Bash

Linux Filesystem cheatsheet Dir What’s in there Quick vibe /etc System-wide config (fstab, ssh/, apt/…) Brain – tweak here, bend the OS /bin Core binaries (ls, cp, bash) First-aid toolkit; always present, even in rescue mode /sbin Sysadmin binaries (mount, ip, systemctl) Same as /bin but root-only toys /usr/bin Full app set (gcc, python) Userland galaxy – 90 % of commands /usr/sbin Heavier daemons (sshd, cron) Admin apps still in userland /usr/local Locally compiled stuff Keeps your builds safe from the distro’s package manager /var Logs, spool, caches, DB files Growing stomach – watch disk usage /run (/var/run) Volatile runtime state (PIDs, sockets) tmpfs in RAM, born early at boot /home Users’ dirs You, your dotfiles, your mess /opt 3rd-party bundles (Chrome, VMware) Vendor playground; easy to nuke /dev Device nodes (/dev/sda, /dev/null) “Everything’s a file” made real /proc Kernel + process pseudo-FS cat /proc/cpuinfo = free hardware probe /sys Kernel objects, drivers Modern cousin of /proc; tweak power/LEDs /tmp Scratch space Auto-purged; don’t stash secrets /boot Kernel & bootloader bits (vmlinuz, grub/) Small, often its own partition Why the weird names? usr ≠ “user” originally—Unix System Resources (/usr/bin). sbin = system binaries (super-user land). opt from optional add-ons in SVR4 days. run split from /var so early-boot services get instant writable RAM. Quick cross-OS compare OS Root Apps live in User homes Mount style 🐧 Linux/*BSD / /usr/bin, /opt /home/ivan Any device mounts anywhere (/mnt/usb) via fstab macOS / /Applications (GUI), /usr/bin (CLI) /Users/ivan External drives auto-mount under /Volumes Windows C:\ C:\Program Files / Program Files (x86) C:\Users\Ivan Letters (D:\, E:\) instead of grafting into a single tree Handy aliases & shortcuts ~ → home dir (/home/ivan, /Users/ivan). . = current dir, .. = parent. /var/run → symlink to /run on modern distros. /bin & /sbin often symlink to /usr/bin & /usr/sbin (the usr-merge trend). Mounting in one breath Linux glues extra filesystems into the tree: mount /dev/sdb1 /media/usb macOS auto-mounts to /Volumes/DriveName, Windows splits the forests into drive letters. ...

My private documentation site setup guide Outcome Local wiki/blog at ~/vault, one command on or off. Edits show up live the second you hit save. Git keeps history & lets friends add stuff. Pushes auto-build to Netlify so you can read it anywhere without opening ports. This one-time setup should take approx 3 min Install Hugo If you haven’t already installed Hugo on your system, use your own apropriate package manager. ...

Outcome Understand how rwx maps to octal digits. Set, fix, and audit permissions quickly using: chmod chown setfacl Remember what SUID / SGID / sticky and ACL do without Googling. Permissions Basics Octal Symbolic Meaning 0 --- No rights 1 --x Execute only 2 -w- Write only 3 -wx Write + Execute 4 r-- Read only 5 r-x Read + Execute 6 rw- Read + Write 7 rwx Read + Write + Execute Mnemonic: 421 $\rightarrow$ rwx ...