Brain on Fire Tim McCormack, distilled.

This is mostly relevant to Ubuntu, but the major GNU/Linux distros share most of these paths.

• / "root"
  • bin "essential binaries"
  • boot "static files of boot loader"
  • etc "host-specific system configuration"
    • opt "config file for add-on application software"
  • usr "shareable and read-only data"
    • local "local software"
    • share "static data shareable among all architectures"
      • man "manual pages"
    • bin "most user commands"
    • include "standard C includes"
    • lib "obj, bin, and lib files for programs and packages"
    • sbin "non-essential binaries"
  • var "variable data files"
    • cache "application cache data"
    • lib "variable state information remains after reboot" [?]
    • yp "data for NIS services"
    • lock "lock files for shared resources"
    • opt "variable data of packages installed"
    • run "info of system since it was booted"
    • tmp "available for programs"
    • spool "data awaiting processing"
      • lpd
      • mqueue
      • news
      • rwho
      • uucp
    • log "log files and directories, often organized by package name"
  • sbin "system binaries"
  • tmp "temporary files deleted on bootup"
  • dev "special or device files"
  • home "user home directories"
  • lib "library and kernel modules"
  • mnt "mount files for temporary filesystems"
  • opt "add-on application software"
  • root "home directory for root user"

Common tasks:

• Find a log file for %PACKAGE% by going to the /var/log/%PACKAGE% directory (e.g. apache2) or finding /var/log/%PACKAGE%.log.
• Restart a service by issuing the command /etc/init.d/%PACKAGE% restart (e.g. ssh). You may have to append "d" to the end of the package or service name -- mysqld, for example. "d" stands for "daemon", a process that runs in the background, waiting to be called.