TopolearnKnowing the standard layout means you can find any config file or log on a machine you have never seen.
Linux has a single directory tree starting at / (the root). There are no drive letters: other disks are mounted at directories inside the tree. The layout follows the Filesystem Hierarchy Standard:
/etc: system-wide configuration (text files),/var: variable data such as logs (/var/log), caches, spools and databases (/var/lib),/home/<user>: users' files;/rootis root's home,/usr: installed programs and libraries (/usr/bin,/usr/lib);/usr/localfor software you install by hand; on modern distributions/binand/libare just symlinks into/usr,/opt: self-contained third-party applications,/tmp: temporary files, often cleaned at boot and sometimes stored in RAM,/boot: the kernel and bootloader files,/dev: device files such as disks (/dev/sda,/dev/nvme0n1) and/dev/null,/procand/sys: virtual filesystems where the kernel exposes processes and hardware as files,/run: runtime state such as PID files and sockets, cleared at boot,/mntand/media: mount points for extra or removable disks.
The Unix idea that "everything is a file" shows up everywhere: devices, process information and kernel settings are all read and written with ordinary file tools.
Example
ls /
# bin boot dev etc home lib media mnt opt proc root run srv sys tmp usr var
ls -ld /bin # lrwxrwxrwx ... /bin -> usr/bin (merged /usr)
ls /etc | head -n 3 # system-wide configuration files
ls /var/log | head -n 3 # log files
cat /proc/loadavg # kernel data presented as a file
ls -l /dev/null # crw-rw-rw- ... /dev/null (c = character device)
echo ~ "$HOME" # /home/ada /home/adaRemember
- One tree from /; other disks are mounted into it
- Config in /etc, logs and data in /var, programs in /usr
- /proc, /sys and /dev expose the kernel and devices as files
Watch out for
- Storing application data in /tmp, which may be wiped at reboot.