Overview
Every infrastructure stack eventually comes back to a Linux shell prompt. This guide covers the small set of commands and concepts that solve most day-to-day administration tasks without turning into a full Linux course.
Filesystem Landmarks
| Path | Purpose |
|---|---|
/etc |
system configuration |
/var |
logs, cache, spool, and changing service data |
/home |
user home directories |
/opt |
optional or third-party software |
/tmp |
temporary files |
/proc, /sys |
kernel and hardware views |
/dev |
device nodes |
Navigation and File Handling
pwd
ls -la
cd /path/to/dir
cd -
mkdir -p /opt/example/app
touch notes.txt
cp -r source/ dest/
mv oldname newname
rm file.txt
rm -rf olddir/
Searching
find /var/log -name "*.log"
find /opt -type f -mtime -7
grep -RIn "pattern" /etc
which python3
whereis nginx
Permissions and Ownership
chmod 755 script.sh
chmod 644 config.yml
chmod 600 id_ed25519
chown root:root /etc/myapp/config.yml
chown -R appuser:appgroup /opt/myapp
Common modes:
| Mode | Meaning |
|---|---|
755 |
owner full, group/other read+execute |
644 |
owner read+write, group/other read |
600 |
owner read+write only |
Text Processing
sort file.txt
sort -u file.txt
wc -l file.txt
cut -d',' -f1,3 data.csv
sed 's/old/new/g' file.txt
awk '{print $1, $3}' file.txt
Pipes and Redirection
command > output.txt
command >> output.txt
command 2> errors.txt
command 2>&1 | tee run.log
ls -la | grep ".log" | wc -l
Process Basics
ps aux
ps auxf
top
jobs
kill 12345
kill -9 12345
nohup command &
Practical Advice
- learn to combine
find,grep,awk, andsed - test destructive commands on a narrow path before going recursive
- use
teewhen you want visible output and a saved log - prefer understanding the current state before restarting services blindly
