Linux & Docker · Lesson 2 of 7

Files, search & permissions

Creating, copying and viewing files, searching with grep and find, and chmod/chown.

Everyday file commands:

mkdir, touch, cp, mv, rm (careful: rm -r deletes folders with no recycle bin).
cat, less, head, tail to read files; tail -f follows a log live.
grep searches inside files; find searches for files by name or age.
The pipe | sends one command's output into another.

Permissions

Each file has read (r=4), write (w=2) and execute (x=1) permissions for the owner, the group and everyone else. chmod 755 deploy.sh gives the owner rwx and others r-x. Use sudo only when you need administrator rights.

Example in the terminal

Run these on your own computer

$ mkdir -p logs && cp app.log logs/
$ tail -n 3 logs/app.log
2026-11-10 10:01:12 INFO  Server started on port 8080
2026-11-10 10:05:40 ERROR Database connection timed out
2026-11-10 10:05:41 INFO  Retrying connection

$ grep -n "ERROR" logs/app.log
2:2026-11-10 10:05:40 ERROR Database connection timed out

$ grep -c "ERROR" logs/app.log | xargs echo "Errors today:"
Errors today: 1

$ find . -name "*.log" -mtime -1
./logs/app.log

$ ls -l deploy.sh
-rw-r--r-- 1 anu anu 220 Nov 10 10:20 deploy.sh
$ chmod +x deploy.sh && ./deploy.sh
Deploying build 42...

Lines starting with $ are commands you type; the rest is what the terminal prints. Use Linux, macOS, WSL on Windows or a free cloud shell. Names and paths are examples.

Key points

cp, mv, rm, mkdir manage files — rm has no undo.
tail -f follows logs live; grep finds text in files.
Pipes (|) chain commands together.
chmod sets permissions; +x makes a script executable.

Quick check

What does chmod 644 file.txt give?

Everyone can do everything Owner read/write; group and others read only Owner execute only Nobody can read it

Practice task

Create a folder with three .txt files, write a word into one of them, use grep to find which file contains it, and make a small script executable with chmod +x.

Interview corner

How do you find which files contain a word?

grep -rn "word" folder/ searches recursively and shows file names and line numbers. Add -i to ignore case.

What does chmod 755 mean?

Owner gets read, write and execute (7); group and others get read and execute (5). It's typical for scripts and folders that others may run or open but not change.