CentOS Question posted in
The official documentation can be found here.

python-crontab: find existing cron jobs is giving wrong result – CentOS

With my python script below, I wanted to check if a cron job is defined in my linux (centOS 7.5) server, and if it doesn’t exist, I will add one by using python-crontab module.. It was working well until I gave CRONTAB -R to delete existing cron jobs and when I re-execute my python script, it is saying cronjob exists even after they were removed using crontab -r..

import os
from crontab import CronTab
cron = CronTab(user="ansible")
job = cron.new(command='echo hello_world')
job.minute.every(1)
basic_command = "* * * * * echo hello_world"
basic_iter = cron.find_command("hello_world")

for item in basic_iter:
    if str(item) == basic_command:
        print("crontab job already exist", item)
        break
    else:
        job.enable()
        cron.write()
        print("cronjob does not exist and added successfully.. please see "crontab -l" ")
        break

list of current cron jobs

[ansible@node1 ansible]$ crontab -l
no crontab for ansible
[user – ansible]

python code results:

crontab job already exist * * * * * echo hello_world

It was working until I removed cron jobs using command crontab -r and now my python output is saying that cron job already exists.

Not sure what my mistake was – please help.. (or if there is any better way to find cron jobs in local user, please help with that).

Tags:

2

Answers


  1. 0

    The problem is that you have initialized a new Cron job before checking if it exists. You assumed that Cron.find_command() is only identifying enabled cron jobs. But it also identifies cronjobs that are created, but not enabled yet.

    So, you have to check if the cronjob exists before creating a new job. Then, if it does not exist, you can create a new cron job and enable it. You can try the below code:

    import os
from crontab import CronTab
cron = CronTab("ansible")
basic_command = "* * * * * echo hello_world"
basic_iter = cron.find_command("hello_world")
exsist=False
for item in basic_iter:
    if str(item) == basic_command:
        print("crontab job already exist", item)
        exsist=True
        break

if not exsist:
    job = cron.new(command='echo hello_world')
    job.minute.every(1)
    job.enable()
    cron.write()
    print("cronjob does not exist and added successfully.. please see "crontab -l" ")
    Login or Signup to reply.
  2. 0

    Another Solution might be to add the items to an list as the output of the find command is an generator object but by putting the items into an list makes it easier to work on. This is what I did to solve the problem you had
    Below here based on everything else already being initialized

        List_A=[]
    basic_iter = cron.find_command("hello world")
    for item in basic_iter:
     List_A.append(item)
#From there you can do more but here are 2 examples
if len(List_A) == 0:
 #create cronjob
else:
 #don't create cron job

 #or you could do a for loop comparing if you want to iterate
 for i in List_A:
  if i =="hello world": don't create cron job
  else: create cron job

    Hope this helps sorry for formatting this is my first time

    Login or Signup to reply.
Please signup or login to give your own answer.

Back To Top
Search