How to find out the service tag of Dell Laptop or computer Running Linux(ubuntu)

You need to use the dmidecode command. It is a tool for dumping a computer's DMI (some say SMBIOS) table contents in a human-readable format. This tool can display serial number or dell service tag without looking on the back of the server. Type the command following command:sudo dmidecode | grep --color -i serial

output:
vishal@Eva:~$ sudo  dmidecode | grep --color -i serial
    [sudo] password for vishal:
    Serial services are supported (int 14h)
    Serial Number: FNFH2BS
    Serial Number: .FNFH2BS.CN7016689N0HB3.
    Serial Number: FNFH2BS
    Serial Number: Not Specified
    Serial Number: 00002043
    Serial Number: 00003043
    SBDS Serial Number: 1F26