how to re-install TWRP from Linux? Android version:       4.4.3
HTC Sense version:     6.0
software number:       2.23.661.2
HTC SDK API level:     6.25

kernel version:        3.4.0-g52343b3
                       and @ABM105 #1
                       SMP PREEMPT
build version:         2.23.661.2.CL3568029 release-keys


Previously I was locked in a loop where only TWRP was available.  The developer option is certainly enabled.  At the moment, not sure how to get back to the TWRP menu.

How do I accomplish a fresh install of a new version of TWRP?  I was going to connect it with Linux.

TWRP says:


  How can I uninstall or remove TWRP from my device?
  
  For the vast majority of devices, you don't actually remove TWRP to
  get back to the stock recovery. Installing a different recovery is
  your only real option. Simply install whatever recovery that you want
  and that will overwrite or replace TWRP. Usually you can follow the
  instructions on our website for installing TWRP manually, only use the
  file for whatever recovery you are choosing to install instead of the
  TWRP file.
  
  Note, we don't keep or maintain a database of stock recoveries. If you
  are trying to reinstall the stock recovery, you will have to find a
  copy of the stock recovery on your own.


although I'm not entirely clear on what they mean by "another recovery", but, how do I actually install from Linux?

see also:

https://www.xda-developers.com/how-to-install-twrp/
https://www.androidguru.eu/twrp-installation-tutorial-linux-mint-ubuntu-users/

basically, so long as I get the correct image it's quite simple?  Since it was already installed I don't need to muck with locked boot loaders??

What does &quot;fastboot oem lock&quot; do?
The quoted text is for "uninstalling" TWRP  

If i understand your question correctly, your only concern is to update TWRP to newer version  

before flashing new image it is recommended to test if it works without flashing (not all devices support this)  

fastboot boot twrp.img


installing TWRP depends on device  

some devices don't have recovery partition. in this case you need another self installing zip file which will install TWRP in recovery-ramdisk in boot partition  

if device has separate recovery partition you can simply flash the partition image  

this can be done from fastboot  

fastboot flash recovery twrp.img


from pc command line  

adb push twrp.img /dev/block/bootdevice/by-name/recovery


or even from TWRP itself in Advanced - Terminal  

cat /external_sd/twrp.img &gt; /dev/block/bootdevice/by-name/recovery


Some TWRP variant does allow backup/restore recovery. in this case you can just rename the twrp.img into recovery.emmc.win, place it into empty backup folder TWRP/BACKUPS/*/recovery and restore backup  

Note: Your bootloader must remain unlocked as long as TWRP (or any other modified partition) is installed. re-locking bootloader is only recommended after you flashed full stock ROM including stock recovery. Otherwise you will brick