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.

[email protected]:/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/
[email protected]:/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
[email protected]:/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:

[email protected]:/sys/fs/cgroup/freezer$ sudo cd mycgroup/
[email protected]:/sys/fs/cgroup/freezer/mycgroup$ sudo rm * 
[email protected]:/sys/fs/cgroup/freezer/mycgroup$ sudo cd ..
[email protected]:/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.

[email protected]:/sys/fs/cgroup/freezer$ sudo mkdir mycgroup
[email protected]:/sys/fs/cgroup/freezer$ cd mycgroup
[email protected]:/sys/fs/cgroup/freezer/mycgroup$ ls
cgroup.clone_children  cgroup.procs  freezer.parent_freezing  freezer.self_freezing  freezer.state  notify_on_release  tasks
[email protected]:/sys/fs/cgroup/freezer/mycgroup$ cat tasks
[email protected]:/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[email protected]:/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
[email protected]:/sys/fs/cgroup/freezer/mycgroup$ cat tasks
[email protected]:/sys/fs/cgroup/freezer/mycgroup$ sudo sh -c "echo 3368 >> tasks"
[email protected]:/sys/fs/cgroup/freezer/mycgroup$ cat tasks
3368
[email protected]:/sys/fs/cgroup/freezer/mycgroup$ sudo sh -c "echo FROZEN > freezer.state"
(teminal 3368 is frozen)
[email protected]:/sys/fs/cgroup/freezer/mycgroup$ sudo sh -c "echo THAWED > freezer.state"
(teminal 3368 is thawed)
[email protected]:/sys/fs/cgroup/freezer/mycgroup$ sudo kill -9 3368
[email protected]:/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
[email protected]:/sys/fs/cgroup/freezer/mycgroup$ cat tasks
[email protected]:/sys/fs/cgroup/freezer/mycgroup$ cat cgroup.clone_children 
0
[email protected]:/sys/fs/cgroup/freezer/mycgroup$ cat cgroup.procs 
[email protected]:/sys/fs/cgroup/freezer/mycgroup$ cat freezer.parent_freezing 
0
[email protected]:/sys/fs/cgroup/freezer/mycgroup$ cat freezer.self_freezing 
0
[email protected]:/sys/fs/cgroup/freezer/mycgroup$ cat freezer.state
THAWED
[email protected]:/sys/fs/cgroup/freezer/mycgroup$ cat notify_on_release 
0
[email protected]:/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
[email protected]:/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
[email protected]:/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:

[email protected]:~$ sudo rmdir /sys/fs/cgroup/freezer/mycgroup/

Regards,
-Chris

ldt

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

[email protected]:/sys/fs/cgroup/freezer$ sudo mkdir mycgroup
[email protected]:/sys/fs/cgroup/freezer$ cd mycgroup
[email protected]:/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
[email protected]:/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
[email protected]:/sys/fs/cgroup/freezer/mycgroup$ cd ..
[email protected]:/sys/fs/cgroup/freezer$ sudo rmdir mycgroup
[email protected]:/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/
[email protected]:/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