Clear memory cache using Crontab

Question

I'm trying to clear memory cache using cron.

Cron file:

*/2 * * * *  ~/clear_mem.sh

clear_mem.sh:

#!/bin/sh
sudo sh -c "sync; echo 3 > /proc/sys/vm/drop_caches"
touch f

File f is created every two minutes. But memory isn't cleared. If I call script by hands everything is fine. Why?

Solution

Because cron runs commands non-interactively, there is no way for sudo to authenticate.

For commands that require root permission, you should use root's crontab (i.e. sudo crontab -e instead of plain crontab -e) and then avoid the use of sudo within your commands and scripts altogether.

You should also give the full path to the script - preferably locate it some systemwide e.g. /usr/local/bin/clear_mem.sh in place of ~/clear_mem.sh

Comments

[Boris Hamanov]

This begs the question... why are you trying to clear memory cache?