Reschedule updatedb.mlocate - Linux

我的系統（Ubuntu 14.04）每天早上六點多都會自動執行updatedb.mlocate
我想把他改到晚上九點多執行
有試著修改/etc/crontab如下，卻沒有預期的效果，重開機也一樣：

# /etc/crontab: system-wide crontab
# Unlike any other crontab you don't have to run the `crontab'
# command to install the new version when you edit this file
# and files in /etc/cron.d. These files also have username fields,
# that none of the other crontabs do.

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
0 21 * * * root test -x /usr/sbin/anacron || ( cd / && run-parts --rep
ort /etc/cron.daily )
22 21 * * 7 root test -x /usr/sbin/anacron || ( cd / && run-parts --rep
ort /etc/cron.weekly )
27 21 1 * * root test -x /usr/sbin/anacron || ( cd / && run-parts --rep
ort /etc/cron.monthly )
#

不知道我哪裡弄錯了，請指教

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