# Solved: Errors in crontab file, can't install

## Cause of the error

You may encounter this error while creating a new crontab or updating an
existing one that has a syntax error.

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## Solution

Crontabs have simple, but strict syntax rules. Every crontab file has to:

- Start whit a correct cron schedule (can be an environmental variable) or
  comment on every line
- Contain a username for each cron job
- Contain valid and executable shell expression
- End with a newline

```bash
# 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
# |  |  |  |  | .---- username
# |  |  |  |  | |
# *  *  *  *  * user  command to be executed
*  *  *  *  *  root   echo 'Hello world!'
```

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