A. First kindly check the RHEL & CentOS supported versions for the Proliant Server in use as per Proliant OS Matrix to identify if the CenOS/RHEL 7.6 is even supported for that Proliant Server or not as we may or may not have the iLO Channel Interface Driver for the same:
Red Hat Enterprise Linux Minimum Operating System Requirements
http://h17007.www1.hpe.com/us/en/enterprise/servers/supportmatrix/exceptions/rhel_exceptions.aspx
CentOS Minimum Operating System Requirements
http://h17007.www1.hpe.com/us/en/enterprise/servers/supportmatrix/exceptions/cent_exceptions.aspx
B. If we have a supported OS Platform as per the Proliant OS Matrix, then reinstall the recommended iLO Channel Interface Driver (As per the Server Model & Host OS Environment from HPESC Website)& Latest RESTful Interface Tool Version: 2.4.1(4 Apr 2019).
RESTful Interface Tool Version: 2.4.1(4 Apr 2019)
https://support.hpe.com/hpsc/swd/public/detail?swItemId=MTX_2be78990743248ad87c6b8beb9
C. The command "ilorest flashfwpkg <file_name.fwpkg>" need to be executed from local host OS. So please check the following if the file "ilo5_143.fwpkg" is available locally on the OS:
1. Check if we have Read/Write/Execute permissions for "ilo5_143.fwpkg".
2. Check for current iLO Firmware version as it's not recommended to jump from an old version to latest & we must do online firmware upgrade step-by-step only.
D. If we are remote then we must use the command "ilorest flashfwpkg <file_name.fwpkg> --url <iLO5_IP_Address> -u <iLO5_username> -p <iLO5_password>" & again if current iLO Firmware is old then step-by-step firmware upgrade process is recommended.
Note: As an alternative, we can also upgrade iLO Firmware from iLO Web Interface & HPSUM
For any further assistance, kindly login to your HPE Passport Account & log a case in reference to this issue from HPE Support Case Manager (https://support.hpe.com/portal/site/hpsc/scm/home) as it may require to capture AHS & SOS Reports for further analysis.
