feat: generic tasks: support startup hooks (#8840)

master/static/srv/generic-task-entrypoint.sh

@@ -4,6 +4,23 @@ source /run/determined/task-setup.sh
 
 set -e
 
+STARTUP_HOOK="startup-hook.sh"
+export PATH="/run/determined/pythonuserbase/bin:$PATH"
+
+# If HOME is not explicitly set for a container, libcontainer (Docker) will
+# try to guess it by reading /etc/password directly, which will not work with
+# our libnss_determined plugin (or any user-defined NSS plugin in a container).
+# The default is "/", but HOME must be a writable location for distributed
+# training, so we try to query the user system for a valid HOME, or default to
+# the working directory otherwise.
+if [ "$HOME" = "/" ]; then
+    HOME="$(
+        set -o pipefail
+        getent passwd "$(whoami)" | cut -d: -f6
+    )" || HOME="$PWD"
+    export HOME
+fi
+
 if [ -z "$DET_PYTHON_EXECUTABLE" ]; then
     export DET_PYTHON_EXECUTABLE="python3"
 fi
@@ -14,6 +31,10 @@ fi
 # to register the proxy with the Determined master.
 "$DET_PYTHON_EXECUTABLE" -m determined.exec.prep_container --proxy --download_context_directory
 
+set -x
+test -f "${STARTUP_HOOK}" && source "${STARTUP_HOOK}"
+set +x
+
 if [ "$#" -eq 1 ]; then
     exec /bin/sh -c "$@"
 else