I recently installed xubuntu 16.04 on an older Macbook Air, and I'm noticing that after 30 min or so the laptop gets really hot and the fan gets really loud. When I boot into the macOS partition this doesn't happen, only with xubuntu.
$ uname -a
Linux macbook 4.13.0-36-generic #40~16.04.1-Ubuntu SMP Fri Feb 16 23:25:58 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 16.04.4 LTS
Release:    16.04
Codename:   xenial
After googling around a bit, I found the sensors and upower commands but I don't really know what temp the Core's or BAT0 should be at. Does this look normal?
$ sudo sensors
BAT0-virtual-0
Adapter: Virtual device
temp1:        +39.6°C  
coretemp-isa-0000
Adapter: ISA adapter
Package id 0:  +58.0°C  (high = +87.0°C, crit = +105.0°C)
Core 0:        +58.0°C  (high = +87.0°C, crit = +105.0°C)
Core 1:        +52.0°C  (high = +87.0°C, crit = +105.0°C)
applesmc-isa-0300
Adapter: ISA adapter
Exhaust  :   4559 RPM  (min = 2000 RPM, max = 6500 RPM)
TB0T:         +39.2°C  
TB1T:         +39.2°C  
TB2T:         +36.8°C  
TC0C:         +57.8°C  
TC0D:         +56.8°C  
TC0E:         +59.0°C  
TC0F:         +60.2°C  
TC0P:         +51.2°C  
TC1C:         +58.0°C  
TC2C:         +51.0°C  
TCGC:         +53.0°C  
TCSA:         +52.0°C  
TCXC:         +57.8°C  
TH0A:         +51.0°C  
TH0B:         +52.8°C  
TH0J:        -127.0°C  
TH0O:        -127.0°C  
TH0a:         +51.0°C  
TH0b:         +52.8°C  
TH0c:        -127.0°C  
TH0x:         +52.8°C  
THSP:         +48.2°C  
TM0P:         +52.5°C  
TPCD:         +67.0°C  
Ta0P:         +54.8°C  
Th1H:         +41.8°C  
Tm0P:         +48.2°C  
Tm1P:         +54.5°C  
Ts0P:         +36.8°C  
Ts0S:         +42.5°C  
$ sudo upower -i /org/freedesktop/UPower/devices/battery_BAT0
  native-path:          BAT0
  vendor:               SMP
  model:                bq20z451
  power supply:         yes
  updated:              17 seconds ago
  has history:          yes
  has statistics:       yes
  battery
    present:             yes
    rechargeable:        yes
    state:               discharging
    warning-level:       none
    energy:              32.985 Wh
    energy-empty:        0 Wh
    energy-full:         39.3975 Wh
    energy-full-design:  50.25 Wh
    energy-rate:         11.28 W
    voltage:             7.834 V
    time to empty:       2.9 hours
    percentage:          66%
    temperature:         39.6 degrees C
    capacity:            78.403%
    technology:          lithium-ion
    icon-name:          'battery-full-symbolic'
  History (charge):
    1529609228  66.000  discharging
  History (rate):
    1529609228  11.280  discharging
There are no background processes being overworked it seems:
$ sudo top
top - 12:40:08 up  3:41,  2 users,  load average: 0.24, 0.39, 0.41
Tasks: 182 total,   1 running, 181 sleeping,   0 stopped,   0 zombie
%Cpu(s):  0.3 us,  0.3 sy,  0.0 ni, 99.3 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
KiB Mem :  3944404 total,  2653820 free,   573536 used,   717048 buff/cache
KiB Swap:  4095996 total,  4095996 free,        0 used.  3019420 avail Mem 
  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND        
 1443 root      20   0  321212  64936  38640 S   1.3  1.6   5:36.48 Xorg           
 1636 user      20   0  356184  25544  19768 S   0.3  0.6   0:22.71 xfce4-panel    
 1641 user      20   0  738776  32060  23072 S   0.3  0.8   0:10.18 xfce4-terminal 
 1787 user      20   0  161604  13104  11592 S   0.3  0.3   0:35.31 panel-2-cpugrap
 4452 root      20   0       0      0      0 S   0.3  0.0   0:00.34 kworker/u8:5   
 4537 user      20   0 2248908 321816 102592 S   0.3  8.2   1:10.53 firefox        
 4589 user      20   0 1800984 176468  88148 S   0.3  4.5   0:42.73 Web Content    
    1 root      20   0  185232   5896   4044 S   0.0  0.1   0:02.29 systemd        
    2 root      20   0       0      0      0 S   0.0  0.0   0:00.01 kthreadd       
    4 root       0 -20       0      0      0 S   0.0  0.0   0:00.00 kworker/0:0H   
    6 root       0 -20       0      0      0 S   0.0  0.0   0:00.00 mm_percpu_wq   
    7 root      20   0       0      0      0 S   0.0  0.0   0:00.04 ksoftirqd/0    
    8 root      20   0       0      0      0 S   0.0  0.0   0:06.79 rcu_sched      
    9 root      20   0       0      0      0 S   0.0  0.0   0:00.00 rcu_bh        
I'm not sure how to investigate further or identify the overheating. Any advice would be wonderful.
 
     
     
    