Lab 2.1 Can’t delete mycgroup.

ldt

Dumb question. But after doing the lab I’m unable to clean up and delete the cgroup that was created. I’m using the LF pre-built Ubuntu 18.04 on Vmware Workstation 15 Player. I’ve completed the lab successfully, but now I get this.

student@ubuntu:/sys/fs/cgroup/freezer$ ll
total 0
dr-xr-xr-x  4 root root   0 Sep  8 07:45 ./
drwxr-xr-x 15 root root 380 Sep  8 07:17 ../
-rw-r--r--  1 root root   0 Sep  8 07:44 cgroup.clone_children
-rw-r--r--  1 root root   0 Sep  8 09:40 cgroup.procs
-r--r--r--  1 root root   0 Sep  8 07:44 cgroup.sane_behavior
drwxr-xr-x  2 root root   0 Sep  8 07:45 mycgroup/
-rw-r--r--  1 root root   0 Sep  8 07:44 notify_on_release
-rw-r--r--  1 root root   0 Sep  8 07:44 release_agent
-rw-r--r--  1 root root   0 Sep  8 07:44 tasks
drwxr-xr-x  5 root root   0 Sep  8 07:44 user/
student@ubuntu:/sys/fs/cgroup/freezer$ sudo rm -r mycgroup
rm: cannot remove 'mycgroup/cgroup.procs': Operation not permitted
rm: cannot remove 'mycgroup/freezer.self_freezing': Operation not permitted
rm: cannot remove 'mycgroup/tasks': Operation not permitted
rm: cannot remove 'mycgroup/freezer.parent_freezing': Operation not permitted
rm: cannot remove 'mycgroup/freezer.state': Operation not permitted
rm: cannot remove 'mycgroup/notify_on_release': Operation not permitted
rm: cannot remove 'mycgroup/cgroup.clone_children': Operation not permitted
student@ubuntu:/sys/fs/cgroup/freezer$ 

How do you clean up after this lab? Thanks.

chrispokorni

Hi @ldt,

Where you able to successfully thaw the process as described by the lab guide? After successfully freezing and thawing that second terminal, where you able to terminate the terminal's process?
Ensure that no process is managed by any of the files in mycgroup/, specifically ensure that mycgroup/tasks is empty, while all other files should be empty or include a 0.
Then try:

student@ubuntu:/sys/fs/cgroup/freezer$ sudo cd mycgroup/
student@ubuntu:/sys/fs/cgroup/freezer/mycgroup$ sudo rm * 
student@ubuntu:/sys/fs/cgroup/freezer/mycgroup$ sudo cd ..
student@ubuntu:/sys/fs/cgroup/freezer$ sudo rmdir mycgroup

If unsuccessful, try adding -f to sudo rm -f *.

Regards,
-Chris

ldt

Hi @chrispokorni,

Thanks for your help. As I expected, after shutting down and restarting Ubuntu, mycgroup was gone. It is not permanent. But I was sure this was the answer to my problem since I had not killed the second terminal process. So I have repeated the lab and I am still unable to delete mycgroup.

student@ubuntu:/sys/fs/cgroup/freezer$ sudo mkdir mycgroup
student@ubuntu:/sys/fs/cgroup/freezer$ cd mycgroup
student@ubuntu:/sys/fs/cgroup/freezer/mycgroup$ ls
cgroup.clone_children  cgroup.procs  freezer.parent_freezing  freezer.self_freezing  freezer.state  notify_on_release  tasks
student@ubuntu:/sys/fs/cgroup/freezer/mycgroup$ cat tasks
student@ubuntu:/sys/fs/cgroup/freezer/mycgroup$ ps -ef |grep bash
student    3143   3134  0 08:47 pts/0    00:00:00 bash
student    3356   3143  0 08:50 pts/0    00:00:00 grep --color=auto bash
(open a new terminal)
student@ubuntu:/sys/fs/cgroup/freezer/mycgroup$ ps -ef |grep bash
student    3143   3134  0 08:47 pts/0    00:00:00 bash
student    3368   3134  0 08:50 pts/1    00:00:00 bash
student    3377   3143  0 08:50 pts/0    00:00:00 grep --color=auto bash
student@ubuntu:/sys/fs/cgroup/freezer/mycgroup$ cat tasks
student@ubuntu:/sys/fs/cgroup/freezer/mycgroup$ sudo sh -c "echo 3368 >> tasks"
student@ubuntu:/sys/fs/cgroup/freezer/mycgroup$ cat tasks
3368
student@ubuntu:/sys/fs/cgroup/freezer/mycgroup$ sudo sh -c "echo FROZEN > freezer.state"
(teminal 3368 is frozen)
student@ubuntu:/sys/fs/cgroup/freezer/mycgroup$ sudo sh -c "echo THAWED > freezer.state"
(teminal 3368 is thawed)
student@ubuntu:/sys/fs/cgroup/freezer/mycgroup$ sudo kill -9 3368
student@ubuntu:/sys/fs/cgroup/freezer/mycgroup$ ps -ef |grep bash
student    3143   3134  0 08:47 pts/0    00:00:00 bash
student    3422   3143  0 08:55 pts/0    00:00:00 grep --color=auto bash
student@ubuntu:/sys/fs/cgroup/freezer/mycgroup$ cat tasks
student@ubuntu:/sys/fs/cgroup/freezer/mycgroup$ cat cgroup.clone_children 
0
student@ubuntu:/sys/fs/cgroup/freezer/mycgroup$ cat cgroup.procs 
student@ubuntu:/sys/fs/cgroup/freezer/mycgroup$ cat freezer.parent_freezing 
0
student@ubuntu:/sys/fs/cgroup/freezer/mycgroup$ cat freezer.self_freezing 
0
student@ubuntu:/sys/fs/cgroup/freezer/mycgroup$ cat freezer.state
THAWED
student@ubuntu:/sys/fs/cgroup/freezer/mycgroup$ cat notify_on_release 
0
student@ubuntu:/sys/fs/cgroup/freezer/mycgroup$ sudo rm *
rm: cannot remove 'cgroup.clone_children': Operation not permitted
rm: cannot remove 'cgroup.procs': Operation not permitted
rm: cannot remove 'freezer.parent_freezing': Operation not permitted
rm: cannot remove 'freezer.self_freezing': Operation not permitted
rm: cannot remove 'freezer.state': Operation not permitted
rm: cannot remove 'notify_on_release': Operation not permitted
rm: cannot remove 'tasks': Operation not permitted
student@ubuntu:/sys/fs/cgroup/freezer/mycgroup$ sudo rm -f *
rm: cannot remove 'cgroup.clone_children': Operation not permitted
rm: cannot remove 'cgroup.procs': Operation not permitted
rm: cannot remove 'freezer.parent_freezing': Operation not permitted
rm: cannot remove 'freezer.self_freezing': Operation not permitted
rm: cannot remove 'freezer.state': Operation not permitted
rm: cannot remove 'notify_on_release': Operation not permitted
rm: cannot remove 'tasks': Operation not permitted
student@ubuntu:/sys/fs/cgroup/freezer/mycgroup$ 

For some reason I'm not getting the same result you do.

Thanks,
ldt

chrispokorni

Can you try to only remove the mycgroup/ directory after you terminated the second shell process, skipping commands from lines (1-3)? Similar to this:

student@ubuntu:~$ sudo rmdir /sys/fs/cgroup/freezer/mycgroup/

Regards,
-Chris

ldt

OK. So rmdir works but rm * doesn't.

student@ubuntu:/sys/fs/cgroup/freezer$ sudo mkdir mycgroup
student@ubuntu:/sys/fs/cgroup/freezer$ cd mycgroup
student@ubuntu:/sys/fs/cgroup/freezer/mycgroup$ sudo rm *
rm: cannot remove 'cgroup.clone_children': Operation not permitted
rm: cannot remove 'cgroup.procs': Operation not permitted
rm: cannot remove 'freezer.parent_freezing': Operation not permitted
rm: cannot remove 'freezer.self_freezing': Operation not permitted
rm: cannot remove 'freezer.state': Operation not permitted
rm: cannot remove 'notify_on_release': Operation not permitted
rm: cannot remove 'tasks': Operation not permitted
student@ubuntu:/sys/fs/cgroup/freezer/mycgroup$ sudo rm -f *
rm: cannot remove 'cgroup.clone_children': Operation not permitted
rm: cannot remove 'cgroup.procs': Operation not permitted
rm: cannot remove 'freezer.parent_freezing': Operation not permitted
rm: cannot remove 'freezer.self_freezing': Operation not permitted
rm: cannot remove 'freezer.state': Operation not permitted
rm: cannot remove 'notify_on_release': Operation not permitted
rm: cannot remove 'tasks': Operation not permitted
student@ubuntu:/sys/fs/cgroup/freezer/mycgroup$ cd ..
student@ubuntu:/sys/fs/cgroup/freezer$ sudo rmdir mycgroup
student@ubuntu:/sys/fs/cgroup/freezer$ ll
total 0
dr-xr-xr-x  3 root root   0 Sep 11 14:14 ./
drwxr-xr-x 15 root root 380 Sep 11 14:11 ../
-rw-r--r--  1 root root   0 Sep 11 14:13 cgroup.clone_children
-rw-r--r--  1 root root   0 Sep 11 14:14 cgroup.procs
-r--r--r--  1 root root   0 Sep 11 14:13 cgroup.sane_behavior
-rw-r--r--  1 root root   0 Sep 11 14:13 notify_on_release
-rw-r--r--  1 root root   0 Sep 11 14:13 release_agent
-rw-r--r--  1 root root   0 Sep 11 14:13 tasks
drwxr-xr-x  5 root root   0 Sep 11 14:13 user/
student@ubuntu:/sys/fs/cgroup/freezer$ 

I didn't even do the lab exercise here. I just created the directory and then tried to delete it. I was surprised first of all to find that mkdir not only creates a directory, but some how mysteriously creates content in it as well. Just as mysterious is that it can't be deleted in the normal way. I suppose that only seems strange to a novice, but at least I have a working solution to the problem. Thanks for your help.
ldt