awk — Process Text by Fields
Where grep finds lines and sed edits them, awk understands that a line has columns. That one idea is why it survives: any time your data has fields — log…
Disk Space — df, du and ncdu
Sooner or later a Linux machine tells you No space left on device and something stops working. This page is the sequence for finding out what filled up and getting…
cron — Schedule Recurring Jobs
cron runs commands on a schedule. It has done so since the 1970s, it is on every Linux system, and it fails in a small number of extremely predictable ways…
Processes — ps, top and htop
When a machine is slow, unresponsive, or something is running that should not be, these are the tools that tell you what is actually happening. ps takes a snapshot, top…
tar — Create and Extract Archives
tar bundles many files into one. The name is short for tape archive, which explains a lot about its design — it was built for sequential tape drives in the…
systemctl — Manage Services with systemd
systemctl is how you start, stop, inspect and configure services on any modern Linux distribution. systemd replaced the old SysV init scripts years ago and is now standard on Debian,…
ssh — Remote Access, Keys and Tunnels
ssh gives you an encrypted shell on another machine. It is the front door to every Linux server you will ever administer, and it does considerably more than open terminals…
sed — Find and Replace in Streams and Files
sed is a stream editor: it reads text line by line, applies the edits you specify, and writes the result out. It is how you change text without opening an…
find — Locate Files by Name, Size and Time
Where grep searches inside files, find searches for the files themselves — by name, size, age, ownership, permissions, or any combination. It also runs commands on whatever it finds, which…
File Permissions — chmod, chown and umask
Linux file permissions look cryptic for about a week and then become second nature. The whole system rests on one small idea: every file has an owner and a group,…