The whole category in one page.
CHECK WHICH MACHINE YOU ARE ON BEFORE ANY DESTRUCTIVE COMMAND
It is the most expensive mistake available, and it takes two seconds to avoid. Recursive deletion with an unchecked path has destroyed more servers than any attack.
THERE IS NO UNDO AND NO RECYCLE BIN
Run ls on a path before rm. Read commands before pasting them. Never use a variable in a deletion path without confirming it holds something.
PERMISSIONS EXPLAIN MOST REAL PROBLEMS
Execute on a directory means the right to enter it, root-owned files inside an account break sites, and setting everything fully open is removing protection rather than fixing anything.
USE A PERSISTENT SESSION FOR ANYTHING LONG
Connections drop, and an interrupted upgrade can leave a machine unbootable. Know how to reach the provider's console before you need it.
TEST CONFIGURATION BEFORE RESTARTING, AND BACK IT UP BEFORE EDITING
A typo takes every site down, and a dated copy is the only quick way back.
READ THE FIRST ERROR, NOT THE LAST
Later errors are usually consequences. Establish the time of the failure, then look at that window.
HIGH LOAD WITH IDLE PROCESSORS IS ALWAYS DISK OR MEMORY
Check the wait figure and swap activity before blaming traffic.
A BACKUP THAT HAS NEVER BEEN RESTORED IS NOT A BACKUP
Practise the restore while nothing is wrong.
