$HOUDINI_TEMP_DIR is where Houdini writes cache files and undo files.
When Houdini crashes it writes to $TEMP. So it's $TEMP you want for crash files and crash logs. Btw, please please try to reproduce the crash and send in a Bug report to support with the steps to recreate the crash, the scene file and the .txt crash log file saved to $TEMP.
For new users the easiest way to see what these variables are set to is to fire up Houdini, open a Textport and type:
/ -> echo $HOUDINI_TEMP_DIR
/tmp/houdini_temp
/ -> echo $TEMP
/tmp
——–
You can echo any system environment variable inside Houdini if you wish. When it fires up, it sees all the system environment variables using the hscript unix command. Btw hscript unix works on Windows and is used to access any shell command. Yes windows has a shell including the defaults shipped with Houdini. Several in fact: shell, powershell, bash and if you want to install cygwin. You can access any of these system environment variables in any parameter or code snippet in Houdini btw preceded with a $.
Again open up Houdini and open up a textport then type unix printenv to print all the system variables seen by Houdini (and note in that list is TEMP and HOUDINI_TEMP_DIR):
/ -> unix printenv
job=/work/user/job
TERM_PROGRAM=Apple_Terminal
HOST=mymachine.local
TERM=xterm-256color
SHELL=/bin/bash
HOUDINI_TEMP_DIR=/tmp/houdini_temp
CLICOLOR=1
HOUDINI_OS=MacOS
TMPDIR=/var/folders/8y/n9vxx_kj1t17b1j5yhf87zl00000gn/T/
H=/Applications/Houdini/Houdini16.0.717/Frameworks/Houdini.framework/Versions/16.0.717/Resources
hou10dir=cd /Users/jeff/Library/Preferences/houdini/10.0
sqa=/n/iowa2/tmp/jeff/user/sqa
HOUDINI_BUILD_KERNEL=15.6.0
Apple_PubSub_Socket_Render=/private/tmp/com.apple.launchd.aiBLuTVS7c/Render
HOUDINI_BUILD_VERSION=717
HDSO=/Applications/Houdini/Houdini16.0.717/Frameworks/Houdini.framework/Versions/16.0.717/Resources/../Libraries
TERM_PROGRAM_VERSION=361.1
HT=/Applications/Houdini/Houdini16.0.717/Frameworks/Houdini.framework/Versions/16.0.717/Resources/toolkit
TERM_SESSION_ID=7A1EDE4D-83F5-4ADB-B803-303F84819980
comp=/work//user/comp
previs=/work//user/previs
render=/work//user/render
HH=/Applications/Houdini/Houdini16.0.717/Frameworks/Houdini.framework/Versions/16.0.717/Resources/houdini
user=/work//user
USER=jeff
TEMP=/tmp
hj=/Users/jeff/houdini.jeff
HSB=/Applications/Houdini/Houdini16.0.717/Frameworks/Houdini.framework/Versions/16.0.717/Resources/houdini/sbin
HOUDINI_BUILD_PLATFORM=Mac OS X 10.11.6
HIP=/private/tmp
vfx=/work//user/vfx
char=/work//user/char
demos=/work//Demos/demo_repository
HOUDINI_MINOR_RELEASE=0
SSH_AUTH_SOCK=/private/tmp/com.apple.launchd.n13VDH4EY3/Listeners
__CF_USER_TEXT_ENCODING=0x1F5:0x0:0x0
HB=/Applications/Houdini/Houdini16.0.717/Frameworks/Houdini.framework/Versions/16.0.717/Resources/bin
ACTIVETAKE=Main
HOUDINI_DESKTOP_DIR=/Users/jeff/Desktop
HD=/Applications/Houdini/Houdini16.0.717/Frameworks/Houdini.framework/Versions/16.0.717/Resources/demo
HOUDINI_USER_PREF_DIR=/Users/jeff/Library/Preferences/houdini/16.0
PATH=/Applications/Houdini/Houdini16.0.717/Frameworks/Houdini.framework/Versions/16.0.717/Resources/bin
Applications/Houdini/Houdini16.0.717/Frameworks/Houdini.framework/Versions/16.0.717/Resources/houdini/sbin
Users/jeff/bin
usr/local/bin
usr/bin
bin
usr/sbin
sbin
HOUDINI_VERSION=16.0.717
work=/work/
glue=/work//user/glue
_=/usr/bin/printenv
POSE=/Users/jeff/Library/Preferences/houdini/16.0/poselib
PWD=/tmp
proj=/work/proj
JOB=/private/tmp
JAVA_HOME=/Library/Java/Home
jwi=/n/iowa2/tmp/jeff
EDITOR=/usr/bin/vim
jeff=~
LANG=en_CA.UTF-8
XPC_FLAGS=0x0
HOUDINI_BUILD_COMPILER=7.3.0
HFS=/Applications/Houdini/Houdini16.0.717/Frameworks/Houdini.framework/Versions/16.0.717/Resources
HOUDINI_MAJOR_RELEASE=16
XPC_SERVICE_NAME=0
prog=/work//user/prog
HOME=/Users/jeff
SHLVL=2
HHC=/Applications/Houdini/Houdini16.0.717/Frameworks/Houdini.framework/Versions/16.0.717/Resources/houdini/config
LOGNAME=jeff
CLASSPATH=.
Applications/Houdini/Houdini16.0.717/Frameworks/Houdini.framework/Versions/16.0.717/Resources/houdini/scripts/java/sesi.jar
HIPFILE=/private/tmp/untitled.hip
HIPNAME=untitled
sesi=/work/sesi
HOUDINI_PATH=~/houdini.jeff:&
SECURITYSESSIONID=186aa