File System Hierarchy
Check the list of top level folder by
$ ls /:
/boot: boot loader files
/dev: device files
/etc: configuration files (originally the etcetera directory for files do not belong to other folders)
/home: users' home directories
/media: removable media
/mnt: mounted file systems
/opt: optional application software packages
/proc: virtual filesystem providing process and kernel information as files, e.g.
$ cat /proc/meminfoor
$ cat /proc/cpuinfo. Only available in Linux.
/root: root user's home directory
/run: run-time variable data, will be cleared at the beginning of the boot process
/sbin: essential system binaries, e.g.
/srv: srv=serve, site specific data to be served by the system
/sys: information about devices, drivers, and some kernel features
/tmp: temporary files
/usr: user utilities and applications
/var: variable files
/var: contains files to which the system writes data during the course of its operation.
/var/cache(contains cached data from application programs),
/var/games(contains variable data relating to games in /usr),
/var/lib(contains dynamic data libraries and files),
/var/lock(contains lock files created by programs to indicate that they are using a particular file or device),
/var/log(contains log files),
/var/run(contains PIDs and other system information that is valid until the system is booted again) and
/var/spool(contains mail, news and printer queues).
/var/run, will be cleared at the beginning of the boot process.
/run/user/$uid: created by
systemd, local to the system, only accessible by the target user, the same as
/usr is for software built elsewhere and then installed on the machine (mostly from your distributions package management system)
/usr/local is for software built locally