[reboot-cause] A broken symlink of previous-reboot-cause file triggers a back trace in syslog and system-running state shows degraded

[mlok-nokia]

Description

When the previous-reboot-cause has a broken symlink, the following back trace is shown in the syslog and system-runing state show degraded. And rebooting the system will not be able to generated a new symlink for the new previous reboot cause.

May  3 22:00:49.145591 sonic INFO determine-reboot-cause[2200]: Traceback (most recent call last):
May  3 22:00:49.145671 sonic INFO determine-reboot-cause[2200]:   File "/usr/local/bin/determine-reboot-cause", line 228, in <module>
May  3 22:00:49.145752 sonic INFO determine-reboot-cause[2200]:     main()
May  3 22:00:49.145801 sonic INFO determine-reboot-cause[2200]:   File "/usr/local/bin/determine-reboot-cause", line 215, in main
May  3 22:00:49.145842 sonic INFO determine-reboot-cause[2200]:     os.symlink(REBOOT_CAUSE_HISTORY_FILE, PREVIOUS_REBOOT_CAUSE_FILE)
May  3 22:00:49.145877 sonic INFO determine-reboot-cause[2200]: FileExistsError: [Errno 17] File exists: '/host/reboot-cause/history/reboot-cause-2022_05_03_22_00_49.json' -> '/host/reboot-cause/previous-reboot-cause.json'

admin@sonic:~$ systemctl is-system-running 
degraded 

Steps to reproduce the issue:

1. Manually made the broken symlink of the previous-reboot-cause file by using "ls /host/previous-reboot-cause -al" to find the soft link destination file and removing the destination file
2. Reboot the system. the system will be in that state
3. Check the syslog for the back trace and using "systemctl is-system-running" to check the result

Describe the results you received:

The following is shown in the syslog:

May  3 22:00:49.145591 sonic INFO determine-reboot-cause[2200]: Traceback (most recent call last):
May  3 22:00:49.145671 sonic INFO determine-reboot-cause[2200]:   File "/usr/local/bin/determine-reboot-cause", line 228, in <module>
May  3 22:00:49.145752 sonic INFO determine-reboot-cause[2200]:     main()
May  3 22:00:49.145801 sonic INFO determine-reboot-cause[2200]:   File "/usr/local/bin/determine-reboot-cause", line 215, in main
May  3 22:00:49.145842 sonic INFO determine-reboot-cause[2200]:     os.symlink(REBOOT_CAUSE_HISTORY_FILE, PREVIOUS_REBOOT_CAUSE_FILE)
May  3 22:00:49.145877 sonic INFO determine-reboot-cause[2200]: FileExistsError: [Errno 17] File exists: '/host/reboot-cause/history/reboot-cause-2022_05_03_22_00_49.json' -> '/host/reboot-cause/previous-reboot-cause.json'

check the system running state:

admin@ixre-egl-board15:~$ systemctl is-system-running 
degraded
admin@ixre-egl-board15:~$ 

Describe the results you expected:

1. No back trace in syslog file
2. checking the running state
   admin@sonic:~$ systemctl is-system-running
   running

Output of show version:

It is the latest code.

Output of show techsupport:

(paste your output here or download and attach the file here )

Additional information you deem important (e.g. issue happens only occasionally):