cron apparently requires a newline character on its own line at the end of the file

Question

I'm trying to understand why cron is refusing to work with a certain crontab file. The manpage for crontab says:

cron requires that each entry in a crontab end in a newline character. If the last entry in a crontab is missing the newline, cron will consider the crontab (at least partially) broken and refuse to install it.

Given the following cron file:

# managed by Fabric$
$
SHELL=/bin/sh$
PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin$
$
# m h dom mon dow user  command$
17 *    * * *   root    cd / && run-parts --report /etc/cron.hourly$
25 6    * * *   root    test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.daily )$
47 6    * * 7   root    test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.weekly )$
52 6    1 * *   root    test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.monthly )$
$
# Postgres monitoring$
*  *    * * *   postgres cd / && /etc/cron.d/pgup.sh$
*/5 *   * * *   postgres   cd / && /etc/cron.d/aws-scripts-mon/mon-put-instance-data.pl --mem-avail --disk-space-util --disk-path=/mnt$
$
# Postgres Backup$
00 00   * * *   postgres /etc/cron.d/pgbackup.sh$

Noting that the "$"character indicates a LF (vim unix format) character.

And I receive the following error in syslog when I restart cron:

Mar 31 17:34:02 postgres-primary0 cron[30852]: (system) ERROR (Missing newline before EOF, this crontab file will be ignored)

And adding a blank line at the end of the cron file results in no error when restarting cron.

Conclusion:

As far as I can tell the last entry does end in a newline character. So it seems like crontab is not recognizing it.

Is this a bug? Maybe what was intended was that there be a newline on its own line at the end of the file, in which case the documentation is misleading. Or possibly I'm not understanding "newline" correctly in this context...Some clarification on this matter will be appreciated.

Answer 1

Is this a bug?

No. I created a file with no newline character at the end. Nevertheless Vim (after :set list) shows $ at the end. It looks like your premise is false, your file is missing a final newline, cron works as intended.

---

Notes:

• POSIX requires a trailing newline character to consider any line to be complete.

  3.195 Incomplete Line
  A sequence of one or more non-<newline> characters at the end of the file.

  […]

  3.206 Line
  A sequence of zero or more non-<newline> characters plus a terminating <newline> character.

  So the behavior of cron is not just an arbitrary quirk (although the tool might not be that restrictive). For more insight see Why should text files end with a newline?

• Vim with default settings will fix the missing newline while saving, unless you tell it not to.

• To tell whether there is a newline character at the end or not, make a hexdump of the file, e.g. hexdump the_file or xxd the_file. In case of your crontab this may be hard. In my Debian the crontab is /var/spool/cron/crontabs/kamil, but since I have no access to /var/spool/cron/crontabs/ as a normal user, I cannot just xxd the file. To overcome this I can use the following trick:

  EDITOR=xxd crontab -e
  

  There is a newline at the end iff the last byte reports as 0a.