Place temporary install files within RAMdisk (#1464)

Resolves https://github.com/tiny-pilot/tinypilot/issues/1462

You can test this PR's install script and bundle via:
```bash
curl \
  --silent \
  --show-error \
  https://raw.githubusercontent.com/tiny-pilot/tinypilot/aca37b26108c7fc7fc24fad48890734859fe9221/get-tinypilot.sh | \
    bash -
```


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---------

Co-authored-by: Michael Lynch <git@mtlynch.io>

bundler/bundle/install

@@ -14,13 +14,8 @@ set -x
 # shellcheck disable=SC1091 # Don’t follow sourced script.
 . lib.sh
 
-# HACK: If we let mktemp use the default /tmp directory, the system purges the
-# file before the end of the script for some reason. We use /var/tmp as a
-# workaround.
-readonly TEMP_DIR='/var/tmp'
-
 # Temporary file for installation settings.
-INSTALL_SETTINGS_FILE="$(mktemp --tmpdir="${TEMP_DIR}" --suffix .yml)"
+INSTALL_SETTINGS_FILE="$(mktemp --suffix .yml)"
 readonly INSTALL_SETTINGS_FILE
 
 # The eventual, permanent settings files. Note, that these might not exist

get-tinypilot.sh

@@ -66,10 +66,11 @@ readonly LEGACY_INSTALLER_DIR='/opt/tinypilot-updater'
 # - The TinyPilot bundle archive
 # - The unpacked TinyPilot bundle archive, after running the bundle's `install`
 #     script
+# - About 50 MiB of temporary files
 # - At least a 20% safety margin
 # Use the following command to help you estimate a sensible size allocation:
 #   du --summarize --total --bytes "${INSTALLER_DIR}" "${BUNDLE_FILE}"
-readonly RAMDISK_SIZE_MIB=500
+readonly RAMDISK_SIZE_MIB=560
 
 AVAILABLE_MEMORY_MIB="$(free --mebi |
   grep --fixed-strings 'Mem:' |
@@ -111,10 +112,21 @@ if (( "${AVAILABLE_MEMORY_MIB}" >= "${RAMDISK_SIZE_MIB}" )); then
     --verbose
 else
   # Fall back to installing from disk.
-  INSTALLER_DIR="$(mktemp --directory)"
+  # HACK: If we let mktemp use the default /tmp directory, the system begins
+  # purging files before the end of the script for some reason. We use /var/tmp
+  # as a workaround.
+  INSTALLER_DIR="$(mktemp \
+    --tmpdir='/var/tmp' \
+    --directory)"
 fi
 readonly INSTALLER_DIR
 
+# Use a temporary directory within the installer directory so that we take
+# advantage of RAMdisk if we're using one.
+readonly TMPDIR="${INSTALLER_DIR}/tmp"
+export TMPDIR
+sudo mkdir "${TMPDIR}"
+
 readonly BUNDLE_FILE="${INSTALLER_DIR}/bundle.tgz"
 
 # Download tarball to RAMdisk.
@@ -147,6 +159,8 @@ fi
 
 # Run install.
 pushd "${INSTALLER_DIR}"
-sudo ./install
+sudo \
+  TMPDIR="${TMPDIR}" \
+  ./install
 
 } # Prevent the script from executing until the client downloads the full file.

scripts/install-bundle

@@ -81,10 +81,11 @@ readonly LEGACY_INSTALLER_DIR='/opt/tinypilot-updater'
 # - The TinyPilot bundle archive
 # - The unpacked TinyPilot bundle archive, after running the bundle's `install`
 #     script
+# - About 50 MiB of temporary files
 # - At least a 20% safety margin
 # Use the following command to help you estimate a sensible size allocation:
 #   du --summarize --total --bytes "${INSTALLER_DIR}" "${BUNDLE_FILE}"
-readonly RAMDISK_SIZE_MIB=500
+readonly RAMDISK_SIZE_MIB=560
 
 AVAILABLE_MEMORY_MIB="$(free --mebi |
   grep --fixed-strings 'Mem:' |
@@ -126,10 +127,21 @@ if (( "${AVAILABLE_MEMORY_MIB}" >= "${RAMDISK_SIZE_MIB}" )); then
     --verbose
 else
   # Fall back to installing from disk.
-  INSTALLER_DIR="$(mktemp --directory)"
+  # HACK: If we let mktemp use the default /tmp directory, the system begins
+  # purging files before the end of the script for some reason. We use /var/tmp
+  # as a workaround.
+  INSTALLER_DIR="$(mktemp \
+    --tmpdir='/var/tmp' \
+    --directory)"
 fi
 readonly INSTALLER_DIR
 
+# Use a temporary directory within the installer directory so that we take
+# advantage of RAMdisk if we're using one.
+readonly TMPDIR="${INSTALLER_DIR}/tmp"
+export TMPDIR
+mkdir "${TMPDIR}"
+
 # Extract tarball to installer directory.
 tar \
   --gunzip \