Cheatsheet

Linux Fundamentals

The shell commands you reach for every day: moving around, files, text, permissions, processes and pipes.

Move around

```
pwd
```
Print the directory you are in
```
ls -lah
```
List everything, with sizes and permissions, in a readable form
```
cd ~  |  cd -  |  cd ..
```
Go home, go back to the previous directory, go up one level
```
find . -name "*.log" -mtime -1
```
Find files named *.log changed in the last day
```
which python3  |  type ls
```
Show which program a command name runs
```
man tar  |  tar --help
```
Read the manual page, or the short help
```
history | grep ssh
```
Search the commands you typed before (Ctrl+R searches as you type)

```
mkdir -p app/logs/archive
```
Create a folder and any missing parents
```
touch notes.txt
```
Create an empty file, or update its time
```
cp -r src/ backup/
```
Copy a folder with everything in it
```
mv old.txt new.txt
```
Rename or move a file
```
rm -r build/
```
Delete a folder and its contents (there is no trash can)
```
ln -s /var/log/app app-logs
```
Make a symbolic link, a shortcut to another path
```
stat notes.txt
```
Show size, owner, permissions and all the timestamps
```
du -sh * | sort -h
```
Size of each item here, smallest to largest
```
df -h
```
Free and used space on each disk

```
less +F app.log
```
Page through a file; press Ctrl+C then F to follow it like tail -f
```
head -n 20 file  |  tail -n 20 file
```
First or last 20 lines
```
tail -f /var/log/syslog
```
Follow a log as it grows
```
grep -rn "error" /var/log/app/
```
Search a folder recursively and show line numbers
```
grep -v "debug" app.log
```
Show the lines that do NOT match
```
wc -l file
```
Count lines
```
cut -d: -f1 /etc/passwd
```
Take the first field of each line, split on ":"
```
awk '{print $1, $NF}' file
```
Print the first and the last column of each line
```
sed 's/old/new/g' file
```
Replace every old with new (add -i to edit the file in place)
```
sort data.txt | uniq -c | sort -nr
```
Count how often each line occurs, most frequent first
```
diff -u a.conf b.conf
```
Show what differs between two files

The output of one command can feed the next, or go to a file.

```
cmd > out.txt  |  cmd >> out.txt
```
Write the output to a file, replacing it or appending to it
```
cmd 2> err.txt
```
Send only the error messages to a file
```
cmd > all.txt 2>&1
```
Send normal output and errors to the same file
```
ls | wc -l
```
Pipe: feed the output of ls to wc
```
cmd | tee out.txt
```
Show the output and also save it
```
find . -name "*.tmp" | xargs rm
```
Turn lines of input into arguments of another command
```
cmd1 && cmd2  |  cmd1 || cmd2
```
Run cmd2 only if cmd1 succeeded, or only if it failed
```
echo "Today is $(date +%F)"
```
Put the output of a command inside another

r=4, w=2, x=1. Three groups: owner, group, others.

```
chmod 640 file
```
Owner read+write, group read, others nothing
```
chmod u+x script.sh
```
Let the owner execute the file
```
chmod -R g+w shared/
```
Give the group write access to a whole folder
```
chown alice:devs file
```
Change owner and group
```
chmod g+s shared/
```
setgid on a folder: new files inherit its group
```
chmod +t /srv/dropbox
```
Sticky bit: only a file owner can delete their files in the folder
```
umask 027
```
New files get 640 and new folders 750 by default
```
sudo -l
```
List what you are allowed to run with sudo

```
ps aux | grep nginx
```
Find a running process
```
top  |  htop
```
Live view of CPU and memory use
```
kill PID  |  kill -9 PID
```
Ask a process to stop, or force it
```
pkill -f "python app.py"
```
Stop processes by matching their command line
```
sleep 300 &  then  jobs, fg, bg
```
Run in the background and manage shell jobs
```
nohup ./job.sh > job.log 2>&1 &
```
Keep a job running after you log out
```
systemctl status nginx
```
See if a service is running (also start, stop, restart, enable)
```
journalctl -u nginx -f
```
Follow a service's logs
```
free -h  |  uptime
```
Memory in use, and the load average

```
tar -czf backup.tar.gz folder/
```
Make a compressed archive
```
tar -xzf backup.tar.gz -C /tmp
```
Unpack an archive into a folder
```
curl -I https://example.com
```
Fetch only the response headers
```
curl -s https://example.com | head
```
Fetch a page quietly and look at the start
```
ss -tulpn
```
List listening TCP/UDP ports and the programs that own them
```
ping -c 3 example.com
```
Check that a host answers

Cheatsheet for the Linux Fundamentals path · Deboistech · All cheatsheets