The following CLI command will show the current Raspberry Pi operating state... wheather the Pi is throttling the CPU due to overheating or an under-voltage condition.

"vcgencmd get_throttled"

The outputs of that command are as follows...

Bit Hex value   Meaning
0          1    Under-voltage detected
1          2    Arm frequency capped
2          4    Currently throttled
3          8    Soft temperature limit active
16     10000    Under-voltage has occurred
17     20000    Arm frequency capping has occurred
18     40000    Throttling has occurred
19     80000    Soft temperature limit has occurred

A value of 0x50000 means 16 & 18 -- from the boot moment up to now Under-Voltage has occurred at some point as well as Throttling has occurred.


"vcgencmd measure_temp" - will show CPU temp in Celcius

Raspberry Pi CPU will throttle CPU at: 
60C - soft temp limit - low throttle - Pi 3B+ and above models
80C - high temp throttle - mid throttle - all models
85C - max temp limit - high throttle - all models


"vcgencmd measure_volts" - shows the core CPU voltage

Outputs are as follows...
volt=0.8xxx - 0.9xxx - proper voltage for Pi 4
volt=1.2xxx - 1.3xxx - proper voltage for Pi 2 and 3


Write the following script into a file called checkthrottle.sh and run it with "sudo bash checkthrottle.sh" for a more plain-English output of the vcgencmd get_throttled command...


#!/bin/bash -e

# Check whether a Raspberry Pi is currently experiencing insufficient
# power or overheating or if it has had such problems in the past.

# From vcgencmd(1)
   # get_throttled

   #      Returns the throttled state of the system. This is a bit
   #      pattern - a bit being set indicates the following meanings:

   #      Bit   Meaning
   #      ────  ────────────────────────────────────
   #       0    Under-voltage detected
   #       1    Arm frequency capped
   #       2    Currently throttled
   #       3    Soft temperature limit active
   #      16    Under-voltage has occurred
   #      17    Arm frequency capping has occurred
   #      18    Throttling has occurred
   #      19    Soft temperature limit has occurred

   #      A value of zero indicates that none of the above conditions
   #      is true.


A=( [ 0]="Under-voltage detected"
    [ 1]="Arm frequency capped"
    [ 2]="Currently throttled"
    [ 3]="Soft temperature limit active"
    [16]="Under-voltage has occurred"
    [17]="Arm frequency capping has occurred"
    [18]="Throttling has occurred"
    [19]="Soft temperature limit has occurred" )

for ((i=0; i<32; i++)); do
    if [[ ! ${A[i]} ]]; then
    A[i]="set, but meaning is unknown. See vcgencmd(1)."
    fi
done

# vcgencmd get_throttled returns a string like "throttled=0x50000" 
eval $(vcgencmd get_throttled)

# If user supplied a number (e.g., 0x50005), use it instead.
if [[ "$1" ]]; then throttled="$1"; fi

if (( throttled == 0 )); then
    echo "No problems with voltage or temperature since boot."
elif (( (throttled & 0xFF) == 0 )); then
    echo "Problems have occurred but are not happening now."
fi

for ((i=0; i<32; i++)); do
    if (( throttled & 2**i )); then
    echo "bit $i: ${A[$i]}"
    fi
done

# Exit with a non-zero value if problems are occurring now.
exit $(( throttled & 0xFF ))



To see all the commands available with vcgencmd type 
"vcgencmd commands"

commands="vcos, ap_output_control, ap_output_post_processing, vchi_test_init, vchi_test_exit, pm_set_policy, pm_get_status, pm_show_stats, pm_start_logging, pm_stop_logging, version, commands, set_vll_dir, set_backlight, set_logging, get_lcd_info, arbiter, cache_flush, otp_dump, test_result, codec_enabled, get_camera, get_mem, measure_clock, measure_volts, enable_clock, scaling_kernel, scaling_sharpness, get_hvs_asserts, get_throttled, measure_temp, get_config, hdmi_ntsc_freqs, hdmi_adjust_clock, hdmi_status_show, hvs_update_fields, pwm_speedup, force_audio, hdmi_stream_channels, hdmi_channel_map, display_power, read_ring_osc, memtest, dispmanx_list, get_rsts, schmoo, render_bar, disk_notify, inuse_notify, sus_suspend, sus_status, sus_is_enabled, sus_stop_test_thread, egl_platform_switch, mem_validate, mem_oom, mem_reloc_stats, hdmi_cvt, hdmi_timings, readmr, pmicrd, pmicwr, bootloader_version, bootloader_config, file, vctest_memmap, vctest_start, vctest_stop, vctest_set, vctest_get"