ReadyNAS couldn't update Antivirus, then System volume 'root' usage was 85 %, now I can't boot...

Nice; sounds like a sweet setup StephenB [SUPERUSER Guru StephenB]. Ultimately my endeavour will be to have a rack-mounter server; I don't think a PC will be enough to give me what I'm looking for [given my insatiable appetite for data storage], but then... $$$.   :smileyhappy:

Anyway, now that I've briefly brushed up on some BASH [command-line] study material; let's start from the beginning (before I somehow mess this all up)...

RECAP: At around the same time as my anti-virus suddenly started stating that it was unable to update, I began getting:

Volume: System volume 'root' usage is 85 %. This condition should not occur in normal conditions. Please contact technical support.

Downloading the logs became impossible, attempting to clear them seemed equally futile and unhelpful. After enabling SSH and unsuccessfully attempting to log in, I got locked out of Frontview as my system became unable to fully boot. Access to Technical Support [as advised/instructed in the error] also appears out of reach.

So, the SOLUTION?...

1. Given that I can't fully boot my NAS normally anymore after enabling SSH on my ReadyNAS 516 via Frontview, I need to boot via tech support mode (given that I've effectively been locked out using all other means interacting with the NAS) using the instructions here:
https://kb.netgear.com/23005/How-do-I-access-the-boot-menu-on-my-ReadyNAS-316-516-716

(hold down the reset button at the back of the ReadyNAS while booting up until the Boot Menu pops up, at which point one should use the arrows to select Tech Support mode).

[According to the LCD panel at the front of my device] This brings me into the "Debugging Mode", along with a number of some sort (a unique identifier perhaps?) in square brackets and the local IP Address.

2. Next, I use Putty to TELNET into my NAS using the following:

IP ADDRESS (now displayed on the LCD of the ailing ReadyNAS on my network)
PORT 23 (SSH would be Port 22 if one had access to that alternative)

3. Next I need to log in [using 'Netgear Tech staff' account credentials(?) based on instructions found here]

root / infr8ntdebug

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- this is where I stopped so far because I'm worried about bricking my device -

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4. At this point, I need to mount the OS using a shell command (based on the same source above)

echo DEVICE partitions > /etc/mdadm.conf
mdadm --examine --scan >> /etc/mdadm.conf
mdadm --assemble --scan
mount /dev/md0 /mnt

OR (based on a different source)

start_raid.sh
mount /dev/md0 /sysroot

Not sure which option to run with here...

NOTE: My understing is that the "md0" portion of the code above implies that I'm utilizing X-Raid, which I'm likely using given that the RAID 5 configuration I enabled on OS 6.9.3 (x86) is said to somehow relate to this setup parameter).

5. OPTIONAL: To view the logs,

# View 5000 lines of system logs via journalctl
journalctl -a --no-pager --lines 5000 _SYSTEMD_UNIT=readynasd.service

 another possible place to look would be:

#--------------------------------------------------#
#\\\\\\\\\\\\|   CHECKING LOG FILES   |////////////#
#\\\\\\\\\\\\|    [for beginners]     |////////////#
#--------------------------------------------------#
# STEP 1: Using the 'cd' command, navigate to the following absolute path address:
cd /var/log

# STEP 2: LIST ALL files & folders [including hidden ones] within that directory in 'HUMAN-READABLE' format SORTED in REVERSE order.
ls -al -h --sort=size -r

# STEP 3: View a Log File directly in the commandline window
cat "<Exact_filename.extension>"
#OR if it's too big, use 'less' to view it in a scrollable page-based format#
less "<Exact_filename.extension>"

# STEP 4: Consider repeating the steps above for the following locations:
cd /usr
cd /etc

6. Given the original error/warning indicating that I should reach out to Tech Support, either:

A) The OS partition is being filled up (typically by a huge log file), in which case the offending file(s) would be copied onto the data volume (just in case), and removed from the OS partition.

#--------------------------------------------------#
#\\\\\\\\\\\\\\\|      WORKFLOW     |//////////////#
#\\\\\\\\\\\\\\\|  [for beginners]  |//////////////#
#--------------------------------------------------#
# NOTE FOR BEGINNERS: Don't forget that you can add the --help flag on most commands to get an overview of what it does
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#-[ PART 1 ]- All items in this section will be non-invasive and non-destructive, so relax, these commands can't mess anything up.
#- - - - - - - - - - - - - - - - - - - - - - - - -
# STEP 0: [OPTIONAL] Display the 'DISK FILE-SYSTEM' information in 'HUMAN-READABLE' format [for reference]
df -h


#- - - - - - - - - - - - - - - - - - - - - - - - -
# STEP 1: Display 'DISK USAGE' of ALL Files & Folders in 'HUMAN-READABLE' format, with 1 LEVEL of folder display DEPTH
## NOTE: The location '/' is the root starting point
du -ah --max-depth=1 / | sort -h

# STEP 1.5: Likely areas of investigation will likely be [var, usr, etc]:
## NOTE: Adjust 'max-depth' to allow the computer to do more work for you (at the expense of processing power & [potentially] time)
du -ah --max-depth=3 /var/log | sort -h
du -ah --max-depth=3 /usr | sort -h
du -ah --max-depth=3 /etc | sort -h


#- - - - - - - - - - - - - - - - - - - - - - - - -
# STEP 2: Based on the outcome(s), navigate to abnormally large looking folders (where <location> refers to the address) and repeat STEP 1
## NOTE: Addresses starting in '/' are ABSOLUTE addresses, whereas those starting in './' are RELATIVE to the current location
cd "<location>"

# STEP 2.5: Alternately, one could plug the questionable folder <location> directly into the code in Step 1
du -ah --max-depth=3 "<location>" | sort -h


#- - - - - - - - - - - - - - - - - - - - - - - - -
# STEP 3: [OPTIONAL] After identifying a potentially misbehaving file, view its properties via:
## OPTION A: "ls" to LIST ALL files & folders in current directory; SORTED based on SIZE in REVERSE order (largest files last)
## NOTE: Includes properties by default, & the '-h' flag makes it 'Human-Readable'
# To view the details of the file in relation to the others in the current folder
ls -al -h --sort=size -r
#OR [same as previous] if the file is in another folder#
ls -al -h "<location>" --sort=size -r
#OR to get the details of ONLY that specific file#
ls -l -h "<location>/<Exact_filename.extension>"

## OPTION B: "stat" to get more STATUS-related details of a particular file
stat "<location>/<Exact_filename.extension>"


#- - - - - - - - - - - - - - - - - - - - - - - - -
#-[ PART 2 ]- All items in this section will be invasive and/or destructive; be very careful from here-on in.
#- - - - - - - - - - - - - - - - - - - - - - - - -
# STEP 4: COPY the suspected offending file/folder to a new location [not on the root volume] by FORCE & use VERBOSE mode for feedback
## OPTION A [if it's a file]
cp -f -v "<original location>/<Exact_filename.extension>" "<new location>/<Exact_filename.extension>"
## OPTION B [if it's a folder]
cp -f -v "<original location>" "<new location>"

# STEP 4.5: Check to confirm that the file has in fact been copied
ls -al -h "<new location>"


#- - - - - - - - - - - - - - - - - - - - - - - - -
# STEP 5: REMOVE the suspected offending file by FORCE from the conflicted location & use VERBOSE mode for feedback
## NOTE: You can string together multiple file in the same line
cd "<original_location>"
rm -f -v "<Exact_filename.extension>"
#OR#
rm -f -v "<original_location>/<Exact_filename.extension>"

#OTHERWISE, if it's an entire directory#
cd "<original_location>"
rmdir -f -v "<directory to delete>"
#OR#
rmdir -f -v "<original_location>/<directory to delete>"

OR

B) The inodes were all being used up, in which case, a different command would be needed [to seek out a huge number of small files on the OS partition].

# Display information of the 'Disk File-System' in 'Human-Readable' format, listing inode info instead of block usage
df -i -h

[I have no idea where I would go from here here if it's an inode-related issue]

7. At this point I need to properly unmount the OS somehow (?), restart the NAS, and evaluate my success based on whether I can boot correctly, access Frontview, and if the logs don't display any errors (?). Otherwise, I should consider reversing the previous changes if conditions remain the same [or deteriorate further], and consult with the community to gauge which file(s)/folder(s) may be a more likely culprit of my issue(s). 

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NOTE 1: In my particular case, given that I have the ReadyNAS 516, the OS partition is only ~4GB in size, so that's something I'll need to keep in mind while looking at the files [for the sake of having a contextual reference point].

NOTE 2: I'm more of a computer artist than a programmer, so I wrote this for absolute beginners [like me] having these issues. 

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Feedback? [please, & thanks again for any help/support anyone can provide]  :smileyhappy:

- Tommy Langzik