Free reference

Cheat sheets

Seven reference sheets for people who keep a terminal open. Every one of them ends with the distinctions that actually cost time, because the commands are the easy part and nobody needs another alphabetical list.

• Linux command cheat sheet

  Octal permissions, systemd and journalctl, and the commands for disk, inodes, memory, load and listening ports. Plus the mistakes that cost an hour.

• Git recovery cheat sheet

  Undo a commit, recover a deleted branch, escape detached HEAD, abort a bad rebase. Organised by what went wrong rather than by command name.

• Subnet, CIDR and port cheat sheet

  Full CIDR table from /8 to /32 with netmasks and usable hosts, the reserved ranges worth recognising, 44 port numbers, and the subnetting mistakes people make.

• The troubleshooting ladder

  A layer-by-layer troubleshooting method, a five-test fast path, how to scope a problem, what to capture before escalating, and severity stated plainly.

• Security headers and TLS cheat sheet

  Every response header worth sending with the actual value, cookie flags, and the openssl and curl commands for finding out what you really sent.

• kubectl and Docker cheat sheet

  The kubectl and docker commands that get used, every pod state mapped to what is actually wrong, probe behaviour, and the container exit code table.