This second part continues the Linux filesystem overview with directories that are commonly used for boot files, devices, temporary files and user-installed software.
/boot
/boot stores files needed early in the boot process, such as kernel images, initramfs files and bootloader configuration. Be careful when cleaning this directory.
/dev
/dev contains device files. Disks, terminals and other devices are represented here, for example /dev/sda or /dev/tty.
/tmp
/tmp is used for temporary files. Many systems clean this directory automatically, so it should not be used for important long-term data.
/opt and /usr/local
/opt is often used for optional third-party software. /usr/local is commonly used for locally installed programs that are separate from the distribution package manager.
Quick check
ls /
df -h
lsblk