Read / Write access to `/sys/kernel/` files not permitted?

jyoun44

Hi There!

First time poster, newbie linux enthusiast here. I'll cut right to the chase:

On a fresh install of Ubuntu 18.04.04: why don't I (as the root user) have read /
write access to the files in /sys/kernel/? Any pointers in the right directions
would be greatly appreciated.

I didn't see any guidelines for posting etiquette so I'll do my best to follow Eric S. Raymond and Rick Moen's "How to ask smart questions essay".

Observations:

I was curious about the devices that were mounted on my computer so I ran the following:

  $ mount > filesystems.txt

and came across securityfs:

  ..other file systems..

  securityfs on /sys/kernel/security type securityfs (rw,nosuid,nodev,noexec,relatime)

  ..other file systems..

I wanted to see the contents of this directory so I ran the following:

  $ sudo less /sys/kernel/security/integrity/ima/policy

and got this message:

  /sys/kernel/security/integrity/ima/policy: Permission denied

I tried openning another file in the /sys/kernel/ directory and got the same
Permission denied message. I didn't find any results on the web so, as a
final attempt, booted a fresh install of Ubuntu from a flash drive, tried
openning another file in /sys/kernel/, and got the same error.

Any ideas on why Ubuntu limits access to this directory? Thanks again for being
a part of this community - any pointers in the right direction would be
apprecaited.

yangbonis

A similar problem is caused by CONFIG_IMA_READ_POLICY of /boot/config-*, but I can access to other file of /sys/kernel/ directory.