Was getting this error when running the upgrade pre-check in SDDC manager:

Disk space on SDDC manager VM is less than required

Minimal disk space is available in SDDC Manager, available disk space is…

To fix this problem I’d had to contact VMware support, who ran the following commands to fix the issue. Basically they cleared out two 10GB log files.

VMware support comments:

We found that /var/log/auth.log around 11G and /var/log/audit/audit.log 10G so we free these files without downtime and upgrade precheck worked with no errors now.

Note:

• Below find statement you can use to find large files 
  • cd /

find -type f -exec du -Sh {} + | sort -rh | head -n 5

some commands that might be useful:

df -h

find -type f -exec -SH {} + | sort -rh | head -n 10

cat /etc/passwd | more

find -type f -exec du -SH {} + | sort -rh | head -n 10 | more

cd /var/log/audit/
ls -larth
*****this is where i could see Audit.log was 10GB*******
****cleared this out using this command *****
> audit.log
**confirm the clear out worked ok***
ls -larth

cd ..
**change to the directory /var/log****
ls -larth
**could see auth.log was 11GB
> auth.log

The commands above cleared 21GB from the / directory of SDDC manager for me.