Linux — the daily commands

Where am I? What's here?

Command	What it does
pwd	Prints your current directory
ls	Lists files & folders
ls -a	Also shows hidden files (starting with .)
ls -la	Long listing (owner, size, date)
ls -R	Lists recursively
cd folder	Enters a folder
cd ..	Goes up one level
cd -	Toggles back to previous directory

Files — read, create, delete

Command	What it does
cat file	Prints file contents
cat > file	Types a new file (Ctrl-D to save)
touch file	Creates empty file OR updates timestamp
less file	Views file page by page (/ search, q quit)
head file	First 10 lines
tail file	Last 10 lines
tail -f file	Follows live (great for logs)
cp src dst	Copies
cp -r dir dst	Copies folder recursively
mv src dst	Moves / renames
rm file	Deletes (no undo!)
rm -rf dir	Deletes folder + contents (dangerous)

Search files

find /var/log -name "*.log"                # by name
find / -type d -name node_modules          # only directories
locate word.txt                            # fast, uses index
which python3                              # where is this binary?
whereis git                                # binary + man page

Processes

Command	What it does
ps	Your running processes
ps aux	Everyone's processes
top / htop	Live view of CPU/RAM
kill 1234	Ask process 1234 to stop
kill -9 1234	Force-kill
pkill nginx	Kill all processes named nginx
bg	Send stopped job to background
fg	Bring background job to foreground
renice +10 1234	Lower priority of PID 1234
command &	Run in background

Permissions

chmod 755 script.sh     # rwx r-x r-x
chmod +x file           # add executable bit
chown alice file        # change owner
chgrp devs file         # change group

The 3 octal digits stand for owner / group / others. r=4, w=2, x=1 → 755 = 7(4+2+1)/5(4+1)/5(4+1).

Redirection & pipes

command > out.log        # stdout to file (overwrite)
command >> out.log       # append
command 2> err.log       # stderr to file
command &> all.log       # both stdout + stderr
command1 | command2      # pipe output of 1 into 2
ls | grep .py            # only .py files

Real-world example

Nightly log cleanup on a small server:

find /var/log -name "*.log" -mtime +14 -delete   # older than 14 days

Combined with a cron job (crontab -e) — hours of manual work gone.