resolved - ipmitool Could not open device at /dev/ipmi0 or /dev/ipmi/0 or /dev/ipmidev/0: No such file or directory

If you met below error on physical servers (not VMs, as VM do not support IPMI)

    [root@localhost ~]# ipmitool
    Could not open device at /dev/ipmi0 or /dev/ipmi/0 or /dev/ipmidev/0: No such file or directory

Then firstly you need make sure your server systemboard supports IPMI. 
Old system-boards might not support IPMI technology.

    [root@localhost ~]# dmidecode | grep -A 6 -i ipmi
    IPMI Device Information
        Interface Type: KCS (Keyboard Control Style)
        Specification Version: 1.5
        I2C Slave Address: 0x10
        NV Storage Device: Not Present
        Base Address: 0x0000000000000CA8 (I/O) #if not all zeros, then it supports IPMI
        Register Spacing: 32-bit Boundaries

If it's supported, then you need enable IPMI related modules:

    modprobe ipmi_devintf
    modprobe ipmi_si

Then add it to /etc/modules to have them loaded automatically:

    ipmi_devintf
    ipmi_si

To start IPMI:
    
    /etc/init.d/ipmi start
    /etc/init.d/ipmi status

PS:
    1. If there's no ipmitool command, try install it by "yum install -y OpenIPMI ipmitool"
    2. You may need add more modules

        [root@localhost ~]# modprobe ipmi_devintf
        [root@localhost ~]# modprobe ipmi_si
        [root@localhost ~]# modprobe ipmi_watchdog
        [root@localhost ~]# modprobe ipmi_poweroff
        [root@localhost ~]# modprobe ipmi_msghandler

Good Luck & Best Wishes