I know that I can have something run every five minutes in cron with a line like:
*/5 * * * * /my/script
What if I don't want it running at 12:00, 12:05, 12:10, but rather at 12:01, 12:06, 12:11, etc? I guess I can do this:
1,6,11,16,21,26,31,36,41,46,51,56 * * * * /my/script
...but that's ugly. Is there a more elegant way to do it?
1-56/5 * * * * /my/script
This should work on vixiecron, I'm not sure about other implementations.
Use your first schedule:
*/5 * * * * /my/script
And add this to the start of your script:
sleep 60
(Yes, this is a joke)
This is quite an old topic, however as so much time has passed there are a few other options now. One of which is not to use cron at all, and use systemd timers. Using these gives you a higher granularity than seconds along with lots of other options
More information is available here https://wiki.archlinux.org/index.php/Systemd/Timers
eg to run a adhoc command
# systemd-run --on-calendar="*:1/5" /bin/touch /tmp/foo2
Running timer as unit run-r31335c4878f24f90b02c8ebed319ca60.timer.
Will run service as unit run-r31335c4878f24f90b02c8ebed319ca60.service.
# systemctl status run-r31335c4878f24f90b02c8ebed319ca60.timer
● run-r31335c4878f24f90b02c8ebed319ca60.timer - /bin/touch /tmp/foo2
Loaded: loaded
Transient: yes
Drop-In: /run/systemd/system/run-r31335c4878f24f90b02c8ebed319ca60.timer.d
└─50-Description.conf, 50-OnCalendar.conf, 50-RemainAfterElapse.conf
Active: active (waiting) since Wed 2017-10-25 09:05:13 UTC; 40s ago
# ls -l /tmp/foo*
-rw-r--r-- 1 root root 0 Oct 25 09:06 /tmp/foo2
# sleep 300; ls -l /tmp/foo*
-rw-r--r-- 1 root root 0 Oct 25 09:11 /tmp/foo2
# date; ls -l /tmp/foo2
Wed Oct 25 09:21:42 UTC 2017
-rw-r--r-- 1 root root 0 Oct 25 09:21 /tmp/foo2
edit: these type of timers wont persist over reboot, if you want them to make sure you generate a proper service file, with the relevant oncalendar line
I'd create a new script "delaystart" that takes a sleeping period as first parameter and the script to run as the rest. I'd make the script check the crontab line for the line with the script and only start the script if the line is not commented out. That makes it reusable, and ps won't report the script as running when it really isn't.
#!/bin/bash
sleeptime=$1
sleep ${sleeptime}
shift
if ( ! crontab -l | grep -e '#.+delaystart '${sleeptime} $* ) then
$*
fi
sean.bright's joke got me thinking... why not use...
* * * * * /my/script
...and within the script do this...
#!/bin/bash
export WHEN=`date '+%M'`
echo $WHEN
export DOIT=`echo "$WHEN % 5" | bc`
echo $DOIT
if [ $DOIT != 0 ] ; then
echo "ha ha ha"
fi
echo "done"
...a kludge... maybe, but as ugly as the crontab... I don't know.
Related
I'm running a docker container with an image:
ubi8/ubi-minimal
The cronjob has correct path and go packet is already installed:
crontab -l
*/2 * * * * go run /usr/local/src/script.go
The file has correct permissions:
-rw-r-xr-x 1 root root 6329 Jun 16 15:10 script.go
However the crontab -e is like this:
/bin/sh: /usr/bin/vi: No such file or directory
crontab: "/usr/bin/vi" exited with status 127
and
cat /etc/crontab
SHELL=/bin/bash
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root
# For details see man 4 crontabs
# Example of job definition:
# .---------------- minute (0 - 59)
# | .------------- hour (0 - 23)
# | | .---------- day of month (1 - 31)
# | | | .------- month (1 - 12) OR jan,feb,mar,apr ...
# | | | | .---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat
# | | | | |
# * * * * * user-name command to be executed
The crontab was added in the dockerfile like this:
RUN crontab -l | { cat; echo "*/2 * * * * go run /usr/local/src/script.go"; } | crontab -
I think is correctly setup isn't it?
the crontab should execute the script every 2 minuts but it's not. Also the image is minimal and I cannot edit any file I just included some permissions to the files from the dockerfile.
If needed to change any Path from crontab I have to do this trough the dockerfile.
As it sounds like a lot of trouble, consider skipping the cron daemon entirely and just sleep in a loop
#!/bin/sh
while true; do
TIME_LOOP_START=$(date +%s) # integer time in seconds
script.go
# calculate offset for 2 minutes in seconds
sleep $(($TIME_LOOP_START + 120 - $(date +%s)))
done
adapted from
https://askubuntu.com/questions/852070/automatically-run-a-command-every-5-minutes
Get current time in seconds since the Epoch on Linux, Bash
You may find this is even better extended by making the time and target executable arguments $1 $2
You need to start the cron daemon. Here's a Dockerfile I made to illustrate
FROM registry.access.redhat.com/ubi8/ubi-minimal
RUN microdnf update && microdnf install cronie
RUN crontab -l | { cat; echo "*/2 * * * * /usr/local/src/script.sh"; } | crontab -
COPY script.sh /usr/local/src/
CMD crond -n
Note that the CMD runs crond with the -n option which keeps crond in the foreground. If we let it daemonize, docker would see that the process had ended and would terminate the container.
Instead of using go, I made a small shell script like this, called script.sh
#/bin/sh
echo Hello from script >> ~/log.txt
It writes to /root/log.txt every 2 minutes.
I am trying to use a docker container based on an Alpine image to run a scheduled cron job, following this tutorial, but after printing the statement in my startup script, the container just exits, without running my other script.
My docker-compose service is configured as follows:
cron:
image: alpine:3.11
command: /usr/local/startup.sh && crond -f -l 8
volumes:
- ./cron_tasks_folder/1min:/etc/periodic/1min/:ro
- ./cron_tasks_folder/15min:/etc/periodic/15min/:ro
- ./cron_tasks_folder/hourly:/etc/periodic/hourly/:ro
- ./scripts/startup.sh:/usr/local/startup.sh:ro
So it runs an initial script called startup.sh and then starts the cron daemon. The startup.sh script contains the following:
#!/bin/sh
echo "Starting startup.sh.."
echo "* * * * * run-parts /etc/periodic/1min" >> /etc/crontabs/root
crontab -l
sleep 300
I dropped a sleep command in there just so I could launch an interactive shell on the container and make sure everything inside it looks good. The script creates another folder for 1min scripts. I have added a test script in there, and I can verify it's there:
/etc/periodic/1min # ls -a
. .. testScript
The script is executable:
/etc/periodic/1min # ls -l testScript
-rwxr-xr-x 1 root root 31 Jul 30 01:51 testScript
And testScript is just an echo statement to make sure it's working first:
echo "The donkey is in charge"
And looking at the root file in etc/crontabs, I see the following (I've re-run the container several times, and each time it's creating a new 1min folder, which is unnecessary, but I think not the problem here):
# do daily/weekly/monthly maintenance
# min hour day month weekday command
*/15 * * * * run-parts /etc/periodic/15min
0 * * * * run-parts /etc/periodic/hourly
0 2 * * * run-parts /etc/periodic/daily
0 3 * * 6 run-parts /etc/periodic/weekly
0 5 1 * * run-parts /etc/periodic/monthly
* * * * * run-parts /etc/periodic/1min
* * * * * run-parts /etc/periodic/1min
* * * * * run-parts /etc/periodic/1min
* * * * * run-parts /etc/periodic/1min
* * * * * run-parts /etc/periodic/1min
The echo statement in testScript is never printed to my terminal, and the container exits with exit code 0 shortly after starting. I want to print this statement every minute... what am I missing?
In the docker compose file you have
command: /usr/local/startup.sh && crond -f -l 8
The intention is to run as a shell command, but it's not at all clear from the question that's what's going to happen; that depends on your ENTRYPOINT. Since it's defined with [] brackets, not additional shell will be provided. The command value will be passed as arguments to the ENTRYPOINT.
Assuming that will become a shell command, && in the shell runs the left hand side, and if that succeeds, then runs the right hand side. So startup.sh needs to complete before crond is executed. startup.sh ends with
sleep 300
crond is invoked only after that 300 seconds.
In either case, crond is either not invoked at all, or sleep has not been completing. The comments show that an error starting crond was discovered.
Using an entrypoint such as this is standard practice to configure the environment before, or provide runtime parameters when, invoking the main executable. To do it right, you should make sure to use exec to run the main executable so that it receives the signals that would otherwise go to the bash shell running the entrypoint script.
So at the end of startup.sh:
exec crond -f -l 8
Will replace the shell running startup.sh with crond, so that crond receives all signals (at this point the shell is gone). It's subtle but important!
In general, keep the invocation of the application as simple as possible. Case in point, your execution process was split between entrypoint, command, and startup script, with no clear interface between them. You wouldn't have gotten hung up on the invocation if you had put crond directly into the Dockerfile and left it at that. Sometimes arguments must be provided at runtime, but environment variables - which have names, not just positions - are often preferred. This keeps invocations simple and debugging straightforward. But, when that doesn't work, a shell script entrypoint is a great solution - just make sure to exec your final process!
uname -r
4.5.5-300.fc24.x86_64
I have appended 0 0 test touch ~/ana.cron to /etc/anacrontab. But there is no effect after rebooting or resuming from sleep or running sudo anacron -f. I can't find the output file ana.cron.
cat /etc/anacrontab
# /etc/anacrontab: configuration file for anacron
# See anacron(8) and anacrontab(5) for details.
SHELL=/bin/sh
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root
# the maximal random delay added to the base delay of the jobs
RANDOM_DELAY=45
# the jobs will be started during the following hours only
START_HOURS_RANGE=3-22
#period in days delay in minutes job-identifier command
1 5 cron.daily nice run-parts /etc/cron.daily
7 25 cron.weekly nice run-parts /etc/cron.weekly
#monthly 45 cron.monthly nice run-parts /etc/cron.monthly
0 0 test touch ~/ana.cron
How to solve this?
I'm not sure period can be of 0.
1 0 test.daily nice run-parts touch ~/ana.cron
If you want your task to be run at startup, then use #reboot
#reboot test.reboot nice run-parts touch ~/ana.cron
This have been discussed several times in previous post. I followed given advise but it does not work for me. I have two scripts which are run by the cron service every minute. To my surprise, only one runs per minute( 1st in the list below), the other fails (2nd in list below). Most surprising, when run direct from the terminal, both scripts execute fine.
Cron setup :
*/1 * * * * /home/user/Desktop/scripts/generatepattern.sh
*/1 * * * * /home/user/Desktop/scripts/getnextfile.sh
File permissions are:
-rwxr--r-- 1 user user 522 Jul 25 16:18 generatepattern.sh
-rwxr--r-- 1 user user 312 Jul 25 23:02 getnextfile.sh
The code for the non-schedulable( not running in cron ) is :
#!/bin/bash
#Generate a file to be used for the search
cd /home/user/Desktop/scripts
no=`cat filecount.txt`
if test $no -lt 20
then
#echo "echo less"
#echo $no
expr `cat filecount.txt` + 1 >filecount.txt
fi
In the last line you wrote cat filecount.txt instead of cat /home/user/Desktop/scripts/filecount.txt
I discovered the main issue was that the new cron settings only get used when the vi editor gets closed. Changes have to be made on the editor and a :wq command issued so that the new settings get installed. Just issuing :w command does not work since no install happens(this was my mistake). I realised this after issuing :wq command on vi and the following output displayed :-
# crontab -e
crontab: installing new crontab
Thanks to all other suggestions made.
I have a shell script that I can run with root user this way:
root#vivid-15:~# ./backup.sh
It's on /root/backup.sh. Now, how do I schedule it on crontab to execute every day at 01:00 AM? I done this:
0 1 * * * root
But now I don't know how to proceed the command to do that.
Have you tried this? Also, a "1" in the hour field means 1am, not 1pm.
0 1 * * * root /root/backup.sh
Edit: changed the 13 (1pm) back to 1 (1am).
Crontab format:
MIN HOUR DAY MON WEEKDAY CMD
I don't know that you need to define what user you want it to run as when its in crontab -- commands will be run as the user who makes the entries with crontab -e. To create a cron process that runs as root, either login as root or set it up with $ sudo crontab -e
I think you're looking for something more like this:
0 1 * * * /root/backup.sh