The following symptoms are indicative of this issue:

• ADM command log status shows status as failed along with a message saying "Command failed Rebooting not found in command output"

  

• ADM log file /var/log/ns.log shows the message "Command failed Rebooting not found in command output"
  Dec 13 11:24:39 <local0.info> mas mas_config: 10.29.1.187 12/13/2017:11:24:39 GMT : DEVICECONFIG CMD_EXECUTED : User nsroot - InstanceIP 172.24.32.152 - InstanceUser nsroot - Command "Verifying task completion" - Status "Failed" - Message "Command failed Rebooting not found in command output"

• Running the installns script on the culprit ADC node generates the message "Error: Please free space on /var and then re-install".
  Note: The number of 1k blocks may vary.

  installns: [15078]: 2355460 1k blocks free space on /var is insufficient to operate the Netscaler Error: Please free space on /var and then re-install. You may want to examine /var/log or in /var/netscaler/nsbackup. installns: [15078]: Error: Please free space on /var and then re-install. You may want to examine /var/log or in /var/netscaler/nsbackup.

• Running "show version" on the culprit ADC node will show the pre-upgrade version.

To resolve this issue the /var partition on the impacted ADC node will need to be cleared so that there is at least 6GB of disk space available. 

Refer to Citrix Documentation to find information on how to remove the disk space for upgrades: https://docs.citrix.com/en-us/citrix-adc/12-1/upgrade-downgrade-citrix-adc-appliance/troubleshooting.html

Problem Cause

The /var/ partition did not have enough free space on the ADC being upgraded.