error running script "check_ceph_df"

Dear ceph nagios community,
we used to use these Nagios checks and they break with the following error

```
./check_ceph_df -i nagios -k /etc/ceph/ceph.client.admin.keyring -W 29.12 -C 30.22 -d
Traceback (most recent call last):
File "./check_ceph_df", line 232, in
sys.exit(main())
File "./check_ceph_df", line 221, in main
one_line = err.split('\n')[0]
TypeError: a bytes-like object is required, not 'str'
```

I see the scripts have not been updated in 5 years
Is this project still active?
any advice with the error above?
thank you

Reproduce the command shown with check_ceph_df and inspect check_ceph_df around line 221, where the traceback occurs while processing err. Check how the script handles the command output under the current Python version. Done means the command runs without the TypeError and produces the expected Nagios check result.

Written by the indexing model from the issue text.