定期重新壓縮 jpeg 圖形檔

以下可以找到目錄底下所有七天內建立的 jpeg 檔案，然後用 GraphicsMagick 重新壓縮一次：

su -m nobody -c "find photos/ -type f -name '*.jpg' -newerct '7 day ago' -print -exec gm convert {} {} \;"

mrtg 錯誤：ERROR: Creating templock /usr/local/etc/mrtg/mrtg.cfg_l_5566: Permission denied at /usr/local/bin/mrtg line 1961.

因為都是用 mrtg 的權限跑 mrtg，結果有一天升級到 2.17.4_5,1 之後，就會出現這個錯誤訊息：

root@xxxx:~ # su -m mrtg -c '/usr/local/bin/mrtg /usr/local/etc/mrtg/mrtg.cfg'
2014-08-18 00:11:20: ERROR: Creating templock /usr/local/etc/mrtg/mrtg.cfg_l_5566: Permission denied at /usr/local/bin/mrtg line 1961.

FreeBSD 錯誤：Can't work out which disk we are booting from.

大概就是開機，還沒進入選單，就出現這個錯誤訊息：

Can't work out which disk we are booting from.
Guessed BIOS device 0xffffffff not found by probes, defaulting to disk0

freebsd-update 出現 failed an integrity check

使用 freebsd-update 升級 FreeBSD 時，如果出現以下的錯誤：

  The update metadata is correctly signed, but
  failed an integrity check.
  Cowardly refusing to proceed any further.