Linux

These guides assume a desktop or small server running Ubuntu, Debian, or a close relative. Commands are shown so you can see them before you run them. If a step would destroy data, it says so.

• Update Ubuntu or Debian without breaking the boxapt update, upgrade, when to reboot, and what to do if a kernel update fails.
• Wi-Fi disappeared after an updateCheck the adapter, NetworkManager, rfkill, and driver packages before you reinstall.
• Permission denied: sudo, ownership, and not wrecking /usrWhen to use sudo, when not to chmod 777, and how to fix a home directory you locked yourself out of.
• SSH key login that will not lock you outCreate a key, copy it, test a second session, then disable password logins.
• The system will not bootGRUB rescue, filesystems that need fsck, and when a live USB is the right next step.
• Install and remove software with aptSearch, install, remove, purge, and why random .deb files from the web are a bad habit.
• Disk is fulldf, du, journals, snaps, and old kernels — without deleting the wrong partition.
• Read hardware information on Linuxlscpu, lsblk, lspci, free, and inxi. This is the real replacement for a Windows HWiNFO report.