IPなしで起動するためのcrontabは機能しません。

私のWebサーバーに問題があります。通常、No-IP-DUCを起動しますsudo noip2。 cronjobを使用して自動化しようとしています。を使用してcrontab -e次のファイルを作成しました。

# Edit this file to introduce tasks to be run by cron.
#
# Each task to run has to be defined through a single line
# indicating with different fields when the task will be run
# and what command to run for the task
#
# To define the time you can provide concrete values for
# minute (m), hour (h), day of month (dom), month (mon),
# and day of week (dow) or use '*' in these fields (for 'any').#
# Notice that tasks will be started based on the cron's system
# daemon's notion of time and timezones.
#
# Output of the crontab jobs (including errors) is sent through
# email to the user the crontab file belongs to (unless redirected).
#
# For example, you can run a backup of all your user accounts
# at 5 a.m every week with:
# 0 5 * * 1 tar -zcf /var/backups/home.tgz /home/
#
# For more information see the manual pages of crontab(5) and cron(8)
#
# m h  dom mon dow   command

@reboot cd /home/username/noip-2.1.9-1 && sudo noip2

うまくいかず、理由がわかりません。誰かが私を助けることができれば良いでしょう。