set ?

SpongeBOB · 2023-07-06 09:13:05

Hi everyone,

I would like to create a cronjob.

I've found a "tutorial" online --> https://linuxhandbook.com/crontab/#the-cron-daemon

But it's start already weirdly...

on his example

christopher@pop-os:~$ ps ux | grep crond
christo+  8942  0.0  0.0  18612   840 pts/0    S+   02:16   0:00 grep --color=auto crond

I can see that the daemon is running for my user account.

for me it's look like that we see the grep process ! not the crond !? Am I right?

anyway I've tried on my Devuan(Chimaera) and I don't see a crond running.. is that normal ?

Thanks.

alexkemp · 2023-07-06 10:25:42

SpongeBOB wrote:

it's look like that we see the grep process ! not the crond !? Am I right?

Correct (I got the exact same result). Cron is NOT running in your system (you have grepped for 'crond', and therefore in the ps listing it shows the full command-line, which includes 'crond'). If Cron *was* running there would be at least 2 ps lines containing 'crond', one for the daemon & one for grep.

Andre4freedom · 2023-07-06 10:51:13

my 2 cents to it:

andre@kyoto:~$ ps -aef | grep cron
root      2403     1  0 09:45 ?        00:00:00 /usr/sbin/cron
andre    11016 10606  0 12:45 pts/0    00:00:00 grep --color=auto cron
andre@kyoto:~$

The daemon is called cron:

andre@kyoto:~$ ls -l /etc/init.d/cron*
-rwxr-xr-x 1 root root 3059 Oct 11  2019 /etc/init.d/cron
andre@kyoto:~$

Devuan 4, Chimaera, up-to-date.

alexkemp · 2023-07-06 13:53:47

I blame forgetfulness (aka old age):

$ ps aux | grep cron
root      1516  0.0  0.0   8684  3460 ?        Ss   Jul01   0:01 /usr/sbin/cron
alexk     8432  0.0  0.0   6372   712 pts/0    S+   14:52   0:00 grep --color=auto cron

boughtonp · 2023-07-06 15:06:25

On the unasked adjacent question, the common solution to grep appearing in ps|grep output is to alter the pattern so it doesn't match itself, e.g. ps aux | grep 'cro[n]'

Another solution is pgrep.

SpongeBOB · 2023-07-07 05:28:07

Thank you all for your reply !

Thank you that have confirmed my thinking. I'm shocked that some people can post "tutorial" without mastering a bit the topic.... Internet peoples..

@boughtonp, oh great indeed I will use also a regex expression in grep to avoid to have the grep itself in the results.

ps aux | grep 'cron$'

Last edited by SpongeBOB (2023-07-07 05:28:49)

aitor · 2023-07-09 18:28:29

SpongeBOB wrote:

Thank you all for your reply !
Thank you that have confirmed my thinking. I'm shocked that some people can post "tutorial" without mastering a bit the topic.... Internet peoples..
@boughtonp, oh great indeed I will use also a regex expression in grep to avoid to have the grep itself in the results.
ps aux | grep 'cron$'

Another way to avoid the unwanted expression might be using the syntax grep -v "unwanted_regex_expression". Therefore, you can avoid the grep itself as follows:

ps aux | grep "cron" | grep -v " grep "

aitor · 2023-07-09 18:56:05

aitor wrote:

SpongeBOB wrote:
Thank you all for your reply !
Thank you that have confirmed my thinking. I'm shocked that some people can post "tutorial" without mastering a bit the topic.... Internet peoples..
@boughtonp, oh great indeed I will use also a regex expression in grep to avoid to have the grep itself in the results.
ps aux | grep 'cron$'
Another way to avoid the unwanted expression might be using the syntax grep -v "unwanted_regex_expression". Therefore, you can avoid the grep itself as follows:
ps aux | grep "cron" | grep -v " grep "

The line containing the grep command itself is supposed to be printed at the end due to its higher pid -and then it'll be ignored thanks to the use of the regex 'cron$'-, but who knows...

boughtonp · 2023-07-09 21:11:27

Neither appending an end-of-line anchor nor doing a second negative grep are guaranteed "lossless" solutions - they both have potential to exclude valid lines. (Might not be very likely with the latter, but is still possible.)

Wrapping one of the characters in a character class will never exclude anything except the specific unwanted grep line, and is only two extra key presses.

And again, an even better solution is to ensure procps is installed, and use pgrep, which never includes itself in its output and defaults to just the pid; if one needs the extra detail ps provides, ps u $(pgrep cron) will do that.

SpongeBOB · 2023-07-29 13:12:01

Thank you all for your additional inputs !

I've tried pgrep = ♥

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#1 2023-07-06 09:13:05

[SOLVED] is cron daemon crond is running when there is no cronjob set ?

#2 2023-07-06 10:25:42

Re: [SOLVED] is cron daemon crond is running when there is no cronjob set ?

#3 2023-07-06 10:51:13

Re: [SOLVED] is cron daemon crond is running when there is no cronjob set ?

#4 2023-07-06 13:53:47

Re: [SOLVED] is cron daemon crond is running when there is no cronjob set ?

#5 2023-07-06 15:06:25

Re: [SOLVED] is cron daemon crond is running when there is no cronjob set ?

#6 2023-07-07 05:28:07

Re: [SOLVED] is cron daemon crond is running when there is no cronjob set ?

#7 2023-07-09 18:28:29

Re: [SOLVED] is cron daemon crond is running when there is no cronjob set ?

#8 2023-07-09 18:56:05

Re: [SOLVED] is cron daemon crond is running when there is no cronjob set ?

#9 2023-07-09 21:11:27

Re: [SOLVED] is cron daemon crond is running when there is no cronjob set ?

#10 2023-07-29 13:12:01

Re: [SOLVED] is cron daemon crond is running when there is no cronjob set ?

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