How to Execute a Script Periodically Without Using Crontab

Different environment

Cron passes a minimal set of environment variables to your jobs. To see the difference, add a dummy job like this:

* * * * * env > /tmp/env.output

Wait for /tmp/env.output to be created, then remove the job again. Now compare the contents of /tmp/env.output with the output of env run in your regular terminal.

A common "gotcha" here is the PATH environment variable being different. Maybe your cron script uses the command somecommand found in /opt/someApp/bin, which you've added to PATH in /etc/environment? cron ignores PATH from that file, so runnning somecommand from your script will fail when run with cron, but work when run in a terminal. It's worth noting that variables from /etc/environment will be passed on to cron jobs, just not the variables cron specifically sets itself, such as PATH.

To get around that, just set your own PATH variable at the top of the script. E.g.

#!/bin/bash
PATH=/opt/someApp/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin

# rest of script follows

Some prefer to just use absolute paths to all the commands instead. I recommend against that. Consider what happens if you want to run your script on a different system, and on that system, the command is in /opt/someAppv2.2/bin instead. You'd have to go through the whole script replacing /opt/someApp/bin with /opt/someAppv2.2/bin instead of just doing a small edit on the first line of the script.

You can also set the PATH variable in the crontab file, which will apply to all cron jobs. E.g.

PATH=/opt/someApp/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin

15 1 * * * backupscript --incremental /home /root

Sometimes running a process from root's crontab may cause issues with initial file ownership and rwx mode; those may not be correctly preserved.

In any case:

1) to create a new user, keep it simple:

 $ sudo deluser my-user  # if "my-user" is a regular user
 $ adduser my-user
 $ sudo gpasswd -a my-user sudo

2) to include a new entry with a NOPASSWD tag in sudoers or in a file (e.g. /etc/sudoers.d/60_my-user_rules), make the colon stick to the tag, i.e. NOPASSWD:
I've not seen it before with interspersed space and yr rule becomes:

 my-user my-host = NOPASSWD: /full/path/to/cmd [parameter1 [| parameter2 [| ...]]]

Adding (ALL) before the NOPASSWD: is optional as the rule defaults to (ALL:ALL) anyway. You may however want to not only run your cmd/script with root privilege but also run it as either a given user (spec-user) or as a member of a given group (spec-group) or both. In that case, the rule becomes:

 my-user my-host = ([spec-user][:spec-group]) NOPASSWD: /full/path/to/cmd [parameter1 [| parameter2 [| ...]]]

This will actually restrict yr passwordless sudo disposition to one user, one host and one command. You can harden this rule by specifying the optional parameter(s) to that command. In that case the rule will apply only for that/those exact parameter(s).
For scripts, you could further harden this rule by ensuring that the rule applies only if the script was not modified in any way. This is a way to avoid script-hijacking. This is done through cmd-aliasing and specifying SHA-sums in /etc/sudoers.d/60_my-user_rules.

HTH. Please report if you experience issues with that answer.