用記憶體作為暫時檔案系統是個好主意，除了速度快，也可以減少寫入 SSD 次數。但使用有點麻煩，又一直懶得動手寫 script 就拖著了 (Story of my life)。前陣子看了這篇SSD Optimization 裡面介紹的幾個工具都覺得不合用，終於決定寫一個，其實也才幾行…
適用場景：打算開始在某目錄下寫程式、頻繁編譯，或類似情況。
使用方式： tmpoverlay.sh <your project dir>
特點：
- 採用 overlay filesystem, copy-on-write, 只有改了才會紀錄，不用「整個 copy 出來用完再蓋回去」，快、也避免 buffer / tmpfs 的重複。
- trap EXIT, 理論上 Ctrl-C 結束或收到 SIGTERM 都會複製回去，不會掉資料。所以就算忘記了直接登出關機應該也 OK. （沒測過）
缺點：需要 sudo NOPASSWD
Code 如下：
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| #!/bin/bash | |
| set -e | |
| # Assuming tmpfs on $TMPDIR / /tmp | |
| function cleanup { | |
| echo | |
| if findmnt -t overlay "$D" &>/dev/null; then | |
| sudo umount -l "$D" | |
| if [ -d "$UPPER" ]; then | |
| if [ x"$(ls -1A ${UPPER})" != x ]; then | |
| echo "Copying from upper dir to lower dir" | |
| cp -av "$UPPER"/. "$D" | |
| fi | |
| rm -rv "$UPPER" | |
| fi | |
| test -d "$WORK" && sudo rm -rv "$WORK" | |
| fi | |
| } | |
| if [ x"$1" == x ]; then | |
| echo "${0} <directory>" | |
| exit | |
| fi | |
| D=$(realpath -e "$1") | |
| if [ ! -d "$D" ]; then | |
| echo "${D} not a directory." | |
| exit 1 | |
| fi | |
| UPPER=$(mktemp -d --tmpdir "$(id -u).upper.XXX") | |
| WORK=$(mktemp -d --tmpdir "$(id -u).work.XXX") | |
| echo "UPPER DIR: $UPPER" | |
| echo "WORK DIR: $WORK" | |
| trap cleanup EXIT | |
| sudo mount -t overlay overlay \ | |
| -olowerdir="$D",upperdir="$UPPER",workdir="$WORK" \ | |
| "$D" | |
| echo "Ctrl-C when you're done" | |
| while true; do | |
| sleep 3600 | |
| done |