I am trying to clear the cache on my laptop running:

Operating System: Ubuntu 20.04 LTS
          Kernel: Linux 5.4.0-40-generic

However when I put in these commands this is the output:

$ sudo sync; echo 1 > /proc/sys/vm/drop_caches
bash: /proc/sys/vm/drop_caches: Permission denied
$ sudo sync; echo 2 > /proc/sys/vm/drop_caches
bash: /proc/sys/vm/drop_caches: Permission denied
$ sudo sync; echo 3 > /proc/sys/vm/drop_caches
bash: /proc/sys/vm/drop_caches: Permission denied

However when checking my permissions I get this:

$ sudo -l
Matching Defaults entries for [MY USERNAME] on [COMPUTER NAME]:
    env_reset, mail_badpass,
User [MY USERNAME] may run the following commands on [COMPUTER NAME]:
    (ALL : ALL) ALL

It would appear that I can run all commands. Why is this happening, and is there a fix?

I have also replicated the issue in root.


You are running sync with sudo, but not the shell's redirection of the echo. Instead do:

sudo sh -c 'sync; echo 1 > /proc/sys/vm/drop_caches'


sudo sync; echo 1 | sudo tee /proc/sys/vm/drop_caches >/dev/null
  • @KevinWilkins accept that answer if it helped – Gryu Jul 3 '20 at 20:00
  • Thanks for the reminder! – Kevin Wilkins Jul 3 '20 at 20:28

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