LinuxFoundation

1. Linux Filesystem Tree Layout

• one large logical filesystem which can contain one or many distinct filesystems mounted at various points

• Filesystem Hierarchy Standard : shareable (can shared between hosts)

	shareable	unshareable
static	/usr /opt	/etc /boot
-----------	------------------	--------------------
variable	/var/mail	/var/run /var/lock

• Main directories:
  • /bin : contains binary executable files (cat, kill, ps) . Command binaries which are deemed non essential enough are in /usr/bin.
  • /lib: contains libraries needed to execute the binaries in /bin or /sbin . Also kernel module are in /lib/modules/
  • /boot: essential files for booting the system (vmlinuz compressed linux kernel and initrd initial RAM filesystem which is mounted before the real root filesystem becomes available, config to configure kernel compilation)
  • /dev: device nodes aka device files (byte-stream or block I/O devices). Network devices (eth1 , eth2) do not have device nodes
  • /usr: can be thought of as a secondary hierarchy, need not reside in the same partition as the root directory
  • /etc: contains machine-local configuration files/scripts (/etc/systemd contains config scripts for starting, stopping system services using systemd ; also /etc/init.d which contains scripts for System V initialization)
  • /var: logs in /var/log and cron jobs, mail file in /var/spool, lock files in /var/lock or cat /var/log/yum.log
  • /proc: is the mount point for a pseudo-filesystem, where all information resides only in memory, not on disk. The entires in /proc are called virtual files with zero bytes in size.

# List files opened by a process
lsof -p PID 
# equivalent more or less with 
ls -l /proc/PID/fd